VCCA Home Forums TECHNICAL - 1945 AND NEWER 1965-1970 250 Six. Rough Idle. Stalls When Accelerated

I purchased a '68 Camaro 250 six last weekend, and drove it 300 miles to my home without a problem, except for a rough idle. The next day I added a bottle of Lucas fuel treatment to a fresh tank of gas. Suddenly, shortly thereafter, it developed a problem.

The car idles rough like before, and will rev up when I press the gas, but will immediately die unless I let off the gas. I cannot keep the engine running while holding the gas pedal down, even a little.

I took the carb (Rochester Monojet) apart, cleanded it and installed a rebuild kit. The problem is no better and no worse.

Any help or advice is greatly appredciated.

I would suspect adding the Lucas junk loosened up some "stuff" in the gas tank and the fuel line is plugged up.....or the fuel pump is weak. You may find it will be necessary to remove the tank and ave it cleaned and to blow-out the fuel lines and eplace the pump.

This question brought back some memories. I'm a "two-footed" driver today when driving an automatic thanks to 15 years of driving a 250 with a Monojet that liked to stall at idle unless my right foot kept it running.

Mine always ran very lean with similar symptoms as you describe, mainly when cold or damp.

You also need to make sure your heat stove in the exhaust is working properly after addressing what Gene suggests. Mine ran great after freeing this up (until it stuck again) They tended to rust in the open position so the base of the intake does not get warmed up enough and will definately cause the symptom you describe.

The 6 cylinder distributors were common to get a lot of play in the shaft and the dwell would very a lot causing running problems. You may also want to try adding fuel when you rev it and it wants to die, use a carb cleaner and spray in the top of the carb, if it starts to run better then you need to look at the fuel system, if not start looking at the ingnition system.

Here's the latest update. I replaced the fuel pump (replacing a 43 year old fuel pump seemed like a good idea, regardless). That did not help. I disconnected the fuel line, connected one end of the hose to the new fuel pump inlet, and put the other end in a gas can. That did not help either, but it eliminated the possibility of a clogged fuel line. I checked the mechanical advance and vacuum advance with a timing light. Both checked out good. I checked for slop in the distributor shaft. No slop. I checked the compression. 130 pounds on all cylinders. The carburetor mounting nuts are tight. All vacuum hoses are plugged, but I still have the problem. Also, I cannot feel any suction at the air cleaner intake. Can it be anything other than a leaking intake manifold?

The 130 psi on cylinders and lack of vacuum at the carburetor strongly suggests a leak between carburetor intake and combustion chambers. Without air flow to the cylinders you can't get 130 psi so blockage is not likely.

The problem I have with it being a manifold leak is that the engine will idle, abet roughly. If the vacuum is low enough to not be able to feel it, how does it idle? And as the engine rpm are increased the vacuum should increase not decrease if the leak is between the carburetor and combustion chamber. But if the problem is in the carburetor then it might be just the opposite. I am betting on a carburetor problem. Plugged main jet? or passage? Denny's suggestion of squirting carburetor cleaner in idling engine carb intake to see if it speeds up should help diagnose this problem.

Thanks, everyone, for your help. Those who suggested that the problem was in the carburetor, even after a thourough cleaning, were right. I finally purchased and installed a remanufactured Rochester Monojet, and the problem has gone away. As a bonus, I now have a new fuel pump, pcv valve, vacuum hoses, manifold gasket, and freshly- milled manifolds. Now -- I'm off to enjoy my Camaro!