q'jet questions

[aaron9999a]

Hi guys.

I've got an '80 K20, 350, auto trans, all stock. Bought it last fall to use as a plow truck. It starts and runs pretty good, but it has no power and gets horrible gas mileage. It's got an M4ME carb, #17081292. I pulled the air cleaner off today to check it out, and it appears to be missing the front vacuum break, and the rear vacuum break is unhooked (according to Chilton). This is the first q'jet I've ever messed with. What is the function of a vacuum break? Would these prevent the air valves from opening? If these are unrelated, what else could be causing this issue?

Thanks,
Aaron

[zieg85]

Welcome from NW Indiana since this is your first post.  The front one (missing) is a choke pull-off.  What that does is slightly open the choke enough to run when the engine is cold.  If it is not there and the choke is closed it will belch out black smoke and really run rich.  The rear is for the secondaries.  I used to unhook that one to save gas, basically turning it into a 2 bbl carb.

[aaron9999a]

Thanks.
 I'll have to check and see if the choke closed back up since the truck's cooled off. If I wanted to hook up the secondary, which vacuum port would it get connected to?

[bobcooter]

How is your air cleaner? Clean or dirty? A really dirty one will cause it act like that sometimes. Just sayin...

[aaron9999a]

Well, the air cleaner was one of the first things I replaced after I bought it. The choke seems to be working correctly, as far as opening after the truck starts. I'm going to replace the plugs and service the distributor, but as it seems to be running pretty smoothly other than the lack of power, I'm not overly suspicious of those.

[hondarider188]

I dont want to hijack the thread but could you elaborate on how you unhooked the secondaries on the Q-jet Zeig. thanks

[Stewart G Griffin]

aaron+zieg,
Not all q-jet applications have a front vacuum break.  My 83 1/2 ton does not.   i'm not sure on an 80---maybe best to get a service manual.     Now, IF the application does not have a front break, then if you look closely at the rear vacuum break, it ALSO controls the choke plate.

If it starts and runs good, then you can probably survive w/out the vacuum break---for now.    This would generally not affect having no power and getting bad mpgs.