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Cold Start Problem

dog

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"I have a 1997 4.3L engine. On

"I have a 1997 4.3L engine. On cold start, it starts fine, runs for about 30 seconds, and shuts down. It takes multiple starts to get it running again and then it runs fine for the rest of the day. The automatic choke seems to be working fine. The spark plugs are getting spark. Any ideas?"
 
"Does it sit for a long time b

"Does it sit for a long time between outings? Can you squirt some gas into the carb to see if it's a fuel issue? Remove the gas cap and listen for suction. If you have this, the vent is probably clogged."
 
Doug.
Kind of sounds like the


Doug.
Kind of sounds like the fuel is draining back into the tank. There may have been enough fuel left in the carb for the 30 second run time and then it runs out. But it shouldn't take that long to pump the fuel back in.
It may be a good idea the have the fuel pump output pressure tested as well as it's suction side vacuum. A quick test of the check valve in tank should be done also.
Keep a watch on the oil level if this is a mechanical pump to make sure fuel is not entering the crankcase from a bad pump. The pump should not be able to leak like this on a boat of that year but one never knows.
Depending on the amount of hours and the way the boat is used it could need a pump. But most pumps do last more than ten years. Good luck.
 
"There's supposed to be an

"There's supposed to be an anti-siphon valve on the tank fitting where the fuel line attaches. If this is stuck open or missing, you can have problems with vapor lock.

I agree- check the fuel pump for leaking. If the diaphragm has a hole in it, gas can get into the crankcase and really screw things up."
 
"Thanks fellas. I do have an e

"Thanks fellas. I do have an electric fuel pump so I don't have to worry about fuel getting into the crankcase. For kicks, I started the boat again and watched it shut down after the standard 30 seconds. As soon as it shut off, I pulled the hose between the fuel filter and the fuel tank. The hose was dry. Is it supposed to be full?"
 
"It's definitely supposed

"It's definitely supposed to have gas in it and if it has been doing this for a long time or you have run it dry repeatedly, the fuel pump impeller is probably toast. That will keep it from drawing the fuel to the pump. I would remove the anti-siphon valve and inspect it. If it's sticking, clean or replace it, then reinstall it.

What kind of boat is it? I was thinking a couple of nights ago about a fuel line recall from close to that year. If you call the boat manufacturer and ask them for a recall list, they can send it to you. If the fuel line was on the list, it could easily be a factor."
 
"..."Jeff- he said the fue

"..."Jeff- he said the fuel line between the tank and filter was dry."

Oops! Missed that. (Senior moment.) That's one of those oil pressure run electric fuel pump circuits: The oil pressure has to come up before the fuel pump will turn on. With an empty carb (from evaporation) it takes a while to get the oil pressure up, THEN the fuel pump runs. By now you've been cranking the motor for a long time.

I installed a momentary button to avoid that mess on my old boat. Worked slick! All you do is take a 12 volt hot lead through a Radio Shack momentary ON switch and power the fuel pump with it. Turn on the ignition, 'prime' the carb, and she fires right up!

Jeff

PS: For those of you with mechanical fuel pumps htat go through this as well, the following trick helps a bunch: Before leaving the boat (or trailering it home), let the motor cool as long as possible, then restart the motor. Let it run for 10 seconds then switch off. That refills the carb with cool, fresh fuel. I do this the next morning after using the boat, before going home, and the motore fire right up."
 
"You could do the same thing w

"You could do the same thing with a Bosch style relay and a "pulse stretcher" (also known as a "555 timer circuit" because of the chip used) on the relay's coil lead. Just turn the key ON, wait a couple of seconds, crank it and go. The pulse stretcher is available from PAC, David Levy, Inc and other sources for 12V electronics. They're used in car audio/security applications."
 
It appears I claimed victory t

It appears I claimed victory too soon. The carb is still running dry on a cold start. The low oil pressure switch checks out fine. The fuel pump is getting power although the voltage is a little low at 10.5 volts on cold start. I don't think it's turning. I can hot wire the fuel pump directly off the battery before a cold start to prime the carb and everything works fine. I'm wondering if I have the right battery. I'm also wondering if I can install an in-line manual primer in the fuel line like what comes on small outboards.
 
"Are you letting it idle for a

"Are you letting it idle for a minute or so after running it hard and shutting it off? Try opening the motor box for awhile after shutting it off, till it's cooler. If it's a vapor lock issue, you'll know the first time you try to restart it. There's no reason you should need a primer bulb- there are thousands of boats with the same motor and they don't have this problem- there has to be a reason for it"
 
"Normally, the engine runs at

"Normally, the engine runs at low RPMs for a while at the end of the day while I'm putting the boat back on the trailer. I'm a little green on vapor lock. Heard about it for years. I've never seen it. Where does vapor lock occur? Wouldn't vapor lock be ruled out if the pump works fine after wiring it directly to the battery?"
 
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