Running lean

If it's broken or just needs tweaked

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Vatch
Posts: 232
Joined: Sun Mar 05, 2006 10:26 am
Location: West Virginia, USA

Running lean

Postby Vatch » Fri May 05, 2006 3:06 pm

I pulled the plugs when I adjusted the valves and cam chain the other day. Cylinders 1,3, and 4 seem to be running lean, and 2 was slightly fouled. Power is fine, but I do need to give it some throttle at startup.

Some history with my bike: I rebuilt the carbs (twice :( ) last summer and balanced them. I replaced the paper air filter with a K&N OEM replacement. I also adjusted the fast idle. I chose the K&N because I was under the impression that the 627cc engine with the Keihin carbs was air-limited. The K&N filter may be contributing to a lean running engine. Can this be fixed by adjusting the idle screws on 1, 3, and 4? Any ideas about how to fix #2 without pulling the carbs? The plugs looked fine last autumn before I put the bike away for the winter.
'99 1500 Drifter

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Ibsen
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Postby Ibsen » Fri May 05, 2006 4:15 pm

These bikes was set up lean from the factory, and the KN filter could be the reason why it is running lean on three cylinders. I have the stock air filter in my bike btw, and I don't think it has got any breating problem. What I have seen mentioned as a compensation for the lean set up. and that is with the stock air filter, is an increase of the main jet size to 98.
If it was running fine on cyl #2 before you parked the bike, and the valves are adjusted, could it be that the float valve doesn't close as it should, and the carb on that cylinder is running slightly rich? Or a loose jet?

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Vatch
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Joined: Sun Mar 05, 2006 10:26 am
Location: West Virginia, USA

Postby Vatch » Fri May 05, 2006 5:55 pm

It sounds like the K&N was great idea :?

The float needle could be stuck. It wasn't before, but we all know that can change without warning. Perhaps I should just adjust the pilot screws, a little leaner for # 2 and a little richer for 1, 3, and 4. 1/4 of turn?
'99 1500 Drifter

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Volker_P
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Re: Running lean

Postby Volker_P » Mon May 08, 2006 12:37 am

From the spark plugs, my CB is also running on the lean side of "still acceptable". K&N's have usually a bit less flow resistance so it seems plausible that it further shifted to lean. You could try with the pilot screws but write down position. I would not expect any effect on the high load mixture. So be prepared you need slightly larger main jets or to place a small cover on the airbox opening.
The #2 problem probably has a different origin, maybe the float level (check with transparent hose on the floater bowl relief against other), the float needle, its seat or just the plug. You could try to exchange the plug with another cylinder to get an idea. With a suitable tool, it is possible to remove the floater bowls without removing the carbs (even at a french motorway parking lot when a bunch of german bus tourists are standing around you watching you burning your fingers :lol: ), more seems difficult but I did not try.

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Vatch
Posts: 232
Joined: Sun Mar 05, 2006 10:26 am
Location: West Virginia, USA

Postby Vatch » Mon May 08, 2006 7:40 am

I did switch the plugs for 1 and 2. However, with the recent choke cable issues, I'm pretty sure it's not running lean anymore :lol:

I did drop the float bowls once without removing the carbs, and I'm sure I didn't have the right tools. After that I replace the bolts with allen bolts because it's easier to get an allen wrench in the small space. Not fun, but at least I didn't have an audience. :lol:
'99 1500 Drifter


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