Weird Vibration

[Flyinfool]

I have an '88 Venture Made in '87 with 35K miles. Not a Royal

I am getting a strong vibration at 3,000 to 4,000 rpm, strongest at 3,500.

I get this vibration in all gears including neutral with the bike not moving.

It does not mater if I am accelerating hard, steady speed or decelerating.

It is strictly engine rpm dependent.

Above or below that rpm and it is nice and smooth.

 

Any ideas of where to start looking?

[GeorgeS]

Guess we need more info.

 

Can you pinpoint it a little more ? Is it a dull sound, tinny sound etc.

 

Any chance loose motor mounts ?

[Venturous Randy]

Mine was a little different than yours in that mine was more noticable under a pull. I synced the carbs and all is well.

RandyA

[Flyinfool]

It is not a sound. It is a physical felt vibration. The whole bike shakes.

[GeorgeS]

Well I guess I would start by checking for Loose bolts, all over the frame, and engine mounts.

[skydoc_17]

Hey Jeff,

When was the last time you did a Carb. Sync? Have you been using your Seafoam in the gas regulary? Have you checked the condition of the Carb. Diaphragms lately? When was the last time you checked the clamps on the air box (there are two sets)?

Take a peek at these items and let us know what you find.

Earl

[Flyinfool]

I have checked all of the bolts that I can get to without major disassemble, they are all still rusted solid.

 

I have not been able to find a local source for SeaFoam so I have not tried that.The bike is just coming off winter storage where I do use StaBil in the gas, The second tank for the season is almost gone so a fresh fill might help. (fingers crossed)

All of the air box clamps are tight.

I guess I will need to acquire/build a set of synchronizers to check that out and do some reading up on the procedure. I will have to read up on how to check the diaphragms.

I know that there are some good threads here on the diaphragms and sync.

[Yammer Dan]

Find sea-Foam run entire can to 1/2 tank and get carbs synced.

[86er]

I have an '88 Venture Made in '87 with 35K miles. ................................................................................................

 

Any ideas of where to start looking?

 

Personally, I don't think you should have bought a bike that was made with 35 thousand miles on it!

[skydoc_17]

Hey Jeff,

Here is a link to a thread that describes the Carb. Sync. procedure with a Carbtune Manometer. It will work on any Manometer.

 

http://www.venturerider.org/forum/showthread.php?t=35274

 

Here is a link to a thread about Changing the Carb. Diaphragms, you can use this procedure to check the condition of the Diaphragms as well.

 

http://www.venturerider.org/forum/showthread.php?t=32052

 

Before I would go and replace motor mounts or a bunch of bearings I would invest in a Manometer and pull the Carb. Diaphragms especially if you do not know the condition of these items. The Carbtune is a great buy right now because the Brit. pound is weak compared to the US dollar. And the checking of the Diaphragms is labor only unless you find out they are bad. When you start checking things out please feel free to PM me with questions as I have two First Gen VRs and have done a lot of work on them

Good luck on your project,

Earl

[IH Truck Guy]

.

 

I have not been able to find a local source for SeaFoam so I have not tried that..

 

Right down the road from ya buddy...Farm and Fleet. Oak Creek...

 

Check where the mufflers mount behind the passenger floorboards.....

Make sure the bolts are tight....

[saddlebum]

mine did something like that and it was a faulty plug instead of the spark going from tip to tab it was jumping side ways to the body of the plug. I put in four new plugs vibration gone

[jasonm.]

I think it could be a slide diaphragm assy. There are 2 tests for this. Test#1- take the bike for a ride...it should pull quickly to redline at full throttle in 2 and 3rd gear. ANY studders in acceleration= bad slide assy. Test#2, get the bike warmed up. Then remove air box cover and air filter , gently turn throttle to confirm all 4 slide want to move. NOTE: the bike won't run smooth as the slides attempt to move.

[GeorgeS]

I have run my 89 with one plug wire disconnected. ( by mistake ) and did not notice any appreciable vibration. ??

[Flyinfool]

OK here is an update.

I did get a can of SeaFoam to add to a tank of gas.

While the SeaFoam was in there it ran great. Got 50MPG out of that tank driving the same route back and forth to work that accounts for 95% of my riding.

I really thought that that did it. Till the next tank of gas, then it ran like pooop and sucked gas like crazy, was down to about 25 mpg on that next tank.

So I checked the diaphragms and could not see any pinholes in them so I put them back in.

 

Now 2 tanks later, it is running good, the vibration is barely noticeable, but still there, and my mileage is back into the mid 40's.

 

I am planning to make the WI MD up in Fond du Lac put on by RedRider. I hope to learn how to do a carb sync there to see if that helps clear anything up.

[Yammer Dan]

Should keep using the Sea-Foam. Couple oz. every other tank.

[painterman67]

another thing you could check is the plugs and wires. New wires helped mine quite a bit and everytime I ran seafome on a heavy dose I tended to foul the plugs. Sometimes they would only foul slightly and burn clean in a tank or two. But once it was real bad fouled and I had to replace the plugs .

 

 

Hope this helps

David

[Venturous Randy]

Are you getting gas at the same place? If you are, try changing it around some.

RandyA

[Flyinfool]

I get gas at the next station after the warning light starts to blink. So it is always different stations and diferent brands. I always use premium cuz it just runs a whole lot better.

 

At Jeff's Maintenance day that he was so kind to host, I did get the carbs synched. they were very close to start with. That has not made any difference in the vibration.

As long as I stay under 3K or over 4K the engine is smooth as silk. at 3500 the keys are bouncing up and down on the dash.

 

Is there some kind of a mechanical timing advance that might be sticking and messing with the timing in that RPM range?

[GaryZ]

As long as I stay under 3K or over 4K the engine is smooth as silk. at 3500 the keys are bouncing up and down on the dash.

 

This very strange to me. My '85 VR starts into the "sweet spot" just under 3k RPM and is ultra smooth at 4k. My guess is you are running on three cylinders. Try the water trick . . . Start your bike cold and run for a couple minutes. Spray water on the exhaust pipes at the heads. If one of the four does not steam, it is not working.