What are the symptoms of an oversized carb?

My buddys 67 350 is running WAY rich!! Just a ton of unburned fuel coming out the tailpipes, idles rough and stumbles bad on acceleration. He pulled the motor out for a rebuild and reassembled it with the stock heads, mild cam (220 @ .050) I think. Rpm manifold and edelbrock 750, HEI. I have jetted the carb down 3 stages, still hurts to keep my eyes open

When you pull off the PCV hose on the carb the rpm's shoot up like its sucking air trying to breathe. Timings around 10 BTDC. Not a lot of tunability in the carb unless I keep the PCV hose off. Is this just to much carb for the engine?

Also how many rpm should the engine drop when put into gear on an auto (TH350). This thing is dropping about 450 RPM wont stay running in gear below 900 (and its not smooth), is this because of the carb also?

You guys cured my fix. I thank you all. Sean

Sounds like the carb needs a good cleaning, or something is set wrong.

You are probably getting unburned fuel out the tail pipe=high HC, and an excess of burned fuel too= high CO.

At low speed and idle the carb size has no effect. Same with main jet size.

Squirt carb cleaner into the idle mixture screw holes (remove screws first).

clean the air bleeds.

Also make shure the floats are set correctly and no fuel is dripping from the booster nozzles into the venturi at idle.
Check for too high a fuel pressure
Check choke setting

Make shure the ignition is working right, if points, check the dwell etc

Too large a carb would cause bogging under quick opening of the throttle, high speed bogging where if you let off just a little the car would go better.
Your carb with a secondary air valve should not have much trouble with this.
David



[This message has been edited by davidpozzi (edited 08-20-2000).]

a 750 on a mild 350 is kinda steep,but possible. i'd opt to try a 600 or 650 if one is available"to try".

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My68Camaro (http://hometown.aol.com/Dougs68Camaro/index.html)
Doug G.
68 Camaro
406 ci.

What vacuum reading at idle? Are you sure the primary metering rods aren't pulling up? Try a bit more initial advance (deduct same amount from mechanical, of course). Good luck!

buy some new mufflers

Vacuum was at a steady 7 in. changed carbs came up to 9 in ran better, going to try a smaller carb first then go from there.

BTW Devil 2.5" Flowmaster systemand headers, unlikely he will change the exhaust