carbuerator adjustments.

[flash9376]

So, ive been having problems getting my carburetor adjusted properly. I followed the instructions in the service manuals and restorers guide but im still having problems. Mainly, the engine idles too fast or the engine will pop and backfire as i accelerate it. I cant seem to fix one problem without worsening the other. Any tips on proper adjustment would be most appreciated.

[Tacoma Bob]

Is this a "fresh" rebuilt carb? if the inside stuff isn't right on the outside stuff can do nothing to make it run properly.

[flash9376]

Its a Zenith. I replaced all the jets and stuff on the inside. Its the original float and it doesnt seem to have any holes in it. Its adjusted to close at 5/8". I have the idle adjustment open to about 3 turns(1.5 to 3.5 turns is recommended) and the adjustment needle at 1 full turn to start. The engine idles fast and when i try to adjust the throttle it usually just stalls outs, doesnt even slow the engine down.

[AL in NY]

I would expand on what Jeff/Illinois said, maybe an air leak. Check the mainifold and carburetor gaskets for leakage by spraying them with WD40. If the engine speed changes, you have a leak. If that's OK, check the point gap and timing.

[Ron in Quincy]

Try i and 1/2 turns open on the air adjustment needle and just one turn open to start a cold engine; choke and release immediately. After it warms up you should be able to close the needle seat. Retard spark, keep engine runing as slow as possible without dying; fine tune air adjustment needle for highest rpm. then readjust throttle rpm for smooth running.

[Mitch//pa]

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here are some movies that might help you. one of them has to do with adjusting the carb. but i suspect you may have some other problem going on there. make sure your points and timing are correct and you have a good condensor. also as was metioned no vacum leaks by spraying around the manifold.

Model A Movies

[30cabriolet]

Originally Posted by flash9376

Its a Zenith. I replaced all the jets and stuff on the inside.

Did you install a rebuild kit with new jets? If so, did you flow test the jets? Too many rebuild kits have junk for jets. It is important to have jets installed that are the proper flow. Also, did you check that you have no leakage past the GAV and the idle air screw when they are closed?

[MBI Houston]

Originally Posted by Jeff/Illinois

If you don't feel comfortable rebuilding, the proper way, a Zenith, then I would get ahold of Steve Pargeter, model-a.org, he is on this site too. He'll set you straight with a great working Zenith that you can bolt on and go, and you will have plenty of good driving ahead.

Chris Pelikan is the expert at model-a.org. His website has a lot of valuable carb information. Steve Pargeter is the author of Zenith Model "A" Carborator Restoration Guidelines his booklet also has a lot of valuable information and is available from the parts suppliers. Both sources are must reads.

[Bob A.]

Check out what Al from NY wrote. You could have the best carburetor in the world but if you have a vacuum leak It will drive you nuts. I know from experience because this is what happened to me. I say this all the time: "use a vacuum gauge when adjusting a carburetor or doing a tune-up".