Have to Pump accelerator repeatedly to start after sitting
Hello, I have a 1987 F-250 with the 7.5 L 460 engine and a Holley 4B carb. When the vehicle sits for more than 8 hours I have to pump the accelerator around 20 times to get it to start. Once it starts it runs great. I read somewhere about some kind of a gasket in the carb that can "backfire". I just want to know if this might be the problem or if it could be something else. Thanks.
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Re: Have to Pump accelerator repeatedly to start after...
Check the choke, with cold engine open throttle all the way and let go, butterfly on top should be open about1/4", also I would check your accelerater pump diaphragm sit in the carb. look in carb. pump throttle and see if you see gas spray, if you do pump diaphragm is good, if none bad diaphragm
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Hi Shirley, I think that the problem may be, incorrect ignition timing, or possibly low compression or the accelerator pump which is part of the carburetor. Before doing any work on the carb, check the ignition timing. If there is no improvement, carry out a compression test. If it gives good results work on the carb. It will need removing, stripping, cleaning, re-jetting, assembling and then adjusting. The job is far more difficult than reconditioning an engine and requires expertise and experience. Hope this info is a help? Regards John
carb is sitting to close to hot intake manifold, need phenolic or some type of spacer ,, fuel starts perculating when vehicle shut off perc.s out of vent tube causes it to flood ,then when you do get it started its rich so you stomp on the gas and blow your power valve out try letting it clear out a bit before accelerating , if it backfires replace power valve
Along with the vacuume leaks I would check the carb. The accelerator pump might be out of adjustment or something else in the carb. Currently I have the same problem with mine and I just adjusted it and for 1 day so far it's ran fine but I have a holley on mine. Carb may be dirty also.
The good thing about a Holley carb is they can be custom built to just about any engine. The bad thing about Holley carbs is you can work on it for months trying to get everything adjusted right. You'll have to figure out if it is a lack of fuel or too much air coming in. The accelerator pump travel can be adjusted up or down as well as the power valve.
That would be a Holley, probably model 4160 carb on it. You need to do a little detective work on this. You either need to adjust the choke or find out where the fuel is going after 12 hours.
First, when the engine is running check the Intake and Carburetor gaskets for vacuum leaks. Also spray by the Vacuum reserve canister (Like a coffee can) with either Choke cleaner or a water mist. Either way the RPM will change if you have a Vacuum leak. Fix the vacuum leak if you find one. The engine needs Vacuum to draw in the fuel for a cold start. There are vacuum ports with gaskets (Hidden until disassembled) where the Choke housing attaches to the main block of the Carburetor. A leak here will mess up the tiny piston inside the Choke. (Its under the Black cover and operates the stepup for cold starts).
The black choke dial should be set for 2 marks rich. You should not need excess force on the choke flap to unload it. The choke flap should maintain an opening about 2 credit cards thick measured between flap and carb housing. To get this space you bend the rod pushing the choke flap. This should help the choke work better.
If this does not help, on the next 12 hour interval check for fuel by taking off the strainer on the Carb inlet and remove the line from the carb to the pump. If the fuel line is dry you are losing the Prime to the pump. You must have either a bad pump or a hole in the fuel line from the tank.
Would like to know what you found. The Power pump inside the front bowl of your Holley has a number and you can go to a Holley website to see if it is correct for your truck. The fuel inside the front bowl of your Holley should be enough start the truck. Even if the bowl went dry overnight, the fuel pump would replenish the supply well before 20 to 50 pumps.
if theres a sensation of bucking this is a transmission selonoid 15 to 30 part only automatics has this
now if theres trouble accelerating theres a couple things to look at
fuel filter fuel pump sending unit
clog in fuel injectors or vacume leaks start with break booster most of time this would be it
hesitating when from a standing start, then running well can be caused by having too big a jet size. I dropped the size of the jets on my Holley 4V, and it solved that part of the problem. The accelerator pump will push in too much gas, momentarily "drowning"the engine til you get enuff air to mix with the gas.