[Red66GTCoupe]

I have a Holley 4160 600cfm with vac secondaries and manual choke. It wont idle well and sputters slightly until you get up over 3,000....after that it runs tops. I have already taken off the front bowl and blown out all of the little crevices and valves and needles. I replaced the diaphram in the accelorator pump. It ran fine for a few minutes after I did this, but now it's going back to sputtering at the lower rpm's.

What could be wrong?

Also, I have a fuel pressure gauge (1 month old) right at the carb and when the motor is cold it's at 5-6 lbs. Once the engine gets hot, it drops to 0-1 lbs.....but here's the kicker...the car still runs fine with the lower fuel pressure reading. Even up to 4,500-5,000 rpm! I have checked the fuel filter and the guage for clogs. None found.

Is this vapor lock? Is my fuel pump bad? Just a bad pressure gauge? ?????????? help.

 

[Axnjxn]

That 0-1 psi while hot, is that while at idle and in park?

If so, you've got issues. Fuel pump I suspect. That, or your needle and seat is letting gas pour in, but then it would probably be gushing into the intake manifold. Why is the fuel pump only acting up when hot (if my theory is correct)? I haven't got a clue.

Edited to note: the above assumes the gauge is working. Is it one of those cheapo Summit deals like I have? If so, I wouldn't rule out a gauge that is inaccurate at higher temps.

 

[camachinist]

Couple questions...

Has the carb always had this problem? If not, when did it start? Had you done any service work to the carb prior to the onset of the symptoms?

Does the engine run this way whether cold or hot? The same? If not, please elaborate...

When blowing out the carb passages, did you remove the metering block? Did you blow out the idle air bleeds in the main carb body?

Have you read the spark plugs since the onset of the problem? If so, what did you find?

Typically, low fuel pressure is problematical more at WOT than under idle or part throttle conditions...although the hot low pressure reading could be of concern, at this point I don't yet know if it is related to the idle problems. How the engine runs when cold, if different, could shed some light on this...

Get back to us...

 

[Red66GTCoupe]

Ok, in response to your questions....

Carb just started having the problems. I had not done any work on the car.

The engine runs just slightly worse at idle when it's hot. When the engine gets over 2000 rpm it runs fine...whether hot or cold.

I did not remove the metering block. I did blow out the idle air bleeds in the main carb body.

Have pulled the plugs, and they look fine.

More help please!!!!!

 

[camachinist]

My bet is either a blockage in the idle/intermediate circuit or a vacuum leak somewhere...

In order to completely clean the carb, it needs to come off and the metering block (and secondary plate) need to be removed. There is also idle fuel flow (albeit non-adjustable) from the secondary side as well...

Carb cleaner then air is my preferred method, flushing in both directions...

Usually, such a problem coming on suddenly means debris somewhere...at least IME...