Vintage Dirt Bike Q & A

Hi,
I have a 1976 MR 250, stock right to the tires, less than 1,000 miles. I have replaced the right side crank seal and overhauled the carb numerous times. At all times there is excessive smoke from this bike, oil will drip from the exhaust and it will not idle well, fouling plugs. The mixture is right, float level and timing etc.
Has anyone come across this, I think there may be incorrect/missing jets in the carb from before I got the bike. Does anyone have a listing for these?
Thanks, The Mad Mechanic

_________________
Thanks, The Mad Mechanic
'05 FJR '76 KZ900 '76 MR250

Old road racers adage:
Stay in the gas until you see God or Elvis, then brake hard.

My 073A MR250 carb had the following setup, which looked all-original to me:

100 main jet
140 power jet
48 pilot jet
200 air jet
130 starter jet
2.5 throttle slide
271006 needle, #3 clip position

Just a few suggestions:

98 main (99101-357-0980)
130 power (N424-52-130 should work)
45 pilot (N424-24-045)
needle clip to #2
NGK BP7EVX spark plug (discontinued, but available)

I'd also check the exhaust for blockage just to be sure, and keep an eye on your gearbox oil level (oil can get into the crankcases thru the gasket joint as well as the seal, especially after the cases have been split).

Ray

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

I never could get my original Keihin to stop running rich. I suspect the needle jet and jet needle were worn, but I couldn't find replacements to check. I finally ended up just putting a new Mikuni 36mm round slide on it. And then the problem was finding the right combination of jets and needle to make it work right.

Hi,
Thanks for the info, I'll source the jets through through the winter. Right now it's about 0 fahrenheit outside. Not even I ride in that weather!!!!!!!!!!!!

_________________
Thanks, The Mad Mechanic
'05 FJR '76 KZ900 '76 MR250

Old road racers adage:
Stay in the gas until you see God or Elvis, then brake hard.

Get a new Mikuni is my suggestion and search this site for suggested jet #'s, etc from those who have been thru it. Good luck.

_________________
1980 Honda CR125R