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Thread: Secondaries sticking on 4150

  1. #1

    Default Secondaries sticking on 4150

    Looking for some suggestions. In short have a 700 cfm 4150 carburetor that originally had manual choke and mechanical secondaries. Converted it to a electric choke and as I was checking the operation I noted that the secondaries would briefly stick in the WOT position. Initially I believed the accelerator pump cam was hanging on the electric choke mounting boss (super close), but after doing a lot of additional looking and checking don’t think that is the case. What I found is the lever that goes to the accelerator pump off the cam is seems to be hanging up once the lever gets onto the cam flat. It’s almost like the secondary return spring doesn’t have enough spring to pull it back off off the cam flat. If I lift the lever manually he secondaries close no problem. I actually gave the return spring an additional wind around the shaft to see if that would help and it didn’t stick anymore on the cam, but I put the spring back the way it was (seemed really soft/weak), but I know you can because shaft wear if the parts are rated for the tension. It has the red accelerator pump cam on it mounted in the number 1 position.

    Carburetor as best I can tell is largely in the out of box configuration. It’s on a mid '70s truck engine with peanut port heads that ended up in a '68 Corvette my brother owns. He’s military and while he’s been out of country I’ve been tasked with getting this thing running as right as I can.

    While I know the basics about how carbs work (grew up on a farm and rebuilt countless updraft carbs on tractors) I generally haven’t messed with automotive carbs much. Is there something else I should be looking at here?

  2. #2
    Join Date
    Jan 2010
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    Brisbane, Australia
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    Default

    Quote Originally Posted by kossuth View Post
    ...and as I was checking the operation I noted that the secondaries would briefly stick in the WOT position. Initially I believed the accelerator pump cam was hanging on the electric choke mounting boss (super close), but after doing a lot of additional looking and checking don’t think that is the case.
    How can the secondaries stick in the WOT position unless the primary is also wide open?

    Add some lithium grease to the cam and pump lever contact area. Running dry wears the cam and lever. Gary

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