Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

Dreaded nozzle drip 17056200

<< < (3/7) > >>

77cruiser:
If it smoothed out by choking a bit, needs more idle fuel or it has a vac. leak.

Cliff Ruggles:
"Really could not get it to run smooth enough to get any reliable reading at any initial advance. Vacuum was fluxuating between 10 and 15 in/va. Started at 8 degrees and moved up to 12 or so. Eventually, I did advance it to around 30 degrees and it seemed to work a little better. vacuum there was around 12, but not steady. Was really hard to get accurate reading as engine was "hunting" so bad at idle."

If you couldn't get it to idle smooth and decent vacuum there is a fundamental issue someplace probably unrelated to the timing and idle fuel delivery from the carburetor.

Could be as simple as how I cured one today.  Was getting my ars handed to me testing a carb done by a good friend.  It was correctly rebuilt, used my parts, and I went over every detail on the carb and couldn't find any issues anyplace.  My friend told me that it ran horrible on his test engine no matter what size idle tube he tried, main jet or APT setting....Hum?

Testing on my engine confirmed his findings.  The carb resulted in HORRIBLE idle quality so I had him take it apart and make several changes to it and with each test no improvement whatsoever.  I was doing other things in the shop each time he made small changes to it but did look it over closely and couldn't find anything obviously wrong.

Right before the last time it went back together for another test I noticed that the carb had been sealed over the bottom plugs with JB Weld at some point.  I hadn't noticed this earlier, but did ask the builder and he said he just left it on because it passed a leak test so I never gave it another thought.  Just to make sure it wasn't causing an issue I did a closer inspection.  I found that on one side there was a very slight witness mark on the glue and low and behold it was sticking up just high enough it was holding the baseplate away from the main casting when the screws were tightened up.

I ground it down flush, put the carb back together and ALL the problems at idle disappeared.  No more lean idle, surging, hunting, no response with the mixture screws, etc.  Yes, one little detail was causing ALL the problems we were seeing.

For what you are seeing it sounds like a vacuum leak someplace, and probably a pretty decent one as you can't get the engine to be happy no matter where the timing is at.  That isn't enough cam in your build to need 30 degrees initial timing to start to get happy......IMHO........Cliff 

Kenth:
What type of ignition system? Does it have correct voltage/current to the coil?

old cars:
"Engine is 9.5 CR using closed chamber heads, with mild bowel cleanup and good flowing valves. Cam is Crower with 224intake, 232 exhaust, .542 lift intake, .514 exhaust. Lobes are at 112 degrees. "

The static CR must be based not only on fuel octane but also intake valve closure point.
If the compression ratio isn't in line with the cam duration , (the closure point of the intake valve) , the dynamic CR, and cranking compression , will consequently be low. This not only kills torque everywhere in the rev range, but also significantly reduces the engines low end output.

A good test to establish that an engine has a high enough CR is to do a cranking test. Assuming that the rings and valves seal perfectly, then even a modest street motor should show at least 180 psi if cam and compression are roughly right. For a regular use performance street motor expect to see 200 psi.

Assuming no pressure is lost to leakage, anything below these levels indicates too low a CR.
For these reasons it is important to follow the CR requirement given for each cam. If for some reason the required compression ratio for a cam can't be obtained choose a shorter duration cam; you will like the results better.

68rs/ss:
Thanks for all the replies. I did manage to get it to idle with no nizzle drip. RPM hovered between 790 and 840. Vacuum was between 12-13. Initial timing was 12-13 degree's. I will see if i can get it any better tomorrow. Hot restarts are not happening. I went through carb again and changed both top and bottom gaskets. I did find the new base gasket was split and separating. Replaced with old one. This seemed to help.
The past few days, I have been doing alot of reading on cam selection and CR. Thanks "Old Cars" for the reply. So what is a desirable Dynamic CR for a good street engine. My cam card says intake closes at 40 degree's ABDC. used a calculator on line and it came up with 8.78: for my combination (if I did it right).
Phil

Navigation

[0] Message Index

[#] Next page

[*] Previous page