Fuel calibration???

[Nelson43]

I pulled the 362 LPG engine out of a 4020 and put a 340 gasoline engine from an old 105 combine in it. Using the intake manifold for the 4020 I hooked everything up and cannot get the engine to run smoothly on LP. A mechanic told me that the carburation for the LP system is set to run on the 362 and it will never work on the 340. Anybody have any suggestions on this. The engine ran fine on gasoline when it was in the combine. Now it misses and backfires continously.

 

[DONMYEIL]

For one thing the compression is lower in a gas engine than an lp, this will make it hard to start in colder weather as well. spark plugs for lp are gapped at .015 as I remember.Timing is different as well. Sounds like you could have an air leak in the intake and/or leaky valves .May have a build up of carbon causing the lp to explode early. Just a thought.

 

[Jerry/MT]

The carb should be adjustable or have replaceable jets. I don't know what the timing or advance should be for this system, you'll have to sort that out. Generally speaking, propane engines run at higher compression ratios that gas engines.
Try advancing the initial timing about 5 degrees and see if that helps. See if you can find the main jet adjustment and open it up some. Do these things separately and keeptrack of what you are changinge and how may turns or degrees, etc so you can find the trends.

Good Luck.