Can't get past 6500 rpm

So I took the old girl on a ride YESTERDAY, 1982 Maxim 650, and she wouldn't get past 6500 rpm. Now it will do it in the first 4 gears as far as I know, didn't actually get on it in 4th, but won't when in 5th. I know there is already an old thread about a similar issue, but it never reached a conclusion. Anyway I've checked my valve shims, all are within spec. Just cleaned my carbs following the guidelines on this site, and they're sparkly clean. Petcock was rebuilt last summer and has no problem allowing gas to flow. Had fresh gas in the tank, a new battery, and a fresh oil change. Frankly I've gone over everything I could think which may be causing it, andc have drawn a blank. I haven't done a plug chop yet, gotta find a section of road here in WV where that won't get me killed, but I'm at a loss. The only thing I can think of is that the aftermarket exhausts the PO put on are too restrictive. Could that cause the lack of acceleration?

 

have you running synced the carbs yet?
have you checked the headers to see if they are all getting hot?
wet set the fuel level?
pull your plugs anyway see what you have.
what are you using for an air filter?

 

Haven't running synced the carbs yet, but don't figured that would affect it too much at full throttle. Air filter is stock, and clean. I bought a new one last summer, an all the headers are hot

 

Where ya at in WV?

 

Can you duplicate the issue while in neutral?

When you cleaned the carbs did you check the slide diaphragms for tears or pinholes?

Did you remove the air jets that are under the diaphragms, and if so did you put them back in the same place (the service manuals have those jets mislabeled)?

Have you checked the throttle cable linkage on the carbs for obstructions, and did you make sure that the joint in it is oriented so that it can be lifted fully without contacting the engine head?

 

Slide diaphragms are in good condition, no tears or pinholes. The 205 jet is toward the motor, which I believe is correct. Throttle cable operates fully with no binding. I can keep twisting when in 5th, but it doesn't crank any faster than 6500 rpm. Will red line in 1st

 

Check that exhaust. Has something built a nest inside?

 

Does the problem occur when in neutral?

 

No. Only in higher gears

 

The old hand behind the muffler feels like there's equal back pressure

 

Filter - you need a set of K&Ns.....
Seriously though, either air filter or exhaust. Easy check on the air filter, the exhaust - take the can(s) off and try it - if you dare without upsetting any/everyone.

 

Why on earth would you think that would upset anyone here?

 

Lol kmoe, I meant his neighbours...

 

Oh... well they don't count lol

 

That it's only happening while under load tells me that you should check the fuel levels in the float bowls. You may be starving for fuel at speed.
Does it at all feel like the clutch is slipping? If you roll on hard at a lower RPM in 4th or 5th that would show up.

 

Clutch feels tight, and low end performance is great. Doesn't seem to have this problem in lower gears, and compression check last year was good. I'll have to check it again tho

 

Also fuel level in the bowls was 4mm, at least on the outside 2. I forgot to check until they were already on the bike.

 

That's within spec if you measured from the bottom of the carb body and at the vertical midline of the float bowls. If you measured at either the front or the back then that measurement isn't accurate since the carbs don't sit level while on the bike.

 

K-moe I throw a block of wood under the front tire to level the bike when it's on its center stand. I need to get float bowl drain screw as #3 is so stripped I can get anything on it to check that one. Took it out for a ride tonight and it was able to get past 6500 rpm in fifth, but wasn't accelerating like it should in the top two gears. 1st through third pulled like a freight train though.