Can someone help me? I have been sent here and was told this was my best chance. I have an '87 f250 4X4 and elected to build the 460 in it but I cant seem to get it running right. I had the motor professionaly built, Heads opened up, RV cam and a high volume oil pump. I got rid of all the emission stuff, And installed an Edelbrock performer intake, Holley truck avenger 770,Pertronix dist (ignitor III) and coil and installed headers. All good,right? Wrong. Now It runs good until it gets good and warm. Then, it wants to fall flat on its face when I take off from a stop, especially when I've been sitting there for awhile like at a red light. Its as if the accelerator pump just took a vacation. If I only stop briefly it doesnt do it. I've checked fuel pressure, vacuum lines, timing, and made all adjustments to the carb that I can think of. I've installed a cold air intake as well as a 2" extension between the carb and manifold to get the carb away from the heat. I've also tried a 50 cc accelerator pump and am up to a 45 nozzle. Can any of you BBF gurus help me? I am very open minded (and desperate) and will answer any questions you have for me

 

Do you know the cam specs?If it's an RV cam I'm guessing ~ .500" lift.What is your timing set at?You don't need a 45 shooter in that carb nor a 50cc pump.Put the 30cc pump back on and the original shooter.What does the engine idle at in park.Is the carb new or rebuilt.Could be floats not adjusted properly.Generally the Truck Avenger carbs are decent out of the box and may require minor tuning to get the engine to run good.Are the vacuum lines properly connected?Could also be a vacuum leak.I would spray carb cleaner around the intake/carb base first to check for a leak.Then set timing @ 10-12 deg. with the vacuum line disconnected from the dizzy and plugged.Verify that the floats are set to just below the sight screw.Also make sure the choke is functionning properly and not closing when the engine warms up.Also,get rid of the 2" spacer.Thats for high RPM,big cam engines and will only make things worse.Unless the engine is set up for the spacer(fatten up the jets for starters),it'll likely cause a flat spot or stumble/hesitation.

 

Thanks for your help. I'll answer these in order. Yes, I know the cam specs. Yes .500 is correct. I have a spec sheet that gives all info on the cam so if you have any other questions, Let me know. Initial timing is set at 16 degrees with the vacuum disconected from the "dizzy". The extra timing is because i live at 5500 elevation (no detenation). The only reason I started changing the accelerator pump/ shooters was trying to fix the problem i have brought to you. I will put them back. Engine idle at park is 700 rpm. Carb was brand new and floats adjusted properly. vacuum in gear (automatic) is 15 psi so i have a 75 power valve installed. All vacuum lines were checked for seepage with a vacuum pump and appear sound. I have noticed that my vacuum guage "quivers" about 1/2 a pound either way when idling. Something to check? The choke works fine and if you think the 2" spacer is not helping then i will remove it. The jets are 70/76 and the plugs are a grey color. I notice that when the motor tries to fall flat, I can "flutter" the throttle or acelerate slowly and have alittle trouble but it wont die on me. and sometimes if I just push on the gas pedal it will backfire through the carb. Does this help?

 

If your truck is fine at cruise and accelerates smoothly(without stuttering/stumbling)when you floor it,it's likely it needs carb fine tuning.First check that you have .015 clearance between the accelerator pump arm(the 30cc factory one) and the lever @ WOT.Engine off of course.Vac. gauge at 16 is good and 1/2 inch up/down is fine.Now,with the stock shooter in place and the engine warm,accelerate from a stop and if it stumbles with black smoke out of the exhaust (rich) reduce the shooter size by one.If it stumbles/bogs without any smoke,(lean) then increase the shooter size.If you change things in small increaments you'll have a better chance of resolving the issues.I know that for elevation you're supposed to decrease jet size (from factory by one size for every thousand feet above sea level,I think).But your off idle stumble isn't due to jet size.I had a similar issue with a 670 Street Avenger on a 351w Eddy heads Stealth intake and it took some time to resolve the stumble.Had to decrease shooter to a 25 from a 31.Try it and see what happens.460ford.com is a very good site for info.Lots of experience there.I have a #32 shooter in my 460 3310 Holley vac sec.30cc accelerator pump,Stealth intake,10.5 CR,headers,575" cam in a '88 f240 4x4.

 

I have a 76 ford crew cab with a 460 that does the same thing. It seems to run smooth all the time.... with the exception of when it is really hot outside. It does not matter if I am pulling a big load or driving home from work; when I stop and sit for a few moments (even stopping to open the gate to my driveway or a long stoplight) if it is hot outside I have SOL. After the long stop, I begin to accelerate and within the next 30 seconds or so the motor will begin to stall. It appears similar to running out of gas or getting too much gas and then it dies. Sometimes I am lucky and able to pull out of the stall by letting of the gas and then maintaining a constant light pressure on the gas pedal (might just me coincidence... I have tried letting off and flooring it, but this seems to be the most successful). Origionally I was thinking vapor lock, but I am not so sure. I do not have a lot of mechanical knowledge but I do understand some stuff. Unfortunately, not many people around here want to work on older trucks so as this summer is approaching, I am gettin a bit nervous. Any tips are very welcome. Oh and by the way, my 460 came out of an RV...or so I was told from the previous owner. thanks for any suggestions

 

All good suggestions above! One thing missing was to check the vac advance canister to see if it holds vacuum. Just a shot in the dark...

 

I agree that those are all good suggestions. I will start checking each of those one by one and hope that together, they will help. I will also try Additional tips like yours; which are also going to be helpful. thanks

 

Vapor lock is another possibility.Holleys are prone due to fuel bowl design.I run a heat shield and insulate the fuel line from the mech.pump to the carb and any where it is close to a heat source.

 

Normally stubling off the line can be attributed to the engine leaning out, one possiblity. As mentioned above, accelertor pump can be the most common cause. But you have a new carb and have changed the pump so that's unlikely.

So if you're not getting enough fuel, the opposite can also be true, getting too much air. Have you checked for vacuum leaks, especially at the intake to head gasket? If you have a manual choke, you can experiment with it a little. If you are getting too much air and leaning the engine out, closing the choke partially can tend to help the situation. Not recomending you leave it there, just for troubleshooting.

You can test for leaks by using propane, choke/carb cleaner or starting fluid. While the engine is running, spray it directly where all the possible leaks may be...if the engine speeds up, due to it sucking the fuel in, then you've found a leak.

Seems odd that it would only be when hot. Sounds more like your overheating the fuel in the bowl. Engine temperature will remain constant but the temperature under the hood goes through the roof when sitting at a light. As mentioned above....insulating the carb and fuel lines from the engine can help with that

 

It has been touched upon above, but I'm wondering if the problem is that the mixture is too rich during acceleration and not too lean. If you're already too rich and making accelerator pump adjustments to richen even further, it obviously won't change things much which could lead to a misdiagnosis of the problem.

I had a 400 Ford with the Motorcraft 2V and the accelerator pump was set too rich - it accelerated just great when cold (1st clue), but would fall on its face when briskly accelerated when warmed up (it was fine if I eased into the throttle very gradually, 2nd clue). I adjusted the lever on the accelerator pump back one hole and it was just fine after that.

In addition to this, the power valve can be another culprit if it is opening too soon (at too high of an intake manifold vacuum, the intake manifold vacuum drops as the throttle is opened of course). The do make a range of power valves that open at different vacuum levels (often they are different colors so you can tell them apart).

Finally, the other possibility is that your high speed fuel circuit is too rich, and the additional fuel from the accelerator pump and/or power valve is putting it over the top into blahsville.

If you really want to know what is going on, invest in a wideband O2 sensor/gauge. This will tell you exactly what your air/fuel ratio is at all times. This technology is so mature and inexpensive now that I recommend it for anybody running an older carbureted vehicle (esp. one that is not stock and for which the carb. has to be properly matched to the engine).

Or, if you want to do it the way we used to, have somebody follow your truck and watch for black smoke when you are accelerating. And somebody good at reading spark plugs can tell you if the high-speed circuit mixture is within range. So the old-time tricks still work too!

 

What's your fuel pressure?

 

Had the same problem, a new HEI distributor fixed it. With older or rebuilt distributors, the distributors quit when they get hot. Bought a new Mallory for $189.00 at JEGS.