Freshly rebuilt 2bbl for a 67 330. Engine will start smooth for a couple seconds and then gets rough. Then fuel starts coming out of the bowl vent and pressure vent, engine stalls and will not restart.

Any troubleshooting suggestions would be appreciated.

 

Seems like float level is too high, dirt under needle or seat, TOO much fuel pressure.

 

Yuo, flooding from a high float level or leaky needle and seat.

Disassemble, re-check, and re-set float drop and level.

Also, is the float new? If not, are you sure it's not heavy?

- Eric

 

pc of crud stuck in the needle and seat

 

Yep a float that doesnt float would also be a problem. If its metal make sure it is dry inside. If its black composite make sure it is hard and not spongy as that will let it absorb fuel and it wont float properly.

 

Thanks for the diagnosis - back to the disassembly.

 

If the float is plastic, was it replaced in the rebuild? Ethanol in gasoline today will attack the plastic floats from the 1960s and 70s. I always replace the float when I rebuild a carb, and I always replace plastic floats with brass if I can get them.

 

OK - new float - not brass. Float level adjusted to specs in chassis service manual. Float drop (1-9/16") seemed excessive - I think the float would rest on the bottom of the bowl - could I have the wrong size float?

Cleaned needle. New fuel pump. Same problem.

 

Did you replace the fuel pump recently? Several years ago I had issues with 3 new ones putting out over 10 psi and causing flooding issues.

 

Replaced fuel pump as part of troubleshooting. How do I determine if the new needle and seat are bad? This is driving me nuts.

 

Note above that I went through 3 new fuel pumps and had the exact same over
pressure issue with each one of them. My point is installing a new pump does not rule out a fuel pressure issue. You need to actually measure the pressure in order to know that it is correct.

 

You mention float drop. Float height controls needle seating. With carb disassembled and float and needle installed, gently blow air in fuel inlet by mouth, raise float. You should feel resistance when/if needle closes.
There are better carb guys then me on here, just guessing and where I would start looking. Did this problem exist before carb rebuild?

 

Float height and float drop are two separate adjustments each independent of the other. They both need to be done and accurate on a 2 bbl Rochester. Float height is adjusted by bending the float arm in front of the needle and seat and float drop is done by bending the tang behind the needle and seat.

 

Installed new needle and seat...added a brass float for good measure...no more flooding. Thanks everyone for all the input and advice!

 

Great!

- Eric