rochester carb problems

[crdnblu]

A couple of other thoughts:

Have you checked the carb mounting base for level?  Some of these old carb bases were prone to warpage.

Also, what happens if you let it idle for 20 minutes or so, set the idle mixture screws for highest idle vacuum, then crack the throttle; any improvement?  It could be too weak on the choke setting.  Cold engine, no choke, always equals big bog!

[chimp koose]

Check for vacuum leaks around the throttle shafts by running the engine at idle and spraying something at the ends of the bushings. If the engine speeds up ,you have found your leak.I have used carb cleaner as the spray but you could use water from a spray bottle or even use propane from an open but unlit propane torch. As for your timing ,are you checking it with the vacuum advance disconnected and plugged? Sorry to ask such a simple question but sometimes we all make little mistakes that send us looking for bigger problems.How many of us have done a tune up only to have a no start problem ,solution ,take the rotor off the bench and reinstall under distributor cap!

[Land Yacht]

Reminds me of my own experience with a 4GC, unfortunately it doesn't help much. To clarify(?), this is the Rochester 4GC, with equal sized primary and secondaries that came before the Q-Jet.  I had the exact same problem on one that had been sitting for many years. It would idle, but just stop dead when the throttle was touched. I could pulse the pedal a little and keep it running, I figured that it was the acc pump that was keeping it going when I did this. Tried soaking it in cleaner,  unfortunately that removed the dirt that was sealing the throttle shaft bushings, after that it would run at about 2000 rpm with the throttle completely closed. Never solved the problem.

[tomslik]

again, have you checked this?


does this have the heat/exhaust passage under the carb?
might need the thin stainless plate under it....


chevy 4gc's have it, so.....
don't tell  us, let us guess, after all, it ain't MY ride home....

[wayne petty]

carbs run on the idle circut when the throttle blades are closed...  this routes fuel past the idle mixture screws...through the round holes that are below the closed throttle blades... these round passages have the tapered tip of the idle mixture screw sticking through them...

once you open the throttle blades a tiny bit.. the idle transition ports are exposed to the airflow/vacuum... these are little slots usually directly over the little round openings discussed above..  it is still flowing around the end of the screw but  this port is metered by  the restrictions  and idle air bleeds......


i really need to get out a carb to better describe it with pictures...  

the idle circut continues to function  and play a part in fuel mixture through out the entire rpm range..

the accelerator pump only shoots a shot when the throttle is opened... once the throttle stops moving farther open the shot stops....


since you have had the carb open...  can you get out the primary booster assembly and use a wire from a wire brush to clean out any tiny holes that you find ...  then put of safety glasses or a face shield and spray carb cleaner through each port until it comes out another hole on the same side...

( i have sprayed B-12 chemtool carb cleaner into my eyes and it is not fun... an i do carb all the time... )( oh and if you lenses of you prescription eye wear is plastic, wear a face shield.. carb sprays can melt the optical surface..... )

[UGLY OLDS]

( i have sprayed B-12 chemtool carb cleaner into my eyes and it is not fun... an i do carb all the time... )( oh and if you lenses of you prescription eye wear is plastic, wear a face shield.. carb sprays can melt the optical surface..... )

You too, huh Wayne :?:  :?:  Now I don't feel so foolish.. :oops:  Melts those lenses  right  NOW :!:  :!:   :cry:

Bob....

[EMSjunkie]

( i have sprayed B-12 chemtool carb cleaner into my eyes and it is not fun... an i do carb all the time... )( oh and if you lenses of you prescription eye wear is plastic, wear a face shield.. carb sprays can melt the optical surface..... )

You too, huh Wayne :?:  :?:  Now I don't feel so foolish.. :oops:  Melts those lenses  right  NOW :!:  :!:   :cry:

Bob....

JOB SECURITY  :!:  :!:  :!:

Vance