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Impco LP system-initial hard starting

Number of messages: 13

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duodeluxe
New Hampshire, United States

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?

-------------------------
gitrucks@adelphia.net

Posted 23 Feb 2009 11:17 PM

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proshadetree
Tennessee, United States

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.

-------------------------
"Work leads to profit, mere talk leads to poverty"

Posted 24 Feb 2009 11:22 PM

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howard_w
Colorado, United States

what make of truck-model# and manufacture?

Posted 28 Feb 2009 06:37 AM

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duodeluxe
New Hampshire, United States

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.

-------------------------
gitrucks@adelphia.net

Posted 28 Feb 2009 09:55 AM

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mrfixit
New York, United States

Are you trying to start them without touching the throttle? I think that would be the best way.

Posted 28 Feb 2009 10:59 AM

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edward_t
North Carolina, United States

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.

Modified 28 Feb 2009 11:15 PM
by poster.

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proshadetree
Tennessee, United States

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.

-------------------------
"Work leads to profit, mere talk leads to poverty"

Posted 28 Feb 2009 11:00 PM

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howard_w
Colorado, United States

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.

Posted 28 Feb 2009 11:46 PM

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Drlifttruck

Doc has an IMPCO training manual if you desire,

Contact me at my email signature.

Regards,

Doc

-------------------------
Lift Trucks all the same, just painted different colors Regards, Doc My Email is: Ulsh1@aol.com

Posted 5 Mar 2009 09:25 AM

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Forkliftt
Louisiana, United States

Duo,
I have run across a few JB2 regulators installed on Japanese engines. The correct regulator is a JO2 (orange spring). These take less vacuum to open for engines with less CID. The JB2 was the best choice for Continentals and Waukeshaw which had more displacement.
Steve

Posted 14 Jul 2009 05:02 AM

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bigGlittlestar
United States

Set your timing with a vacuum gauge (when the needle stops bouncing your on the money) if these are older machines. Check plug gap and proper heat range, check mixer adjustments, cleanliness and coil voltage. If you are getting good voltage readings but weak spark check engine and chassis grounds. These are the most common causes I have found in my 20+ years at it.

Posted 14 Jul 2009 01:47 PM

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danny_k
Buckinghamshire, United Kingdom

Hi Doc,
Is there any chance that you can send me over that Impco manual? it would be much appreciated.
My e-mail address is in my profile.
Cheers

Posted 14 Aug 2009 05:54 AM

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ICanFixAnything
Maryland, United States

Hello,

Usually hard initial starting is caused by one of two things in an LP unit. (Once in a while it's something else but 99.999% of the time...) 1st it's usually dirty fuel components. After you start it the goo thats clogging up the fuel system gets a little softer and allows more fuel to flow. 2nd the fuel system MUST be adjusted when the engine is cold. If you tinker around with the adjustments when its warmed up you're usually going to find the next morning its a hard start. Make an adj then give it a try, if it starts right up fine but if it hesitates shut it right off and change your adj then try again. If it gets hot during you're adjustments then you'll have to wait (take your best guess) and maybe come back the next morning and try again (Before they start it up)

Posted 14 Aug 2009 11:34 PM

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