Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Another carb idle mess
richie49:
My quadrajet is off a 1976 cadillac. The engine is a 500 basic stock except the cam. The cam is a high duratian 296 in 296ex 554 lift with a lsa of 108 set on a 104 center line. Lots of overlap. Of course my best bet is to replace it with a cam with a higher lsa like a 112 ,113 ,or even a 114. But Id like to try this out now and replace it in the summer.
Right now it is acting strange and I'd like to see if someone can point me to where to look. Now the problem.I got the idle tubes from Cliff sometime back,I'm slow too many things going on.The engine would start fairly easy but didnt like under 850 rpm in gear. ran rather rough. And that was after I put in a 2500 stall converter.I pulled it back off and enlarged the tubes and down restrictions. Now it starts the same fairly easy.set the idle at 900 rpm and goes into gear with a decent idle. But the longer in gear at idle it goes down to 800,then 700 all the way to 500 still in gear.put it in park and the idle stays at 500 for a few seconds and then kinda snaps back up to 900. It also seems to have a slight hesitation when you try to rev it up. What all you think I need to look at? Oh yes the carb is a 117056230
Richard richie49
Kenth:
I would check distributor centrifugal advance for approx. 1200 rpm start. Too weak springs may cause wandering idle.
And, fuel inlet system for leaks, i would use a new float set at 13/32", a new .135" inlet valve and no more than 7 psi fuel pressure.
For calibration recipe based on intake manifold vacuum signal i recommend getting Cliffs book.
richie49:
Well the thing is the carb wasn't doing this problem before I took it apart for cleaning. While apart I enlarged the Idle tube one size up and the restrictions next size and set the float to 9/32 . Before I changed the tubes and restrictions it wouldn't idle below 800 to 850 in gear.now it will idle down to 500. The only thing I would think is the float level is being affected. The timing isn't moving between idle in park or idle in gear
Richard richie49
Cliff Ruggles:
If the timing is rock solid at idle I'd look at a leak at the needle or under the fuel inlet seat. A tiny leak may not show up as a problem until the engine idles for a while when the leak rate becomes greater that the fuel consumed at idle speed.
I actually see this a LOT these days, leaks under the fuel inlet seat or right at the needle on the seat. High fuel pressure is another culprit we're seeing more and more as fuel pumps are almost all off-shore parts these days. Difficult to diagnose and makes idle tuning impossible......Cliff
richie49:
Thanks Cliff
That's one problem that could be happening because I did pull the float and needle out to check the carb and make sure the various hole were't plugged.
I guess it's time to look again.
Richard richie49
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