bike engine troubles

[colemanbales]

Hey guys, so recently i have had some problems with my bike engine. Do realize that i am new to motorized bikes, and to taking apart and working on internal combustion engines all together. So it all started out when i gave my bike a wash with the garden hose. I then realized that the cdi boxes these bikes come with are not what you would call water proof..... anyway i ordered another one in the mail, and thought i would pull the head off the engine and check some things out while i was waiting for the new cdi to come in. so i pulled the head off and found this (look at pictures). It looked like some significant carbon buildup to me, so i thought i would show you guys and get some feedback from some more experienced users. I am pretty sure that i have my air/fuel mixture set too rich judging from the pictures and the performance hasn't seemed quite right (does ok, but not great on the bottom end up to maybe 3/4, and then gets a little worse going up to full throttle.) I was also concerned because when i used to drive it (before the wash) every now and then it would kind of act like it missed an ignition or something and just go PFFFF and lose power until then next strokes kicked in and it started running normally again. Now after i washed it i tried to take it for a ride, and it was doing this very frequently and had significantly less power and was extremely difficult to start. (its not the spark plug, i just changed it after the wash). I blame this mostly on the cdi hanging onto life by a single thread, but thought it was worth noting. any ideas? I am also concerned about maybe having a slight air leak where the head and engine meet the gasket. i hadn't properly torqued the bolts and nuts before and i could see some oil slowly seeping onto the engine cooling fins over a long period of time (also refer to pics to see what i mean). one time right after turning the bike off, i was close to the engine examining it, and swore i could hear some air from inside the engine seeping out similar to the sound of a flat tire. Sorry for the super long, and kind of tedious description i typed up, but i have a lot of problems and thought that i should let you know so that you could help diagnose the problem/problems.

 

[bluegoatwoods]

Well, I'm not seeing anything obviously wrong. That carbon buildup is about what I'd expect from an engine that's been run a bit.

But it's been a long time since I looked down into my cylinder. And I'm no expert on the internal stuff in any case.

But the fact that you washed your bike and now have trouble starting it makes me suspicious of the magneto. It doesn't take much water in there at all to cause you trouble.

They're easy enough to test with a cheap ohm-meter. I've forgotten that numbers that you'll be looking for. But they're easy enough to find. Just go to the 'search' box at the top of these pages. Type in 'magneto troubleshoot' or something like that and it'll point you toward threads with all sorts of info.

Good luck.

 

[colemanbales]

Its not the magneto, i tested both the cdi box and magneto for ohms, and according to the video bikeberry put on youtube, the magneto was in the healthy range, but the cdi box was totally dead...

 

[thunderhead289]

the problem you describe is called 4 stroking where the mixture is set too rich. try to run a bigger spark plug gap to about 5 more than you are and adjust the mixture screw and idle adjustment on the nt.

lean the mix screw then reduce the air top idle speed adjustment down. youl need to do this because when it is leaned the rpm will rise.

 

[Fabian]

The carbon on the piston is normal.

The oil leaks are completely normal - be thankful you have oil leaks because the day that the engine stops leaking oil is the day when the engine stops operating.

Air leaks are normal with these engines, but they are not desirable.
The gaskets compress over time; reducing effective clamping pressure of the bolts holding the parts together. After the first 20 miles of use, you must go around the attached parts and re-tighten the bolts and screws, then repeat this process at 100 miles and every 200 miles after that, especially with the cylinder head, as the aluminium head gasket will continue to compress over time.

Correctly jetting the carburettor will eliminate the 4-stroking.

As far as i am aware, there is an idle screw, but no mixture screw on the NT carburettor.