KDXRIDER.NET

Got my first 2smoke bike. 85 kdx 80 little run time but had been sitting in a basement for around 15 yrs. Got few missing parts and got it running. Spent all day cleaning tar and sludge from tank, shut off valve, and carb with wire brushes, wires, degreasers, small pics, etc, looking through jets with flashlight everything is definitely spotless and clean. Initial ride was great with open carb, no air filter, new plug. After installing air filter rev at wot it sputters and riding at wot would just bog and not accelerate. No air screw on carb it has a throttle slide stop screw as only exterior adjustment. Moved needle clip down first and it almost didn't make it back up hill to house. Moved clip up and new plug and ran better but still sputtered at wot. Plug look fairly good but maybe a little dark. Removed muffler and ran even better almost no sputter and plug got little cleaner. So my thoughts are after installing air filter choked off some air and made rich. Moving needle clip down, richer, made worse. Moving clip up made leaner and removing muffler allowed more air through motor to compensate for rich condition. So should I move clip back to middle and try leaner main? Also clean out exhaust? I don't have much area close to test. All test rides were done on fairly steep uphill 3/4 mile road. Rolled downhill with bike off to not foul plug, only run it uphill hard on throttle. Also at 1600-2100 ft elevation. Taking to about 600ft in a few weeks to ride. I think the lower elevation may help it run better but take leaner jets just in case.

james85kdx80 wrote:Got my first 2smoke bike. 85 kdx 80 little run time but had been sitting in a basement for around 15 yrs. Got few missing parts and got it running. Spent all day cleaning tar and sludge from tank, shut off valve, and carb with wire brushes, wires, degreasers, small pics, etc, looking through jets with flashlight everything is definitely spotless and clean. Initial ride was great with open carb, no air filter, new plug. After installing air filter rev at wot it sputters and riding at wot would just bog and not accelerate. No air screw on carb it has a throttle slide stop screw as only exterior adjustment. Moved needle clip down first and it almost didn't make it back up hill to house. Moved clip up and new plug and ran better but still sputtered at wot. Plug look fairly good but maybe a little dark. Removed muffler and ran even better almost no sputter and plug got little cleaner. So my thoughts are after installing air filter choked off some air and made rich. Moving needle clip down, richer, made worse. Moving clip up made leaner and removing muffler allowed more air through motor to compensate for rich condition. So should I move clip back to middle and try leaner main? Also clean out exhaust? I don't have much area close to test. All test rides were done on fairly steep uphill 3/4 mile road. Rolled downhill with bike off to not foul plug, only run it uphill hard on throttle. Also at 1600-2100 ft elevation. Taking to about 600ft in a few weeks to ride. I think the lower elevation may help it run better but take leaner jets just in case.

"Initial ride was great with open carb, no air filter"

That is THE worst thing you could have done.

Keep the air filter on and clean the exhaust and go from there. Taking stuff off to attempt a repair won't help.

After it sat for 15 years, it could be ANYTHING. It's not like it was running perfectly, then put into storage by a proper mechanic.

Good luck on it. Check more and more items to rule out possibilities.

If it runs well with no airfilter and bogs with the air filter it means you need to lean out the jetting, the air filter does restrict the airflow a bit.

Riding briefly, on asphalt, or after a rain, with no air filter can be a good diagnostic tool to determine jetting issues IMO.

I know running without air filter is detrimental to carb and top engine. I got bike for free without a filter and wanted to make sure the motor was good before dropping cash on a pile of junk metal. My question was am I correct in my thinking that since it ran good without filter then after installing filter it slightly restricted air flow, especially at wot, making it run rich so I should use leaner main jet?

Yes that's the correct thinking. Especially since the bike was free and you're not wanting to dump money into yet so try to get it running clean on the main and have fun with it. Jets are cheap. See what main it has in it and order 2-3 smaller sizes. Work it down one size at a time. I'd keep it a little rich (not stuttering rich) and just try to get as many hours of riding as you can out of it. Spend the money on gas and oil.

Looks like it came with a 35 pilot, 210 main