4100 carburetor is acting up after complete rebuild

[andy2175m4]

Hi Folks

My 65 Bird has the Autolite 4100 carb (stock) it did not run so I rebuilt the carb with the complete kit, and it worked ok, but had low vacuum, 15 inches, idled very rough, and was spitting fuel out of the main and secondary venturis, at idle, the car revs up just fine, so the problem seems to be isolated to the idle circuits.

So I just took it apart, again, put a wire thru all the holes and passages, again, reassembled it carefully, and then it seemed to work much better, vacuum was back up to 20 inches. Idle was not completely smooth but was a lot better. Then I shut off the car and went to bed.

Next day I get up, and start the car, and it's right back where it started: low vacuum, spitting fuel out the venturis and idling very rough. I did not touch anything, what happened ?

any ideas on why this is happening ? what dismays me the most is the low vacuum. that is alwasy a very bad sign. I checked all the vacuum hoses, brake booster, PCV, etc, all are good, so the vacuum leak is in the carb, somewhere. Visually it looks fine, the throttle plates close well, the throttle plate shafts are tight, all the holes and passages appear to be clear, power valve and accel pump are brand new, what the heck is going on ?

thanks

andrew the frustrated tuner !

[Tbirdgul]

Andrew, just a recent experience I had and hope it helps lead you to a solution. I recently got a rebuild kit and had inadvertently forgotten to add a gasket before installing the power valve. It couldn’t idle and very rough. Since there a quite a few O-rings, perhaps double check one was not left off. Thanks Tony G

[andy2175m4]

I figured it out. after carefully reading all of this excellent free doc. https://www.carburetor-parts.com/assets ... _eBook.pdf i realized that I did not verify that the primary and secondary throttle plates were in the right way, they fit 2 ways, the wrong way and the right way, and you have to verify they fit very snug in the barrels, if not then they are upside down. also I had the main and secondary jets (48 vs 55) swapped, a minor glitch.

so I took it all apart again and then put it back together correctly, made sure the primary and secondary barrel throttle plates were all installed correctly, then it worked fine............OMG what a big difference, now it runs great. the 4100 is a good carb, simple, I am again a believer.

[bbogue]

Andy,
Congrats on figuring out your carburetor rebuild error. Some of us oldsters have made similar mistakes. Myself, it took 3 efforts at rebuilding and correcting initial mistakes with my carburetor. I believe you are correct in posting that these are good carburetors. Well suited for our cars. Pretty simple. Clean the orifices. Flatten the sealing surfaces. Pay attention. I have the same manual from Mike’s Carburetors. They’ve been helpful to me with parts and advice. Mike often answers the phone himself.
All the best.

Bill