Hi all...new to this forum because I have been beating my head against the wall with my sons little 50. A little background on the problem...I removed the exhaust and throttle restrictors years ago. Piggyback jet is still in, intake restrictor is also still installed. Problem is the engine will not rev freely anymore. It was fine and reasonably powerful for years and then it lost power. Plug looks fine , maybe a tad lean. It just doesnt want to rev anymore. I have done searches here and read everything I could but havent found this exact problem.Here is what I have done with no real positive results. My son is too big for it now but I am going to be a grandpa soon so I am going to keep it and get r ready for the little one ! Any suggestions/help appreciated.

1) went thru carb completely. All jets and passages clean. Float working proper but not sure about float drop.

2) removed exhaust pipe from head to see if muffler clogged. No difference.
3) removed baffle/arrestor from muffler,no change

4)Checked compression and got 90 psi. This seems low from what I have read on this site. Seems like very little vacuum at intake manifold when I removed carb and pulled it over with my finger blocking intake

 

went out to work on bike. I think I have a weak spark..it's an orange wimpy spark. Coils are 90 bucks !!! Is there a way to test a coil ? I would hope its not a magneto issue. Is 90 psi cranking compresiion ok for this 2 stroker ?

 

Posting this solution in case anyone else has a similar problem with a KFX50. Turns out the exhaust port in the cylinder was nearly closed up with carbon deposits which created a breathing issue. Cleaned out port...all is well. Tricky little problem.

 

i'm sorry that i had no answer for you. i'm glad you got it going. i learned something from your thread.
thank you!!!!

 

No problem. I just had to keep looking after all fuel and electrical was eliminated. Last resort was pull the head. Very surprised to see how it was blocked up. I wonder if this could have been avoided had I opened up the intake side restricter. The exhaust was open. It may have created a lazy situation in the exhaust stream due to the imbalance. At least I found it !

 

Might as well remove the intake restrictions as well, it will only flow as good as the most restricted part in the intake/exhaust. having an opened up exhaust wont do you much good without the intake flow to match up to it, you can always restrict the throttle if it makes it "too" peppy.

 

Already removed it. It ran strong with just the exhaust removed a few years ago. I havent been able to take it back to the cabin to see if the intake restriction removal will make a huge difference but I assume it will definitely be quicker.