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Airbox Mod Causing Starting Issues?

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I have a 1990 DR250, swapped engine from DR350 with Mikuni TM33 carb. It has an aftermarket FMF exhaust. It has the airbox mod with holes punched in the top of the airbox. But the jetting is 130 for the main jet and 37.5 for the pilot jet. I'm having issues getting it running and it'll start up for just a split second, then die. When it has run before it loses power at higher RPM.

Could the jetting be incorrect for the airbox mod and that may be what's causing the starting and bogging issues? It seems like the bike is starved of fuel or something.

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Airbox has nothing to do with starting. Considering you have a pumper carb, twisting the throttle a few times will throw fuel in head making possibly run for just a moment.
Check pilot jet and clean all air circuits. Your idle may be too low, so hold the throttle open just a little when starting too.
Airbox will influence the main jet and needle further up the RPM range.
Stock 350 had a 27.5 pilot, so your 30 should be a good starting point.

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49 minutes ago, InRoostWeTrust said:

Airbox has nothing to do with starting. Considering you have a pumper carb, twisting the throttle a few times will throw fuel in head making possibly run for just a moment.
Check pilot jet and clean all air circuits. Your idle may be too low, so hold the throttle open just a little when starting too.
Airbox will influence the main jet and needle further up the RPM range.
Stock 350 had a 27.5 pilot, so your 30 should be a good starting point.

It does seem like the idle is too low for it to fully start, but when I turn it up it doesn't give any indication that it wants to start. When the idle is low, almost to the point that the idle screw isn't touching the throttle seems to be the only time I can give engine to start if only for less than a second.

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Don't forget about the pilot fuel screw (located between carb and intake manifold) - opening it will feed more fuel when starring and is an adjuster for off-idle performance.

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49 minutes ago, InRoostWeTrust said:

Don't forget about the pilot fuel screw (located between carb and intake manifold) - opening it will feed more fuel when starring and is an adjuster for off-idle performance.

Yeah, when I first got it and it ran the pilot fuel screw was set to 1.5 turns out (I'm assuming that a turn would be one 360 degree rotation), and I've tried anywhere from 0.5 turn to 3.5 turns out, but seems to have no effect on starting.

Edited by stevemcqueen1968

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Would kicking it over so many times without it running cause an issue with the top end not getting oil? In that maybe there's too much friction between the camshaft and rocker arms that's preventing it to kick over?

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Maybe you have a poor spark? Try a fresh plug and in the sparkplug cap there is a resistor under the brass insert (should have screwdriver slot) - replace this with a brass or copper rod of same size and then try... the resistor can create problems or can be dirty.
I pulled mine off my '94 DRS and it didn't seem to cause any odd electrical noise on anything, and I think the plug us a resistor style anyway.

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14 hours ago, InRoostWeTrust said:

Maybe you have a poor spark? Try a fresh plug and in the sparkplug cap there is a resistor under the brass insert (should have screwdriver slot) - replace this with a brass or copper rod of same size and then try... the resistor can create problems or can be dirty.
I pulled mine off my '94 DRS and it didn't seem to cause any odd electrical noise on anything, and I think the plug us a resistor style anyway.

Yeah, I thought of that. I have used the old plug and a new plug, replaced the spark boot and replaced the ignition coil. I had it running a week ago, although it didn't seem to run well.

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