Vibration at high RPM

[sakari]

Hi all, I've had a problem for a while with my 96 NTV. For a while, there's been a very noticeable vibration in the handlebars, fuel tank and footpegs when the revs get over 4000. This also occurs when the bike is in neutral, so I know it's an engine issue. I've done a visual inspection of the carb boots (without removing the air filter housing completely), and they appear to be fine and uncracked. I also tried retorquing the engine bolts, they are in spec.

Another issue which may be related is a strong hesitation when acceleration full-throttle from under 3000 RPM (but it pulls fine in higher revs). I suppose this could be a carb balancing issue or dirty carbs, but as I'm rather uneducated when it comes to carbs, I haven't tried disassembly. Any tips are greatly appreciated!

[slug]

hi sakari, l stripped down carbs,,. used one of threads on here.. technical
info carbs with photos...not that difficult if you take time.use good carb cleaner.
strip one at a time. so parts don't get mixed..shows how to check carb heights.
the little channels tend to get blocked. is awkward to replace on inlet rubbers..
worth trying, air screws on mine were 2and a quarter turns from fully in position.
did not balance seemed ok after clean,,. pay attention to small filter above carb needles.
also check fuel pump filter.. cheers the slug..

[richie318]

When I did my carbs it was the little filters behind the float needle that were the problem, I ultrasonic'd them and was fine after that.

I had to take carbs apart twice as the first time did not know about these little buggers and could not for the life of me work out why no power. The forum educated me as to my error and we now have nice purr from the engine following a carb sync too.

[gills]

Here's the link to the carbs stripdown/rebuild on the Hawk forum: hawkgtforum.com/forum/showthread.php?t=4844.

[sakari]

Thanks for the info! I'll have to do a carb rebuild when i get a chance. I balanced the carbs, but that did nothing to alleviate the vibrations.

[kuriso]

I also have a problem like this since last week. A high pitch vibration at 4000 rpm and above. Also at lower rpms but it realy gets anoying at 4000 rpm. Bike runs perfect.

Please help.. any suggestions towards solving this problem would be much appreciated. Thanx

[sakari]

I finally got around to cleaning the carbs. It seems that my bike is actually running worse after cleaning and balancing, with a more erratic idle than before. I have an aftermarket exhaust, and the pilot screws were set out 3 turns (front) and 2.75 turns (rear). I tried setting them to the default setting of 2.25 turns, but there was a whole lot of backfire, so I went with the same settings as before. Any ideas on the erratic idle? I didn't find any vacuum leaks in the carbs or exhaust. My bike (96 model year) had newer mesh-style filters behind the floats, and they looked clear to me.

The carb cleaning didn't do anything to help the vibrations. However, the acceleration hesitation is gone. I've also replaced the inline fuel filter.