carb problems

[jay 7]

I have a 30 hp nissan.It runs fine when you run it at half to 3/4 throttle when you open it up to full throttle it will run for about 400 yards then die down to idle.You can let idle for about 20 seconds run it at full throttle for 300 yards and it dies down to idle.I've changed the fuel pump,tank,fuel hose & bubble.cleaned carburator.Whats left that I'm overlooking.

 

[TOHATSU GURU]

Re: carb problems

"Whats left that I'm overlooking."

That would be the troubleshooting...You have to test the engine's systems and various parts to determine where and what is causing the problem. Or, you can randomly replace parts as you are presently.

Pick up a service manual, pick one of the engine's three major systems(fuel, mechanical,ignition) and start ye olde test procedures. Chances are it is in the fuel system, as you probably already believe, and is either a problem with a system leak or, much more likely, a carburetor that has not been cleaned successfully. However, it could be an ignition component or a block/gasket issue....There is no shortcut to testing other than a wild guess that just happens to be right. The wild guess, at this point, points to the high speed jet in the carb.

 

[pvanv]

Re: carb problems

What TG said. Especially if it's a single-carb 2-stroke. You didn't mention model. If it's a 3-carb 4-stroke, that's another animal altogether. Same rules apply, but synchronization is more complex, and you really would need a Factory service manual, which is recommended anyway.

 

[jay 7]

Re: carb problems

The high speed jet is what I was thinking. But if the high speed jet is not working it would not open up and run at full throttle right. It acts like it not getting enough fuel to keep it running at full throttle.When you let sit at idle the carb fills back up.Does the carburator have rubber o rings that have gone bad and loosing its prime.while you run at fu throttle and it starts to die down I've pumped the bubble and it doesn't affect it .

 

[Sea Rider]

Re: carb problems

The high speed jet is what I was thinking. But if the high speed jet is not working it would not open up and run at full throttle right. It acts like it not getting enough fuel to keep it running at full throttle.When you let sit at idle the carb fills back up.Does the carburator have rubber o rings that have gone bad and loosing its prime.while you run at fu throttle and it starts to die down I've pumped the bubble and it doesn't affect it .

If it's a two stroker, check carb needle valve for tip wear and float for wear or out of height adjustment, check gas pump check valves are properly seated on housing and diaphragms for wear, deformation. The only rubber carb part is the big float chamber o'ring.

Happy Boating