[yukonjon]

So I just had my engine torn apart and put back together and now I have some issues I cant figure out. (rebuild was for a broken shift linkage) I reinstalled the engine, added cobra exhaust, pod filters on carbs, rejetted, and coastered the bike. It took some work but I can start the bike and it will idle about 1200 rpm fairly well. Been working and riding on and off for a week now. It drives fine and shifts through the gears with no issues. My issue is that it vibrates like crazy. On a 20 minute ride my butt, hands, and feet were all falling asleep. This is at all speeds and even at idle. One of my carbs has a tendency to backfire through the air filter/carb occasionally after warming up as well. Im not sure if the 2 problems are related or not.

I have checked all mount bolts, intake leaks, removed carbs and checked, etc. Im not sure what I am missing or whats causing the issues. I tried checking my carb sync and it seemed like it was pretty even. Does any one have any ideas what might be causing these problems?

 

[Bat]

Were the timing chains installed with all marks lined up and at TDC? Could anything have slipped during the installation of the next parts? Were all the pieces put back or replaced correctly in the balance wheel? Sounds like something is rotating out of line or out of sync with the rest of the engine. Just thinkin' ....

 

[yukonjon]

Im sure its possible. After reading im kind of leaning towards the balancer not being installed in line with the rotor. My mechanic rebuilt the engine and hes been excellent with everything but he might have messed up. Im just trying to rule anything else out before removing the engine to check AGAIN (4th time)

 

[l3rice]

I agree with bat but, could it be as simple as carbs out of sync? As far as i know (and thats not a whole lot) but the not liking to idle with the vibration could be timing or carbs or both. if it were me i would start with the easy most accessible possibility the carbs, as for the other possibilities ie timing or balance that is a motor pull.

if im wrong one of the others here will chime in.

 

[clock152]

I was thinking Carb sync as well.

 

[OlHossCanada]

You don`t say how old the bike is, so I don`t know if deteriorating balancer dampers are a likelihood.

 

[flitecontrol]

^X2 he probably should have replaced those too while he was in there.

 

[yukonjon]

The bike is a 91. Im not getting any chunks or pieces in my oil screen or anything but it might by installed wrong. I checked my sync and it seems right on. Ive had vibration issues from out of sync carbs and it seems much worse than that. How hard is it to check the balancers if i pull the engine? is there a large amount of disassemble or fairly easy to see. Im going to double check the carb sync but im almost sure its not that.

 

[yukonjon]

So it is def not the carb sync. Checked it again and its right on. All bolts tight and its def coming from motor. How hard is it to check the balancer?

 

[DavesVulster]

Might be a silly suggestion but what about the engine mounts? I mean if it runs through the gears, revs and idles well, I would think the internal balancer and valve timing should be ok or it wouldn't ride well at all. Just thinking that if a damper in one of your engine mounts is out of place, or a mount is too tight, the engine vibration is now being transferred through the frame to your hands and feet. I have a hunch that this may be your problem. Good luck,
dt

 

[Knifemaker]

Because they are CV carbs, a carb sync would only be noticed at idle speeds, once you got on the gas, the cabs would not cause vibration. Timing / balancers would be the culprit.

 

[OlHossCanada]

So it is def not the carb sync. Checked it again and its right on. All bolts tight and its def coming from motor. How hard is it to check the balancer?

You are going to have to remove the left side engine cover and alternator rotor to get to the balancer gear.
See roach`s video #4. He gets to the balancer gear about 2 minutes into the video.
http://www.youtube.com/watch?v=aK7uDj2Xo6s :smiley_th

Index of all of roach`s rebuild videos to date:
http://www.vn750.com/forum/showthread.php?t=18289

 

[camai]

I agree that the vibs are most likely the balancers. I have bad vibes after mine was worked on. I'm pulling the cover this off season and checking it out. If that is the case I'll post pictures. the backfire is the air/fuel adjustment I'd say. I was having bad backfire so I marbled, used 1/2 in copper pipe caps. Then adjusted the mixture screws about 2 and a half turns and backfire gone. Really nice cause now I don't worry about the neighbors shooting at me at 5 am.

 

[kanuck69]

The balancer gear has a mark on it to line up with the shaft it mounts to. There is also & mark on the edge of the balance gear that has to line up with the rotor. This is easy to overlook & I have done it myself. Nothing like getting it all back together & realizing you forgot something. If it's off even a bit it will shake through all the gears quite bad. It feels like your sitting on a Harley.

 

[kanuck69]

Youkonjon! Did you get this figured out? I'm curious of the outcome.

 

[RakerBill]

Check the engine mount bolts. If they are loose, it can make it vibrate pretty bad. I had to recheck mine because after my engine pull, I had a bad vibration.
Went in and pulled all 3 mount bolts, cleaned them, then lubed them, and reinstalled them, then torqued them to specs. Vibration is gone.
Worse case scenario are the vibration dampers.
Both engine cases will have to come off to check balance dampers.
There are alignment marks on the damper gears, and if they aren't lined up it will make it vibrate real bad.
Hope you don't have to tear it down.

 

[yukonjon]

Youkonjon! Did you get this figured out? I'm curious of the outcome.

Sorry for the slow reply. Been traveling a lot and hadn't checked back in a while. As for figuring it out we got the vibration to stop but aren't completely sure how. We tore the engine apart again and checked all the balancers and mounts. No issues there. Put it back together and noticed that the rear cylinder was filling with gas rather quickly while sitting. Ended up cleaning the carbs and doing a petcock rebuild. Choke system seemed to have some issues so cleaned that too. Cranked it up and vibration gone.

Were thinking that the large amount of excess fuel in the cylinder was not igniting and was sloshing around the whole time creating the vibration. Not sure if that was the case or not but the only thing we could come up with. We know it wasn't the balancers or the mounts though.

Runs with no vibration now but still has issues. Will idle and drive fine but randomly goes from running rpm up to about 4500 rpm randomly, will stay there for a while regardless of what I do, then eventually go back down to idle (1000rpm). Im gonna replace a few gaskets in the carbs, fix my jetting, and put a new air-valve in, hoping it fixes the problem. Obviously ill check for vacuum and exhaust leaks while in the process.

If you have any suggestions im all for it. Thanks for all the help guys.