help me diagnose engine problem

[jaguar]

My bike has a modified CDI and aftermarket ignition coil, PC pipe, wiseco piston, and the two side KIPS valves epoxied in the open position..
The other night I was coming home (on the street) and was winding thru the gears with good crisp power, slowed down and turned a corner and then buah – no power – just blubbering – kind of like when the main jet is too big and you crack the throttle all the way open. Only at idle it runs good, but sometimes even at idle it blubbers. I can’t get it to go more than a few mph now but at first sometimes it would kick in and run good for a few seconds. That on and off symptom indicated electronics to me but I have explored what I believe to be all in that area. (true? help!)
3 months ago I had replaced the crank bearings and seals (with OEM. Can they go bad in 3 months of daily riding on the street? (Only 10 miles at most) Last replacement period was 11 months for the seals.
I took the motor apart and verified a good condition for:
the top gasket (which is brand new), bottom gasket, piston, rings, reeds, carb (needle in position, no obstructions in main which I replaced anyway, float valve good), air filter, pipe (no obstructions), and noted no drool coming from ignition side crank seal.
Then I replaced the following:
Spark plug (B9EGV), CDI (std), stator coil (Electrex), ignition coil (OEM). I also cleaned and assured all good connections for the stator coil and measure normal resistance for it.
At first I took the ignition cover off and used my timing light to verify the correct timing all through the rev range since I have a modified CDI. It was right on. The bike in neutral would rev clean thru all the rev range. But now it stutters at anything above idle and won't rev higher than 6000 in neutral.

I’m really tired but want to fix it now so I can practice tomorrow on the MX track since there is our once a month race in a week. HELP! Through any crazy ideas at me. I’m ready to do/try anything.

 

[skipro3]

Start with the fuel system since it sounds like you've looked into everything else. Fresh fuel and oil mix.
Does the problem change with the choke applied?
Try it with out the air cleaner for a short run and see if there is a difference.
Check oil consumption if you suspect it may be a bad seal.
An obstruction in the exhaust? The symptoms sound just like my bike behaves when I forget to pull the plug from the tail pipe. Try it without the muffler, just the pipe.
Good luck and let us know what happens.

 

[jaguar]

yeah, I had drained the tank and put in new fuel/oil. Also I removed the silencer but the problem persisted.
I finally found out what it was. It was a combo of changing/failing ignition coil and large spark plug gap. Testing the ignition spark with the plug removed and placed snug between the radiator hose and the head, I could see that with slow engine turnover there was no spark. I had gapped it .1mm more than the suggested maximum gap since I figure the high voltage coil could handle it. Well it did for awhile. Probably the new Nology ignition coil is on the verge of failing. I’m going to leave it in for Sundays practice but carry the OEM spare with me. Now I switched plugs to a resistor type and gapped it at .7mm. Also I put a .47 ohm resistor between the CDI and the ignition coil primary in order to limit the input current to the coil. With those changes it still works OK although probably less than its capable of. And maybe it will keep it from failing. This aftermarket coil only has a .3 ohm primary. I wanted the one with a .6 ohm primary but it wasn’t in stock. The next step up is one with a 3 ohm primary. The reason my bike was only running half way good at idle is because the CDI voltage sent to the primary of the ignition coil is highest at idle and progressively lower at progressively higher rpm’s.
Well, at least I can practice tomorrow although I’m all tired out from all the wrenching and pulling my hair out. No wonder there aren’t too many (percentage wise) motorcycle enthusiasts.

 

[skipro3]

Glad you were able to figger it out for yer self there jag. I've always been impressed with your tenacity as well as intellect. Hope you do well in your race.