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rough vibration under load @ 4000rpm

Old 09-08-2011, 05:09 PM
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rough vibration under load @ 4000rpm

Hi all,
I have a 97 VTR with a vibration problem from 4000rpm to +/- 4700rpm under load. From the gas tank to the handles to the foot pegs, the vibration is more than obvious!!! I've looked around for loose parts. Everything is tight. 'Had both sprockets and chain and CCTs renewed for obvious reasons. I hoped that the vibration was due to these worn parts, but no chance, it's still there. Also had the carbs freshend up with new jets and pilots while on a dyno. The dawm vibration is still a mystery!!!! Other mods are KNN filter and MIG exhaust.

Anybody have a clue what might be going on?

Martin
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Old 09-08-2011, 06:36 PM
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I guess I get this one huh......lol

As this is the internet..... I can tell you what it sounds like but will need a lot more info before I can try to help you out.

First, you might want to do a search on the K&N filter. It is not held with much regard by most people here and yes I am one of them as I spent 2 yrs trying to get one to work the way I felt it should. You gain a couple of HP on top but usually end up with a 4-5 HP hole somewhere in the powerband because of it.

Second, what exactly did you do to the carbs? You say mains and pilots but which one and what size? Also did you change the needles?

Then there is dyno tuning. If the person doing the tuning has no real experience with twins, this can be a problem. If you try to tune it for top end HP, like an I4, you will end up with a poor running bike.

So to what your issues sound like. I would say it is either a pilot or needle (maybe both) adjustment is needed.
Once again, I can't see the plugs or hear it run but it sounds like you are going very rich and the engine is misfiring, that is where the vibration is coming from.
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Old 09-09-2011, 03:58 AM
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This is really interesting. I've only had my S'Hawk for 6 months, so I am still learning the bike's character. Several sessions on the street the bike has felt like vibrations are more intense than what I expect, and then the next time I ride it, it seems fine. Was thinking maybe it's just my imagination.

I have been wondering about the possibility of carb issues, this sounds like a clue. I think mine are probably dirty and needing synch. Air Filter and Exhaust are stock, but I really don't know if the PM ever messed with jetting.

Apology for the thread jack- hit send before thinking.

Last edited by CrankenFine; 09-09-2011 at 03:59 AM. Reason: post script comment
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Old 09-09-2011, 04:49 AM
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The bike was running great for the last 4 year with the KNN filter. Here are the carb changes:
-the ''pilots'' were: 2 x .45mm changed to 2 x .48mm.
-the ''mains jets'' were: 1.75mm and 1.78mm changed to 1.80mm et 1.85mm.
The dyno guy has the Canadian 1/4 mile record and most of his customers have H-Ds or V-twin cruisers. And... he's my neighbor(lol)!
I noticed last night that my gas tank was kinda loose, but all fasteners are tight. How much freeplay do you have on your tanks? My vibration is so intense and for a short period of time that I am now thinking it could be body related.
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Old 09-09-2011, 04:58 AM
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BTW' (forgot that!!) the spark plug are new. I bought 4 of them and tried all 4. There is no misfire felt at all. Bottom line the bike rides great and pulls all the way to the red line. Low end is perfect and fires up real fast. In any case did the vibration show on the dyno graphs.
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Old 09-09-2011, 06:03 AM
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Originally Posted by plum555 View Post
The bike was running great for the last 4 year with the KNN filter. Here are the carb changes:
-the ''pilots'' were: 2 x .45mm changed to 2 x .48mm.
-the ''mains jets'' were: 1.75mm and 1.78mm changed to 1.80mm et 1.85mm.
The dyno guy has the Canadian 1/4 mile record and most of his customers have H-Ds or V-twin cruisers. And... he's my neighbor(lol)!
I noticed last night that my gas tank was kinda loose, but all fasteners are tight. How much freeplay do you have on your tanks? My vibration is so intense and for a short period of time that I am now thinking it could be body related.
No, the bike was running as best as you knew for 4 years... It's potentially a big difference between that and what it can run like... Just saying... Like hawk said, we are a bunch here that have tried the K&N and given up on it... I spent several hours on a dyno, trying to get it working as I felt it should work, and it's still sitting on a shelf to this date...

The tank is mounted in rubber at both end, so it has freeplay, check the condition of the rubber pieces if you think they are the culprit...
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Old 09-09-2011, 02:49 PM
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Originally Posted by plum555 View Post
Bottom line the bike rides great and pulls all the way to the red line. Low end is perfect and fires up real fast. In any case did the vibration show on the dyno graphs.
Well I'm just some guy on the internet but I can tell you what I see and I do kind of have a pretty good rep when it comes to setting up carbs if I say so myself.

Anyways you didn't say what needles you are running but with the info you did provide I will now stick to my first impression.

What you are feeling is the bike going so rich in the low mid-range that the plugs can't fire the mixture.

You made the classic mistake of swapping both the mains and the pilots. This make the bike too rich. While the bike is a "touch" lean, it's not off by much. The problem can either be fixed by swapping the pilots or the mains as no matter what the "charts" say the circuits do effect each other. One or the other is plenty.

A full Stg 1 engine might need both pilots and mains but anything else it will be just too rich.

The other thing I change on the carbs is the lift hole on the front slide. This is to address the problem that you are seeing. While with "proper" jetting it isn't noticed that much, there is a spot between 4-5K where the front carb goes rich due to the short stack. This is why you feel the "vibration" you loose the front cyl. because it is too rich to fire.

Another way to tell your too rich is your it fires up real fast. You should have to use the choke on a cold engine if you are jetted correctly.

Anyway I covered it all in this thread:https://www.superhawkforum.com/forum...-set-up-24769/

and it would be the advice I would give you now. Get a stock air filter, go back to stock main jets, modify the front slide and set the needles(or just print it out and hand it to your neighbor and say could you do this..... ) and you just might be surprised how hard this bike really can pull....... IMHO

Last edited by 8541Hawk; 09-09-2011 at 02:56 PM.
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Old 09-09-2011, 02:55 PM
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Originally Posted by Tweety View Post
I spent several hours on a dyno, trying to get it working as I felt it should work, and it's still sitting on a shelf to this date...
I tried to set mine with the butt dyno.... that is why I took some much time.

Though I will also say that anytime I got it anywhere close to working "right" the weather would change and it would be back to square one.....

Though some folks have had reported good results with them. I just couldn't do it.......
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Old 09-09-2011, 02:55 PM
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quick fix..... just adjust your idle to 4700. u'll never feel it then. lol ;-)
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Old 09-09-2011, 02:59 PM
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Originally Posted by uebergang View Post
quick fix..... just adjust your idle to 4700. u'll never feel it then. lol ;-)
Well that would work too......
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Old 09-09-2011, 07:07 PM
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Originally Posted by uebergang View Post
quick fix..... just adjust your idle to 4700. u'll never feel it then. lol ;-)
I'm glad someone else has a sense of humor. I was going to throw the traditional "That's what she said" to the title of the thread, Rough vibration under load. Ok I'm ashamed of myself for that one... Carry on with the good tech info...
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Old 09-10-2011, 09:06 AM
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This is all good infos... And good humour. I like this forum. I Will make the most out of all this and keep you posted and add the graphs.

Thanks
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Old 02-09-2012, 02:48 PM
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The Fix

Is this fixed yet?
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