New gas mixer= less power?
 

Hi all, Not a Volvo related question but an LPG one all the same.

I have an LPG converted 1986 Audi 100. It has the 1.8 4 cylinder golf type engine and a carburettor. Originally it had a gas mixer on the end of the air filter nose but after the air filter was damaged by backfiring and subsequent fire it now has a mixer bolted to the mouth of the carb, underneath the air filter (although at the moment no air filter is fitted) Having the mixer in this position has greatly improved starting and idling and the engine feels much smoother and quieter, overall i'm very pleased! The only problem I have found is that the engine doesn't seem to have the turn of speed it one had and acceleration at speed can take an age, e.g 50MPH to 70 MPH. The car was never fast by any stretch of the imagination but performance definitely feels limited.

Is there anything that can be done to improve the situation? I have been told that there's two brass nuts on the vaporiser, one controls idle speed, the other top end performance, is this true? Any advice or opinions welcome!

A lot of the problem will be down to the lack of air filter. The air filter provides some restriction to the air flow giving more suck to the venturi allowing a richer mix.
Is the venti the same size on both mixers?

It is possible to adjust the fuel mixer, but i need to know what vapouriser you have. The main adjuster is in the pipe from the vaporiser to the mixer - on some systems this is electronic.

I fitted the mixer over the mouth of the carb. Couple of things to look for:

Are there any other pathways for air to get to the engine after the mixer? (e.g. any breather pipes from the crankcase.) If so you will need to redirect them over the top of the carb so that the set up is stable.

There should be, if the system is anything like mine, a 'power valve.' This is essentially a restrictor that curtails the top end flow of vapour to the engine. The way mine is set is to fast rev the engine, then adjust to power valve until the engine rev begins to drop. Then back it off a half turn. It's possible that your alteration to the system has changed the top end flow, though don't ask me how!

I don't know how stable the vapourisers are. I naturally suspect anything with a diaphragm, but have to admit any problems we have had, are largely due to other factors. All the same, the mechanical set up is extremely sensitive, it could be that you overall vapour concentration has dwindled a bit with time. Get a garage to run an emissions test to see how it conforms.

The mixer is an OMVL type (ill go and check the exact model tomorrow), I had to crank the idle speed down on one of the brass knobs on it after I fitted the new mixer. Ill have to double check that there's no other route for air to get in, I don't think that there is though.

The absence of an air filter made me experiment a bit though, with my hand hovering over the carb the revs do seem to pick up and the engine smooths out a bit, also the engine needs a bit of choke to run on petrol correctly. Looks like I deffo need an air filter before I can tune or look at anything else!

The venturi are about the same size on both mixers, although I haven't actually measured them.