I do not remember seeing if your mixer was new or not. The reason I ask is whether it has been altered or not. On Impco mixers the power mixture is preset when assembled and should not need to be adjusted. You cannot set a propane engine by ear, it is too easy to get it way too rich. You can set the idle by ear and get close though. Checking plugs will not tell you whether it is running rich or lean unless the electrode is melted off since propane burns completely clean and leaves no residue on the plugs. Realistically you cannot treat this engine like it is gasoline powered, the two fuels are completely different and the rules are not the same. I played with timing in the shop on an engine one time and kept adjusting it until it had the absolute smoothest idle and then checked it with the timing light. It had 50 degrees timing at idle. As soon as the throttle was cracked it would start detonating and shaking though.
The problem might well not be the fuel system at all. There was no mention of how the engine is timed and that is critical on propane. High timing has a hugh effect on creating too much heat in the engine. The cooling system also needs to be in peak condition. Other factors such as a high compression ratio require greater cooling.
Here are guidelines for setting the timing on a propane engine.
On most applications, the timing should be a total of 30 degrees(base and centrifugal) with all of it in by 2500 rpm. What we normally do is disconnect the vacuum advance, run the engine up to 2500 rpm, set the timing at 30, lock it down, then let it idle with the vacuum advance disconnected. See what your base timing is running. If it is low,4-10 degrees for example, you can alter the centrifugal to lower that number and increase the base, still keeping a total of 30 degrees. As you increase the base timing check to see if the engine spins and starts smoothly when hot. If you reach a point that the engine bucks or loads the starter, back off about 3-4 degrees and that is your base timing. Subtract that number from 30 degrees and that will be the advance you need to have. This will provide a good start, strong idle and proper advance curve. We have had some engines run as much as 20 degrees base timing but 14-16 degrees is normal. The vacuum advance should be connected to ported vacuum and have no more than 10 degrees. This helps fuel economy at light throttle positions.
I have 27 years in the propane conversion and repair business and there are several of my systems on crawlers.
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Sincerely,
Buddy Gamel
Precision Sales & Service, Inc.
451 64th Place South
Birmingham, Ala. 35212
877-403-7827, office
205-837-8871, mobile
205-591-2267, fax
[email protected]
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www.alternatefuel.com
www.workhorseservice.com
