Weber Pump Control Rod
 

Just curious if anyone has experimented with pump control rod length with their weber carbs? The reason I ask is because I just recently bought one from Pierce Manifolds to include in my rebuild. Bought the one listed in the parts fiche. When I got it I noticed it was quite a bit shorter and came with a much weaker spring. Upon installation my car would fall on its face above about 3500 RPMs. I read in my "how to build and power tune" book that this is a sign of a control rod that is too short. I put my old one back in and it ran like it should.

Anyone have any similar experiances? The book says a car should run well with 11mm of stroke. My original rod has about 16mm of stroke and runs great!

Any other experiances with different lengths or stronger/weakersprings?

I have been looking for someone with the same problem for so long! Recently rebuilt my 12a bridgeport but it will barely rev over 3500. Starts and runs like a dream but wont want to go past 3500 rpm. My 48 ida weber has the same spring and pushrod in it as it used too but i wondered if it was a carby issue like this. Can they wear out at all?

I don't know if they "wear out" or not or what the symptoms of a worn out one would be.

The length determines how long your pump jets will spray fuel. When I put in the shorter rod I went up two pump jet sizes to see if that would solve the problem and also played with the air bleeds but didn't have any luck. Also with the longer rod in the throttle plates have a hard time returning to zero so I have to run an external spring. With the shorter rod and lighter spring it would come back on its own but the pedal felt like it wasn't even there.

Its actually more like 13mm

Hmm ok. When you said that it would fall on its face at 3500, what does that exactly mean? Mine seems to just hit a wall like ' brrrrrrrrrrr BAP BAP BAP BAP!' until i back off the throttle... Hope that makes sense. Is yours similar when you were messing around with the lengths?

Power just ceased to exist above 3500. RPMs may have been a bit higher than that but as I was accelerating you would just feel the power band die. Wideband also went to like 18.