Lack of Top End Power - Please Help

[zuschke]

Hello! I have been searching and chasing a problem for weeks. Asked on Facebook and got lots of ideas but none ended up being the issue.

I had a 2001 KDX years ago and sold it. Last month I found another 2001 that is very low hours and bought it. The bike runs perfect except it feels like the top half of the RPMs cannot be accessed. The bike sounds like it is hitting a rev limiter and sputtering. It will not even close to pull the front wheel up in first or second.

Tried so far:
Brand new top end.
New reeds
Carb rebuild including stock size jetting and jet block gasket
32:1 and 40:1 mixes with no ethanol
Swapped CBI and voltage regulator with one from ebay
New coil and plug wire, plug
Tested stator to be OK
Tried adjusting timing from stock to retarded
Checked behind stator for case leaks
Cleaned up KIPS when doing top end and they are very clean and smooth acting
Tested KIPS activation and it moves with RPM.
Cleaned out and repacked silencer
Tried calling Freddette a couple times but he has been busy.

Any other ideas from anyone on what it could be? TIA

[SS109]

Have you verified that the KIPS valves are timed correctly? In other words, have actually used your eyes, looking up through the exhaust outlet, to verify that all three valves open while you actuate the KIPS shaft by hand?

Unless at sea level the stock jetting is very rich. Too rich and you'll kill top end. Is your throttle cable adjusted properly and fully opening the slide? Might even be worth doing a leakdown test on it to make sure the engine doesn't have an air leak somewhere.

[zuschke]

Have you verified that the KIPS valves are timed correctly? In other words, have actually used your eyes, looking up through the exhaust outlet, to verify that all three valves open while you actuate the KIPS shaft by hand?

Unless at sea level the stock jetting is very rich. Too rich and you'll kill top end. Is your throttle cable adjusted properly and fully opening the slide? Might even be worth doing a leakdown test on it to make sure the engine doesn't have an air leak somewhere.

When I had the top end out I was actuating the KIPS and noticed it moved section under the cylinder leading to the exhaust but I do not remember 3 of them. I will check this though!

Replaced the throttle cable too when I did top end and same issue.

I ride in South Florida at sea level.

Heard back with an email from FRP and he said replace the stator. Even if it tests OK it can cause this issue. So trying that too.

[John_S]

What you’re describing could be as simple as jetting. I’m in Florida and my kdx wouldn’t rev clean at half throttle or full throttle if my needle and main jet were at factory stock settings.
I quickly installed my 33 carb recently to test something and it had the stock 145 main jet in it. It sputtered like crazy at full throttle. I installed a 140 and the sputter was gone and it revved out fully.
Check out the jetting guide on this site and follow it word for word.

[zuschke]

What you’re describing could be as simple as jetting. I’m in Florida and my kdx wouldn’t rev clean at half throttle or full throttle if my needle and main jet were at factory stock settings.
I quickly installed my 33 carb recently to test something and it had the stock 145 main jet in it. It sputtered like crazy at full throttle. I installed a 140 and the sputter was gone and it revved out fully.
Check out the jetting guide on this site and follow it word for word.

Isn't the main jet a 160 stock? That is what RMATV says. If you had to run way leaner in FL, maybe that is my issue. You have a 200 same year?

[MoonStomper]

Definitely check all three KIPS valves, I had a broken one and this is not unusual. Make sure they are correctly timed, you don’t know who reassembled them last time.

Have you cleaned out your pipe? Is it OEM? It could be plugged up with years of spooge.

Curious… Was it doing this before installing the new piston?

Betting (hoping!) smaller jet fixes your issue.
Good luck!

[John_S]

Mine is an 02 220. The stock carb is a 33mm and stock settings are 42 pilot, 145 main, and 3rd needle clip. Mine needs a 38 pilot, 2nd needle clip (from the top) and a 140 main. When I bought the bike the guy had never touched the jetting from factory stock and it sputtered at 1/2 throttle and full throttle and would hardly idle. He said “it’s a 2 stroke, they’re all cold blooded. It runs better once you rev it and clean it out.”

I use a 35mm air striker carb and it needs a 40 pilot, 145 main, and 2nd needle clip. The only tuning I’ve done for a couple years now is turning the air screw 1/4 turn one way or the other for the weather but mostly I just keep it at 1.5 turns out. It’s worth the effort to get it jetted correctly.

They make them rich from the factory to be safe for all the areas they sell the bike in. In Florida even though it’s sea level…with as humid as it is, we end up with similar jetting as someone who’s at a high elevation.

[DonnyV]

Make sure the little circle tab on the reed block is on the left side of the bike. I've read on here before that it makes it not rev out if not lined up with the carb . Do you have a manual? If not you should get one, very valuable to have. Just my thoughts

[zuschke]

Definitely check all three KIPS valves, I had a broken one and this is not unusual. Make sure they are correctly timed, you don’t know who reassembled them last time.

Have you cleaned out your pipe? Is it OEM? It could be plugged up with years of spooge.

Curious… Was it doing this before installing the new piston?

Betting (hoping!) smaller jet fixes your issue.
Good luck!

OK I can check they are all operating but how do I check if timing is right?

My muffler what clogged solid when I got the bike. Not sure how it ran at all. It is cleaned out and repacked now but I did not touch the pipe. Does the pipe have chambers that can clog? I have a FMF knarly woods pipe.

Yes before and after new piston.

I ordered a few leaner jets from RMATV. Hope it helps

[zuschke]

Make sure the little circle tab on the reed block is on the left side of the bike. I've read on here before that it makes it not rev out if not lined up with the carb . Do you have a manual? If not you should get one, very valuable to have. Just my thoughts

Yeah tab is on left side. I have the PDF version of the manual.

[MoonStomper]

If the silencer was clogged up, it may have backed up into the pipe. Try blowing air through it, if you get any resistance you’ll know. If it’s plugged you can probably soak it overnight in solvent? I think there’s a good description of checking your KIpS timing on this site somewhere if you do a search.

Will be interested to learn what jets you have in there. My buddy’s KDX was like this when he got it, spoogey as heck, no top end. Smaller jet solved his problem.