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Since early October I've run into a warm start issue, basically morning cold start is just a turn of the key and tap or the peddle to engage the choke to idle at roughly 1500 to 2000 rpm. After the engine is warmed up and stopping for fuel or quick run into the store, say less than 30 minutes, I have to pump the gas and try several times to get the engine to start, sometimes not every time, turning the key to the off position pressure puffs out of the carb and a couple times even backfired while trying to start and turning the key to the off position.

What I am running and have tried,

79 4x4
G200 block
G180 head shaved .015 with cam and rockers from G200
Weber 32/36 with Offy intake (thanks again Moke )
Pacesetter header, 2 1/2 inch exhaust all the way out with Magnaflow muffler
Pertronix ignition and coil.
16" electric fan on a thermal switch (might install some kind of manual switch so it does not turn on when trying to warm start)
Airtex 2.5-4 lbs electric fuel pump.
Replaced all the rubber fuel lines.

Prior to the start problem I was running a bypass line to relieve some fuel pressure and everything ran great, Weber was tuned to specs except main idle jet had to be adjusted out a little for more fuel at idle. Timing set around 10 degrees from ported vacuum at base of carb and pcv running off the manifold. For the check valve from the oil pan and fuel vapor line I attached a tube to the bottom of the air cleaner, since it pulls air it may as well be clean air. So I don't have any vacuum leaks or spewing oil from the oil cap or dipstick.

Since the problem suddenly started I have pulled the carb checked the float level, checked for dirt and any internal problems, found no issues. Bought a re-jetting kit and found the .75 main idle jet works best with the updated Weber adjustments, also tried up sizing the main jet with no luck. I did increase the air correctors on both primary and secondary to 180 and 170 and that did seem to improve performance some, not sure if the average elevation of 1,100 feet here in Phoenix warrants bigger air correctors.

Of course the first thing I checked was the fuel filter which looked clean but I changed it anyway, fuel pump was about 2 months old in early October and worked fine. Removed the bypass fuel line and put a proper fuel pressure regulator on, recheck the carb idle adjustments and float level. Had to replace the 3 month old Airtex pump last week since it was not working properly, 1 year warranty and it lasted 3 months . Re-check everything again set pressure regulator at 2 lbs, 3 lbs seems to bog things down a little, probably going to reset it to 2 1/2 lbs for in town driving and use 2 lbs for off road since Weber recommends 3 lbs normal street and 2 1/2 off road.

As of today with all the fine tuning The LUV runs amazing, have the idle set about 950/1000 rpm very smooth, acceleration is smooth, even prior to all of this everything ran great but I have noticed if I drive conservatively my mpg has climbed to almost but not quite 30 in town. (still need that 5th gear)

Sorry for rambling on, just trying to be thorough. So has anybody else had this warm start problem? I have searched for info on why this happens to the Weber 32/36 and most common issue is fuel heating in the bowl, I am sure this is not my problem since it did not happen during the 110+ days here in Phoenix. The only conclusion I can figure is the fuel mixture change they do in October through April.

Please, any suggestions on what I may have missed? It does get frustrating/embarrassing to start especially if it backfires or when it does finally start I have to pump the gas to get up to idle speed.

Almost forgot, I was running plugs for a 1.9 and switched back to the G180 plugs after the problem started, gap set around .40. The color seems right when I checked them the other day, golden brownish but with a little buildup possibly from having to pump it so much to get it started.

Thank You in advance for taking the time to help.

Two things only come to mind. As backfiring is nearly always a too lean fuel mixture my long range guess would be either a weak accelerator pump shot of fuel, or--- my next guess would be a change of fuel mix---more ethanol for example.

I'd be thinking choke related. My 79 with a Weber was behaving like this shortly before I quit driving it full time. Started great cold, but was hard to start warm. My theory was that the choke was out of adjustment or something had gone wrong with the wiring to it. However, I never got back to working on it to confirm the problem.

There is a pretty good doc here: http://www.webercarbsdirect.com/v/vspfi ... 0Guide.pdf

A ways down into it there is a description of the choke adjustment procedure. Make sure you can get back to where it is set now though.

Another heat related item to look at is the vacuum switching valve and EGR if you have them hooked up. I'm not sure on the offy intake but on the stock into there is a valve on the front of the intake (usually blue) that opens up when warm to activate the EGR. If there is a leak there that could cause a vac leak and lean out the mixture, and with the VSV it would only open when warm.

_________________
95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)

MEPR: Man, my 4x4 makes all other LUVs look good

Thanks for the suggestions, I'll give them a try and let you know what I find.

Checked the accelerator pump, it seems o.k. rebuilt the carb almost a year ago, push it in while the motor is running and it revs up. Pulled it off and no tears, spring is good.
Choke works, settings are good. Have not tried different fuel yet but I can get it to start with a shot of WD directly into the carb.

The Weber was on the truck when I bought it so it's seen some wear, linkage works fine, although it does have a little play in it. So if different fuel fails to solve the issue I may have to invest in another re-build kit I think I saw some type of replacement bearing for the throttle valve so I may have to look into that.

One other issue I forgot to mention, I do get some dieseling once in a while when I shut it off.

Thanks Again

Cleaned up the spark plugs, ran the tank to almost empty and put in some Chevron 91 octane fuel. Back to 1 key start, no pumping the pedal for 5 minutes . On the positive side got the carb well tuned.