Honda express sputtering

socialdistortionkid

socialdistortionkid

New Member
hey guys i have a 1979 honda NC50 2 stroke express moped that i cant figure out what is wrong. It starts up cold with the choke on fine then it will run for about 5-7 minutes of riding, then sputters out after the engine warms up at WOT. It will restart immediatly only with a combination the choke on and giving it a little gas. It idles fine when i restart it and if i get on it to ride it sputters out. :-|| I pulled the Spark plug and is brownish tan color. I just drained the tank and put new fresh 32:1 gas in it. that didnt seem to help....put a new ngk spark plug and tested for spark (blue spark) shortly after i then tested the fuel petcock.... works great. I just took apart the NT carb thats been working fine for the last 6 months (its full of fresh gas, the float looks normal and the carburetor jet is not gunked up) ive been a mechanic for 6 years and i cant figure this simple 2 stroke out! I need help please thanks! :)
 
If your carb looks good on the inside and the spark plug also looks good, run a compression check with it cold, then run another one with the engine hot, typically the compression will read higher on the warmed up engine. It's possible you could have an air leak somewhere that appears when the engine is warmed up and goes away as it cools back down, but the compression check could show you a cracked head or a bad head gasket where the heat expansion of the parts is enough for your compression to go away.

Other things that work cold and not so good when warmed up are failing ignition components, you can also ohm check your coil cold and see if it's still the same once the engine starts to cut out, the reason it could idle in this situation is that it's got enough to barely get by on but with added cylinder pressure from opening the throttle or under load is enough to make it not strong enough to jump the gap anymore.
This could also hold true for a bad plug wire or boot.
Also check your case for air leaks by introducing about 10 to 15 psi into the case then use the soapy water test at the base, the manifold, and the split line, check the crank seals too if you can access the seals without removing too many parts, just keep the water away from the electrical parts.
The way you're going to find the problem tho is to check all the vitals with the engine cold, then again fully warmed up and look for anything that changes when the engine is hot.
I don't know if yours can vapor lock but if the carb is enclosed where heat can't escape it could.
 
Have you actually checked for good fuel flow from the tank? The carburetor might be full when you check it but if your fuel supply is restricted with dirt or a collapsed fuel line it will idle but not run under power/load.

I ran into this with my Toro mower last summer. I found the fuel line soft and squishy and collapsing, choking off the flow. The engine would start and idle fine but sputter and shut down when I'd open the throttle. I replaced the fuel line and everything was good again. Just an idea based on what I found.

Tom
 
Okay everybody! thanks for the comments.... i put some new 32:1 gas in it and i can ride it for hours and hours, it runs good, plug is brown/tan. It but it wont restart when its hot... it only wants to restart when it cools down.

Anybody know what this means ive never had this happen to me??? thanks! :)
 
2door said:
Have you actually checked for good fuel flow from the tank? The carburetor might be full when you check it but if your fuel supply is restricted with dirt or a collapsed fuel line it will idle but not run under power/load.

I ran into this with my Toro mower last summer. I found the fuel line soft and squishy and collapsing, choking off the flow. The engine would start and idle fine but sputter and shut down when I'd open the throttle. I replaced the fuel line and everything was good again. Just an idea based on what I found.

Tom
Click to expand...
New fuel line, the petcock may be the problem, the bike has been sitting in a garage for 15 years so maybe there is rust in the tank??? It runs good now for a long time but will refuse to restart when hot,,, any ideas tom?
 
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