Is this normal

I have been having problems with the bike. Something happens when it gets hot and under load. The idle goes up very high and it looses power. I have cleaned the carb and searched for air leaks with no luck. I took it off just to see if everytghing seemed okay. On other bikes I have had there has not been so much bubbling going on.
 
It sure looks like you are getting combustion pressure into your cooling system. I think you have a cylinder head inner O-ring leak or potentially a crack in your cylinder or head. Most likely it is a O-ring seal leak.
 
I will check the o-ring. Is it common that they break? The bike has only 50 hours on the meter. I did however make a kind of stupid thing that day I first noticed it wasn'r running as it should. I pushed it pretty hard through a lot of snow when the motor was still cold.
 
I have checked the cylinder head o-ring and it looks fine to me. Can it be faulty but still not broken?
 
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Had the bike been losing coolant during use? This could indicate combustion gases over pressurising the cooling system, or coolant making its way into the combustion chamber and being burnt off, which you should be able to smell and feel. From your video its hard to tell if the coolant is bubbling or its just turbulance from the pump (which increases with revs).

What else have you checked? You cleaned the carb, but did you check your jetting specs? It sounds like its running lean when up to temp. I wouldn't make any judgement calls on how a bike sounds after running for 30 seconds. Mine sounds lean off choke, or rich with choke on when just started. Too much choke and it'll load up and run rich until you can get it up to temp and clear it out.
 
Check and see if the head provides a smooth sealing surface for the O-rings. It is also possible that it is warped from overheating and you will need to get the head or cylinder mating surface trued to get a flat surface. If so it is a good time to check your head squish so you can get more power out of it at the same time.
 
I have not noticed any water loss nor any white smoke with smell of coolant. When it gets up to temp it feels very lean. If I ride up a hill and rev it out it looses power and the idle is like moments before you run out of fuel, very high and unstable but not like ju have twisted the throttle more like the one on a racecar. If I pull the choke at that time the idle will settle for a while. It became like this from one day to another. Same outside temperature and everything else the same. If I take a rest for 10 minutes it seems fine again but after a couple of minutes it going like crap.
 
Zman said:
Check and see if the head provides a smooth sealing surface for the O-rings. It is also possible that it is warped from overheating and you will need to get the head or cylinder mating surface trued to get a flat surface. If so it is a good time to check your head squish so you can get more power out of it at the same time.
Click to expand...

How do I check it?
 
Have you checked the stator side crank seal? Replace (not just clean) the pilot jet. Double, triple check the carb needle and position. I wouldn't expect the reeds to have this impact, but no harm in checking. Pay good attention to the manifold between the carb and reed block.

How's the transmission oil look?

Also, check the breather line for the fuel tank. Pull the fuel line off the carb and drain some fuel into a bowl/jar. Check the flow rate, and make sure the fuel is clean. A blocked breather could result in flow not being able to keep up with demand.
 
Jakobi said:
Have you checked the stator side crank seal? Replace (not just clean) the pilot jet. Double, triple check the carb needle and position. I wouldn't expect the reeds to have this impact, but no harm in checking. Pay good attention to the manifold between the carb and reed block.

How's the transmission oil look?

Also, check the breather line for the fuel tank. Pull the fuel line off the carb and drain some fuel into a bowl/jar. Check the flow rate, and make sure the fuel is clean. A blocked breather could result in flow not being able to keep up with demand.
Click to expand...

Havent checked the crank seal or reeds. I will do that. I pulled the cylinder so I have to put it back together with new gaskets first.

Replaced the pilots and main jet with new ones. Tried different needle positions. I have checked flow and tried different caps and breathers.

I am now running 180, 42 N3EG #3.
 
Also, check the crank case drain bolt and crush washer on the bottom of the engine.

When you replaced the cylinder how many base gaskets did you run? As suggested, measure the squish. Has the head been modified at all? I've seen bikes with too much compression behave the way you describe, but again its not something that just happens over night (without someone playing with the tools).
 
A cooling system pressure check would be a good place to start.
I had a wierd problem that sounds similar to yours.
Bike would run fine for several miles then start running crazy lean. stop, check runs fine a bit then lean again. Turns out a pinched carb vent hose had changed my float level. Ice blocking a vent hose could have the same effect.
 
Could the float level be too low? That explains why it would run fine for a few minutes then go lean.


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