81 KZ750e wont rev past 7k

Would not suspect either sync or pilot mixture issue to be causing loss of power under load (being 1/4 or more open throttle position).

Exhaust popping on decel might be reduced by slightly enriching the pilot mixture in each carb.

Good Fortune!

Would not suspect either sync or pilot mixture issue to be causing loss of power under load (being 1/4 or more open throttle position).

correct, I just figured what you said, that it was possibly the cause of the popping.

I've emailed wiseco to see if they can recommend any jetting settings for their 810 kit. Probably not, but it's a shot in the dark. Bike has pod filters so it won't be exact. Maybe stock airbox would yield better results; I know the honda twins do NOT like pods due to the CV carbs.

I should start with the barebones basics- make sure boots are not cracked/leaking, vacuum lines are plugged/sealed, and linkages are working correctly. I did clean and re-oil the K+N pods last fall to rule that out.

I will check jetting and post numbers when I get a chance. I will also make sure that diaphragms are not torn or cracked and there has been no other tomfoolery while I am inside there.

If not already done, spark plug readings may provide some diagnostic info, especially following a high speed throttle-chop with simultaneous ignition kill and clutch disengagement until the bike has stopped.

The objective is to inspect condition of the spark plugs when operating under full load at speed.

Removing hot plugs at road-side risks burning fingers, so would carry along a short length of oil line to grasp the loosened plugs for removal.

Good Fortune!

Unfortunately it's not practical to do plug chops where I live. Freeways are too dangerous to be fiddling about on the side of the road, and speed traps everywhere. Side streets are all low speeds and lots of cops. I can't afford a ticket, I drive fire trucks and ambulances for a living. While I may have some diplomatic immunity if I get pulled over while riding through my district, they would call my chief and it's not worth the ass chewing or possibly disciplinary action.

I've been doing a lot of research today (not many calls) so I'm getting quite a list of things to do/check together. I'm hoping I can work on some of it sunday possibly after a swap meet. I need to change fork seals and oil though, kinda takes priority at the moment, because I don't often run the bike past 7k due to the aforementioned reasons lol.

runmikeyrun wrote: Unfortunately it's not practical to do plug chops where I live. Freeways are too dangerous to be fiddling about on the side of the road, and speed traps everywhere. Side streets are all low speeds and lots of cops. I can't afford a ticket, I drive fire trucks and ambulances for a living. While I may have some diplomatic immunity if I get pulled over while riding through my district, they would call my chief and it's not worth the ass chewing or possibly disciplinary action.

I've been doing a lot of research today (not many calls) so I'm getting quite a list of things to do/check together. I'm hoping I can work on some of it sunday possibly after a swap meet. I need to change fork seals and oil though, kinda takes priority at the moment, because I don't often run the bike past 7k due to the aforementioned reasons lol.

no long straight backroads anywhere that you could give the ole girl a good goose and then shut her down on? maybe have a friend follow?

If I ride about about 45 mins from home there are some. Might give that a shot! Make one pass to check for cops/hazards, then open her up on the way back...

The main jet size is most crucial at WOT.

The wide open throttle chop test is often used for plug readings to help determine influence of main jet size at WOT -- wide open throttle. This is WOT under load, but doesn't necessitate running at top speed. Of course, road speed would be expected to increase while the throttle is being held in wide open position.

At less than WOT, the jet needle position inside the needle jet governs the mixture.
For example, different size main jets won't make much if any difference at say 3/4 throttle.

But the test may be performed at any throttle position. For example, while the performance is faltering.

At less than WOT position, the jet needle taper inside the needle jet -- not main jet size -- has the most influence on fuel mixture, until the slides are lowered enough for the fuel mixture to become largely influenced by the pilot circuit.

Clip position on the jet needle helps determine lean-ness or rich-ness of the fuel mixture at any particular throttle position in the mid-throttle range.

Simply removing and inspecting the spark plugs without any throttle chop maneuver may be helpful toward diagnosing a mixture issue. Such as oily-black or sooty-black or clean-tan or white-burned, etc.

Would remove the plugs from cold engine and inspect them -- what do they look like?

Sooty plugs could result from any or a combination of the following: inadequate compression (for whatever reason); weak and/or improperly timed spark (for whatever reason); too rich fuel mixture (for whatever reason).

Even if everything else is perfect (compression, ignition, clean as new perfectly synced carbs with correct jetting and pilot screw settings), a too high or too low fuel level can result in a too rich or too lean fuel mixture.

Even if everything else is perfect, including fuel levels, fuel starvation (for whatever reason) may result in a too lean fuel mixture.

If not already done, would perform the clear tube test on each carb.

Good Fortune!

To rule out possibility that the engine isn't combusting on all four cylinders, would start a cold engine, and after a few moments of running, spray water mist onto the exhaust header pipes.

If the cylinder is combusting, the spray will sizzle and instantly evaporate off the header pipe.

If the cylinder is not combusting, the spray will form droplets that run down the header pipe.

Good Fortune!

Patton, thank you very much for the info! I have the clear tube test on my list of things to check. I know for sure that all cylinders are firing.

I made some sheets to fill out when I disassemble and reassemble the carbs to make note of jet sizes, pilot settings, etc. I want to tear into this tomorrow because weather is bad for riding all next week so it will allow me some time to find new jets if things are amiss.

Ok, now that i've recovered from the hack, I'll post an update.

I checked over some things before pulling the carbs: vacuum lines, fuel delivery, intake boots. Everything seemed normal so I yanked the carbs.

Upon removing the float bowls, I found this:


Notice the second carb from the left is missing something: a secondary jet! It was just hanging out inside the float bowl. I'm guessing this was my problem. I reassembled them, took the bike for a spin, but couldn't take it past 6500 in first and then second gear, as the front wheel was coming up in first and by the time I had it in second at 6500 i was going 60mph on a wet residential side street. I figured I should wait until I can get her on the highway. So i'm not sure if she'll pull past 7k yet, but boy did it run strong up to that point! No popping, no sputtering, nothing.

Anyhow, my main jets were all at 62 (stock) and secondaries were 136, which is right where everything I've found recommends them. Pilot screws were out 5.25 turns which is quite a few more turns than they should be... ideally i should go up one on the pilot jet, but as far as i'm concerned its running and idling great so I'm not going to mess with it. I don't want to screw it up.

I'll report back after a freeway ride above 7k. Thank you for all the help!

Ah ha
well spotted
always nice when it's something simple
hopefully thats your problem and all you need now is good riding weather !

well, weather finally broke and I had a chance to open her up yesterday. WOW. Ran great to redline and pulled like crazy. What a fun bike she is now! lol.

Thanks for everyone's help