The Stovebolt Site Forums The Shop Area Engine Shop I need Help! Monojet driving me crazy won't Idle

I'm still having trouble getting my monojet to Idle on my 1970 C50 with 292. I have been through everything carb has been cleaned out twice. all new tune up parts set points/timing checked several times for vacume leaks etc. It runs better off Idle but rough at Idle. Idle mixture screw must be almost all the way out for it to run. This is a carb that was apart before I got it. looks like it is together properly now. It was leaking down originally, that has stopped. is there anything comon on these monojet carbs that gives them a rough Idle? I've had several monojets in cars over the years and never ran into this? It runs better with choke slightly closed, but not much better. Definitely appears to be running lean. I've been looking for another carb to rebuild but no one has any left around here.

Sounds like a blockage in the slow running circuit. I had a new holley like that , drove me nuts , had a piece of swarf in one of the drillings. Took 4 pull downs and various picklings and high pressure blow thru (both ways) to eventually dislodge the offending bit of stuff.

Can you find out why it was apart before you got it?

Look over the lower gasket between the throttle body & fuel bowl real good. There were 2 different ones. One has 2 holes in a group & the other had 3. If the wrong gasket was used or in backwards it can cause that.

Thanks, how can I tell if I have the right gasket for my application?

The 2 gaskets usually come with the kit. Compare them to the castings or the old gasket. Did you adjust the metering rod acording to the directions?

yes, metering rod adjusted

My 250 with a Mono jet would idle rough, but drive good, turns out it was a bad compression ring on one cylinder. I hope that is not your issue, but you might want to run a compression check. Mine was a new engine too...

make sure you don't have a intake manifold leak. this is a common problem as due to their length they warp. this problem caused me tons of head scratching before it was found. spray a little wd40 around it similar to checking for carb base leak. good luck

When running, spray carb cleaner around the throttle shafts and intake gaskets. Not uncommmon for throttle shafts to get sloppy and provide extra air. A listhg vacuum leak elsewhere (like on intake or bad brake booster hose) will do it too.

look in carb when idling see if you have gas slobbering in if so float level,,float,,seat,, if not pull plug wire one at a time see if you can find problem....doc