jetting a bing 54

[quiggs00]

ok so i just found out my 77 gs6 400cc has had a little motor work like some porting.  So the motor had been rejetted but when i ride it it bogs in the mid to high end and then will take off screaming all of a sudden.
What might this be? I have many jets for the bike do you think i could just put a different main jet in it?

thanks in adavnce!

[firstturn]

Quiggs,
  I noticed that no one had made a post on your requests so I think we need a little more information.  Is this a new bike to you?  Have you cleaned out the carburetor?  Just more info would help.[8D]

Ron Carbaugh

[John Ehrhart]

As I remember, I had a great deal of trouble getting my 400 jetted at first, even enlisting a passing member of the Penton clan for help.
And I will get my jetting notes from my son (current custodian of the bike) which may help get you in the ballpark.
Please do give us a little more info.

1969 Husqvarna 400 Cross
1974 Monark
1975 Jackpiner
1978 GS6 400
1981 250 MX

[Steve Minor]

This is the specs that Bing sent me for my 1977 400 GS6
Hope it helps.......
Steve


Stock Jetting Specs @ sea level are:

44-051-185 Main Jet
45-120-3,22 Needle Jet
46-360-401 Jet Needle in position 2 from top
44-353-50 Idle Jet

[quiggs00]

ok sorry about the quickness of the post

the bike is new to me but i have been through the carbs?  the bike has been ported the original owner told me so.  also from looking through my    
manual i see that when it cam to me it did not have the stock jets in.  This is probably good for when he wsa racing it brand new 20 some years ago but now i cant imagine that it is helping it any.  i ordered the stock jets from bing and installed them and cant even start it now.  so i was thinking of going back to a bigger idle jet to see if it will get running.  as for the high end bogging then crazy acceleration problem do you think i could jsut throw a smaller jet in im in the process of trying these things as i have been for quite some time

thanks in advance!

[Big Mac]

Quiggs, I have a 77 MC5 400 that's had some light porting done and has a GEM reed valve added. Jetting is 190 main, standard 3.22 NJ, standard #1 needle (#1 not marked as such, marked with one groove just below the clip grooves), needle clip in middle groove, #40 pilot.

If it ran fine, then changed to the current symptoms, I'd look for other problems like maybe a bad ignition side crank seal or air leak in intake. If it came this way or you made other changes that preceded the symptoms, re-jetting may be in order. Sounds like you're lean to me and you definitely can't break anything by fattening it up anyway. I had similar ill symptoms on a 250 HS after I added a reed valve. If I blipped it quick, at about 1/4 throttle it would just die. If I held it there it would shut all the way down. If I accelerated slowly it would catch and build revs, with a sudden burst after about 4000 rpms.

I went to one larger size main and clipped needle in lowest groove and it improved but wasn't totally gone down low in rpm range. So I went to next larger needle jet and it seemed to be the cure. Bing Agency tech told me that NJs for 54 carb go up in increments of .03 (as in 3.22, 3.25, etc) and each .03 increment is same as one groove change on the needle clip---down one = up .03 on NJ, fyi.

Once it's in the ballpark, fine tuning should be acheivable with the air screw...twist in richens the very low end, twist out leans it. If all else is about right, should run/accelerate best with air screw at between 1-2 turns out. I was fiddling with fine tuning at the RR, and met Mr.-all-knowing-guru Kip Kern for the first time--his recommendation of fine-tuning the air screw with nimble fingers while on the fly worked like a charm... a lot easier than carrying a screwdriver in the back pocket and stopping every 100 yards to fiddle until it's right. Good luck, hope this helps!  Mac