Vintage Dirt Bike Q & A

Hey all,

Long time reader, first time poster. I've got my Honda Mt250 Elsinore that I think I am having problems with. I bought it about 8 months ago and it seems like when I get to 5th gear it bogs down and I am not able to get max power. I'm only able to get it up to struggling to make it to 55mph on flat ground. Going up hill it will start to bog down even more and drop to 50 or 45 and I have to downshift to 4th and have high rpm in 4th to start to get back up to highway speed.

I'd really just like to be able to do 55, 60 with no problem. I can't get any reasonable rpm in 5th gear, it struggles to get to 4000rpm and drops down from there. Even with full throttle it just won't do it. I weigh 190lbs which I don't think is super heavy. Most guys are saying they top out at 65-70 mph. I've done a compression test and it read 150psi. Is that normal? I have tried to clean any carbon build up, there was practically none. The exhaust is not clogged. My first sprocket is upgraded to 15:40. Any ideas?

I'd suggest some simple stuff to start:

1) a 14T front sprocket. This is one of those rare situations where gearing down will result in faster acceleration and higher top speed.
2) a CR250M copper head gasket. My MR175 felt sleepy at 150 psi, and wide awake at 185 - the CR gasket should take you up to maybe 170 psi or so.
3) checking the ignition timing. The fact that this can be difficult to do accurately makes it no less important.
4) pop off the plastic grating behind the airbox and let the motor breathe a little.

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

Don't expect to get too fast on an MT. At 60 you are practically redlining. Also, make sure you aren't too advanced with your timing. You will get an odd metallic pinging when you let off the throttle at higher RPM's. I have had mine lock up at 45 mph in hot weather (98 degress).