Carb problems

[homer]

Need some help -- have a holly 750 that was working quite well until today but had a habit of backfiring through the carburator on cold starts. Engine would stall and a smoke cloud would puff out of the carb. Today the engine would sputter under acceleration and even while standing still while revving. Tried some carb cleaner which seemed to help a bit. Have to admit I am a novice in this area but have tried to research what the problem may be -- timing, power valve, possibly condensation??? Any help would be great.

[pbrown]

Your initial timing is probably off or you have a problem with your distributer. This may have blown a power valve in the carb due to the back firing problem.

--Patrick

[homer]

What is the best way to identify the cause of the problem -- prior to today the engine ran great no issues with sputtering while underway.

[Brent]

So many things could cause this.

Check the easy stuff first. Timing could be slow, is the dist. tight? Pull the valve covers and check the valve lash you could have a problem in the valvetrain causing a backfire. Then check the timing and see what the initial timing is first, then see how the mark acts when slowly increasing rpm (does it jump and bounce around or act smooth)If it acts rough check the dist. adv. mech. Does it total where you want it? Then check the plugs and see if you find one that is suspicous. A blown power valve will cause a motor to be very rich and emit black smoke but will not usually cause a backfire throught the carb.If the intake gasket lost seal or had a seal get sucked in you could have a very lean cylinder causing the problem. With the motor running spray carb cleaner around the gasket area on both sides and see if the motor reacts to it. If the motor rpm increases, that cylinder is leaking and you just found it.
What ignition system are you running?

Brent

[homer]

Running MSD 6AL -- after spraying carb cleaner in the carb engine ran well while revving in the driveway -- I do get a small puff of black smoke on the initial rev but then seems to be ok --

[WBofTN]

Homer:
Let me know what corrects your cold start issue. I am experiencing
the same exact problem.
WB

'93 Unique 427/351W/4sp

[WBofTN]

Homer:
Let me know what corrects your cold start issue. I am experiencing
the same exact problem.
WB

'93 Unique 427/351W/4sp

[spd4me]

I had that problem with a Holley Double pumper once. The major problem was the floats were either sticking and not letting any gas in the bowls or they were not sealing off and gas was just dumping intoo the intake and enentually flowed out onto engine. That's scary!
Make sure your floats are adjusted to right level by removing the small screw on side of bowl to see level of gas and installed new gas filter. If any of you guys that are having probelms with carb adjustments, I have a four page instruction sheet that came with mine and explains how to adjust all this stuff.

[nolastyankee]

All,
There are several books on tuning and rebuilding Holley carbs. Check HP motorbooks or type in Holley carburetor on Amazon. The book I have is 200+ pages of building and tuning tips for every make and model. They also cover exhaustively the operation of the carb. It is not light reading by any stretch of the imagination, but is by far the best source. There is a reference with 40+ symptoms and suggested remedies. It is the best $20 I spent on my Mustang.

Unique 9122 - 289 FIA Cobra - The Legendary "Spence" Car

[Oldtimer]

Here is a good source for Holley tuning help
http://www.bob2000.com/carb.htm

Rich

[homer]

tried the simple solution first and thankfully it worked -- took of the air cleaner and sprayed quite of bit of carb cleaner into the carb -- did the same thing while the engine was running -- took the car out for a spin and the problem had been corrected -- I think that the backfires through the carb caused junk to build up that needed to be removed -- also tried a different sequence when starting the engine -- pumped the gas to the floor 4 times and held the pedeal 1/3 of the way down to the floor -- engine fired immediatly and did not struggle with fuel supply at all

[eliminator]

On the Holley books, there is some great material in all of them, unfortunately in all I have read they assume your a "Drag Racer" and not a "Street and Road Racer". So you just can't take everything they say as the Gospel.

Rick