Highway riding abnormal jolts of acceleration.. carb problem?

[spd264]

I have a 97 Kat and I was taking it on a 120 mile ride home from college and i noticed that in 6th gear going about 80mph and around 7.5K rpm i would get sudden jolts of acceleration, and at one point i had the bike at full throttle and the revs would only go up up about 7K and the bike would not go faster than 75mph. I pulled over and as soon as got completely off the throttle, bike still rolling, the revs dropped to 0 and the engine turned off. I started it back up and revd it up to about 10k several times just to clear any minor blockages in the carbs if there were any and i thought the problem was fixed. and the bike accelerated smoothly and with plenty of power back up to 95+ mph... but after another 15-20mins of riding i felt a severe loss of power and the even at full throttle the revs were around 7.5K rpm and the bike would struggle to get past 85mph and the jolts of random acceleration at a constant throttle position conitnued for the rest of the ride. I also stopped for gas once in the middle and the revs died again as soon as i got off the throttle. However, at the end of the ride as i was pulling into my driveway, the revs did not drop down to 0 upon returning the throttle to it's idle position. any suggestions on what this may be? i recently had new spark plugs, carbs synced, new throttle cable, choke cable, sprocket and chain. plus valve adjustment less than a year ago.. i'm confused, should i try putting a engine / fuel system cleaner in the gas tank?

[kevin2502000]

Check your petcock function.

[Helmet_Hair]

Sounds like it could be electrical. Check the major connections right off the battery for any grounding.

[spd264]

i'll check into the petcock.. what is the function of the petcock besides a valve to switch to reserves when gas is low? would it cause this kind of a problem only at high speeds? I'm not very experienced at servicing bikes but i have worked on cars, would a petcock rebuild be something that takes a great deal of knowlege / skill? I doubt the problem is electrical because it runs fine ( smooth acceleration and normal throttle response ) with plenty of power in city driving 30 - 60mph but i will look into that as well.

[md86]

I BELIEVE what dude's getting at , is see if it acts better in the "pri" position .... which ain't a BAD suggestion .

[Kreylyn]

Petcock not only serves as a selector for the prime (always on) position, but also reserve and "On" which is only on if vacuum is being applied.

I would double check the petcock (see if it does it on prime), double check your gas lines (made any changes, been under the tank recently?).

What you described is very indicitive of a limited gas flow issue. You stop, the carb bowls are filled. You take off, and the flow to replenish the bowls is limited, and at higher RPMs your using more than it flowing in... so eventually your running out of gas and stop, at which time your use is greatly less, so the bowls refill.

So basicaly, I just repeated what everyone else said, but I used more words.

Krey

[spd264]

thanks for the info guys.. I havent done any major work under the tank. Last time i took it to the shop they informed me that they fixed a vacuum leak, maybe its back? i'll have to see.. but if the problem goes away when i run it on pri should i just leave it on pri or is that not a good way to run the bike?

[Kreylyn]

If your carbs are good, it normally won't hurt the bike. I would suggest fixing the issue ASAP instead of leaving that way.

If your floats are not set right, you could drain the tank into them, and then onto the ground, the bike, or worse, into the engine oil.

Krey

[FlyingWheelsCycleCourier]

i had this same problem. an irreplaceable spring collapsed in my petcock thus resulting in no/minimal fuel reaching the carbs. riding my bike back to the house was like a freaking carnival ride.

haha on another note my bike was running on 3 cylinders for a day so pulled the tank etc and one of my spark plugs broke OFF this was all in the same week.

[rice_rocket]

I am experiencing a little bogging too, just the last two days.. not sure if it's gunk from putting stabil in the last 3 or 4 tanks...

But one thing I noticed on my petcock, is that I can't turn it while the bike is on or hot. When the bike has been sitting I can turn it. Is this how the vacuum is supposed to be working.. or is my assembly wonky?

Also going to work on the air filter next... or we'll see, if winter comes too soon, i'll just do the whole carb clean and sync for next season.