Can't rev above 5k rpm and go faster than 65

[Glowyeast]

So I bought this bike about 6 months ago and in that time I've replaced the petcock, spark plugs and had the carbs rebuilt, checked the cam chain, tightened the drive chain and it still refuses to go above 65. I have a few suspicions though and wanted to see if you guys think they're valid. So the previous owner cut the mufflers off the tail pipe and put resonators on could that be causing issues? or could I have the wrong ignition timing? Did the shop that rebuilt the carbs do a bad job? Something else entirely? When it comes to fixing this I'm pretty stumped and don't know what to do so any help would be appreciated.

 

[5twins]

There might be small rips or tears in your carb diaphragms. That would not allow the slides to lift fully, limit RPMs, and top speed.

 

[Raymond]

Make sure you have good battery earth.

 

[Wingedwheel]

When you hit 65 does it stutter And fall flat? What symptoms are you having?

 

[Glowyeast]

When you hit 65 does it stutter And fall flat? What symptoms are you having?

It does stutter. You know that feeling when you let off the throttle a little and the bike slows a bit? When I get up to 65 it gets that feeling then it will speed up just a tiny bit then have that little slow down again and it does it in kind of a random pattern,

 

[drgonzo]

I vote for damaged slide diaphragms fluttering up and down a bit. The slides are porpoising like a ground effects Formula 1 car..lol. Maybe. IDK.

 

[RustiePyles]

I also think that sound like leaky slide diaphragms.

 

[Wingedwheel]

Doesn't a leaky choke circuit cause the diaphragms to lose their seal? IDK if that would cause the symptoms described but it does let the slides drop in the seal test. That would be a question for 5T

 

[650Skull]

All answers are theories, are next to useless unless more information about the model/year of the bike, and post pics so we are able to see if there are other visuals that will contribute to your problems............

 

[joebgd]

If the sprockets where changed. I'm at 17 30 and if there is any incline I sometimes need 4th meaning you can hit a point by changing sprockets that 4th gear is faster than 5th.

 

[Glowyeast]

All answers are theories, are next to useless unless more information about the model/year of the bike, and post pics so we are able to see if there are other visuals that will contribute to your problems............

It's a 1983 Yamaha xs650 heritage special. Here are some pics of the carbs. If you would like pictures of anything specific I would be more than happy to provide them.

 

[Jim]

Those K&N pleated filters have a well known history of messing with the slides. Take 'em off and go for a run.... see what happens.

 

[Wingedwheel]

Damn you type fast Jim lol

 

[Glowyeast]

Those K&N pleated filters have a well known history of messing with the slides. Take 'em off and go for a run.... see what happens.

i had the speed problem before I got the air-filters

 

[RustiePyles]

What RPM are you at at 65? Does it do the same thing if you try to maintain that RPM in a lower gear at a lower speed?

 

[arcticXS]

i had the speed problem before I got the air-filters

Ok, but adding a known bad filter setup for the carbs you have will definitely not help with an engine running poorly......

 

[650Skull]

Those K&N pleated filters have a well known history of messing with the slides. Take 'em off and go for a run.... see what happens.

i had the speed problem before I got the air-filters

Cost you nothing to eliminate/confirm this answer to your problem that will help us eliminate and pin point

 

[650Skull]

It's a 1983 Yamaha xs650 heritage special. Here are some pics of the carbs. If you would like pictures of anything specific I would be more than happy to provide them.View attachment 217461View attachment 217462

Thanks for the pics. Does help. We love pics of bikes so don't be shy.

Thing i did notice is the rubber grommet for the side-cover holder and the connector plug going to the Reg/rect are deteriorating and braking down. This is due to a lack of maintenance, (especially the grommet), by the PO, (previous owner), and if it was me i would be looking at the whole loom/Harness for couplings and connectors, (both plastic and bullets), that may not be doing their job properly. Earth/grounds need to be checked/removed/cleaned as well...........That is they may be loosing or causing a loss of power.

May be contributing or not but it is a cheap, (maybe replacing a connector or 2), way to ensure your bike is electrically up to scratch and is well maintained..........

 

[Glowyeast]

Thanks for the pics. Does help. We love pics of bikes so don't be shy.

Thing i did notice is the rubber grommet for the side-cover holder and the connector plug going to the Reg/rect are deteriorating and braking down. This is due to a lack of maintenance, (especially the grommet), by the PO, (previous owner), and if it was me i would be looking at the whole loom/Harness for couplings and connectors, (both plastic and bullets), that may not be doing their job properly. Earth/grounds need to be checked/removed/cleaned as well...........That is they may be loosing or causing a loss of power.

May be contributing or not but it is a cheap, (maybe replacing a connector or 2), way to ensure your bike is electrically up to scratch and is well maintained..........

I actually did recently replace the entire wiring harness, all of the electrical accessories haven’t been replaced though.

 

[Glowyeast]

Cost you nothing to eliminate/confirm this answer to your problem that will help us eliminate and pin point

I currently don’t have any oil in the bike but when I get it filled up I’ll be sure to try it and give an update.