Vintage Dirt Bike Q & A

I just got me a MT250 but I cant get the damn thing to start, I cleaned the carb out, but it appears to be fouling the plug with petrol, It will start (sometimes) after it is cleaned - run for a few seconds then putt out, then its dead, any ideas?

Also seems stay in gear when the clutch is pulled it doesnt free wheel??!

Great site btw.

Cheers Ryan.

Did you clean the pilot jet (one separate from the main jet which is on the bottom of the needle tube) out real good? Remove, soak and clean with small wire then blow out. In addition, since it appears you may be getting too much fuel rather than not enough, check your float level height. Centerline should be parallel with base of carb where bowl attaches. Make sure your needle valve is clean and shutting off fuel flow.
And make sure you don't have any air leaks between the carb and the cylinder.
If all that is fine, you may have a weak spark. Hold base of plug (attached to wire) against cyinder and kick it over. You should have a crisp blue spark. If bike has been sitting a while, you may need points or at least run a dollar bill between the points about 30 times to help clean them. Points for the MT are about $25 or so through HOnda dealer. Since you appear to have some spark, it is also possible your coil is weak.
As far as the clutch goes, this is normal if the bike has been sitting a while. A little riding often takes care of it. Make sure you have oil in the transmission. If you are worried, take side case off and remove clutch plates. Make sure they have enough material on them. If they do, put piece of 400 wet-dry sandpaper on flat surface and run them lightly in a figure 8 over the sandpaper. Oil them up real good and reassemble. You don't need to remove clutch basket to do this. If, however, the clutch basket fingers (the aluminum protrusions on the basket that the clutch plates have tabs that go in between) have grooves, you might need to lightly file away the grooves or replace the aluminum basket.
And whatever else you do, buy a manual. You will absolutely need one.

Ryan, get a new plug, first off, even if you got spark, that plug may be weak.
I have a mt125 and didn't bother to check the needle in the slide and the clip was pushed up about an inch, didn't notice, til I decided to move the needle. This probably happened because the guy before me put the slide in and the needle hung and he forced it down causing the circlip to slide up the needle.
Again, I"ll say get a new plug, weak plugs can cause major havoc and cause you to look at too many other things, like coil, points, carb, etc.

Now heres a problem that caused me major problems....got a bike and the guy before me did not put the flywheel nut back on....got the bike started and the flywheel got loose and a small piece of metal shaving came off and landed on the points and grounded them out...took me forever to figure that out and only found it when I went to take the points off.
Good luck, keep us updated!!

_________________
Garry Mainer
#33m (retired)
Honda Cr250r 1980
Honda Cr250r 1980
Yamaha TY250C 1976
Arctic Cat 650 H1 2007

Thanks for the speedy reply,
Well, the oring on the brass sleave part of the float valve is not even touching the sides of the alloy, so the valves being bypassed and flooding, Im off to pick up a new oring, fingers crossed...

Also Ive noticed that when the bike is turned over slowly the piston head appears to be loose, is there suppose to be be up and down movement between the crank and the piston?? could this be the crank bearings? how much movement is acceptable if any?

Well today I replaced the float valve brass oring, adjusted the floats to 20mm and it started and ran for about 2minutes then died, so I cleaned the plug and kicked it over then ran the bike with the fuel cock on the tank off. as soon as I put it in the on possition it started to die, so off it went, and it fired up again, It was like juggling just to keep it running, anyway would this be contributed to a dodgy float valve? or is there more to it?

Ive got a guy that sells old honda parts and reckons hes got a CR125 carb kit that will fit the MT250 carb is this true?

I would pull the exhaust off and turn crank shaft until piston blocks exhaust port.

then hold piston steady with your finger or thumb through port while rocking crank shaft back and forth.

If you detect Any slop in bearings.......rod, big end then better stop kicking it over and time to open it up.


Stuck clutch can often be freed by holding clutch lever in and rocking bike back and fwd in gear..engine off.
may need to rock it hard but should free up.

_________________
'84 Honda CR500
'84 CR125
'85 KX125
'83 IT490
'82 Maico 490
'80 YZ465
'75 Husky CR360 GP Mikkola
'75 CR250
'72 DT2MX
'91 XR200

What a day!! turns out it was bad fuel (to low octane 91!) so it runs perfect on a mix of avgas (100 about?) and 96 pump gas, but the carb did need a rebuild anway, riding the old elsinore was great fun its going to be a great summer!

Thanks for answering my question, Im sure I will have many more in the future.





Ryan.

Cool beans...glad you got it figured out.

_________________
Garry Mainer
#33m (retired)
Honda Cr250r 1980
Honda Cr250r 1980
Yamaha TY250C 1976
Arctic Cat 650 H1 2007