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hesitation at 2200 rpm???
I have a new 392 in my shell valley and I have geood performance at idle and WOT but at slight acceleration I have a hesitation or surge (where it seems to fall on its face for a second) at about 2200 rpm. I have a 750 dbl pumper. I adjusted float levels, adjusted idle mixture to max vacuum (14 inches) at 900 rpm, changed jets from..72, 74, 76, in promary and 78, 80, 82, and 84 in secondary. I have used squirters from 25 all the way to 40 and used all the pump cams. I am pretty sure my problem isnt carb.....Oh, I used the following power valves...9.5, 8.5, and 6.5 and none changed the 2200 rpm problem. my timing is 38 degrees full advance and its the ford dist that comes in the 392. Anyone have a clue???????? PLEASE HELP! Its a crate 392 and I cant get rid of this 2200 rpm problem.......Its only under mild or light acceleration like I said under full power its no problem but when I lightle take off from a light right at about 2200 it lunges forward and the tach drops a few hundred rpm then picks back up. Any ideas??? Is it carb???? Ignition curve??? I am most desperate!
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I say the car lunges forward, I meant to say I lunge forward cause the car stops accelerating...just has a big stumble or flat spot where it stops pulling and even drops rpm at 2200 rpm then picks back up again.
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Just some thoughts, recheck carb base gasket seal, power valve could stand to go to 10.5, clean air bleeds, these have given me fits before, and you might want to set/reset your valves, good luck.:)
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Is this a stick car? At what rpm does the ign. advance come in?
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5 speed car, air bleeds are clean (and its new carb) all gaskets have been checked. I know total advance is 38 degrees, I have not checked when it starts to curve though.....
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valves are per ford, Its a crate engine with a hyd roller in it. I will try a 10.5 power valve but it would seem if it were a power valve issue going from a 6.5 to 8.5 to 9.5 would yield some difference??? no change???
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I'm trying to understand the circumstances that this happens under. So, when you are cruising along at 2200rpm, are you completely off the throttle- then slowly tipping back into it? I'm going to suggest checking the accelerator pump arm travel. If that's the case, maybe there is not sufficent accelerator pump shot to cover the slight opening of the throttle plates. The slightest movement of the accelerator should cause even the smallest amount of fuel to be discharged. The pump arm could be out of adjustment. There should be no freeplay between the arm and pump cam. But in the same respect there must be enough clearance that when you apply full throttle you don't push the arm beyond the pump limit. Set it up so the arm just makes contact with the cam, and when you tap the accelerator you see a bit of fuel shot. I wouldn't go toying around with the accelerator pump cams just yet. This sounds more like a simple a fix. Another thought is what rpm does this car idle at? Do you have the idle set screw turned in more than one full turn? If you have the- You know what, check the pump shot first then get back to us.
Ed !!DISCLAIMER!! NOT RESPONSIBLE FOR BURNED OR SINGED EYEBROWS-NOSEHAIRS.(engine off while doing this:LOL: ) |
I believe your advance curve is coming in too quickly
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Do you have a vac-advance distributor? If so, try disconnecting the vac line and see if that clears up the problem. I had the self-same light throttle shenanigans on my old car, turned out to be too much advance at light throttle/low rpms. I threw away the vac advance on that one.
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If I am reading your post right,you have the Ford crate 392" - 430 hp.
The engine should have come with a print out from Ford.It deals with ignition timing,oil,retorqueing head bolts. It looks like you have too much advance. 34 degrees is the maximum. I would have it all in by 2500-3000 rpm. I would disconnect the vacuum advance too.It throws in too much advance.Ford recommends not using it as well. I would put your carb back to its orginal configuration for now.It should be real close out of the box.Maybe slightly rich. I have the same crate motor but with a MSD dist.,6al and the 750 HP Pro series. Runs Great. Hope this helps some. |
I checked idle mixture screws...I have about 1 1/4 turn out on primary side and about 1 turn out on secondary side. As for the accel pump shot, I have swapped nozzles until I have bogged the motor with too much fuel and starved it for not enough but the that seems to be an off idle thing for my car. I have a 3.00 rear end so at 2200 rpm I am at about 25mph or so. Car doesnt really car how I get to 2200 rpm just as long as I am there,,,,when I get to 2200 it runs bad. Anything under 2100 or over 2300 is exc. As for the dist...The the ford crate unit but I am not utilizing the vacuum advance per everyones advice. I am pretty certain my problem isnt pump shot. Since the 3 power valve I used didnt fit it I dont think it a power valve but I am not an expert on them (I will install a 10.5 today to vertiy that the biggest holley makes wont solve my problems) what do you guys recommend as far as mechanical advance kits for the ford electronic dist with msd box???
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I'm leaning toward timing, or mechanical advance curve. The curve binding, dropping off erratically, or not operatin smoothly under light throttle conditions.
Idles at 14" so asumming no intake leaks or tight valves that is simply your somewhat "radical" cam as 14" IS a low signal. 18 is more "normal" (stock). Off idle up to 2200 rpm under light throttle accelleration is OK, then BAM 2200 rpm and a "stumble" occurs. Something is makeing a transistion right there. Hook up your vacuum gauge and run the hose into the cockpit so you can watch it while you drive. My guess is vacuum is REAL low when you take off and builds UP as you approach 2200 rpm and THEN the advance curve changes. Vac advance suddenly kicks in? Kickc out? Mechanical advance wieghts or springs binding/sticking until higher rpm is gained? Ernie |
The following is from the Ford instruction sheet that comes with the engine.
" The engine is equiped with a duraspark distributor.The timing advance curve starts at 1500 RPM and reaches full advance ( 20 degrees)at 2500 RPM.An MSD 6al or 7al ignition module is recommended to complete the ignition system." " The 392 made best power at 32 degrees total timing." I would advise you leave the vacuum disconnected and set the initial timing at 12 degrees. Also put the carb back to stock for now. |
checked vacuum at idle......14 inches and at 2200 rpm (when car craps out) I have 16" of vacuum, I ran hose into cockpit this am.....so its timing curve?
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Quote:
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On the subject of power valve sizing, With your vacuum gauge visible while driving take the car on an open road to approx. 40-45mph and in your cruise gear(4th-whatever) accelerate up to 60mph as if you were increasing speed but not racing or trying to pass a vehicle. Note what was the lowest vacuum reading you registered. Now take that figure and -.5 that that would be your power valve size. So if you cruise with say 20in hg, accelerate and it drops to 7in. hg. Use a 6.5 p/v. You only want the power valve to open during heavy acceleration.
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- per holley -
A competition or race engine which has installed a long duration, high overlap cam will have low manifold vacuum at idle speeds. If the vehicle has a manual transmission, take the vacuum reading with the engine thoroughly warmed up and at idle. If the vehicle is equipped with an automatic transmission, take the vacuum reading with the engine thoroughly warmed up and idling in gear. In either case, the power valve selected should have a vacuum opening point about 2" Hg below the intake manifold vacuum reading taken. |
I am going to the dyno this weekend if the weather is good, Maybe total timing will cure my problem. I am hoping max HP on the dyno will also take care of the hesitation. Right now I am at 38 degrees total. for tech says 30-32 degrees isright for a 392 but most guys in the room ru more, I will let you know how it runs on the machine if the weather holds. I plan on running it at 32, 34, 36, and 38 total
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