Help needed with bogging 1975 250 HS

[Alan Mason]

Just finished restoring this 250 and I can't get it to run cleanly off the bottom or lower mid range. New crank bearings and seals, fresh rings, stock bing with stock jetting and carb is spotless inside. Motoplat and coil both just rebuilt by Vance Smith. Starts easily and runs great on top end but seems to be loading up badly at lower speeds. I can't lug this bike at all and end up downshifting and pulling in the clutch and revving the motor up to keep it going. Deck height and timing are set correctly, new air filter, and I'm out of ideas. My kids bought me this bike for Christmas 2008 and I've just finished getting it back together. I'd hoped to ride it today with some friends but couldn't get it to run well enough. I had to repair the stock mx exhaust but I rebuilt it as close to original as possible. I do have a good enduro pipe I can try. Any ideas???

[brian kirby]

You have a worn needle/needle jet or the floats are misadjusted or full of fuel. I'd bet on the needle/needle jet.

Brian

'72 Berkshire

[chicagojerry]

brian's probably right. look at your needle jet, i bet its out of round.
if that's not it, post your jetting specs and i'll tell you how close it is to mine. good luck     chicago jerry

[garrettccovington]

I was having the same problem with my 79 KTM MC80 250:( and as strange as this sounds.  I finaly built a fire with some Matchlight Brickettes charcol, threw the pipe in there, rotated a couple of times to burn all the gunk out.  It sat on the coals until they were gone. Repacked the silencer and it runs pretty darn good now.

Fellow POGer's recommended this and I thought it was crazy, but it worked.  Now I'm a beleiver!:D


72 six-day
79 KTM MC80 250

[garrettccovington]

I finally put the pipe in the coals after I was confident the pipe wouldn't warp on me.  You should have seen all the blue/green smoke that came out of that pipe.

I bought a beater pipe (for racing) on evil bay and i'm gonna build a proper fire for that one this weekend and do the same thing.  I'll post soem more pics.

g

72 six-day
79 KTM MC80 250

[Mickey Sergeant]

I just finished a 74 berkshire.I'm having the same problem your experiancing.Replaced needle and jets that someone recomended to me.Helped a little.Wont Idle wants to die.Checked plug shows signs of being rich.One thing I noticed was when checking float level was that float tab would push float needle down.Am I wrong or should floats be resting on float needle without pushing it down?If this is the case could this be my problem?All feedback needed.

[G Ellis]

I would junk the carb. You can get a new bing for 150.00,this will fix your trouble. I had the same trouble on my 78 175, got the new carb no trouble now. Your 30 yr old carb is worn out. Hope this will help. Later Gary

[Mike Horton]

I interested, where can I purchase a new bing carb for $ 150.00 ? Thanks

[Mickey Sergeant]

Do the new bing carbs mount like the old one's without any motifications?

 74 Berkshire

[gooddirt]

The NOS guy on ebay has the 26mm body and slides ;for a  bone stock ported 100 sachs motor should work fine. All parts are under a $100. try and find the automizer #40-44 (I think this is the number) and go with a richer jetting with it. Or find a MIC. LG

[Alan Mason]

Thanks to everyone for all of the ideas. I think I'll first try my enduro pipe on it. If that doesn't work I'll try a new float, float needle and new needle and needle jet. When I pulled the left side panel and air filter to help hold the airbox to carb boot in place, when reinstalling the carb, there was some fuel that dripped out, so I'm thinking that the float might be saturated causing the over rich mixture at lower speeds. Thanks again for all the help.

[Kip Kern]

I agree with Brian, Needle/Needle Jet.  Blow out all orfices, check float level, install new CORK bowl gasket and try her out. CIAO

[Alan Mason]

Here's an update on my progress. Tried the enduro pipe with no change to the crappy low end. Pulled the carb again and the needle looked ok but the needle jet did look worn. Decided to make a new needle jet on my lathe but had no idea of the original size of the hole in the jet. I measured the needle toward the top and made the new needle jet slightly larger than the needle. First try was starving for fuel so I opened the hole up a little further and tried it again. It's running pretty good now with the needle clip in the center position, so I think a little fine tuning of the needle position should have it running great. I'll post an update and some photos of my restoration in the near future. Thanks to all that replied with help.  Alan