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1990 DR350 - Hard to start, runs for 1 second then dies

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I have a 1990 DR250, swapped engine from DR350 with Mikuni TM33 carb. I've been having issues after I got it on Craigslist, and have been trying to hone it in. It has an aftermarket FMF exhaust, the airbox mod with holes punched in the top and a Mikuni #130 mainjet. Also new ignition coil and I have tried using a new spark plug.

So far I've finally got it to run, but it's a pain to start and seems to have a mind of it's own. Right now it wants to start but only runs for about a second then dies. I've tried playing with the fuel screw setting, the idle and the choke in a number of different settings. When it does run, it feels bogged down whenever I would give it throttle and not give a lot of power until it dropped in RPM. But it's rare that I'm able to actually get it running. I would think that maybe it's running lean, but the spark plug is black with carbon so it would seem to suggest otherwise. What am I doing wrong here?

Oh and today I had it running and was trying to hone in the fuel screw setting and may have had it too rich, because black smoke started coming out of the airbox. Not sure why it was coming out of the airbox though, because I recently adjusted the valve clearance to be in spec.

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Well all these motors need to run is spark air and fuel, so if it bogs down, smokes black and pops no matter what you do than its not the carb. Make sure you set the valves after the intake valves shut this is the proper tdc. If you set it right and it still does this my best guess is the timing jumped.

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Have you overfilled it with engine oil ?

thinking maybe excessive crank pressure blowing oil past the rings and snuffing your plug .

excess oil could be blowing through crank breather into airbox, if i remember right it vents into airbox

Edited by paint it black

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1 hour ago, paint it black said:

Have you overfilled it with engine oil ?

thinking maybe excessive crank pressure blowing oil past the rings and snuffing your plug .

excess oil could be blowing through crank breather into airbox, if i remember right it vents into airbox

Possibly, I changed the oil after I got it because it seemed like gas had mixed into the oil. I didn't want to run it was the bad oil, but also wasn't able to start it and get it warm in order to change the oil. But when I changed the oil and oil filter, I added two quarts like the manual recommended. But I did also have some oil spill out when I did the valve adjustment, maybe a few ounces.

What would you recommend? Draining off some of the oil?

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