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Well, right now im running a 351w, edelbrock alum heads w/2.02 intake valves, TFS 1.6 roller rockers, .528 282 duration comp cams solid flat tappet cam, Performer RPM intake, and a holley 850. (i know the carb is too big but its all i have to use for now) My problem is, when i hit the gas it wont want to move anywhere, and then after a few seconds, it finally catches itself and moves. At about 1000 RPMs its running rough, and popping/coughing, but once it hits about 5000 RPMs it pulls like hell (sometimes). I have a 2 - 5 powervalve in it right now, (thats all it would idle with) and the primaries are tuned right... (i KNOW the secondaries arent tuned right) but why would it be coughing before the secondaries open? (mechanical secondaries)
 

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I have a 2 - 5 powervalve in it right now, (thats all it would idle with)
The power valve has nothing to do with the idle circuit. 2 - 5 power valve? Do you mean a 2.5? That sounds small to me. A 5.5 or a 6.5 might be a better choice. What's your vacuum at idle?

So I'd say the hesitation is from the power valve opening too late (maybe never) or your accelerator pump linkage isn't adjusted properly, see if there is play in it with the butterflies closed. . .

Also, how much of the idle transfer slot is exposed on the primaries and secondaries? If too much is exposed then you may be idling on the main metering circuit. . .
 

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First of all, carb size has no difference on the way a car idles, if it is set up correctly. You could make an 1100 carb idle on a 260 engine...

But, the 850 is a bit too big, you do have a lot of cam and that is what is causing your idling problems. You need to open up your idle air bleeds inside of the carb by .003-.005 and that will make all of the difference in the world. Also, you have to make sure that you have your secondary throttle plates opended up just a bit. There is a small screw that accessable from underneath to adjust those. Also, it sometimes helps if you drill a .125 dia hole in the primary throttle plates....

That would get you started......

Gary......::
 

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To add, a warped main body from tightening the bowl screws too much will cause fuel to escape from the accelerator pump passage to the power valve vacuum chamber causing a hesitation.
Is the power valve diaphragm wet with gas when you tear it down?

A flat mill file can be used to file the main body back flat.

Size of the carb has nothing to do with the idle or the engine running too rich. Too many times a malfunctioning carb is "jetted down" to fix something as simple as a leaky needle and seat or a stopped up air bleed.....
 

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Discussion Starter #7
The car has no problems whatsoever idling, but when actually driving it hesitates untill about 3000 RPMs. It coughs and sputters when you get on it a all, so im stuck just accelorating slowly... like granny slow. :(
 

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Your problem is big mechanical secondary carb, heavy car, no gear and automatic trans, coupled to racing camshaft (engine is essentially the same combo I run in the race car). This means everything needs to be gnats-ass to operate perfectly. Very little margin for tuning errors.

Questions:
Converter stall speed?
Carb list number? Current jet size? Current primary and secondary squirter size? Primary and secondary pump CC capactiy?
Current ignition time at idle and at 3K rpm?
Engine compression ratio?

Examine intermediate circuit of carb for obstructions. Verify sealing and correct function of power valve.

Get back to us...
 

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I wouldnt jump to the fact that its an overcarb problem (I know it is overcarbed but it should run that ****ty) Sounds to me like a secondary power valve thats bad (or either front or back is leaking due to warped surfaces)

I'd block the back PV using a plug they sell cheap, then over square jet by 4 numbers, If you run 82's up front, run 86 in the back. My guess is 80 front 84 in the back if you block the PV, 80/80 if you run 2 PV's.

The last thing if both PV's are good (or the back one blocked) make sure your accel pump is working.

Bottom line to me, that 850 is too much for optimum, but it shouldnt be THAT bad, something is wrong
 

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The engine has too much camshaft and too much carburetion (mechanical secondaries to boot) for the rest of his drivetrain. I'll bet it doesn't have enough compression either. Now, if that 850 was on the combo in your sig line, I'd have no complaints at all. Just as much as the combo in your 70 is right, his is wrong.

I've raced his combo for the better part of 15 years so I would know...
 
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