Hello,
I have a 64' CB77. I put new points on about 500 miles ago. On Sunday I decided it was time to set the gap again as the new points have probably done their new-points thing and settled into the cam. I've done this many times and have my strategy down, I even got the gap so perfectly that when I checked the static timing it was still right at "F" so I didn't even have to move the points plate. Anyways, I set the timing and rode the bike around the block, all seemed perfect.
My morning ritual when the engine is cold is to turn each idle screw 1.25 turns in. As I ride and the engine starts to warm up I turn them both back at stop lights until it's fully warm. By then the engine is idling just below 1,000rpm and it's fully warm.
But I noticed something weird the day after setting the timing. Although my ride to work presented nothing noteworthy, all systems normal, I noticed on my way home that around the time I had dialed back my idle screws to their fully-warm setting as the engine warmed up, the idle was actually creeping UP instead of settling in to the usual 1k rpm idle. Now it seems to idle at 1500rpms after warming up... and the weirder part is I can unscrew the idle screws ENTIRELY and it will stay right there, no change. When I let it cool down fully and try to start it again with the idles all the way out it doesn't start at all of course, I have to dial them back to roughly where they were before and fully warm the engine up again before the symptom is present once again.
After I noticed this on Monday I filled her up with gas since it was low and when you're getting low your idle can creep up, simple things first right? I also removed the tank and popped the slide out of each carb and screwed them back in to ensure they were properly seated and neither of them were getting caught up on anything and somehow holding open a bit... occasionally my left-slide gets hung up at WOT if it's not seated properly.
Took it for a quick test drive and everything seemed fine. Drove it to work today and everything seemed fine again, but on my way home for lunch.... crept up to 1500 again.
Now I suppose I could re-check the timing, and I'm going to do that. Although it does seem weird for it to be sort of an erratic issue like this. I would expect if the timing had slipped it would ALWAYS present a problem, not just when the bike warmed up. I am also going to check for air leaks around the carbs, maybe as things warm up the metal opens an air leak somewhere that's increasing idle. Aside from that, I'm not really sure what to look for. For what it's worth, my mixture screws are set at about 1 and 1/8 out, but are ALWAYS set that way, and all the times I've set my timing/valves, etc I've never fussed with the mixture screws so I don' believe it could be that either.
Any other things to check that I may have missed would be great.
Thank you!
Odd Idling Issue after Setting Timing CB77Ok...
I re-checked timing with my strobe and it's fine. I also checked everywhere for air leaks, none were found. I also pulled and re-seated the carb tops. What I noticed is if I unscrewed the right-side carb top, the rpms would completely shoot down, although I realize that could be from loosening them enough to let air in. But I played with then anyway, just barely tightening it enough that there was no air leak, but not tight enough that it would raise rpm. I know you can sort of overtighten them so you distort the throttle body and the slide can get hung up. Now I'm not sure if that's my problem because with minimal necessary tightness it still idles with the idle screws all the way out. Could it possibly be that the rubber gaskets in the carb tops are flattened too much? thus to keep it from leaking you have to tighten them down so much that it squeezes the throttle body and causes the slide to not return to bottom all the way? It's really the only other thing I can think of.
Sounds to me that you should just keep riding and not go home since the problem only exists when you are on your way home. Seriously, maybe you might want to try and adjust the slide stop screws instead of the air screws. What is the reason that you have to always set the air screws. I think those should only be set once for low speed air/fuel mixture. My understanding is that the choke and slide stop adjustment should take care of the idle issue if everything else is working properly.
Could be: 1 Low fuel flow to the carb bowl.....possibly/not likely 2. Slide stop adjustment.....possibly 3. Air leak after the engine gets warmed up....possibly 4. improper timing either right or left side, or both.....possibly 5. Cam advancement weight spring weak......not likely Might suggest Ed Moore's tune up recipe located in the search area.....follow it to a tee! Good luck, and will be watching this thread for further info from the experts.
This observation may seem a bit obvious, but is there enough play in the throttle cables? I mean are the slides allowed to bottom out and leave a couple of millimetres or so of outer cable movement?
If this is so, then there seems to be a weakening of the air/fuel mix. Get the motor up to temp, pull the plugs and clean them off, then refit them and let the motor idle for ten or fifteen. Then pull the plugs again and check the colour. If there's a greying of the insulator & electrodes then I'd be inclined to suspect lean idle screw settings. Remember: idle only. The air screw is only responsible at less than one-eighth openings.
idleI don't lock down the throttle cable adjuster nut at the handlebar, that way I can turn it out a bit with my fingers for faster idle warming up, then turn it down to a good idle once engine gets hot... usually at the first stop light I come to.
'62 CB77. "It's a rider."
Steve, yes, there is enough play in the cables. When the engine is off I can hear the slides click down in the bottom of the carbs, both sides. I did not adjust the cable play before this became an issue.
It does seem as if something could be weakening with the air/fuel mix causing the idle to creep up, like an air leak (but I can't find one), or a slide is hanging up in a carb, in which case it's just a mechanical issue. At any rate, it's not the idle screws or air mix screws. Air mix screws are set where they've been set for 2 years, and have never needed to be changed. And remember, the idle screws, that hold the slides up so you can actually idle, those can be screwed out ALL THE WAY once this symptom is present... which really leads me to believe it's a slide-sticking issue. jleewebb, I leave the cable adjusters locked in place so my throttle pulls both slides equally, I use the idle screws to dial in the idle as it warms up (not mix screws..... IDLE screws). Today I'm going to pull air filters and run the bike with them off so I can look in the back of the carbs and see exactly what is happening when i back out the idle screws all the way. If I see the screws coming out but the slides staying put I'll know it's that. Also will re-check static timing since I'll have all my tools. Will report back my findings.
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