Bing Carb Tuning For 325 Sherpa

[cvgmmartin]

I have just finished rebuilding my 1976 325 Sherpa after many years of storage. Way back I converted it to a Mikuni carb as was the fashion years ago but now am going back to the Bing unit based on the comments I have read on other posted topics. The bike was not run for long with the Bing and the slide is not loose in the body so I think it is in reasonable condition. I have it running and it idles nicely but when opening the throttle from idle the power comes in quicker than I would like, I would expect it to be a smoother transition as the throttle is opened. The air screw is one turn out, the needle is in the middle position, and the timing is between 2.4 and 2.6mm BTDC. Not having access to other Bultacos around here I don't know if this is typical of a Bing or not. Does anyone have any suggestions on tuning to smooth power from idle.

[kramit]

I remember installing a Mikuni 28mm round slide on my 199 and the power was much softer and smoother than the Bing. I eventually went back to the Bing as it felt better overall. Maybe retard the timing to 2.0. After the engine is run in awhile, it might smooth out somewhat.

[nigel dabster]

I have just finished rebuilding my 1976 325 Sherpa after many years of storage. Way back I converted it to a Mikuni carb as was the fashion years ago but now am going back to the Bing unit based on the comments I have read on other posted topics. The bike was not run for long with the Bing and the slide is not loose in the body so I think it is in reasonable condition. I have it running and it idles nicely but when opening the throttle from idle the power comes in quicker than I would like, I would expect it to be a smoother transition as the throttle is opened. The air screw is one turn out, the needle is in the middle position, and the timing is between 2.4 and 2.6mm BTDC. Not having access to other Bultacos around here I don't know if this is typical of a Bing or not. Does anyone have any suggestions on tuning to smooth power from idle.

not too sure on the nedle without looking but make sure the floats are set as weak as poss ie it runs out flat out in fith on the road and tweak it a bit back from there. St the tickover at about four beats to stop then mess with small adjustments on air and it should be a tad rich at the bottom.

Make sure the slide doesnt have a step in it

Edited March 13, 2010 by Nigel Dabster

[cvgmmartin]

Thanks for those suggestions. The flat out in 5th test will have to wait for the snow to clear and the first trial since the bike is not licenced for the road and I live in the city. Is there any physical measurement of float position relative to carb body that can be checked to make sure I am in the right ballpark?

[nigel dabster]

Thanks for those suggestions. The flat out in 5th test will have to wait for the snow to clear and the first trial since the bike is not licenced for the road and I live in the city. Is there any physical measurement of float position relative to carb body that can be checked to make sure I am in the right ballpark?

nope they all vary.check the slide though

[cvgmmartin]

The slide seems O.K. there is some discolouration on the bottom of the slide skirt matching the choke dia but there is no wear ridge that I can feel when running my fingernail over it.

[cvgmmartin]

Thanks for the advice and the problem is now resolved. I lowered the float level slightly, dropped the needle one notch and readjusted the air screw a little further out. Engine now runs smooth as silk.