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MC21 - Chasing problem


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80XAR

 
Posts: 395
Joined: 22 Jan 2007

Location: Springfield Lakes, Australia
1992 Honda NSR250 MC21
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MC21 - Chasing problem

Tue Sep 28, 2010 10:30 pm » Post: #1 » Download Post

Hi guys
Ive been try to track what i though was a missfire for a while now. Everytime i try something, the bike does something new. Its great Evil or Very Mad
After checking alot of other things, the bike is now doing this :-
Starts fine. Idles fine.
On light throttle (0-25 percent, idle to about 6k) it sounds almost fouled. Simular sound to when they run out of fuel. It wont accelerate, but doesn't die completely either.
Open throttle above that (25-100 percent, idle to 10k) and its a jet. Pulls real well through the mid range towards the top end.
Catch is, it breaks down at 9500-10000rpm. I call it 4-stroking, but basically, it wont pull past 10k and sounds very course.

Once warmed up, it idles fine. Starts first kick no problem. Bliping the throttle is fine up to 6-7k. Didn't try bliping any higher as it was getting late, and raining.

Mods - Std engine. Orange wire splice, GPS splice, Tyga end cans, drilled airbox. Carb jetting - standard.

Any advise on what to check next ? Ive check coils, cleaned ignition pick ups, multiple spark plugs. Pulled the carbs and inspected them. Previously it had the front cylinder cutting in and out, but that seems to have fixed it self. Im starting to think possible crank seals.
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nxrsr20

 
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Location: Sydney, Australia
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Wed Sep 29, 2010 2:10 am » Post: #2 » Download Post

check your reeds are sealin properly, check your rubber boots (like carb mounts) aren't old and perished. Are your PJ soloenoids operating, and have you checked that your slow jets aren't blocked?
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80XAR

 
Posts: 395
Joined: 22 Jan 2007

Location: Springfield Lakes, Australia
1992 Honda NSR250 MC21
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Wed Sep 29, 2010 3:52 am » Post: #3 » Download Post

Cheers mate
Reeds are ok. Checked them and the holders. They are fine. Mounts looked ok. Slow jets - might be worth a 2nd look, but from memory, all the carb internals checked out ok.
But
How do i check if the PJ solenoids are opperating ? Not something ive done before.
The exhaust powervalves are cyling as they should, and are clean.
Thanks again
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Kubira

 
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Location: Adelaide, Australia
1992 Honda MC21SE
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Wed Sep 29, 2010 5:53 am » Post: #4 » Download Post

sounds like a similar issue i once had, turned out to be powervalves. Look closely at each of your power valve assemblies and ensure that not only the valve butterflies (pulleys) are turning, but also the power rod. Lightly jiggle each butterfly and look closely at the rod to see if it is moving, if theres slack between the fly and the rod, it will hamper power at 10k rpms (or anywhere for that matter)

You could also try cleaning the points, maybe even swap the coils around for a splurt
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