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

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