Hope to find some hints here.
I have a 12A I want to get on the road. It has new NGK spark plugs. It seems to start up okay when the plugs are clean. When running it sounds good.
Problem is, after running for about 20 minutes in the driveway, they are all coated in black crust (not wet). Once this happens it is really hard to start. What could cause the plugs to crust up so easily?

 

Cracks in the housings?

Not sure if thats it?

 

may be to rich adjust carb

 

And you base this guess from what? The Ouija board or pulling a rabbit out of a dark space behind you?

If the plugs are fouling that badly, and I take it the engine is idling all this time, check the idle mix setting. Turn the idle screw in until it gently seats, then back it out 3 full turns. Also check the lever on the mop and make sure it's not stuck up. It should be moving in sync with the mop rod. Check the fuel levels in both sight windows.

Are you getting excessive smoke out the exhaust, if so, what color is it?

 

I'm thinking the carb still needs some adjusting. I've rebuilt it and tried adjusting it a few times, but I can seem to make the plugs not do this.
It does give off a little bit of white smoke once warmed up but not for a few minutes. It hasn't been driven since I got (months now) cause of problems. It's just been started for about 15 minutes at a time every now and then while trying to work the bugs out.
I'll go play with the carb adjustments some more in a day or two. Any other possible causes in the meantime?

 

In the FAQ section there is an article by Sterling that walks you through the steps on setting idle speed and idle mixture. Worth reading...

 

I had a look thru the Sterling FAQ and a couple other Nikki carb write-ups.

Did some more adjusting. Seems a little better now.

I was able to start it fairly quickly 4 times in a row. To do this I did the following:
- turn the key to 'on' so the fuel pump was pumping
- pull the choke out about 1/4 inch
- press the gas all the way twice
- and crank

Ran it for about 3 minutes each time. On the fourth time, shortly after starting I was able to push the choke in and it was idling nicely. After a minute or two of warming up, I revved it to about 5000 rpm in park then let off the gas and let it come back down. It went all the way down and stalled out.

Currently the Idle mixture screw is out, at most a turn, which sounds low, but is much leaner than before. It is idling at 750 rpm when in drive. Idle mixture is supposed to be 3 turns, so maybe a little more and it won't stall? What is normal setting for the larger screw above it? Do they vary quite a bit?

What is meant by the 'mop'? Is thet the oil metering pump?

 

Correction, idle mixture is at 1 1/2 turns.
It only starts smoking when revved up.
If in drive and give it lots of gas, it can stall out when returning to idle.
Harder to start when warm.
Plugs look better now.
Sounds good otherwise.

 

What condition is the cap, rotor, and ignition wires in?

I would recommend that you perform a compression test also.