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.