Airhead Missing with vibration question

[grumpyone]

Got a 1986 R80 with a vibration miss. We have changed the plugs , wires are new, set the valves , made sure the cabs are level... When it is running it vibrates like you have a vibrator on your knees and it is there at idol and at high rpms.
I figured it was an electrical problem but dont find anything any suggestions on where to look and test???
Can a vibration steady miss like this be from carbs not set right or in the carbs any way???
Bike has 28K and has been riden very little over the past 16 years but it seems to run good otherwise and compression is low but very close on both jugs.
Thanks for any suggestions.
Jim and Esther

[jforgo]

Questions:
Did you synchronize the carbs?
Did your carb rebuild included replacing diaphragms?Floats? float needles?

BTW, if you have low compression @ 28K on a Nikasil bike, I suspect the what the odometer says is not the true mileage. In such case, you may be getting to early stages of valve recession - see recent thread on this topic.

[jforgo]

I'm sorry - it doesn't look llke you did a carb rebuild - suggest you do rebuild including floats/needles. If the bike did in fact sit around a lot, there is likely a lot of crud in there.
Also check rubber sleeves on air intakes - they may well be creating vacuum leak, and need replacemnt.
I still suspect actual mileage on bike - therefore incipient valve recession (?)

[AnnapolisAirhead]

For what its worth, I just went through my carbs (first airhead for me) and when rebuilding them, I did not get the main needles adjusted identically, and in fact one was set on the first notch...came loose and the bike vibrated like mad. It still ran, although all I did was start it. The functioning side cylinder became very hot almost immediately, the other side was cool to the touch.

Made a carb synch and adjustment believer out of me. Also, others much more knowledgeable than I suggested right away that I adjust the valves first thing. What a huge difference it makes. My bike has 59k on it and is a 1983 R100.

Does it backfire at all? Any smoke (black, blue or white) coming out of either or both pipes?

[20774]

Check the engine mounts, too.

Can you tell if the problem is due to one side or the other? Is one cylinder firing just fine and the other is not? You might be able to tell be feel the temperature of the exhaust and/or putting your hands on the valve covers or VERY carefully, touching the header pipes quickly. If you side is measurable colder than the other, then it is probably not the engine mounts and you'll need to look into spark and/or fuel. Trouble shoot spark issues by swapping parts side to side - plugs, wires, coils...

[AnnapolisAirhead]

...oh yeah, like 20774 implied check for spark if one side is noticeably cooler than the other. I pulled the plug, put the wire on it and let the tip rest on the head (near the header, not the carb), then cranked a couple times to see a blue spark. It that works, a simple compression test on each side should reveal any valve adjustment issue.

In the end, I had good spark and good compression on both sides. That left a fuel delivery probably on my cool cylinder side. If both of yours are about the same temperature, could be an engine mount.

When idling, do both exhaust pipes feel like they are pumping out the same amount of force? This may sound odd, but do they smell the same when they are running? One of mine was richer than the other so I tuned the carb.

[grumpyone]

OK GUYS; We got back out and did more test thanks to all your wonderful help and we have some more info for you.
We work on guns with baked on finish so we have inf. themometers and so we fired the bike and warmed it up to operating temp.
The Pipes at the head , the valve covers and the pipes just ahead of the cat converter on both sides are all running within 5 degrees of the same spot on the opsite side so the temp is very good match.
We dont think there is a miss and I ask my UPS driver who came by (young and has ears left) if it was missing and he thought not only a vibration.
Is it possible to be runing good and have a steady vibration in the bike at idol and fast rpm. Such as someone said the motor mounts or ?????
We have had K bikes (very smooth) and airheads before and cant remember anything like this I remember my r 90/ 6 as a very smooth runner like the K75?
I would not think it could be fuel if the temp is that close on both sides? and I have just about exhausted the spark situation.
Thanks very much for all the great help we really appreciate it.
Jim and Esther

[20774]

Well, getting deeper, I'm wondering if maybe there's something wrong with the clutch mechanism...has something broken off such that it's out of balance??

[26667]

Just to 2ble check, did you, in addition to synching the carbs, adjust the mix and check the float level? I'd been dealing w a similar vibration and first found the plugs carbon-fouled (rich mix). So we carefully synched and set the mix. Then found float level was too high by about 6mm. (I believe 19 -24 is the range)Did an adjust on the float level and it runs much better, but I think I need new floats. Apparantly w age they soak up fuel and sink too low in the bowl.
Good luck, and keep us posted.