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I'm having lots of problems with the 2bbl rochester on my 283. It runs real rough at idle and I have to keep my foot in it to keep it running or else it stalls. Have to put the pedal to the floor to get it to restart. When I shut it off, too, I can smell gas. Also, when I do start from a stop it hesitates real hard, then picks back up. I have rebuilt the carb and tinkered with the idle mixture screws and the float level. Your suggestions are appreciated. Thanks...Tom.

It sounds like the float is to high and flooding over. Is there a lot of black smoke out the pipe?
Also check for a vacumn leak under the carburator. Use a long small hose and listen for any leaks. Joe

Tom, sounds like it might be a vacuum leak. Check carb flange bolts for tight and vacuum hose for leaks. Jacques

As a matter of fact, yes, there is lots of black smoke under hard acceleration. I thought it was because there is too much unburned fuel in the cylinders washing past the rings. I can smell gas when I change the oil.

I sprayed starting fluid around the base of the carb yesterday and there was no difference in the idle rpm. By vacuum leak do you mean to check the vacuum advance or something else? I have a gauge to check it with.

Thought that the flooding problem was due to the needle not seating in the valve correctly or being the wrong size and fuel is seeping past the valve when shut down. Why would the carb bleed down into the manifold flooding the engine when it's shut down?

Also, by the float level do you mean when the float is seated at the top of its stroke or the float drop? Thanks for your help

There is too much unburned fuel in the cylinders, but its because the fuel system is screwed up. The engine is getting too much gas at some situations (acceleration), and too little in others (idle).

A carb with a leaking internal gasket, or a float level too high will let fuel drip into the intake when the engine is shut off. The gas can actually siphon itself into the intake.

A float that binds on its shaft, or dirt and crap from the fuel lines/tank will also cause the needle not to shut off fuel when the fuel bowl is full, thus the carb floods. Black smoke can also be caused by a sticking choke or an accelerator pump that is out of adjustment. Loose main jets, metering rods or fuel enrichment circuits could be out of adjustment or broken or plugged.

Poor idle can be caused by a bunch of things. Ign timing, plugged idle passages in the carb body, vacuum leaks in carb gaskets, any vacuum line, or intake manifold, or misadjusted carb can make an engine tend to stall at idle. The vacuum advance canister can go bad, the brake booster can leak, and the vacuum modulator on TH-350 and 400 trannys can cause problems if they fail.

good luck

chip

Poor idle can be caused by many things, among them vacuum leak, ignition problems, or carburetor problems.

Assuming there is no vacuum leak, and the ignition is working correctly (check these FIRST), we could then turn to the carburetor.

Using a vacuum gauge (setting for highest vacuum), or setting for the "fattest" idle can cause both erratic idle and hesitation from stop. Highest vacuum will always occur when the throttle plates are closed (vacuum is measured below the throttle plates). This forces all of the idle mixture to be drawn through the lower idle port (behind the idle mixture screw), and nothing being drawn from the idle transfer slot (vertical slot just above the throttle plate). The idle mixture screws will have to be out several turns. This causes a phenomena in the intake manifold known as "puddling" where droplets of fuel adhere to the intake manifold (not sufficient runner velocity to pull them into the cylinders). This is a VERY rich condition, and the idle will "hunt" as the mixture actually reaching the cylinders is not uniform. When the throttle plate is opened (starting from a stop) the runner velocity is increased, and pulls ALL of the droplets into the cylinders causing a too rich momentary stall (hesitation), followed by tailpipe smoke when the engine catches fire again.

Solution: set the idle mixture screws leaner, and use the idle positioning screw (on the side, the one that rotates the throttle linkage) to set the idle RPM.

Remember when adjusting idle, an adjustment to a rich engine may make no difference unless the engine is REVed to clean out the intake manifold.

Jon.

It sounds to me like your power valve is stuck open. I had a Rochester 2G on my jeep. The dreaded PO had bent the power piston shaft and it hung up. A replacement fixed it. It ran way too rich.

CarbKing....WOW!!! I came to this thread looking for a clue on how to adjust the Rochester "2 Jet" on the '56 3/4T I just bought, and instead, I get the reason behind the goofy things my 500 cfm Holley has been doing since I set the idle mixtures with a vacume gauge. What you said makes perfect sense and is EXACTLY what my carb/engine have been doing. The Holley is on my 1964 GMC 1002 w/305E. Mine just cuts out and when I hit the accelerator it fires back up. In lower altitudes, when it fires back up, it would give a HUGE backfire!!