OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Victa Two Stroke Engines G4/ LM interchangeability.

Hi. I'm in the middle of pulling apart a G4 plastic carburettor and have a couple of old LMs lying around and would like to know what components are interchangeable, apart from the float cap, needle and float?
I have already found the metal plate that sits on the diaphragm is very rusted and would like to know what other bits I can swap in case I discover more worn bits.
Would I be better off just trying to rebuild an LM and fitting that to my 500 twin instead?

I mix and match most of the bits, I don't use the black poppet from the G4 and the cam in the G4 needs an adjuster screw so it can come up against, so I prefer to use an LM cam, apart from that I can't find any difference

The main jets are NOT interchangeable. They are quite different, and so easy to tell apart.

Time to post this link again - the full Victa Tech Bulletin collection from G4 intro to LM changeover;
https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=38908

Hi Gadge, I have pulled a number of G4 carbs apart and I have only seen the LM jets in them, so far I have not come across an original G4 carby main jet. I will pull a few more G4 main jets out tomorrow if I get a chance and see what is in them. I guess people have changed them over the years trying to get these things to work, and probably in most cases they would have failed

G'day Norm,
Yes; if they have changed the jet to the LM type, and put the G4 'spray tube' back in loose, 'cos the equivalent LM type tube won't fit in the G4 body, it would always run severely rich.

However, the G4 jet and tube combo can be used in the LM body, and Victa sold LM bodies both with and without the pressed-in LM type tube, under separate part numbers.

These mix-and-match options have probably resulted in the creation of more than a few hybrid LM/G4 carbies...

I have only one two-stroke Victa here, a 1982-3 Mayfair Ute 160 full crank. So most definitely an LM carby, but it has the idle speed adjust knob!

Gosh this is mega confusing. Those service bulletins are tough to follow in parts.
My G4 is going to have to be given the forensics before deciding what bits to chose for final assembly.
I notice it's poppet valve has no abc markings, so does that mean you just put it back in any position?

I discovered that the reason there is no throttle control ( and the motor doesn't stop) is because the cable outer has broken from corrosion. This is why the lever was moving normally but no action with the cam downstairs.
I'm still glad to have pulled out apart as the carburettor has admitted all this gunk mainly made up of rust scale, so this is a great opportunity to clean it all out and see how it runs when put back together properly, with another throttle cable scabbed from a waterlogged power torque.

That's correct. The marked poppet valve is the late LM type, IIRC introduced at the same time as the 'turbo blade disc' fitted to the Vortex series, among others. See p.10 of the G4 carby doco in Section 4 HERE - free download. BTW, some of the earlier pages in this doco are not in the correct order, which does make it hard to follow.