propane pain

yellowhood

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Mar 25, 2005
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wondering if anyone knows what the big adjustment screw is on the front of an IMPCO propane system..Turned it in and it idles great but when you give it gas hard it feels like it is 2.73 gears instead of 4.56 low power...It is a chevy 350 with an eps intake ,the rest is stock...Is there any instruction web sites??Should I turn it back out and readjust the timing and idle??Please help...:(
 
That is your air/fuel mixture screw. you can use your nose and eyes to set it; if you adjust it to rich - youll smell raw propane in the exhaust badly, if its too lean - you smell none. You want to smell a little in the exhaust, but not overpowering where you get sick.

Or the best is to use a wideband 02 and set it for about 14.5 stoich.
 
The big one is the WOT screw.. If your stuff is working right, it won't affect anything until you're WOT. open that one up a 1/2 turn until WOT acceleration doesn't get any stronger.. That's the poor man's approach.

Your idle mixture (the thin one off on the side) is what you want to do to keep the raw propane smell to a minimum.

Between idle and WOT, the mixture is totally controlled by the amount of air the engine is drawing, and the Impco gas valve. Don't go looking for a new gas valve. The one in yours should run your engine fine.

There's a ton of info here :http://fuelsforum.rasoenterprises.com/viewforum.php?f=5
there's also a site like franzh.texas.net that has a bunch of propane info.

P.S. the screws are just like a carb. in is less, out is more. However, unlike a carb, too rich doesn't keep things cooler...

Yeah, shoving a sniffer in the tailpipe and dyno tuning it is the best thing, but that's up to you.

P.S. Read up on re-curving the distributor.. it can help.
 
pane pain

I turned the idle mixture screw way in ,it was very far out then set idle..Then turned WOT screw in .it was almost out to the point of coming out..still needs
some fine tuning I think.Not sure .Doesnt want to rev out very fast when under a load...But it in alot better than it was...A rough running truck is better than a non running truck.
 
What have you done with your ignition system?
 
pain

all the ignition is factory ..I did adjust the timing and it cranks better and
seems to run better.Any Ideas on getting more power on upper RPM range..
 
propane

anyone got ideas on lack of power on climbs?Does fine on flat ground ,just seems weak when under a load on hills...The WOT screw doesnt change anything that I could feel..I turned it in and out did not feel that much difference..
 
Ignition.
 
pane

what do you mean??Ignition Timing?It should not be a bad ignition because when I pulled the carb off it ran fine .just lost power when went to propane..Impco 425 mixer...
 
Rich said:
P.S. Read up on re-curving the distributor.. it can help.
Click to expand...

This is the advance weights and springs in your distributor. You can change them to make the timing advance quicker or slower based on RPM. As the engine revs, the weights pull on the springs and move, advancing the timing. I guess Rich was saying you could change this around to help some too.
 
pane

Just say I get the curve kit at autozone. do I need to go a little more advanced or alot??I am not sure where my timing is now..It starts good and
has good response..sorry I am not very engine educated..
 
Its gonna take a few trys to tune it. LP gas likes higher compresion,hotter spark and more timing. You cant help comp. so youll have to play with timing and make sure the rest of the ingniton is in top shape.
 
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