Re: carburetor

Posted by Steve@Advance on September 13, 2019 at 15:34:09 from (66.169.147.211):

In Reply to: carburetor posted by kenfarmall on September 13, 2019 at 10:14:21:

If it was blowing black smoke, or dripping gas running, or dripping gas any time the fuel is on, that's caused from flooding (float too high, float bent or partially sunk, trash in the needle/seat, bad needle seat).

Black smoke but no dripping, could be the choke not fully open, high float level, clogged air cleaner. If black smoke only at high engine speed, the main jet is set too rich.

What was the original reason for going into the carb? Most carb problems are caused from storage with gas in the bowl, or a contaminated tank. If the tank is flaking rust, or is fouled with water, dirt, or old gas, the carb will be quickly clogged or the needle/seat held open with trash.

If you believe the fuel supply is good, and the carb is now functioning, try adjusting the mixtures. The engine needs to be up to operating temperature, and tuned as well as possible.

The idle mixture is the small screw up top. The idle speed needs to be down around 400-500 RPM. Any faster and the idle circuit won't be in use. Adjust the screw for best idle.

The main mix is the larger screw on bottom. It can only be fine adjusted while under actual load, hard to do in the shop. A good starting place though, turn the screw in carefully until it just seats, then back it out 2 turns. With the engine at idle, open the throttle suddenly, listen for the response. If good response, turn the screw in 1/4 turn, repeat the test. Keep leaning the mix until the engine stumbles, then start backing the screw out 1/4 turn at a time, repeating the test until the engine will take sudden full throttle without hesitation. A single puff of black smoke is the goal.

But...

The carb can only function as well as the rest of the engine. Make sure the ignition system is right, check the points, point gap, distributor shaft for side play, plugs, wires, anything that can cause weak or no spark to a cylinder.

Check the compression, valve train. Low compression on a cylinder will cause the loaping you describe.

The gray smoke could be harmless condensation, but it could also be unburned fuel, especially if it smelled like gas and burned the eyes. Unburned fuel is commonly caused from low compression, ignition problems, or a vacuum leak.

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