I have been running down a issue with my 03RkClassic for a year now. Problem was a stutter or a miss at low throttle. I've replaced every sensor, injectors, coil, plugs, wires, check the harness, replaced intake gaskets. Took it to 3 dealer all said it was okay. Installed a Powercommander w/custom map. Poblem still there. Even tried the Thundermax ECU. I have just put on a set of true duals, upon removal of the stock y pipe I noticed a crack right at the y that exits the rear jug, about 3 inches long. Could this have caused damage to the motor? I have now narrowed down the issue to the rear jug. The front cylinder fires strong and steady. Rear cylinder runs uneven and has a tendancey to suck back through the pipe. Ive checked for leaks and have found none. I'm now to the point I belive it is a bad valve? I did a compression check and both jugs are at 150psi. The rear jug took more cranks to achive this number. Took it to an independant mechanic and he said he did a leak down test and all is fine. Can anyone chime in and give me their opinion.

Thanks in advance
zz

 

That crack would let more pressure out of the pipe (less back pressure) and that would affect the mixture in that cylinder. Like running one drag pipe and the other a stock system. I THINK that may cause an imbalance between the cylinders. The rear cylinder is rich compared to the front one anyway and less back pressure would make it richer. I don't think a bad valve would let the compression build to 150.That's my theory and I'm stickin to it.[8D]It may take some time to burn out the crap in the rear jug from running rich. Good luck with it.

 

clean the crack real good...........apply some j b weld to the area.......let it set up, and see if problem goe's away......if so, at least you know for sure before you go and get parts etc......

 

By the sounds of the symptoms you describe, I'd suspect the crack you discovered is a result of the root cause and not the root cause itself.

Possible root causes could be a bad cam,or possibly if it's a twin cam, one cam is out of time. I have found on more than one occasion a porous intake manifold on both cars and bikes. If EFI, the leak would have be downstream of the point where the fuel and air are mixed. I don't have a schematic for EFI, so that's just a hipshot.