Runaway Rochester

[DT1]

I've been having a problem with my Q-Jet for some time now. Every once in a while the throttle will stick when I punch it. I thought it was the throttle cable and I figured I'd replace it when I rebuilt the Carb. I just finished rebuilding the engine and yesterday I was in the middle of breaking in the cam when the carburetor ran away on me again. I also rebuilt the carburetor and everything inside and outside looks fine. I disconnected the throttle cable and started it up and gave it a couple of quick jabs and it did it again. I shut it down and started looking for a problem with the linkage. Nothing looked out of the ordinary so I started it up again. It idled like nothing happened. I tried a few times to get it to do it again but it wouldn't. The linkage looks good and I'm pretty sure the throttle plate inside isn't sticking or I could see it from the outside.
Anyone here ever had a similar problem like this? Any suggestions?

[Lee H]

What kind and how is the return spring mounted. I think one of the primary throttle plates are sticking at full or near full throttle. Try to look down the bore and work the linkage through it range and see if the plates get anywhere near the bore. Might be only a fraction out. May have to remove the card and loosen the throttle plate screws, move the plate a little, run the plate through its full range and see if it gets close.

[Wrenchbender Ret]

If it does it when you really get on it enough to open the secondaries then the secomdary throttles are sticking.

[haysonj]

Originally Posted by Wrenchbender Ret

If it does it when you really get on it enough to open the secondaries then the secomdary throttles are sticking.

I had one on my 85 that did this found it to have a bent shaft on the secondary butterflies

[rustyrodknocker]

check that linkage between the primary and secondary throttles is straight. the bend at the rear should be 90deg. I'm thinking you have checked the springs on both shafts. so next on the other side, see that the choke likage that keeps the secondaries closed is not hanging up and actually holding it open. and at that same pin in the end of the throttle shaft which also is the throttle stop when it hits the tit [which is sharp and wears down easy] on the throttle plate, almost all of these carbs [exept for the ones with a different stop for the smaller motors, this is how the factory limited cfm] will allow for more than 90 degrees of opening. this is pointless because at that point the throttle is closing again. but more importantly it breaks over that fulcrum which makes it hard to overcome on the way back. this is a bell crank no no. you can mod the tit or the pin to limit this like they should have been in the first place.

[Legolas894]

I'll chime in with a little story. I picked up a 350 intake manifold with a q-jet already on it. It was a M4MED. I was going to swap it for my 4MV that needed a rebuild. Anyway, this guy said he pulled it from a his mother's car and it had all the hoses and everything. When I pulled it off the manifold, the secondaries were stuck shut-couldn't budge them with the linkages. I sprayed a lot of carb cleaner getting the gum out and was finally able to move them freely. I was thinking that the old lady probably never drove on the highway and only ever used her primaries.

Long story short:just thinking that you might have a gum problem and the plates are sticking.

[C-10 simplex]

The other thing you'll want to check in addition to the throttle springs (a pic would be nice) and other suggestions as noted above, is do you have a carpet or rubber mat inside?