LPG Troubleshooting

[73GreenMachine]

I have had an Impco 225 with an L series converter in my 73 Cortina (250 pre xflow log head) for a couple of years and yet still don't have the car running right.

Some days it will have moments where the car will perform brilliantly, and yet not 24 hours later (in similar weather conditions) it will be out of tune again.

Does anyone know how to set up an Impco 225 mixer? I am aware that they have little numbers written on the gas diaphragm(I have seen 85, 92 and 107 written on them) as well as shims that can be placed between the gas cone and the diaphragm. I think these numbers and shims may be a method of altering the mixture but am not exactly sure how they work.

Is it possible for the converter to have worn out and if so, could it cause the above problems?

Also, if anyone knows of a good LPG tuning place in Adelaide I would like to hear about them.

Thanks,

Brett.

 

[xdee]

Are you using a "clean air" or "feedback" mixer? And how close is the converter to the mixer?

 

[73GreenMachine]

Its a clean air mixer with an L series converter mounted about 15" or less. The pipe between them is fairly short if that is what you are getting at. Here are some pictures:

 

[GTLexus]

Ok a little more info needed

By out of tune again what do you mean, eg, rough at idle, hard to start, not reving cleanly

Are you running points or electronic ignition?

What timing set at?

Majority of LPG issues are caused from ignition issues, check everything, it could be even a lead not sitting correctly (seen this a few times).

What do the plugs look like after the car has been running rough?

 

[73GreenMachine]

GTLexus,

The main issues are rough idle, and not revving cleanly. It feels like power varys 25% between a good and bad day. The state of tune will also change depending on the amount of LPG in the tank.

Ignition timing is 14 degrees BTDC and its an XD Falcon dizzy with a custom bush to fit properly in the pre crossflow block. The distributor has been recurved for LPG, mechanical advance is around 15 degrees (or so one tuning shop told me) and vacuum advance is run off manifold vacuum.

Over the last few days, I have gained some more insight to the operation of the mixer, it seems that the idle mixture screw has a large impact on cruise air fuel ratio, so I have been playing around with that and got it to run very well, although the car felt flat in the cold weather last night and the mixture changed again when I filled it up this afternoon. Does this point to a faulty converter?

 

[johnsixpot]

Having played around with different L.P.G. set ups back in the eighties, I would say that there isn't too much that you can do about the variation in pressure from the gas tank. When the tank is full, the higher pressure will affect the converter to some degree. As the tank empties out, the lower pressure will result in a slightly leaner mixture being supplied to the engine. There is an Adelaide mob selling an injection system that might offer you a more consistant mixture, not to mention more power from the intake mixture cooling effect that you get with the injection set-up.Try www.lpgli.com/index.html for more info on this.