The Stovebolt Site Forums The Shop Area Engine Shop Hesitates bad - Rochester B

I've searched and read as much as I can but still have some questions. I put in a rebuild kit in a Rochester B on a 235. It seems to idle ok after warm up but hesitates or bogs badly when hitting the gas, to the point of dying if I don't pump it.

How do I check if the accelerator pump is working properly and what's the best way to check for vacuum leaks? These seem to be the common consesus issues for this problem.

I also noticed an exhaust leak where the exhaust pipe connects to the manifold...don't know if that has anything to do with it. Thanks.

Magfarm,
The easiest of these options to me is the vacuum advance. The distributor should turn when you hit the gas. If it does not, the diaphragm is bad or the vacuum line to the distributor is blocked or open. if that works, then check the accelerator pump. With the engine off look down the carb and hit the gas. You should see a stream of fuel.

Mark

Thanks Mark. The dist. does move when hitting the gas and the pump does put out a stream of fuel. I also sprayed starting fluid around the base of the carb and along the manifold with no change in rpm's. I'm going to check the timing and double check the point gap to see if that may be part of it.

Also check the heat riser, if it it not closing there is not heat to the base of the carb and less atomization when cold.

Try setting the timing up a little. That might help but it sounds like the carb is lean. Pull the top off & recheck the float level. It should be 1 9/32 from the gasket to the bottom of the float with the air horn upside down. You can tailor it a little by raiseing it to 1 8/32. Look at the main jet & the size should be stamped on it. When these carbs go through the rebuilders they mix up parts & applications. If its a 216 engine the jet will be around .052-.053. A 235 will have .055 to .058. You can go to a 1-2 thous. larger jet. Make sure the power piston goes into the hole & kicks the ball off its seat. They have been known to get bent.

I had this issue. Mine was cause by low fuel pressure. I ended up replaceing fuel lines and filters as well as the pump. It ran better for a while. Soon had to replace the carb. Im thinking some rust got in mine somewere and I was unable to get it out. But since I replaced it all has been great.

All else being equal, I'm wondering if you can check for a lean carb situation by giving it partial choke, and repeating the experiment? If it's improved by partial choke (may take a few tries to get a "sweet spot"), think it means it's lean without, and bigger jet and/or higher float will help.

Does this make sense? Somebody set me right if I'm wrong . . .

-Michael

Very good. Makes real good sense. Another way to tell is it works better when warmed up real good.

Are your points and condenser new? If so and the timing is correct, the off idle circuit in the carb may have some junk in it. Do you have a manual? It will explain all the functions of the carb. It doesn't take much junk in a carb to give you headaches. The B is not hard to clean and put a kit in.
Let us know what you find.
Mark

How far (how many turns) out is the idle mixture screw? Bog can occur if the idle mixture screw is out to far, and the throttle plate is completely closed.

Try turning the curb idle screw in slightly to raise the RPM, then turn in the idle mixture screw to lower the RPM back to the correct idle RPM.

Jon.

Where can you get main jets for these carbs ?

Just a follow up here as I was having the same problem. Wrenchbender hit the nail right on the head in my case. I had an .052 jet for a 216 carb in my Rochester that is feeding a 235 cu. in. motor. I couldn't find a bigger jet so I mic'ed a few drill bits until I found one that was .058" and drilled my existing jet out reinstalled the carb for the umpteenth time and my off idle lean stumble was gone ! No more leaving the choke out half way to accellerate.

Moral of the story: check that jet size !