Hi nsr brothers.
My mc18 r5k model doesn't want to pull after 9000rpm. Bike is after full top and bottom end rebuild. It's completely stock except the wire splice. I run premix as well. Please help any advices are welcome.
Tried so far :
128 mains 130 and 135. 135 seems too rich according to me.
Power jets are not blocked.
Carb was stripped and fully rebuild.
Tank breathing hose is not clogged.
Exhaust system was stripped and cleaned.
Plugs are new.
Battery is new.
Reeds are not cracked.
Air filter is new.
Servo motor is manually turned to HI position and disconected.
Compression is perfect no leaks.
Starts first kick and idles perfect.
I have no idea what could it be i tried everything.
Runs great untill i reach 9000rpm it feels like a power drop.
Thanks in advance.
Greetings from Bulgaria.

Almost certainly RC Valve related, if everything else checks out good.

Try altering the RC Valve position. I would align the holes in the pulleys/backplates first, and see if that helps.

Is the PGM dead? Is that why the servo is manually rotated?
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Andy.
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Thanks for reply Andy.
Measured the Pgm, servo and tps with volt meter.
According to the manual everything is giving the right signals.
I disconected the servo because it stucks to low position and doesnt want to move when i rev the engine. I aligned the holes so my power valves are fully open and disconected it.

Nobody can help in the forum ?

I assume there's enough fuel in the carbs for a quick rev, so probably not the float height.
Do you have spare coils to swap out?
Is there any damage on the loom coil wires?
Are the plug ends of the ht leads tight, i.e. good connection
Do you have any spare ignition pickups to swap out?
If the power valve cables are removed at the cylinder end can you see it cycle when the ignition is turn on and at 2000 revs?
Are the power valve cables connected the right way aroun
With the power valve cables disconnected can you moved them freely?
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Why do things simply when you can complicate them

Thanks for the reply.
Float height is set to 13mm.
I tried different coils it's the same.
There is no damage on the loom.
Servo motor doesn't move even with the cables off it stucks at low position. It's moving only one ditection. Power valve cables are connected right way. I moved it manually to HI position and disconected it. I can move the power valves easy by hand.
Is it possible the pickup sensor to fail ?
I didn't swap pickup senaors yet.

I swapped different pickup sensors and there is no difference.
Measured the voltage and reaistance it is in range by the manual.
It seems to be running rich.
Ignition coils are showing 7.6 ohm with the caps.
Could it be worn needles on the carbs or something else in the carb to make it run rich
Regards

I experienced a similar issue on my mc18 which had two causes.

1. One of the spark plug caps had a big crack in it which was effecting spark to one of the cylinders.
2. The crank center seal was stuffed.

If your bike has developed this issue suddenly than it could be #1 (if you have ruled out RC valves etc). If it has been sitting for a time, then it could be #2 which is a lot more expensive to rectify.

Good luck.

Plug caps are in good condition and the bike is after full bottom and top end rebuild. The crank is with new bearings and seals and it passed the leak down test.
Any more suggestions?

If you run power directly to the power valve motor, does it move?
Seems like you've covered all options other than swapping out the CDI and power valve controller
_________________
Why do things simply when you can complicate them

Hello buddy

Sorry to hear your still having problems !

Maybe try a new PV servo motor as Andy suggested its likely a PV related problem. I would consider performing a leak down test on just one cylinder at a time, with the opposite cylinder open to atmosphere to test if your new crank centre seal is damaged or not seated properly and leaking across to the open cylinder ?

If that doesn't cure your problem, it is likely something simple that you have missed or overlooked during your rebuild so retrace your steps back to the rebuild start.

Hope this helps you.

Cheers

The only thing i haven't done yet is to swap the CDI but here in Bulgaria nobody has NSR250 and to do the test i must pay 300pounds for a used pgm in unknown condition.
Mc 18 R5k has the center seal integrated in the bearing like the mc21.
I will try to do leak down test the way you recommend.
Maybe the solenoids are not working and causing rich conditon ?
I am thinking of blanking the power jets and removing the solenoids.
At which cables i should apply voltage to test the servo motor ?
Greetings

Hey buddy

I have been told that Nick at "2 stroke Race Lab" in Greece can test and repair your PGM2.

Google 2 Stroke Race Lab

Email : tonelessdiy@yahoo.gr

I bought a battery eliminator and leakdown tester from him a while ago without any problems so he seems trustworthy.

Cheers

Andy

Thanks for the help guys.
Finally i fixed it.
Did the airbox modification and installed new needles and needle valves.
Now i am pretty happy with the performance
Soon i will do a dyno day and i will post graphics with the results.
Greetings

I would get a dyno setup just to be sure. The last thing you want is to break it after all the work you've put in
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Why do things simply when you can complicate them