I am looking for an answer on why most, if not all, trucks outfitted with Impco LP with model J converters start hard on intitial start up. Once they have been started once they start immediately after that.
My first impression was that the vacuum needs to build up first before the fuel lock opens up which then sends fuel to the converter and the reason that the truck starts quickly after that is that there is now gas in the converter whereas on initial start up the gas in the converter has bled off.
Well that theory is blown because on initial start up when the engine cranks and cranks if you push the "choke" button on the converter it is hard which signifies that there is gas in the converter.
So why does it crank and crank on intitial start up and start immediately subsequent to that?
Showing items 1 - 7 of 7 results.
what mixer or carb do you have,if you have a ca55 impco, the venturi in the carb is probably worn and not pulling open due to the worn sealing ring on the main venturi.It has to pull open to allow fuel into the engine and that opens with engine vaccum during cranking.
Also air fuel ratio.Mine start better when leaned out.Ie no propane smell from exaust.All but the oldest t50 will start off the trck fairly fast.
the vff30 is one clue, and age of cranking battery is another. any impco (pre-tier1 CARB) system needs to crank pretty fast, to draw the fuel in, and using the vff30 lockoff (instead of an electrical solenoid activated lockoff) makes that requirement even greater. put NEW batteries in these trucks and see how they do.
And don't touch the throttle, and do have the the idle speed where it should be, do have the tune up timing and spark plug gap to be correct for LPG machines (which should be different than for a gasoline motor).
I am amazed at how often this complaint is related to spark plug gap.
Are you trying to start them without touching the throttle? I think that would be the best way.
My point is they all seem to have the issue. Right now I have a Cat GP18, a TCM FCG20, TCM FG20......and others.
The symptoms are absolutely identical. Crank, crank and crank on initial start up then start beautifully after that. None of the trucks are equipped with a low oil pressure fuel shut off switch. All of the truck are equipped with a VFF30 fuel lock.
what make of truck-model# and manufacture?
Depends on the truck.Some have a oil pressure fed electric fuel lock.Some electric.Some vacuum.Iv seen jets in vac side slow truck start.Also if you have a stoped up vaporizer they will be hard to start.At least 1 if i remember right has a kill that it oil pressure feed to ignition.
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