Hunting at idle.

[slicer87]

 After tightning the body screws on my CCC Qjet I can now get the engine to idle under 1000 RPM. The problem now is that it hunts at idle and the M/C dwell either hangs at 20 deg or 40 deg. The dwell will not hang around 30 deg like it should. Also the idle motor is not even mounted on the carb.

[Cliff Ruggles]

Still sounds like you have a vacuum leak.

Use propane or carb cleaner and check around the carb and intake.

Also check insider the secondaries to see if it is pulling some air around the throttle plates...Cliff

[slicer87]

 The vacuum gauge said it is pulling 19 in of vacuum. The engine does have a mild performance cam in it. It seems to hunt in both open and closed loop modes. It hunts at both fast idle and curb idle speeds. The engine does seem to idle better with the air cleaner on.

[slicer87]

 Could an intermittent vacuum leak cause problems but not show up on a vacuum gauge?

[Cliff Ruggles]

A larger camshaft usually requires idle system modifications.  Have you tried using the idle airbleed system to increase idle fuel delivery to smooth out the idle some?.....Cliff

[slicer87]

 Yes I have, it seems that and the idle mixture jets are not affecting idle very much. I have replaced most of the emission hoses but I will spray carb cleaner to see if I have a vacuum leak somewhere. I am thinking that maybe the purge valve for the EVAP system is bad.

[Cliff Ruggles]

Try this.  Find the best settings with the airbleed adj and idle mixture screws.  Gently "tip in" the choke flap, or place your hand over the choke housing.  Just richen it up slightly, don't choke it out.

See if idle quality improves.

Next, pull off a small manifold vacuum hose, and see what happens to idle quality.  Re-adjust the mixture screws and airbleed screw if/as needed.

Let us know what happens?....Cliff

[slicer87]

I tried what you said Cliff and here is what happened. When I placed my hand over the choke housing the idle did improve. When I pulled off a vacuum hose to cause a leak there was no chage in idle quality. This is with the carb set at prelim settings, idle jets set at 3 3/8 turns and the idle air bleed set with the special gauge.

[Cliff Ruggles]

If idle improved then you need more idle fuel, or less idle air, or both.

Those mixture screws are fine pitch metric threads with tiny holes under them.  Not uncommon to have to back them out 4-5 turns or more to get enough idle fuel. 

I would also turn the idle airbleed screw clockwise a bit and see if this helps?.....Cliff

[slicer87]

 I was able to get the M/C dwell to stay in the 25 to 35 deg range but the engine will still not idle below 1000 RPM. It just stalls out immediately but it needs to idle at 650 RPM.   

[Cliff Ruggles]

Did you try increasing idle fuel delivery to the mixtures screws? 

If it smoothed out in the test above, it needs more idle fuel.....Cliff