my secondaries stick

[85stanggt]

My secondaries intermittently stay open causing my car to rev up to 2000 rpm. After a few blips of the throttle, I can get them to close or I can manually close them on the side of the carb. I have sprayed all moving parts of the secondary system. It's just when I get on the gas, secondaries open, and I take it out of gear, the car revs high. So is it still the linkage, the diaphram, or something else?

[anthonydalrymple]

Tough to answer without seeing the carb.....

What color secondary spring do you have in there? The tension of the spring could be too light with a strong manifold vacuum signal......

What condition is the secondary throttle blade shaft in? Lots of slop in the main body of the carb to where it might bind? Throttle blades could be hanging up in the bore; you should be able to open them up, shine a flashlight into the bore, & see wear marks.....

[85stanggt]

I don't know the secondary spring color. I wanted to take the cover off to see what is was, but only got the two outer screws out before I said forget it because I would have to take the housing off the carb. The throttle blade shaft I believe is fine. With the engine off, the secondaries spring closed with no problem. The high manifold vacuum interests me though, because I have been tuning the car and currently get about 21.5-22" of vac. at idle. At one point, I was looking into the diaphram spring being too light because the car was stumbling/bogging at low rpms and around corners and getting bad city mileage. This sticking problem seemed to just happen though, which would not be consistent with high manifold vac. that existed before the problem.

[grtskydog]

If it worked fine before, all other things being equal, it sounds like you have a sticky throttle shaft or plate in the bore. I wouldn't tear into the baseplate unless you know what you're doing, though. Heck, for 30 bucks my local carb shop completely rebuilt my baseplate and it looks new now. You have to get those little shaft bushings in there just right or they'll leak and/or bind. If it's a 20+ year-old 4180, it could probably stand a good cleaning/overhaul anyway. Good luck.

[85stanggt]

Wouldn't the primary throttle blade shaft need rebuilding before the secondaries? The secondaries spring back with the engine off with no problem...

The tension of the spring could be too light with a strong manifold vacuum signal......

Don't the secondaries run off ported vacuum from the primary bores? I did make some adjustmens before it more frequently occurred and was getting about 22" vac. Just thought the secondaries were affected by how much air was going through the primaries, creating a vacuum in a pickup line. How does manifold vacuum affect the secondaries?

[grabbergreen84]

There's that metal linkage rod between the primary and secondary throttle plates, I think that's what pushes, and holds the secondaries shut.

[85stanggt]

Yea. What I did was spray the throttle shaft again on the ends and on either side of the blades. Helped alot. Springs back all the way except for like a 50 rpm difference. Then I took that metal rod off and bent that out so it is pressing firmly against the secondaries exactly when the throttle is closed. It's working great now. The spray may not last again but the rod will do its job.