ATC90 Plug Fouling

[Frankencelery]

I have only about 10-15 hours on my ATC90 engine rebuild, and it's started smoking and fouling the plug. The fouling doesn't look oily, but more like carbon, but I'm having to clean or replace the plug after every 20 minutes of riding. I'm not quite sure what's changed. I had rebuilt the carb at the same time as the engine, which got new valves, rebore, piston & rings.

Anyone have any ideas where I should look? I'm tempted to replace the carb, because it's always had a problem idling anyway.

[super90]

It could just be your jetting. If its smoking black, its probably too rich. Mine smokes a little black at high rpms, and my friends smokes blue (oil). You could play with the carb and rejet it and lean it out some and it should stop fouling them. Mine was really rich before then i went down a couple sizes, lowered the needle clip, and played with the screws and got it to run a little leaner. It still is a little rich but never fouls plugs. I also drilled the airbox lid and it breathes alot better now.

[Frankencelery]

I'm pretty sure I already moved the needle clip down one notch a couple months ago, and played with the pilot screw (which really only affects idle anyway) and had no luck. I have the stock ATC90 air filter, which has that crazy routing through the frame. Replacing it with an aftermarket filter would surely lean it out, but I'd rather leave it stock if possible.

[team-red-rider]

moving the clip down makes it richer...aka the needle gets lifted more letting out more gas

[maxfior]

Can you tell if the engine is using oil at all? You said new valves, did you put new seals in too? New gaskets and all that. Hard to tell, it could be Jetting like Super90stated, would it be possible to run a plug with a little higher heat range with out causing damage? Let us know what else you find...

M.

[super90]

moving the clip down makes it richer...aka the needle gets lifted more letting out more gas

Thats what I meant. I always state it literally. As in actually moving the needle "down". I forgot you had to move the clip up for the needle to go down.

[Frankencelery]

Uh...yeah what you said super90. I think I was saying it wrong too. I think I moved the NEEDLE down which means I moved the clip up...but now I'm not sure! I'm going to have to tear it down and make sure I did it right.

I spent an embarrassing amount of money getting this engine redone. I took the head and cylinder to a machine shop, got the valve seats redone and matched to new valves, new stem seals, new piston and rings, etc. It shouldn't be burning any oil...but I must admit that my first thought when I saw the smoke was that it was bluish in color, and I'm still in denial that was what I saw.....

Let me change the plug, check the needle clip, and report back to you guys.

[super90]

I thought mine was blue at first too. Try it in a dim lighted area. When I did it in my garage with less light and watched it against it a white wall I realized it was black/gray.

[Frankencelery]

I'll be damned. The problem was between seat and handlbars after all.....the rider, that is. As it turned out, I HAD moved the clip the wrong way, and moved the needle up rather than down. So I moved the clip two notches UP this time, cleaned the plug, and ran it around for a bit. I'm still not happy with the idle, but it's not smoking anymore. Must've been too rich. I pulled the plug after running about 10 minutes, but couldn't really tell much. It didn't seem to be carboning up again, so I'm hopeful that I've got it resolved. Seems like maybe I lost a little power though. I'll ride it more later and work it some more.

[Frankencelery]

Ok, I rode the hell out of it tonight, and i have lost some power. I now have a hesitation at low RPM, but no smoke and no fouling. It's especially problematic when switching gears. I need to really wind it up in first before shifting, or it bogs when it hits second. I need a notch between the notches! Or do I start playing with jet sizes?

[03 ORANGE SHEE]

my 1973 us90 does this, 100% stock, and stock plug. ive never messed with the carb, but i too get the carbon (dry) on the plug. on the us90 models , you do NOT oil the air filter it states this in the owners book

[Frankencelery]

Well, my 90 is mixed. It started out life as a '73 US90 but I've changed the engine, which is now a '76. However, the carb and air filter is still probably '73. Not supposed to oil the oil filter, huh? I'll have to check that. Can't remember if I did that or not.

[03 ORANGE SHEE]

yep, oiling the filter makes the little engine run rich, i think a newer year 90 they changed the carb and air filter and then from that year on you oil the filter like all the other trikes