OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Victa Two Stroke Engines Victa 160 Plastic carburettor

Hi team,
I've just built up a victa 160 carburetta from several old units I've had lying around together with some new parts and I cannot get the engine to run less than wide throttle position. The engine spark is strong and timing is spot on. I can get the engine to run on full throttle OK but the moment I back off the throttle a little it stalls. The cut-out mechanism in the carby is not causing the fault as proven with multimeter. I've done the foillowing work on the carby:
1. Replaced inlet manifold O-rings (block o-ring and carby o-ring)
2. Stripped, cleaned and blew out the carby body.
3. Blew out the main jet.
4. Replaced the inlet needle
5. Checked the float - OK
6. Removed the top cover and large spring - all OK
7. Removed and checked diaphragn - OK
8. Removed and checked the bottom small spring - seems OK
9. Removed the spider and checked it - seems OK
10. Removed the cam and checked it - seems OK.
11. Replaced the throttle cable - The original one was a bit sticky.
12. Re-assembled the carby and started engine but stalled when throttle was moved off maximum throttle opening.
13. Repeated the above exercise at least 5-times using different bits from different carbys but same result.

About the only thing I haven't tried is changing the de-conpressor???

I honed the cylinder and fitted new rings. I also fitted new bearings and seals so i am resonably certain that the crank case is leak tight and that the head gasket is holding..

Can anyone out there offer any ideas as to why I cannot get the damn engine to idle or at least operate at less than wide open throttle??? ...... It appears to me that the angle moulded into the cam is mis-matched to the spider or to the poppet valve that is actuated by the spider as it falls down the incline of the cam? I guess what I'm asking is ... "Are all parts in the plastic carburetta that have been manufactured over the years interchangeable with one another" and can you offer any other fault diagnostics?

far as i know the only differences are to lm and g4 . the jets are different and body to take said jets , one has a long plastic tube inserted in the jet the other doesnt just a fine mesh on the outer and cant be interchanged .
LM i think is the earlier of the two . is the "spider" in the three slots inside the body ? cable adjusted correctly ?
any jets there with a white(or close too white) tube in the end ? might be as simple as changing the carb' body making sure the jet is the right one , small short jet will fit in wrong body but long one will not as the tube is built in .
hope it helps

Does the jet have a groove around it half way in the face or is it a plain face jet?
As below.



vccomm the G4 carby was the earlier model,by 1978 the G4's were replaced by the LM carbys and are still being made today.

Here is a parts view of how it should be.
The only thing I can think of at the moment is the earlier poppet values use to have letters on them and they had edges on them and for certain mowers they had to be in a certain position.The newer poppet valves however don't.
Does yours have the letters on the inlet side,or is it a plain face one?

so its why everyone still calls them g4's . they were that scary

The G4's are actually starting to get very hard to find,as when they break or need replacing they are replaced with an LM.

so externally the same just internals is the difference then , so which ones had the idle adjustment cap ? as seems both did .
apart from part numbers how to tell ? or is it just the jet tubes ...... one with one without .
i have both here but hard to take a photo of the jet tubed g4 !
onya blumby only things i have in my book is they are different but doesnt really explain it .
there was a place here that it was explained im sure but i dont know how to link mr davis and your good self i think went through this some time ago and hard to find it now
. Dave

sorry to interject. i have been looking through the forum for the same info, apparently you can not interchange parts if you have a black poppet vv you can not swap it. (in my limeted experience it doesnt matter). those plastic carbies suck, if they work they work. go the G3

If changing various bits in the carb doesn't change the outcome, and it's only revving flat out, something else is not right, like the cable is not seated right in the cam or it has a massive air leak, otherwise it may run a bit off with wrong bits, but it wont just run flat out or nothing....double check assembly.

squizzy i hate the things. i just went out the back and started a mower with g4 i know works perfectly and then started one thats a bitch. swapped carbies. they are both set to c and no problem with either starting. i dunno. i know heaps of people hate the G4.
Just my 20cents worth

goodo squizzy . the cam lifter (spider. never seen a three legged one but there ya go) will do it if its not in its three slots in carb body . cable adjustment too if the lifter isnt placed properly it can have that effect . cable has missed its hole and all it does is move full throttle to nothing .
follow the diagram and be sure the lifter is in place . not too hard just takes patients and a little harder if made up from others as they do wear different so its a matter of matching bits for the best outcome .
grooved face is for 125cc plain face is 160cc btw
oh and did you have the starter off ? sounds like a powertorque ?? if you did don reuse the large "o"ring or try n seal it just replace it as they can lead to start/running worries too

they sure can be fickle seanw, but i think most peoples problem with them stems from a lack of understanding how they work and what to look for when things don't run right....like this case here, without seeing how it's set up, it's almost impossible to tell what's happening, i haven't come across this problem before, that i remember anyway!!

mate its like a lucky dip, i want to put a g3 on a 91 model, wont fit. i wish i could help you out more.
i will shut up now and go and paint my missus lawnmower...again

I once had an old mayfair with a g4 on it , it started and ran fine, but something didn't seem right, when i put my hand on the carb it just came off the port, there was no manifold, just the g3 port!! go figure

Yes I think your right we did get over it and it would take a while to find it,as I'm not even sure it was titled about the carbys.
The only difference is the spray tube,which both have.However the G4 has that tube fastened to the end of the jet where as the LM has the tube installed into the carby body.Once the tube is installed into the carby body it is there forever as it can't be removed.
See tubes here.

I believe it was only on the LM,however I have found some on G4's but they could have been changed.The paper work I have points to the LM only.

Thanks fellas for the swag of replies. Just to clarify some suggestions and my earlier report:
1. Engine just runs above idling speed at WOT (wide open throttle)... it will not rev out!
2. Cable adjustment is good - i have verified cam operation from full closed position to WOT position.
3. The spider (lifter) sits in three (3) groves in the carby body and rises and falls nicely as the cam rotates.
4. The carby has the idle adjustment knurled nut on the back cover but it does nothing.
5. The main jet screw does not have the inner ring machined in it so I'm sure its the correct one for the 160 cc engine.

It actually appears to me that the poppett valve is not falling enough to supply sufficient fuel to the engine and I'm reasonably sure its not flooding. Additionally, I don't understand the lettering on the bottom of the poppett - Can any one tell me the significance of the lettering? It appears to me that the poppett is symetrical so it's final resting installed position should be irrelevent????

How can I tell if the carby body is type LM or G4?.... But I'm resonably sure that the internals are a mixture of both and this is where the problem lies..... Maybe the poppett ..??

But really, its got me suffed why the engine does not rev out???

- BUMPS

It's a LM as you said it has the idle adjuster screw.G4's didn't have that.I'll get some pictures for you of the poppet value and show you what I mean.
In the mean time if you have something like start ya bastard,start the engine and squirt some down the air filter tube and see if it revs or not.
That will help as to whether or not the carby is working correctly it may be something else.

Hello Blumbly,
Fisrst of all thanks for the reply
. Just to clarify some suggestions and my earlier report:
1. Engine just manages to run above idling speed at WOT (wide open throttle)... it will not rev out!
2. Cable adjustment is good - i have verified cam operation from full closed position to WOT position.
3. The spider (lifter) sits in three (3) groves in the carby body and rises and falls nicely as the cam rotates.
4. The carby has the idle adjustment knurled nut on the back cover but it does nothing.
5. The main jet screw does not have a groove machined in it .

I don't understand the lettering on the bottom of the poppett - Can you tell me the significance of the lettering? It appears to me that the poppett is symetrical so it's final resting installed position should be irrelevent???? I've tried black poppetts and clear plastic poppets but neither have cured the problem.

It actually appears to me that the the cam contour is NOT allowing the poppett valve to fall sufficcinetly to supply enough fuel to the engine.

I suspect that that the internals inside the carby body are a mixture of both LM series and G4 series carburettas and this is where the problem lies..... Maybe the cam contour and poppett mismatch???

But really, its got me suffed why the engine does not rev out???

- BUMPS

Sorry Bumps I tried to take some photos of the different poppet valves with flash and without flash there bad photos.I'll take some tomorrow when i get home from work (In daylight hours) and show you what I'm taking about.
So maybe you can try the aerostart and or start ya bastard and see if that makes any difference.

sorry to say Blumby, G4 carbys did have the idle adjustment screw. Dad had a Mayfair 125cc when I was a kid and this mower definately had one. Worst carby ever made always had trouble starting this mower

It could well have been changed as all the documents I have here point towards the G4 not having it.

sounds like a blocked exhaust??

have you got the diaphragm on the right way? Don't know that it would cause THAT problem but Iv'e had heaps brought to me for repair after the owner "Hasn't touched it" and the diaphragm has been on upside down. It's an easy thing to do if you rush the install without thinking about it...

Your problem is the fact that the carby is a bitsa. The The parts from the G4 and LM are not interchangeable. The only interchangeable parts are the primer face.
The poppet valve must be set to "C" facing the fuel inlet hole. The "seat" of the valve has 3 distinct steps around the perimeter of it. The different heights determine how much its going to rev. The only domestic machine that doesn't use setting C is the vortex as it has a bigger heavier blade carrier and hence need to rev less.
Are the 2 governor springs in the right place? The longer one goes in last between the diaphragm and the end cap. It also might be too light, and not pushing the valve open enough.

phew !

Different strokes for different folks.

See the link below. Good explanation of the G4 and LM carby. depends on the needs/specifications of the engine.

https://www.outdoorking-forum.com.au/pages/Victa/Carby%20Information/Late%20Model/Victa%20G4%20Carby.pdf

Thanks,
Pete

Thx Big Ted - I'll have another look at the poppett - at first inspection it seemed symetrical in all regards so I thought its position in the carby body as irrelevent despite the numerous letters moulded into it. If indeed the seat is stepped then incorect positioning would certainly make a difference. .... You may have hit the nail on the head! But i still would have thought that shifting the position of the idle adjusting screw would have had some impact on the engine speed?

One last thought after reading the posts is the positioning of the boss of the diaphragm boss - With it facing upwards towards the big spring it will certainly cause a higher loading on the diaphragm that in turn will force the popett to a greater opening and incraese engine speed so I have something else to think about! ..... Conversel,I did read the attachment you kindly sent and I notice that the instrcution was to install the diaphragm with the boss facing downwards - ie. Against the smaller spring but this would unload the diaphragm and reduce poppett opening and re4sulting in an lower engine speed so buggered if i know??????

- Think I'll despatch the mongrul plastic carby heap of sh#it to the shizenhouse and try and find an OLD amal and fit it on!

- BUMPS

I'm sorry Bigted ,but I have to strongly disagree.The only internal parts that were not the same was the diaphragms.Shown below,and the main Jet.Tha carby had a different part number due to the spray tube being installed which can not be removed once in.

This is the G4 with diaphragm and clip.

This is what the LM setup was.Although they are different they can be changed over with one another and work.I myself have done this.
Also every other part is the same and have the exact same part number on them (for the parts that have part numbers on them that is).
This also depends on which poppet value you have as there was (From my knowledge) three different types some don't need anything done.Like the black has the same surface all around it,and no letters on it.
On 100% of the G4's they had a different face which was grey in colour and some not all used a remote primer as there was no primer bulb on the front of the face.
I really think that Bumps carby isn't a G4 as they really didn't have a big run and currently they are hard to find.I know as I've been trying to find more as I have some in the collection with LM carbys and they should have G4's.
Apart from from if he has G4 parts mixed with LM's except for those mentioned it won't make a rats behind of difference.It's all the same.

OK Bumps here's some questions nobody has asked.
What is the mower your trying to get running?
What type of engine is it?
Can you post some pictures for us?

Hello all Contributors

From a historical perspective the original design intention with the G4 was
to make a prime-less carby. It wasn't a success.

My understanding is that there is significant difference in the G4/LM.
Interchangeability between the two is something I can't answer.

Here is a good technical description taken from these forums.
It may be of some help here:-

One paragraph in the ahe attachment that Cyber-Jack kindly provided is qite interesting.
It states that the "newvwhite plastic poppett valve that has a small spigot and some lettering one of which is marked "C" must not be used as replacement for the original bleck poppett valve" (that had no markings.

.... It seems that Victa stuffed around with the LM carburette and made several design changes over the years? I think that I have unwittingly stripped down 4-carburettas and mixed up the parts never imaginging that there could be small but important changes within the mouldings and the internals..... A trp for the in-experianced!

Please also note that in desperation, I acted on the recommendation to change the muffler. When I did this I looked inside the export prt and discovered broken bottom piston ring. I've now sripped off the cylinder and found the bottom ring was broken in tw0 places with one fracture being right on the exhaust port. Top ring and cylinder bore was OK........ I'm now wondering if a broken bottom ring could cause my engine symptoms:
- Erratic up and down engine speed at wide open throttle position
- Unable to idle
- Little if any control of engine speed using throttle lever
I still have concerned with by "Bitza" carby as someone has called it but could the root cause be the broken ring???? ..... Your thoughts please gentlemen.

- BUMPS

Dear Ihatewetsocks,

I can confirm that the diaphragm was correctly installed.
Thx for the suggestion
- BUMPS

All,

One additional thing I should have metioned regarding the poppett is that I has a choice of two - unmarked black poppett or the newer style white poppett with the lettering and the short spigot on the moulding. For no real reason I chose to install the black poppett. If the engine still doesn't run properly after fixing the broken ring issue, should I change the balck poppett for the new white poppett and installing it as described on the earlier posts - Letter "C" facing the carby spray hole???

One other matter that may be important - all the carburettas that I stripped to produce one "good" on had the large diameter clip that secured the diaphragm. I noticed on the parts diagram that cyba-jack provided that one view showed a small circlip as the means for securing the diaghragm. Given that the 4- carburettas that I stripped all used the same large diaghragm, could this mean that all carbys were in fact the same model?


THX - BUMPS

That's why I wanted to to squirt some areostart down your air filter tube as I really thought you were not experiencing carby issues.There not the sort of problems you have with these carby's unless the accelerator isn't connected.I was trying to get to that but I guess in this occasion you just got bombarded with to much information and was taking note of every one.Don't worry it does happen especially when you have three people helping and three different views,but I guess that's what happens on open forums.

Stick with the black poppet value the white one is the older one and the black one should be fine to use.
The cir-clip ones were from the G4 carbys only,the LM's didn't have them.As was shown ealier
Heres another look.
Top two G4's (Of which I'm fairly sure you don't have).
Bottom two LM (which most likely your would be).




If you could post some pictures of what you do have,then that way instead of chatting about the differences we could help with what you do have.

so the powertorque didnt have the small clip ? and the ones i have pulled down here have all been changed i guess . early to late ones too . seems they use either or but enough , good luck with it mate , hope it works out well

I guess it's like everything vccomm use up all the old parts first before using the new ones.
My documents show from a Technical bulletin that the LM was introduced in November 1978.
So I'm guessing that the older bits could still have been used,after all from a business scene it would be silly just to throw out parts that can still be used.This is making me want to count how many G4's I need and ask if anybody has any.I should as I know I'm short on them.

OK well due to this particular topic I decided that I'd better have a look at what G4's and LM's I have and what are some of the differences.Just before I go any further I think somewhere above I have made the wrong statement.I think I said that the earlier G4's had the white poppet values and the LM's had the black.Sorry I think that is around the wrong way.Not sure why I wrote that but I did.
Now vccomm yes I found also that a lot of my G4's had had other updated parts put them I guess due to work being made by a Victa dealer and I too found other diaphragms changed to the newer ones but I still stand by what I've as I have documents that state this and the changes that were done by Victa.
Here is some pictures to help with the things that were different.
Caps.G4 left LM right.

Main Jet G4 left LM right.

Diaphragms G4 left LM right.

The same here,G4 left LM right.

Poppet valves as far as I know there was only three types.If anyone really wants to see the shape difference between let me know I have other pictures to show the difference.

Bottom side I hope you can all see the letters we were talking about earlier.



All in all I had fun checking the changes and seeing how many of each carby I have.Now to work out how many I really need for my collection.

Just re enforces the fact that the first step is ALWAYS know the condition of your engine FIRST

I agree I always make sure engine is worth my time to start with. However when I first started I did the same just jumped in and then found problems. I guess it's how we learn.

Excellent photo Blumbly but one quick question:
Are the three poppetts all the the same length?
....... I'm trying to acertain if one type was specically made to suit the idle adjuster screw on the caby cap? ie. Given that my adjuster has no affect on engine speed it may be possible that the screw is not contacting the poppett and forcing it down to either limit or increase the idle speed?

Are there any comments as to whether a bottom broken ring could cause spasmotic engine operation under no load conditions??? I'm going to replace the rings of course but I thougtht I'd ask the question.

Thx- BUMPS

Yes the poppet valves are the same length they just have different groves and step ups. Expect the black one is just all round and a smooth surface. They all will work with the idle adjustment screw. Just have to make sure the large spring is in place.
Yes broken ring or rings will cause what your problem is. I've found that with 2 strokes they will run with broken rings ,but just have problems like you've found.
I had one of my Twins run and run well it just didn't seem right. I thought it was a vacuum leak or a decompression valve problem. I found (when I pulled it apart to restore it) that one cylinder had two broken rings and a chunk out of the piston,but it still run ok.
So yes that will be your problem.

As Blumbly says Bumps, broken rings will cause running problems in a two stroke because they will cause a loss in compression. Depending on the sealing of the piston in the bore, the symtoms can vary often making it hard to work out, From what i understand, the biggest difference between the 125 and 160 motors was the hardness of the bore and the thickness of the pistons, this resulted in 125's still running , and often really well, with next to no rings left as the sealing was so good, where as the 160 barrel was a lot softer and piston much lighter resulting in wear that affected the running much earlier. combine that with worn crank seals etc, etc, it's mostly why it's the 160 that causes headaches.....

Also with a 2 stroke they (being the rings) have to suck (or have compression) on both the up and down strokes. As to pull the fuel air mix from the carby and through the crankcase to allow for the bottom end to be lubricated. Then pull the fuel mix into the combustion chamber. Where as 4 strokes only needed compression on the backwards stroke. Due to having a sump with oil to lubricant it's bottom end. So less work is needed by the rings in a 4 stroke.

Giday all,
Just a quick note to say thanks to everyone who assisted in this battle.
Case is now closed! .... Replaced the broken bottom ring (top one too but it was OK) and engine sprang into life. It now starts easily, idles beautifully and revs out ro full speed. I was really surprised with the problems that one bottom broken ring posed. Every issue I had with the engine pointed towards the carby but I was on the wrong tram. One suggestion however still puzzles me a little - I think it was Blumbly who suggested spaying Aerostart of "startyahbastard" into the air inlet to determine whether it was carby or "something else" .... I must query how spraying this compound into the engine would help diagnose the problem .... Could you please expand on this fault finding tool??
Anyway it was an interesting journey compunded by the may changes Victa had made to the G4 and LM carburetta ove the years and the uncertainty that exists when a novice strips several units and then mixes up all the parts and starts the reassembley based on using the best bits and the fact that every item mechnaically fitted together.... there were different length main springs, different caps, different poppetts, different diaphragms and even the cams that had subtle differences to their countour profiles(but they did have different part numbers moulded into the unit)and all the bodies "appeared to be the same but part numbers had eroded away so it was impossible to tell if they were in fact differenct from one another. I've attached a few photos to illustrate the differences. I've also added a photo of an Amal 361/1 that I fitted to a Victa 160 for use on my Grand Childs go-Cart .... It superior in every way to that heap of plastic shi#t that Victa produced. I did a lot of research on trying to locate another one but there as scarse as an honest politican ..... they were used on a number of mowers and stationary engines in the 60's msot notably the "Hurrican" Engine (manufactured in Sydney) but Amal (UK) originally supplied it to BSA for use on their 125 cc Bantam D1 motor bikes in the 1950'2 and early 60's. There is a huge cult following in the UK on restoring and even riding the old Bantams and the Amal 361/1 is highly sortafter and I can understand why ....it really fired up the Victa 160 and the gocart literally flys....... and such a simple robust design and manufacture! ...... Don't know why Victa didn't follow Hurricans lead and use them as well???
Anyway as I opened up with .... Case closed!

Well done Bumps and a great outcome, one of the best learning curves possible!!

Bumps I was just looking around and stumbled across this, I realized you had been struggling with this motor for a long time but I didn't think it was quite that long. Anyway we now know how to solve the LM carbs and can mix and match any parts from a dozen carbs and get them to work as a carby should work with a tick over idle and full control over whatever revs you need depending on how high the grass is you are mowing. Great carby once setup, but most things I have read about getting them to work is just folklore and myths