OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Victa Two Stroke Engines G4/LM carby repair/modifications

Here is a step by step detail of how to get a LM carby to work properly, G4 is at the end of this post, only difference is the cam modification, all other steps are the same

You will require a 6mm or 1/4 tap and two 25mm bolts (cut both of these to 18mm), 1 nut of whatever thread gauge you choose.
You also need a kill switch, this can be either a momentory contact switch or toggle switch, a little bit of electrical wire, lug and a connector

It requires a marker, hacksaw and 2 sockets to act as spacers to hold the cam steady in a vice, do not over tighten the vice as this will damage the cam








Thread this with a 6mm or 1/4 thread (whatever matches the bolt you have), cut this bolt to 17/18mm long

Total thickness of washers is approx 1.6mm



Thread this the same size as the kill switch hole




This is your new idle adjuster screw, this is the 2nd bolt you cut earlier to 18mm

You no longer use the factory kill switch, use the momentary contact switch as shown, just fit one lead to the frame and the other wire to the wire that comes through the side of the original kill switch, the other wire is just cut off.


Once you have everything re installed and the motor running, you then adjust the idle screw as shown above, to set the engine rpm start the engine, pull the throttle back to stop position and then adjust the idle screw to get the idle revs you require.

This is how to modify the G4 cam, all other steps from the LM carby modification are required

You will require 1 x 4mm or 5/32 screw and tap











Lifter / Spider height adjustment to the highest point on the cam and no further

Thanks for going to the trouble of doing this, this will keep Powertorques running for another 30 years.

Not only the Powertorques Tiger, all those full cranks fitted with the G4 carb

well done. that seems to be a major improvement.

Very interesting stuff ! Thankyou for sharing it.

That's certainly given us viewers a better idea of what you are talking about.
You have made a very clever ( in some ways) carby reach it's full potential.
Is it possible, just possible, that you have made it better than the G3 carburettor??

Mowerfreak, not sure if it is better than the G3 and it doesn't really matter, there is buckets more of the plastic carbs out there, if you do this mod correctly the carb is guaranteed to work and that is all that matters

It would be necessary to run some dynamometer tests with Exhaust Gas CO or O2 monitoring, to answer that one.

In any case, it's a moot point, as G3 carby spares are in the process of drying up - they have long been NLA from Victa, and at least one of the two major aftermarket OPE spares suppliers has now deleted most of them [GA Spares].

Many thanks for your superb how-to, Norm.

I hate to think how many Victa pumped out over decades, but you are right, , of we spread the gospel that these things can actually have their bugs removed, we would at least partially stem the rapid ( and I mean RAPID) disappearance of this Aussie iconic backyard noise.

Mowerfreak, one thing with this mod is the iconic backyard noise does not need to be so loud if the Powertorque is not revving its tits off mowing grass that is 1" high.
Gadge, my son is over from NZ and IT is his game so that is why it is clear, I just did the leg work

Hello NormK,
I will save this and do it on my new PT project. I just have to sort out my base. it a lot of sanding , but will get there soon..
thanks for your effort.
speedy

excellent work Norm,we can all save a two stroke now thank's to you..cheer's

Does this result in a first time every time starting experience or do you still need to work on getting a strong spark and good sparkplug for that to happen?
One think I remember with a near new Power torque was the ridiculous ease in starting.
You could do it with your teeth.

Coils on Powertorques rarely fail or give trouble and the carby has little control over the spark plug. If all the ducks line up they are usually a one pull start, unless the useless float needle is giving problems and I have little control over them because they are just expensive to buy,cheap Chinese junk and poorly made

Another mod I did on an LM today, because the owner wanted to retain the kill switch was to drill and tap through the kill switch ramp on the cam in the same manner as I did with the G4 cam and this then allowed me to adjust the kill switch position and prevent it from running up to the flat on the top of the ramp and becoming stuck which results in having to pull the carb apart to free it up again. So far it is working well

Getting back to the float needle problems I might have a crack with these and see how it works out. Getting the brass needles made they came back with a stupid price of $35 each. These are a bit better priced.
http://www.ebay.com.au/itm/252780607048?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Hello NormK,
Did the mod, works well, smooth power. I used a fine hacksaw and got a really smooth surfaces on the gray part...
speedy

Hi speedy, glad to hear it works well, problem is now that you have seen how well they work you would never go back to the original design

Yes, I will get my new pt going first then do the mod. I didn't put the kill switch in or the bolts... but the rest works well.
speedy

Thanks heaps for taking the time to complete this mod, photograph it and post it.

1: I will be applying it asap to my twin, which should sort one of it's problems once and for all.
2; Off to the "Green Shed" to see how many G4's I can score (attached to cheap mowers of course!)

On that, most municipalities have a Green Shed where folks donate unwanted/broken stuff.
Always plenty of mowers, some in surprisingly good order. Just got to be quick though because they are usually stored outside and the fuel cap is the first souvenir to be taken.

The next thing that you will find is the float needle, this horrible little part is responsible for the early demise of millions of Victas. The new float needles and primer caps solve this although I have had a couple of issues with them, price on them is an issue if you only want one or two. Do not waste your money buying the ebay ones with the plastic needle they will mess with your head

Hi Norm,
I have a couple of questions for you about your carby mod, if you could offer some answers that would be terrific. I have been thinking about doing this to a spare carb for some time, as I have a couple of machines I use regularly that I think are in overall pretty good shape (seals, viton tipped needle and seat, clear jet, good spark, good compression etc.) which I can never get to start first pull cold. They often start second pull, run perfectly and restart easily hot. I don�t run them out of fuel to stop them but use stabil in the mix. What is the starting procedure with the modded carby? Throttle to run, single prime then start etc? Or are they all different and once you find a procedure that works for that machine go with it? Can I do the cam mod and not do the idle control screw or kill wires portion of the mod? I know I could try this all myself but wondered if you had some ideas already.
Cheers,
John

Hi John, I usually start them on full throttle then back it off but I find they will usually start pretty much anywhere, but full throttle is the spot I prefer as it makes sure there is fuel going straight in. I usually give 2/3 primes. You don't have to do the idle screw, just means that if you pull the throttle back fully the motor will usually stop because it will idle down too low. The idle screw just means you can just crack open the poppet to allow it to idle. This can be played with by only fitting 2 washers under the cam, but this usually keeps the revs too high for my liking, when you are emptying the catcher etc. You can use the existing kill switch but I found them too problematic and this is probably because all the aftermarket kill switch rubbers are not fit for purpose, I was spending way too much time trying to get them to work only to have them play up. The most annoying thing with the whole setup is the lump on the cam that once the lifter goes over the top into the stop position it often becomes impossible for the throttle cable to fight the spring tension and get the lifter to rise back up over the hump. Cutting the hump off gets rid of this problem but then you need to put the washers under the cam to lift it up to the same height as to what was the top of the hump. If Victa had just kept the hump height all the way, none of this would be a problem and the kill switch setup would have probably worked fine. The big problem is the cable has to fight going back up over the hump, fighting the spring and break away from the kill switch rubber which can often jamb all at once.

Thanks Norm, love your work. I think I�ll give it a burl and see how I go, cheers.

I made the cuts on the cam today, easily done with a dremel. I have a couple of G4 idle adjust caps, might try one of those. Just need the washers under the cam and will twist it on and try

Hi jds303,
I should have done it that way instead of using my hacksaw. I still haven't completed one fully, as the machine I was going to try it on has other issues that need fixing first. I should get it done pretty soon.
What grinding head did you use. I have a couple of sets with assorted grinders, but never know which ones to use for a given task.

I've been trying to get my head around this fix for a while now and wondering how best to go about it. I know virtually nothing about Victa mowers. New territory for me! I am going to see if I can fix the old carby as it is before I start attempting any modifications. I have a bad habit of making mistakes that I can never "undo".

The most annoying part with the modification is that if the raised section on the cam had continued right through to the stop position the washers to raise the cam would have not been needed, you could then just cut the ramp to a gentle grade and it would work perfectly. The other issue the washers under the cam cause is because it lifts the cam it makes fitting the cable more difficult and you have to be very careful because you get a slight bend in the cable and then it becomes notchy. Sure if you can get an unmodified carby to work and some do for some reason, just keep it that way but I find I have to modify 98% of them and then I know they will work without problems

Hi Mowerfreak,
I used a plastic cutting disc. A couple of sockets the right size (small enough) in a vice as per Norms instructions, and it makes the cut in one straight drop from the middle of the cut. It was surprisingly easy. Turned out well although yet to try it out.
Cheers,
John

My issue now is I would like to find another 20/30 cams so I have spares to work with because I usually avoid the G4 cam because it can cause me a few issues, mostly with the stop on the cam not having the ramp, so I have to mess about with it to fit a screw in it so I can adjust the stop so the lifter sits on the high point of the cam in the stop position.

I finally fitted my modified cam to one of my mowers today. I left the factory kill wires in place and didn�t modify the cap for adjusting the idle. It just so happens it idles nice and low with the throttle down as low as possible before moving it to the stop position. There is then a decent throttle response up to the run position. I didn�t let it fully warm up to see how it runs when at operating temperature but I was happy with it. I may also change the large poppet retainer over to a small type at some point, I�m not sure if this will affect the speed of throttle response or only the governor response. Overall my one worked well from idle to run, kill wires worked as normal and was a first pull starter with the cam mod and metal needle. I�ve gotta thank Norm for his work on this one and input to the forum in general.

Hi John, glad to hear you are happy with it. The idle screw is not needed if you get the washers under the cam exactly right, but I only seem to get it every 4th or 5th time, just pot luck. The main reason I started removing the built in kill switch was because you get people who want to force the lever back too hard and then the switch would jamb because of the design and then they would try and push it back and the cable couldn't get it to free from the switch. It is a pain fitting another kill switch but at least it comes up against a solid stop so it can't jamb up

Last nights entertainment in front of the telly, another 14 diaphragm caps, no idea how many of those I have made up.

Hi Norm K,
a Victa LM factory on your coffee table. What are other rooms are dedicated to this craft? I hope you don't put them together in the bathtub lol!

MF the rest of the inside of the house is fairly safe, just the outside is fair game, but at least I'm not finding much on ebay and gumtree these days and that makes my wife happy, I think.

Another thing I have been experimenting with on these carbs is the springs in the governor setup. I have cut the big spring in half and put one half on the lifter and the other half on the diaphragm and this seem to work fine. This seems to equalize the pressure on both sides and allows the poppet to move freely. To be honest I was running out of small springs that made me try this mod and the shorter spring under the diaphragm cap reduces the tension on it which is another good thing. Once set up these are the best carby I have ever worked on and I have worked on a few over the years

I finally completed my first NormK special using G4 bits. A lot of fine adjustments and some grinding and searching for the right sizes of bolts and screws were required, but it was a lot more fun and interesting doing it, than I expected.
Well, the moment of truth when I fitted it to this mule and it fired first pull .
It was already dark so I didn't want to annoy people, but it went well the few seconds I ran it.
I think I will stick to LMs if I do any others, as that screw in the G4 cam was quite an ordeal finding the right size to fit!!
But I'm very pleased so far and it was a lot of fun modifying it. Thanks for sharing Norm!!
Does anyone have a suggestion where I can mount the kill button, which is loose at the moment as there is not much clearance under the engine cover on this machine?

Full cranks are dead easy to fit the kill switch, I use a round one that fits in the existing hole in the steel cover above the carby and the earth wire from the switch I just put on the steel cover with a pop rivet. It is good when they start so easily and come back to idle and not revving the guts out of it and a nice tickover at idle when you go to empty the catcher. The G4 cam is a bit of a pain because of it not having the kill switch ramp. One thing you have to be careful of is to not pull back on the throttle too hard because you can pull the cable out of the cam and this splits the cam.I am putting a stop in the air filter housing to stop this happening.The six mowers I got a couple of days ago all rev way too high so I have to modify all of those to get good throttle control

You must have it down to a routine NK, but it was quite a learning curve for me ( though nowhere near like you, who had to come up with it). My next one will be much easier and better than this one.
Regards the kill button placement, I was considering that hole only to remember it's for the vacuum tube from the decomp valve. So you just blank it of at both ends and not bother with it?

MF you still need the decomp hose hole, the other hole is further forward. I usually don't run the decomp hose through the cover because it is too messy, trying to get it connected up and hoping it doesn't come off while you struggle to get the cover into place.Sometimes I have cut a slot up to the hole so the hose can be put in place and then the cover can go straight over the top. It is easy to see why Victa wanted to design the Powertorque because just fitting this in a production situation is just too time consuming, this part of the production line would have been a bottleneck. As you can see in this pic the hose is run up inside the cover and the governor fitting has just been removed

I soldered the wires on only to have a d'oh!! moment when I wanted to fit a bracket and realised I could no longer fit the nut and washer or put it though a hole.
My soldering skills aren't exactly above par, so I used a zip tie to mount it vertically to avoid having to de-solder and attempt to re-solder such intricate electrodes again. I quite like this solution as it lets the wires hang in their natural state and looks quite tidy for what it is.

MF, why would you put the carby on facing that way, you can't get at the primer cap and with them around that way the snorkel sticks out too wide and gets caught on everything. I hope that is not a latching switch, because you will get caught out not knowing if it is on or off, I use the momentary ones where when you let it go it is ready to start again.

Don't worry, it's a spring one you have to hold down to "turn on" the kill.
Unfortunately it has to face that way because it's on a . VC-160 frame which doesn't allow enough clearance for a right hand snorkel to fit between the frame and the fuel tank. I wanted to use the opportunity to try your carby mod on a charity case like this Franken-mower I found, and I don't have the original left hand snorkel for this configuration, so made do with stuff I had lying about. Yes it sticks out too much but it stays in place and I'll replace it down the track + watch extra carefully where I'm going! This project was mainly to learn.

OK you're forgiven. I picked up another Powertorque today from Gumtree and the bloke told me he couldn't get it started. When I got home it was obvious why, the primer cap was upsidedown, but at least it had a full tank of fresh fuel in it, runs fine but as usual needs the carby mod done

I gave Frankenmower a longer test today and it took only four pulls with the throttle moved up to medium to start, without pushing the hard to reach primer. I think I will fit a G4 grey primer-less cap to this one if it keeps starting this well from cold, and save the white cap for when it can be more useful.
It went well but I'll have to watch more carefully how I trim the cam next time, as I definitely shaved to much off. I had to file away a bit of the bottom of one of the spider legs to clear the screw on the cam as it rotated and lifted the spider up!
I'm grateful it goes despite that, but the result is most of the throttle rise occurs only in the first quarter of the t bar movement and the rest of the way, it rises just a little bit more to max revs.

MF what you can do with the G4 cam is you can adjust it so that when the cam is up against the stop/bolt the 3 leg lifter is sitting on the highest points on the cam. You can get this exactly in the right spot by adjusting the screw in and out

I did that as best I could and carefully observed each leg of the three prong lifter. Problem is that I cut too much off one of the ramps on the cam, so I had a situation where the legs on the other two were starting to lower again, but the third leg still hadn't reached its peak, so I had to have a compromise. Also, I didn't have much thread protruding by the time I adjusted the G4 cam screw.
I'm quite happy with the result anyway. I'll do a better job next time.

I made up 14 of those primer caps a month ago, and I just used the last one, no wonder I'm going through needles like there is no tomorrow.

That's a good indicator of how many you are moving!

That is 40 days since I made them up, there is still a few waiting to be sold so it probably works out to one going every 5 days but on average it takes me at least 2 days to get them repaired and sorted properly so it works out about right

Did a carby on a full crank this morning and it still wants to rev like crazy and I can't see any reason for it, I'm guessing it has to be something wrong with the carb body

Changed the body and used the same internals and it works fine, now I have to set the problematic body up with another set of internals to prove if the body was the problem

You may have made a blunder in assembly, but may be a hairline crack in the body?

Had it apart a couple of times couldn't see anything wrong, I will put it on a PT sidethrow slasher that belongs to a mate and see how it goes. I told him last night that I want it gone because I have had a number of people here asking if it was for sale. I have one here with a full crank but the base is rusted out and they are getting a bit scarce on the ground now
I had a bloke come and get a PT a couple of days ago and he brought his old PT for me to look at. He bought it new 25 years ago and it had only had new blades fitted a number of times, but sadly I think it will end in the dead motor pile

Ok MF, I fitted the carby to the sidethrow and it behaved erratically, didn't rev hard like it did on the other motor but had to keep opening and closing the throttle to keep it running. Changed all the internals to another body and it works perfectly. This is only the second body I have come across that had a problem and just would not work, apart from the obviously damaged/broken ones.
Will my mate appreciate the effort I put into it? probably not but he will say thanks because he always does. Not only that he would have to be the only contractor running around with the oldest collection of old Victas mowing lawns in the inner leafy suburbs of Melbourne. And he is still pressuring me to fix an old full crank 550 self propelled I have here for him. He says the looks he gets from other contractors is priceless

Only a billion or so more out there. No great crisis. It was interesting to find out though.
It is indeed unusual to see Victa two strokes being used by mowing contractors/ runs.
I'd be a bit concerned about the fumes day in day out, but I don't imagine four strokes have catalytic converters either.
Councils used high output powertorques for years in their commercial grade equipment.

Thought I would add this in here, I dodgily added a missile style switch and cover (had to reverse the contacts to the body) up to the air filter housing with some flexible round black speaker cable, and crimped on some spade terminals to the existing kill wires since the long terminal snapped off from the wire. I will crimp some spades on to some lengths of wire with the victa kill pins on the other end so I can install them in to the carb before it is refitted, then plug the wires in to the other ends when the carb is back in place. Should eliminate fiddling with the kill wires if and when they ever go back in. I used a champion brand 10mm vacuum cap to go over the spigot in the carb body, all works well. I had to give the body and jet a good run in he ultrasonic cleaned as I was having starting problems again. Starts first easy pull now. I may try and insulate the back end of the switch a bit better, mount it to a bracket and run the wires in the snorkel if I get really bored at some point.

If you do get super bored you only need to bring the black wire up from the carby inside the snorkel tube and you can set it up so that when you pull the throttle back to the stop position the lever contacts the wire and earths the ignition out as it is earthed to the handle already

Never thought of that, might look in to it

I had a carby that I modified yesterday that I could not get to come back to idle. I had fitted 5 washers under the cam , this was reducing it but it was still way to high. Got another carby body, swapped all the internals, 3 washers under the cam and it works perfectly. Out of all the carbs I have modified I only have 3 bodies that won't work for some reason, the one yesterday an 2 previous ones that would not start. Remove the internals to another body and no problems. Why I have no idea

^ air must be seeping in somehow. Probably requires examination with a sophisticated scanner of some sort to find it. Fortunately it doesn't often afflict them and there are still tonnes of the things around. Into Mr Sulo with them.

I was doing a later PT the other week (Chinese block) had the exact same problem. Changed the carby body, then no issues. I noted that the cam was easy to turn part of the way, but became harder as it went back to what would be the idle position, then became easy as it went back to the cold start and stop position.

It was as though the cam 'legs' were snagging up on the carby body (maybe the plastic had age expanded), then suddenly letting go. Perhaps with the lifter, and diaphragm with springs, the resistance meant the throttle cable just twisted/moved in the snorkel without changing cam position in these difficult spots.

Just a theory, I don't know exactly why either.

Can't remember if these are the "O" rings I got for the primer caps but they are cheap enough
https://www.ebay.com.au/itm/10-Piec...-39-Mm-X-43-Mm-X-2-Mm-G9V5/264065839030?

Hi MF,

How fast do you think he'll burn out his bearings? :-/

Don't get me wrong, the modification looks awesome, and kudos to them for getting it done.

I just see the mower overheating, wearing parts, etc. But it'd be a fun project... how much power can you get from your PowerTorque?! I'd enter that contest... haha :-)

That is not overworking a Victa 2 stroke, they are easily capable of that work, be a bit better if it had the fan shroud to get some cooling over the motor. Also the motor does not have a lot of compression because as you can see when starting it shows little resistance on when he pulls on it without a decomp valve in it. The other thing that will kill it is the use of a pod filter down there, they are only good for keeping out rocks and quails. Another thing that makes it a lot easier on the motor when chewing through that sort of grass is having the rear flap lifted a bit so the grass can be ejected out, not getting bound up inside the mower. Then the will really get through that stuff easily

Just as an update on the carby mods I am no longer fitting the external kill switch, on probably the last 10 I have done I run a wire up the inside of the snorkel and use the throttle stop screw I fit to earth the ignition out, much better idea

G-day NormK,
can you post a pic of that set up?

I'm doing one right now but it is a bit hard to take a pic while I am doing it and at the end there is nothing much to see. I drill a 1/8th inch hole in the underside of the rubber hose near the carby, feed the wire up the inside, drill another 1/8th hole just below where the throttle cable goes into the filter chamber and the wire is connected to the button head screw I use in the throttle stop. This is how Victa should have done it in the first place and not used that abomination of their long lunch, we are smarter than the rest of the world, kill switch.

Lol pictures please Norm.

Ok MF if you insist, not a lot you can see

That helps -me to stick with the existing kill switch or the spring button.

I'm finding it easier and better that fitting a switch

Yes Norm,

That is a better idea. I will go that way on the next one whenever that is. I'm just about Victa'd out at the moment after finishing the 24.

Its hard to get a durable kill switch at a reasonable price. I have been using an ATV/motorcycle/gokart kill switch. Its about $5.00. It looks durable but I have to remark the "Stop" & "Run" signs on it and its easy to try to start without switching to run and then of course nothing happens.I also have to remark the throttle with a "Start" at the "Run" position and "Idle" at the other end.Otherwise my machanically challenged extended family can not get them to go. By the way I also have to put "Oil" pn the fuel cap and highlight the 25:! words as well. The other day I got a call that one would not go. Trying to start at trhe Idle position of course but just as well it would not go, the tank was filled with straight petrol.
All the best
Jeff

I'm open to anything. What sort of screw is that in the throttle slot? Can you tell me which wire goes where?

MF, the screw is just a button head screw, I use those because they have a big head and won't fall through the slot. I cut a small square piece of metal for the inside so the screw can sandwich the wire eyelet between it and the plastic housing. The wire that needs connecting is the black wire, I just cut the other one off

Wish I had kept some record on the number of these caps I have modified over the time, seem to be always making up a batch of them

I just did the mod today on the old G4 someone fitted to the PT I was given - and it gave all the symptoms of the one you mentioned last september - sometimes rev, sometimes stall if not throttle not flicked, then occasionally revs its guts out.

With 3 washers under the cam, the cable ball wont engage properly in the cam, with 2 it works alright but the lowest idle I can get is 1500 rpm (on tach).

Going to change the body and see how it goes - but its 40 degrees tomorrow so probably will be inside

Hi Tyler, yes I know the 3 washers can give problems getting the ball to fit which is why I only clip the cable in the first slot, if you try getting it into the second slot you end up kinking the cable. If only Victa had extended the top of the cam instead of putting the hump on it the washers would not have been needed and an idle could have been achieved easily.
On a couple I have had to fit 4 washers to get the idle to come down enough so I could adjust it with the screw but it is very rare, 3 is usually the right amount

Thanks Norm

I will try removing the cable and only latching it in one latch (then adjusting the screw on the air filter housing as it will probably be a bit out) - I guess it allows it to pivot a bit and not kink.

It was quite strange how the behaviour kept changing - it was smoking badly at one point and went through 1/2 a tank in 10-15 minutes

Flat stick, I was getting 3600 rpm, but couldn't get a good idle unless I took the long spring out (was playing around at one point trying to see what was wrong)

Hi Tyler,
another thing I started doing ages ago was to just cut the big spring in half, sometimes I just use one half on the lifter and the other half under the cap, either method seems to work fine and by cutting the big spring in half it reduces the pressure on all the bits in there and and puts less pressure on the cable so using the first notch isn't a problem

Hi Norm

I am pretty sure there is something wrong with the carby body. Even tried a lm cam, better but not great and of course the stop position was miles off.

When I put the cable in one notch, it wouldn't completely pull back to the stop position

Without the big spring, idled great but wouldn't rev - might try cutting the spring thanks

I am going to put a LM as it is really annoying me

It does happen Tyler, I have had a few bodies that wouldn't work, swap everything to another body and they work fine. I know what you mean about annoying

Ok Something isn't right. I grabbed a LM body, used a different diaphragm, different primer cap, different needles, checked the decomp for carbon, put in a cj8 and tested, tried different combos of washers, cleaned jet, checked starter o ring, changed inlet o rings, checked fuel flow and it all made absolutely no bloody difference

If I hold the diaphragm back (with cap off) it will idle to the point of stalling

Next steps are ripping a carby off one of my other ones and putting a good known carby on it or cut the spring

I reckon its a governing issue - sometimes if I blew into the governor port on the cap, there was a air leak, I managed to get a great seal, but the cable is snagging (must be slightly warped) so will have to remove a washer. Ran out of time tonight - legal noise restriction 7pm

Both the cams I was trying with were the short legged versions - one seemed to cause the stop pins to actuate a lot lower down on the throttle control

Hi Tyler,
It is something you are doing or not doing. I have never had 2 carbs in a row that cause me problems. I might get a problematic one in 50 I modify, usually everyone is just set and forget

Norm, finally fixed. cut the spring (first 3/4 length then down to about 1/2), put a different diaphragm on, put the long legged cam in.

Idle can go down to about 690 (set it about 1200 for now), full throttle control, revs out to 3450rpm.

It wouldn't start at one point eventually got it going and revved hard and stopped, I thought whats wrong now - turns out I was out of fuel haha

I was thinking about building up the top of one of the cams that didn't work with araldite purely as a experiment

Hi Tyler, you are a few years behind me with that idea, I tried extending the cam ramp but I was unable to get anything to hold to the cam because it also gets petrol in there and all the bits I glued in just eventually let go. If you could achieve that it means you could use the original kill switch idea which would save me a lot of work but at this stage I have not been able find any suitable way to extend the ramp. I sure hope you can come up with a method because that also removes the need for the washers under the cam. I had thought about trying to get new cams made but they would probably want an order of a min of 5000 or something like that. Keep trying as I am hoping you come up with an answer

Norm, I have sat here thinking about this, but the only way I could think of was pushing the plastic over with a soldering iron instead of hacksawing the cam down - there's more than enough of its own plastic there to fill the low point.

But that would be too fiddly to be good I think

Tyler we could try plastic welding a piece on but I don't have a plastic welder to have a play with it. Would probably have to cut up some cams so you had the same plastic to weld it with

Hi gents,

Know anyone handy with a 3D printer?

Cheers,

John

Hi John,
Now that is a clever idea, I don't know anybody with a 3D printer and I don't know how the 3D material would stand up to the fuel getting on it but I'm sure it could be a solution. I would love to get one of those cams just to try it out and see if it would solve the problem, be amazing if it did, now I won't be able to sleep tonight

I've often wondered about that, since I started working on mowers, but 2 things stopped me. 1, I don't know if the material would stand fuel, 2, I don't have a 3D printer haha.

Be interesting if someone has/can try!!

I think I still have access to the software that we can use to make a 3d drawing of the cam and then can export the files to a file type the printers use

But I don't have a 3d printer either

From what I have been reading, fuel resistant 3d print material is hard to find - the best solution I read was to make one, make a mould from it, then use a different material to make the usable one

If we could ever manage to do it we want the cam with the ramp modified as I have been doing but the top of the ramp needs to be extended back so that it comes back to shut the poppet completely just before it activates the kill switch section on the cam. Wish I knew how to draw it up so I could put a 3d drawing of how I want it on here

I have had to put 4 washers under a cam today to get the revs to come down enough so I could get it right with the idle screw. Not very often I have to fit 4 but I guess there is just slight variations in the carby bodies

If someone can do the drawings, I might well be able to get a couple of prototype cams printed up

Hi Tyler,
remember I said recently that I had had a few of carb bodies not working properly over the time. Well yesterday topped it, I picked up a PT in the morning, put my test carby on it, ran fine, modified a carby for it and it wouldn't keep running and was all over the place. Did another carby using the same inner bits and exactly the same, did a third one and it runs exactly as it should. I think when I did the third one I used a different poppet so wondering now if it might just have been a poppet problem. Guess I will have to build another carb to test that poppet now otherwise it will end up in the poppet container and I will get caught again