Odd vibration.

[Air Ready Auto]

The temp was nice enough yesterday that I got Lucy out for a few miles (77.4). I let her warm up good then hit the road. She did fine in town then I got out to the country back roads. I noticed a vibration (almost like an engine misfire) between 40mph and 60mph. There was no vibration below 40/over 60 or when accelerating through to 65. Im about 90% sure the problem is not the tires. Anybody have any ideas on where to start checking?

[snyper316]

Your saying like a missfire, I have has vibrations due to exhaust being loose.. I don't know if that would be your problem at all. Another vibration happened when my carbs were out of sync, then another time a spark plug I guess wasn't 100% happened after I dropped it on the ground when I was changing plugs out. That is about all I can think other then the normal possibly need sync on the carburetor.

[7 lakes]

Did you try pulling the clutch and coasting to see if uncoupling the engine made any difference? If it feels the same then its likely an out of balance or worn rotating part of the drivetrain. If it calms down with the engine out of the loop then you know its there. Was it doing this at light cruise, light throttle, steady speed and then cleared up when you accelerated? Any chance your gas is old?

 

Tim

[Marcarl]

Did you try pulling the clutch and coasting to see if uncoupling the engine made any difference? If it feels the same then its likely an out of balance or worn rotating part of the drivetrain. If it calms down with the engine out of the loop then you know its there. Was it doing this at light cruise, light throttle, steady speed and then cleared up when you accelerated? Any chance your gas is old?

 

Tim

 

Yep, my thoughts!

[Yammer Dan]

Sea-Foam???

[bongobobny]

Yup, you need to determine if the "vibration" is engine related or not! It could be something like the steering head nut needs to be properly torqued or something like that if it is non-engine related...

[Air Ready Auto]

Did you try pulling the clutch and coasting to see if uncoupling the engine made any difference? If it feels the same then its likely an out of balance or worn rotating part of the drivetrain. If it calms down with the engine out of the loop then you know its there. Was it doing this at light cruise, light throttle, steady speed and then cleared up when you accelerated? Any chance your gas is old?

 

Tim

 

I did not try pulling the clutch and coasting. We got more snow today so I will have to try that later. The vibration was steady when holding any speed between 40 and 60 and went away if I let off the throttle or accelerated. I left for the ride with 2gal of fresh fuel on top of what was left from last fall. I treated the fuel before parking her and have started her at least once a week and let warm up.

 

 

Sea-Foam???

 

 

I added a half can to a full tank when I put her up for the winter.

[Yammer Dan]

Buy some BerryMan's Chem Tech and give it a shot. Then run that old fuel out before you worry much.

[7 lakes]

I would try pulling the clutch while it's doing it, if it fades away as rpms decrease then you know it's the engine for sure , always a good first check. In my experience, light throttle cruising issues that go away when accelerating are almost always a fuel starvation issue. Although folks like to measure performance with their wrist low and their eyes wide, I pay more attention to light throttle behavior and transitions as a measure of tuning. It's actually pretty simple to get an engine to idle well, or cruise well, or accelerate well, but moving between those conditions smoothly and maintaining a smooth light throttle cruise is all about those four hunks of pot metal with all the little holes drilled in them.

 

A small obstruction in a carb passage or jet can cause slight fuel starvation, but the condition is masked when you open the thnrottle and overcome it with more fuel, or when you close it and aren't asking anything of it. I would suspect a small obstruction in the pilot circuit, I would first drain and rinse the tank then fill, add half a can of Seafoam and ride it. If it doesn't clear in that tank then it's time for a carb clean. Im not a fan of adding fuel system cleaners without dumping and rinsing the tank, if you have an issue with crud breaking loose, it makes sense to me to try to remove the crud from the source before loosening more of it and flushing it through the system.

 

Also, did you treat the fuel with Seafoam at the end of the season? It's a good cleaner but not really a preservative treatment.

 

Hope this helps some,

 

Tim

Edited March 2, 2018 by 7 lakes

[Venturous Randy]

Have you ever pulled the driveshaft and inspected the splines and greased them? This could also be the universal joint on the driveshaft by your description, but this is not a common failure. The splines on the driveshaft is if not greased good.

Randy

[Air Ready Auto]

Have you ever pulled the driveshaft and inspected the splines and greased them? This could also be the universal joint on the driveshaft by your description, but this is not a common failure. The splines on the driveshaft is if not greased good.

Randy

 

I have not pulled the shaft yet. It's on my list of things to do.