eyhonda - 63 cb77 cafe project

e3steve · Post by **e3steve** » Sun May 30, 2010 2:06 pm

eyhonda wrote:e3steve- thanks, I'll try all that. That's a good idea about checking idle air-fuel ratio.

It might not be entirely the correct way, but it's the angle from which I'd approach such a problem. I'm a physicist, so logic & rationality dictates my thought processes!

eyhonda wrote:But what is the popping from? Is it missing (due to ignition or lack of fuel) or is it backfiring due to too much fuel?

I take it you're speaking of 'popping' back via the offending carb? Usually, weak (lean) mixture, so not enough fuel / too much air. The CB/CL range notoriously suffers from this phenomenon during its warm-up, especially if the rider tries to dump the choke before the motor's properly warmed through and then attempts wide(ish) throttle openings.

eyhonda · Post by **eyhonda** » Sun May 30, 2010 3:18 pm

Ok that makes sense. Thanks for reinforcing that. I was leaning towards that (pardon the pun). I think if it was backfiring, it would sound more like firecrackers rather than a loud pop of air.

Yeah, I went thru the LM tune-up.

I may raise the needle to richen it a bit.

I have not touched the mixture screws. I always hear them referred as air screws but they are located towards the front (near the motor). I had thought that due to the location they would be fuel screws. I thought air screws are near the intake. Either way, they are still at 1 1/4 out. If they're air screws, I turn them in to richen - correct?

Yeah, I know about the throttle response on these bikes. They work better with slow rolling throttle rather than snapping them open.

LOUD MOUSE · Post by **LOUD MOUSE** » Sun May 30, 2010 8:22 pm

Remove the air pods. .........lm

eyhonda wrote:I got a new carb cap (thanks LM!) to solve my air leak on the right. So I went for a test ride yesterday and i'm getting popping thru carbs on acceleration. I'm running aftermarket air pods, mufflers (baffles but no packing), 140 main and #3 needle. Any ideas? At first I thought the popping was a lean/air leak condition. It starts and idles fine. It acclerates fine up to 4-5k in 4th gear until the popping starts. Plugs are light black on left and light grey on the right. The right side had the stripped carb cap.

eyhonda · Post by **eyhonda** » Sun May 30, 2010 9:46 pm

I already tried that. No change. It seems to be just coughing most of the time. A couple of times, it seemed to clear it's throat and start to take off right around 6k then stop. Now I'm thinking it's starving for fuel since the jetting or needle position has no effect. So I pull the carbs and the float level is low a couple mm's. It's easier to set the float level when the carbs are off. When I check it against a home-made gauge, the bottom if the floats should be about 2 mm above the bottom of the main jet holder. I set the levels & let the gaskets dry. They deform quite a bit when they soak with gas. I'll road test it tomorrow. Too late today.

I did the high speed idle test and it the plug are ok (light black). The idle jets are 42. I'll report again tomorrow. My gut feeling is the floats were too low and it was starving.

eyhonda · Post by **eyhonda** » Mon May 31, 2010 12:03 am

I have an idea on float level measurement. When you drain the bowls, you have x amount of fuel. If the level is correct, you can measure this amount as reference. So now, based on the fuel amount, I have the same level on both carbs. I just emptied the fuel on one side into a plastic container, marked the level with a sharpie and compared it to the other carb.

So now, can someone with a good running bike (most of you), empty your fuel bowl with the fuel off, of course, and measure it in oz or cc? This will kind of tell me if i/we are in the ballpark of correct float level.

e3steve · Post by **e3steve** » Mon May 31, 2010 1:59 am

eyhonda wrote:I did the high speed idle test and it the plug are ok (light black).

Should be a sandy-brown/beige, bro'! WTF is 'light black'? Dark grey? If so, then that's lean; slightly sooty grey and that's too rich. Wet is poor combustion. Allow the high idle to run a bit longer, maybe 15 or 20 mins (place a desk fan, or similar, in a good position to assist cooling); get a better idea of the plugs' colours. This would be where a Gunson Colortune pays off!

Another basic test: have you tried removing the fuel cap when the symptom manifests itself? Just in case the cap breather is impeded and the tank is 'vacuuming'.

I'll measure the float bowl content, if no-one else does so first, later today. Do you have flat-sided bowls and brass floats? Both will make a difference to the liquid volume.

Spargett · Post by **Spargett** » Mon May 31, 2010 3:19 am

Steve, that colortune seems too easy to be true!? Have you tried it?