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I just brought an 89 back from the dead. After riding this bike I realized my 90 has no top end power

Both bikes are very similar build only small differences to which I feel should give my 90 the edge like the RB head, answer silencer, rad valve and 36mm carb the 89 has the same pipe but a stock silencer also has stock reads and head. From a rolling start same gear the 89 pulls away from me with ease even if I get a jump on it I still get toasted!

I pulled the cap off the silencer and the packing and tube look good nothing has shifted or plugged up.

I pulled the resonator and the Kips is activating

Pulled the expansion chamber and can't feel anything rolling around or plugging that up

It has started to get real hard to start hot after sitting for 5 minutes or so but im not positive what to check next. Has anyone had a cdi or ignition coil start to go bad and cause these type of symptoms?

Also because I know it will come up
jetting is nearly perfect for the way it runs now I'm sure it will need adjusted when I finger this out.
also cold compression is 180psi on the 90 170 on the 89
both bikes are geared the same 13/49

Also now as of tonight the bike seems to be hard to start cold as well now. Carb is clean gas is fresh engine is healthy and I have good blue spark

If you solve the cold cranking problem, please post it here!

Try the '89 carb on the '90. If it likes it, rejet the 90's carb to what is in the 89's. Maybe post the jetting specs that are in both, too.

david wrote:Try the '89 carb on the '90. If it likes it, rejet the 90's carb to what is in the 89's. Maybe post the jetting specs that are in both, too.

Jetting is good both are very similar 150/42 CEL FOR THE 89 152/45 CEL the air screw is very effective on both bikes and plug chop turn very good-looking plugs I have played around with some other needles but nothing I do in the carburetor is changing my top end performance. I do plan two pull my expansion chamber back off and verify that the side valves for the kids were not installed backwards I have never had them out.

KDXohio wrote:

david wrote:Try the '89 carb on the '90. If it likes it, rejet the 90's carb to what is in the 89's. Maybe post the jetting specs that are in both, too.

Jetting is good both are very similar 150/42 CEL FOR THE 89 152/45 CEL the air screw is very effective on both bikes and plug chop turn very good-looking plugs I have played around with some other needles but nothing I do in the carburetor is changing my top end performance. I do plan two pull my expansion chamber back off and verify that the side valves for the kids were not installed backwards I have never had them out.

Does sound like a KIPS related issue. If one or both of the side valves are broken or stuck, your top speeds will Peter out.

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Friedom wrote:

KDXohio wrote:

david wrote:Try the '89 carb on the '90. If it likes it, rejet the 90's carb to what is in the 89's. Maybe post the jetting specs that are in both, too.

Jetting is good both are very similar 150/42 CEL FOR THE 89 152/45 CEL the air screw is very effective on both bikes and plug chop turn very good-looking plugs I have played around with some other needles but nothing I do in the carburetor is changing my top end performance. I do plan two pull my expansion chamber back off and verify that the side valves for the kids were not installed backwards I have never had them out.

Does sound like a KIPS related issue. If one or both of the side valves are broken or stuck, your top speeds will Peter out.

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That is exactly what I thought but I pulled the pipe and both valves are extremely clean and move easily and freely I then put the pipe back and opened the resonator to ensure they opened with it running and that checks out as well but at the time I didn't think about them being in the wrong holes

KDXohio wrote:

Friedom wrote:

KDXohio wrote:
Jetting is good both are very similar 150/42 CEL FOR THE 89 152/45 CEL the air screw is very effective on both bikes and plug chop turn very good-looking plugs I have played around with some other needles but nothing I do in the carburetor is changing my top end performance. I do plan two pull my expansion chamber back off and verify that the side valves for the kids were not installed backwards I have never had them out.

Does sound like a KIPS related issue. If one or both of the side valves are broken or stuck, your top speeds will Peter out.

Sent from my SM-G930V using Tapatalk

That is exactly what I thought but I pulled the pipe and both valves are extremely clean and move easily and freely I then put the pipe back and opened the resonator to ensure they opened with it running and that checks out as well but at the time I didn't think about them being in the wrong holes

If you can see both side valves opening through the exhaust when actuating the KIPS, then they kind of have to be in the correct spots.

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If it won't start hot you may have a bad coil, which may also lead to loss of power.

Sounds legit.

Welcome to the forums.

Get some freeze spray to spray on it to cool it down and see if it changes anything.

I will swap coils and see if that helps I pulled the flywheel tonight and found some water under the cover. I'll clean that up before doing much else

Don't judge a book by its cover I decided to remove the silencer core and packing to have a closer look and found half the packing is gone so this would have no affect over starting problems but maybe is affecting my top end loss regardless it will need repacked

It will not harm it to be properly packed, so go ahead and do that.

Jason wrote:It will not harm it to be properly packed, so go ahead and do that.

My thoughts exactly, fix one thing at a time!

So how's it going?

It's been a slow process. I had a boyesen rad valve with one season on it the reeds were pretty gapped that seemed to take care of the starting problem. I am waiting on a new exhaust coupler to re-install the silencer so I can ride it to test the top end power.

KDXohio wrote:It's been a slow process. I had a boyesen rad valve with one season on it the reeds were pretty gapped that seemed to take care of the starting problem. I am waiting on a new exhaust coupler to re-install the silencer so I can ride it to test the top end power.

I used a slice of ribbed tin can wall for a coupler once. Worked excellent and turned pretty colors from the heat!

Friedom wrote:

KDXohio wrote:It's been a slow process. I had a boyesen rad valve with one season on it the reeds were pretty gapped that seemed to take care of the starting problem. I am waiting on a new exhaust coupler to re-install the silencer so I can ride it to test the top end power.

I used a slice of ribbed tin can wall for a coupler once. Worked excellent and turned pretty colors from the heat!

Haha yeah I have some heater hose and radiator hose I've used for other pipes but none of it seemed to fit the kdx right may have to try the tin can!

KDXohio wrote:

Friedom wrote:

KDXohio wrote:It's been a slow process. I had a boyesen rad valve with one season on it the reeds were pretty gapped that seemed to take care of the starting problem. I am waiting on a new exhaust coupler to re-install the silencer so I can ride it to test the top end power.

I used a slice of ribbed tin can wall for a coupler once. Worked excellent and turned pretty colors from the heat!

Haha yeah I have some heater hose and radiator hose I've used for other pipes but none of it seemed to fit the kdx right may have to try the tin can!

The ribs help because they'll crush when it's clamped.