Vintage Dirt Bike Q & A

hey all you experts,
i'm posting for the first time, and i could use some help getting my '75MT250 to act right. when i got it it wasn't firing, and i determined it had a short in the points. so i had an ATOM computer module (a very little, flat red box with live and ground wires coming out) designed to replace points on any 2 stroke outboard boat engine. i wired it into the stator assembly in place of the points. as far as i understand, this module can detect the charge accumulating in the coil and knows when to make it discharge on down the line, so it replaces the whole timing function of rotor and points. sure enough, i now get a strong blue spark when i kick it every time. however, much to my dismay, i still can't get any fuel combustion. i tested it by spraying starting fluid directly into the cylinder with the carb off for several seconds. then i kick it while a friend holds the intake shut most of the way to maintain compression, which is good. it still won't ignight, which seems really weird. could this have to do with: 1) improper compatibility of the ATOM module with this engine?; 2) plug too hot or cold?; 3) faulty reed valve? (i haven't torn it down that far yet); 4) doing something wrong during this test?; 5) or do i need to put a charge on the battery (seems that's only needed to run blinkers, etc.). i'm not an expert on the electrical componets, and i would really appreciate some feedback. sorry for being longwinded, i'm looking forward to doing some good foruming. thnx,
ben lieb

(this may sound dumb) but is your plug fouled even the least bit?, i have a '74 mt,, and once the plug's fouled even a lil bit,, that does it,, gotto take 'em out and clean them, not shure that it'd matter all that much, but is the plug gapped right? . Also, be careful just using starting fluid to start it. may damage the piston.. have the carb on it,, and try pouring a little gas into the spark plug hole,, possibly this may get her fired ! good luck

jeff

_________________
If you want big rewards, take big risks.
'74 MT250E
workin gettin another
definitely an addiction

For timing I just park my MT next to my car and use my inductive pickup timing light with the power leads hooked to my car battery. Just make sure you put a spot of white paint on the timing marks.

If it were me I would give the points another try to see if it runs. I just picked up an MT that the top end was so far gone it had no compression and wouldn't fire. All I had to do was new rings/piston and it fired right up. The original point will eliminate timing issues.

To hot wire an MT around any shorts or bad connections you just disconnect the harness coming out of engine and the coil. go directly from the black/white stripe from the harness to the black/white stripe of the coil.

That ATOM sounds interesting. Are they still available forsale?

I put one of those things on the Briggs and Stratton engine on my snow blower. It does work. Not exactly sure how it picks up the timing but I thought it may be related to the position of the coil. On those engines they sit at the 12:00 position on top of the flywheel. When the magnet in the Flywheel passes the coil it start the firing sequence? Anyway the separate coils on the MT are for the Headlight, Ignition, and the remaining accessories. One for each. Off hand I’m not sure which is which and there may be more than one magnet in the flywheel. If it's firing too far away from TDC you may not even get a back fire. I'd put the points back in.

_________________
74 MT-250
06 Husky TE-450

http://www.smallenginebusiness.com/Merc ... de=7-01751

It says here, if the url will load, that they aren't for engines that run accessories like the MT. I think you could get it to work but you would have to do some fancy stuff like removing all but one magnet and rebalancing the flywheel. That or just hoping the coil can keep up with firing several times as fast as the engine RPM w/o missfiring.