Vintage Dirt Bike Q & A

Hi. I'm a newbie who just inherited a 1974 MT 250 Elsinore. It hasd been sitting for an undertermined amount of time and initially only ran for a few seconds with a shot of starter fluid. Previous owner said it had developed a rattle, so he parked it.

I pulled the air box and the carb. Gave the carb a good squirt-out and basic disassembly/cleaning with some carb cleaner. Mixed some new gas (the oil injection system had been removed) and eventually got it to idle between 2500 and 3000 rpm with the choke on. (I'm assuming that the choke is "on" when the lever is flipped to the down position. I suppose I should mention that this was with the air box off the bike and the carb open to the air. The bike never did start without the assistance of some starter fluid.

When I flipped the choke lever up the engine almost immediately raced to about 6000 or redline. I tried this a few times with the same results.

I'm completely new to to 2-strokes, so I'm lost as last year's easter egg.

I also don't know whether it's worth mentioning that the exhaust pipe doesn't seem to be seated well on the cylinder. I'm getting some exhaust blowing past that connection. The pipe also has a crack in it.

Thanks to any and all who respond. My education has to start somewhere.

Adam

Adam,

Try doing a search here for 'mt250 carb idle' - I got 134 results.

I would also turn your idle speed screw (on the left) way out so that the motor idles at a reasonable speed with the choke off. If turning the screw has no effect, you may have a throttle-cable problem.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

download the shopmanual at www.honda-elsinore.com
it may help you.

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80 CR250Ra
80 CR250Ra
78 CR250R
80 CR80
82 Bultaco Sherpa 340
78 Bultaco Pursang 250 MK12
76 Bultaco Frontera 370 MK10
76 Bultaco Alpina 250
73 Bultaco Lobito 125 MK6
76 Suzuki RM125A
90 Kawasaki KX250

Would a cracked carb insulator cause the motor to rev like this?

PS: Located the shop manual. Thanks!

Absolutely. Whenever you get a racing engine, one of the first things to look for is an air leak, which leans the mixture.