Vintage Dirt Bike Q & A

Hi, I just bought a 74 mt 250 approx. 3 months ago.In its 32 years existance,it has become an off road only bike;which is fine for my purpose of following my 9 year old son, and maybe teach him a thing or two.It has no lights,ignition or locks.there is only A coil and wire leading from the pickup. I had to wire in a kill switch,as the previous owners would either stall it or choke it out.I have probably only ran this bike a total of 8hrs. I have two problems #1- The bike wouldn`t start one day(cold),so I changed the plug and it ran fine,but on three different days since,the bike had backfired(sounded like)and not restarted until I changed the Plug,and will always start first kick threreafter.What is my problem? #2- It has excellent throttle respnose,and I can actually begin to pull A whellie;with my 260 lbs,but the it just drops right off.I can actually achieve good speed as long as I keep the revs to about 1/3-1/2 throttle.Is this A solvable problem;or do I have to go on A diet?!!! Any and all help will be greatly appreciated,Thanx,Reid.

You didn't say what the dud plugs looked like.
Are they wet fouled (fuel or oil) or choked with carbon??

Look at the electrode and insulator....is it glazed white/ yellow in colour or speckled with black spots..... is the earth / ground arm still intact or burnt away??

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'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

I had a problem with my mt 250 pinching the rubber tube that goes between the aircleaner box and the frame under the seat shut at more than half throttle.I simply removed that tube and the problem was cured.it causes a rich condition when that happened and it will foul plugs like crazy.other things to consider is float level and needle and seat in the carb,crankshaft seal leak on the primary side.engine excessively carboned up and the pipe carboned up.these are a few ideas.

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(2) 1968 DT1 1970 RT1M,1970 DT1C 1971 RT1B Enduro 1974 MT250 1974 DT250A (2) 1975 DT400B 1974 DT100,1978 DT175
1975 CR250M1 1979 CR250R 1979 Kawasaki KZ400H1 Jesus is Lord!!

Thanks for getting back to my question so quickly.The spark plugs show only minor fouling(slightly black)and wet in a normal sense.I only kept 2 of 4 plugs to go on.There doesnt seem to be any burning or high temp. marks anywhere.I also checked for that tube between the airbox and carb,nothing was pinched.i would like to know if maybe this could be to the points,as I have never worked on anything with points,so I don`t know what kind of problems can arise from them.It still runs great otherwise;but I think I have a problem that just might not go away.

Another thing.........drain your carb float bowl and check for water.

I had water in a float bowl......KDX200..... bike would start and run up to 1/2 ...2/3 throttle but die out completely at higher throttle settings when the main jet blocked /sucked water. would clear out and run great when throttle backed off a bit.

Cannot relate this to your dead spark plugs though.

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'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