ill running 400

[tim bowers]

Just had my 400 totally rebuilt and I am
having problems with it wanting to stay running. It starts right up but will not
idle and when you adjust the cable to get it to idle it revs to the moon.THe idle screw on
the Bing has no effect on the idle whatsoever.The carb may be fairly worn, but
where do you start?
Thanks
Tim

 

[Paul Danik]

Sounds like an air leak.  Did you replace the ignition side crank seal when you worked on the engine?  Anyone with more ideas just jump right in.
Paul

 

[Rocket]

Sounds like maybe the pilot jet is plugged.
Rocket

 

[ktmkirk]

I had a bike like that and the head was not torque down as well as the exhaust/ carberator mounts were loose as well.. sometimes when putting things together we overlook tightening something....Kirk

 

[tim bowers]

YEah, I have looked at all those things
and I am thinking the pilot jet now too.
The engine was completely overhauled from
rod to seals, pistons, rings, clutch etc.
I ordered a Bing carb rebuild kit and 2 new pilot jets. A couple steps bigger etc.
A new carb is around 300.00+ so this was an
easier fix. The airleak thing bugs me too
but I start here first. Thanks for all
your help.I looked at Mikunis but I wanted to stay with what came on the bike.
Thanks again
Tim

 

[DKWRACER]

Sounds like fuel starvation, I would open the petcocks for 5 mins them tap the sides of the carb, then pull the float bowl off and it should be at least 1/2 full, can also do this with the carb removed using a remote fuel canister, some Bings had poor/old floats which will sink or barely stay afloat, can check by putting in a cofee can of gas and see how well it floats, my 400 has 38mm Bing with 40 pilot, 180 main, air screw 3/4 turns out, this at 5180 ft altitude
Tom.....

 

[DKWRACER]

Try this too, once it is started, hit the tickler a few times to add gas, this may keep it running for 15 to 30 seconds, if it does, sounds like the low speed circuit,pilot and needle jet, maybee need a 283 or 286 etc...
Tom...

 

[tim bowers]

Ok, got the carb figured out with rebuild
kit from Bing USA. Now I keep shearing the
key on the crank, mag side. What gives??

 

[Rocket]

I would say that you need to "lap" your flywheel to the crank.  The taper may not match up perfectly.  The key is only for timing, the taper is what locks the flywheel to the crankshaft.  You can get lapping compound at an auto parts store.  Put a small amount on each piece, and put the flywheel on, no key and not tight, and work the flywheel back and forth in about quarter turn movement.  Pull flywheel off, rotate 90 degrees and do it again.  Keep repeating through the 360 degree rotation.  Clean both surfaces.  You should see both surfaces starting to match each other.  Install key and torque to proper spec.  As long as crank and flywheel aren't scarred up too badly, it should hold.  
Hope this works for you, sorry it is so long winded.
Rocket

 

[tim bowers]

Thanks Rocket, I will try that. Thanks for
taking the time to explain the process. I
always say more information is better. Thanks
to all who have helped out. I should be
running this weekend. I'm shooting for a race
on Monday at Log Road here in Michigan. It
is an AHRMA regional and part of the Great lakes series.
Thanks again to all
Tim