GX 200 Lacking RPM

M

mcleod89

New member
I bought a modified gx 200 from NR Racing last year and installed it in a zr 200 snowmobile. Engine has 280 Cam, 27/24 valves, 26lb srings and 10.7-1 head. Governor has been removed.

When I first got it the engine ran great and had tons of power, but then the carb broke (22 mikuni round) from hitting the frame. So I went with a new set up and installed a 26mm pwk. Jetted it to chocolate brown but the engine still wont rev past 3400-3700 rpm. I'm stuck and not sure what to check next.

Could the valves or springs have gone bad or could it be something electrical? Any help would be great.
 
First thing I would do is check the compression pressure. You probably didn't do it before so you have nothing to compare it too, but get an idea what it is now. Then I would pull the head and see if the head gasket is still there, or maybe leaking. I would check the gaskets under the carburetor and under the manifold. Make sure everything lines up. Wouldn't hurt to check the timing. Put a new spark plug in it. Check the spark plug wire for cracks. Check the fuel line for restrictions. You never know. Breaking that carburetor off had to be real hard on the block. Never know.
 
The carb didn’t exactly brake off just broke off the drain tube on the bottom but it was leaking after that from the float bowl.it has a new carburetor manifold and gaskets on the intake so it can’t be that part.
 
Sometimes cam lobes go flat with big springs, check your valve lift. You can take your rocker off and check it with a 100ths ruler and get a ballpark idea if there's a problem. Also is the engine just worn out or did this happen suddenly with the carb change?
 
Sounds like the carb is to rich! How did you jet it to "chocolate brown" if the engine wont rev past 3600, did you jet it going on spark plug color at idle? And from everything I have been told which holds true for my own engines, its hard to read a plug when these things are tuned right. Even when you run it wide open than shut it down and check plug.
 
mcleod89 said:
The carb didn’t exactly brake off just broke off the drain tube on the bottom but it was leaking after that from the float bowl.it has a new carburetor manifold and gaskets on the intake so it can’t be that part.
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You can plug the drain with jb weld as a test .
Full throttle no load is not going to give correct plug read .
If you did it this way , was the rpm still 34-3700 rpm ?
Three things as stated carb , valve lift and ignition timing .
How does it act at full throttle 3600 rpm ?
Any sputtering, popping or sounds fine just won't rev farther ?
Since the only stated change was carb thats number 1 .
 
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