Took the '67 CL77 out for a spin yesterday with my new homemade baffles, primary chain, new 165 Mains, and other winter sprucing up items. Bike ran superb with one minor exception.
With the bike at just about any speed, with the throttle wide open, as I backed off the throttle the engine would stumble for just a second. It sounded just like a lean mixture stumble when you accelerate, only this was on decel. And if I went to WOT, it would not stumble on the way up. But every time from WOT almost within the first few degrees of rotation back, it would stumble. I tried to find the spot to see if it would continue to stumble, but I could not get it to do it.
I'm thinking that the needle needs to come up a bit. But I suppose it could also be just a tad rich and as the slide comes down the accelerate flow thru the venturi picks up too much gas for the air flow and it goes rich. I wish I had eyes behind me head to see if there is a puff of black smoke.
In all my years of monkeying with engines, I've never run into this.
I did not notice this last year. But it may have been there, but I just did not notice. Although I'm doubtful I would have missed it.
Here are the changes since last year.
Removed stock exhaust, which was really striaght thru with a gutted muffler and the tip cut off. Installed straight pipes with my homemade baffles, for which I posted pictures here a month or so ago.
Went from 160 Mains to 165 Mains. Jets are NOS from Honda.
I bumped up the Mains because of the wide open stock exhaust. My understanding is 165 is what came in the bike from Honda.
Anybody ever experience this. I'm going to play with the bike today, but thought I'd ask here before I head out to the garage. I'll let you know if I figure it out.
Thanks,
Rob
Interesting engine stumble at speedOkay, today I moved the circlip in the needles down one slot. It was in the second slot from the top and now is in the 3rd. It appears that the stumble got worse. Today I noticed that is is more RPM and load sensitive than I initially observed. Or that could be the result of the moving of the circlip.
At high revs, pulling a good load, with the throttle at WOT, if I back off it stumbles, almost like you shut off the gas or ign for a split second, then recovers. I tried again to get it to continue by holding the same position, but it won't. It is purely a momentary thing. Same revs and load if I back off the throttle slowly, it does not do it. From closed throttle to WOT throttle, I cannot get it to bog or do anything else indicating bad mixture or jetting. It's only backing off from WOT. At lower revs and loads it more like a quick stutter than a stumble. Engine for a brief second sounds like a machine gun, then goes smooth again. My initial thoughts are as the needle lowers into the jet, it is either closing off the mixture too fast for the air flow thru the venturi or perhaps not closing it off enough. The fact that it seems to have gotten worse (although temps are colder today than last time) might be skewing my data. It is supposed to rain tomorrow. But it might just be showers. I'm going to try putting the circlip one slot above where it was originally, or two higher than it is now and see if it gets worse, better or no change. Nobody has ever experienced this before? I thought LM would reply with a one liner that either confirms or poops on my theories. Again, here are the variables that changed. 1. Went from 130 mains to 135 mains 2. Went from orginal exhaust with gutted muffler and 2 inch opening due to end of muffler being cut off to straight pipes with homemade baffles. If moving the circlip has no effect or no improvement, I'm thinking of putting the 130 mains back in. What do you think about the needle jet being worn? Bike has 14K miles on it. This would make for a richer mixture. I would expect a momentary rich mixture to not cause it to stumble like this, but I could be wrong. I have no way to be sure that the needles are the correct needles. Could be somebody just found needles from another bike and put them in. Does anyone have a set of original late model CL77 needles that they can measure for me? Thanks, Rob If the Keihin tuning graph is accurate, then it should be either main jet or needle taper.
Have you tried with and without baffles to see if there is any difference. Since you added baffles, and upped the mains, I would initially think too rich on mains or too skinny needle taper, or maybe both. These kind of questions are exactly why I installed the A/F meter so I hopefully see whats going on. Also, don't underestimate the effects of muffler and pipe changes, especially at specific rpm ranges. 66 dream, 78 cb750k, 02fz1, 09 wing
Have not tried the bike without the baffles yet. But that was going to be my next test since it is a lot easier than pulling the seat and tank off again.
If she clears up, then I'm going to try the 130 mains again. I know I'm breaking my own rules by having mutiple variables in play here. I should go back to basics, return the bike to the config in which it ran well and then try the baffles. It could be I did not need to bump up the mains to stock size. Thanks, Removal of baffles did not improve anything. I also checked my needles and did find a number on one of them. It is the correct needle for a CL77 24304, according to Silver's book. I measured both needles and they are identical.
So now I will replace the 135 mains with the 130's that came in the bike and that seemed to work fine last year. I also noticed a lot of soot on the baffles and although I did not do a plug chop, I did check the plugs and they were a tad sooty. Everything seems to be pointing to the 135 mains being too big. I'm headed back to the shop. Will let you know what I find after I change the mains. regards, Rob
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