annoying engine vibration at 3900 - 4500 RPMS

[maro]

{{{PROBLEM SOLVED it was the damn seat. read last post for details.}}}

and by serious I mean, it's dayum noticable and it hurts my "undercarriage". I feel it most in the seat obviously. It's definitely the engine as it happens in all gears at that range. I thought maybe I just need a good snych as I pull through all gears and ranges with no hesitation.

I re-synched this past weekend. #4 was way off. I thought, "thats the culprit" I got it all synched up at 4000 RPMs. While the bike does feel a bit smoother, that nasty rough patch at 3900 - 4500 still remains.

I did my valves a 2 years back, but have maybe put about 2k on it since then. I just bought a gasket and will do a valve check this weekend. Would valve issue cause this? any other thoughts or suggestions.

it really makes the bike uncomfortable to ride as I seem to always be riding in the 4000 RPM spot.

[tkent02]

Look for a loose motor mount bolt, footpeg mount or something else big.

[maro]

Thanks, no doubt I will. I've seen that as a common response to bike vibration. But how or why would that only effect a RPM range. It tends to smooth out after 4500 or so

Look for a loose motor mount bolt, footpeg mount or something else big.

[tkent02]

Dunno, harmonics or something?

[TheCafeKid]

There is another, much more insidious possibility.....

[maro]

Oh Boy, are you eluding to the ol, take the carbs apart, clean and start over.

noooooooooooo!

There is another, much more insidious possibility.....

[TheCafeKid]

Oh Boy, are you eluding to the ol, take the carbs apart, clean and start over.

noooooooooooo!

Nooooo...I was eluding to the possibility that you've got a twisted crank...

I've never experienced the issue, but perhaps you should ask around? I know a couple of other members have, and IIRC one of the symptoms was a sudden heavy buzz out of the bike...
I certainly hope that isn't the case and it is something silly, but the possibility is there with that motor.

Otherwise, how ya been Josh?? When did you ditch that nice Yosh you had in favor of the stock system? Gonna make it down for RRR?

[maro]

UHG I've read a bunch about twisted cranks here for the 1100E. really hope that's not the case. I'll do some research on Twisted Crank symptoms.

Things are well my dude. I picked up a spare 1100E (minus the engine) a year back. decided it wanted to get all the jetting and exhaust back to stock so I could stop tinkering and just enjoy a smooth ride.... (oh the irony, better not be the crank!)

Sold the yosh to someone here.

I'm planning on some big trips this summer on the bike if I can get her straight. Would love to join everyone for a meetup. How are you and the wifey!!.

Nooooo...I was eluding to the possibility that you've got a twisted crank...

I've never experienced the issue, but perhaps you should ask around? I know a couple of other members have, and IIRC one of the symptoms was a sudden heavy buzz out of the bike...
I certainly hope that isn't the case and it is something silly, but the possibility is there with that motor.

Otherwise, how ya been Josh?? When did you ditch that nice Yosh you had in favor of the stock system? Gonna make it down for RRR?

[tkent02]

I would think (hope) a twisted crankshaft would vibrate and any and all RPMs?
Dunno, never had one of those either.

[mike_of_bbg]

Put cylinders 1 and 4 at mid-stroke; pull those two plugs and use a chopstick or similar to measure the distance from the spark plug hole down to each piston and compare.

UHG I've read a bunch about twisted cranks here for the 1100E. really hope that's not the case. I'll do some research on Twisted Crank symptoms.

[maro]

anybody got anything else aside from the dreaded twisted crank...

[hampshirehog]

Faulty plug / lead / coil and she's misfiring (you would probably spot that but if it's only just minor it'll throw things).

Something else in the carbs out of whack. Damaged needle, slide, spring, diaphragm - does the vibration happen at all throttle openings?

Chunk fallen off the rotor; that would probably affect all rpms, though resonance does amplify vibes of course.

[Big T]

As weird as it seems, it could be your horns vibrating and being amplified by the gas tank

Mine did that after I changed the horns

[gearhead13]

Strange that I come across this in a search. I am getting a vibration at about 4k rpm too, fine below and above that but at that rpm it feels like the bike will vibrate apart. I am getting an '83 crank from a member here. I am thinking that I should have it fully welded and indexed
The crank that is in mine is factory welded, but the factory didnt weld every throw

[Suzuki_Don]

The rev range you are talking about here, 3,800 to 4,500 is the typical area where buzzy vibration sets in on the smaller 4-cyl motors, 550, 650, etc. On my bike once I was in this rev range there was a vibration I could hear but not really feel that disappeared above 4,500.

I rode it in this range and ran my hands over the front fork legs, the headlight, the instrument panel, the horn and whatever other parts I could reach without falling off the bike at 60+ mph. To no avail. I removed the front guard and both front calipers in case they were the culprits. Alas they were not, the vibration was still there.

It took about 6 months but I eventually found the culprit and it was the flap on top of the fuel tank. The problem is fixed now. But this is just as an illustration of where the vibration period is on these 4-cylinders motors with the 1,2,4,3 firing order. All cranks develop some vibration somewhere in the rev range, you can move it around by balancing the crank, but you cannot eliminate it.

It is well documented in the 550, 650 road tests that there is a vibration period on these models. I know we are talking about an 1100 but I think it is no coincidence that the rev range is exactly the same as the smaller motors and verified by my experience with the vibrating fuel tank flap situation.