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