john deere surging still
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I have a Toro with a Briggs engine that, among other problems I had to fix, was surging. What fixed the surging was replacing the intake manifold and gasket. When I took the old gasket off, it was very brittle and literally crumbled in my hands.
My JX 75 surged when I bought it 3 years ago but I cleaned the carb and ran some Techron through it and all is well. Over on 'mytractorforum.com' it seems to be a pretty common problem with the Kawis if the carb gets the least bit dirty.
Is this at idle, or operational RPM?
Most air cooled engines have crude governors. Sometimes the governors are internal to the engine and use oil, sometimes they use an air vane by the flywheel fan. Not sure on this engine.
As mentioned before surging is often caused by a lean condition. The engine does not produce enough power at certain (low) throttle positions, causing the governor to increase throttle, and, of course, the RPM. At which point, the throttle closes due to high RPM, and the cycle starts again.
The other thread you started had a good bit of info. But, since it's still a problem, let's review some theory.
The governor uses some RPM related force to pull against a spring. That spring holds the throttle open. The governor closes the throttle (against spring pressure) as the RPM increases. Simple.
If, you were to replace the spring with an infinitely long spring, the governor would not function. Even if the spring pressure was the same!
Here is why: As the spring stretches, the force required to stretch it more, increases. The "less linear" the spring is, the more governor control it has. BUT, the less accurate the RPM control is, loaded v unloaded.
For example: a generator must maintain 3600RPM-60HZ. At no load, it's probably 61HZ and full load 59HZ. That's a function of the spring length! There is no easy way to maintain exactly 60HZ without electronics. If you take that governor spring and simply reduce the number of coils, you increase the rate of "rise". The generator can still be adjusted to 60HZ. But, no load will equal 62HZ and full load will be 58. HOWEVER, the governor will be less likely to hunt, and will maintain better control over frequency-RPM swings as loads are added and removed.
Also, "IF" you are using fuel with Ethanol, it's probably a touch lean.
Most air cooled engines have crude governors. Sometimes the governors are internal to the engine and use oil, sometimes they use an air vane by the flywheel fan. Not sure on this engine.
As mentioned before surging is often caused by a lean condition. The engine does not produce enough power at certain (low) throttle positions, causing the governor to increase throttle, and, of course, the RPM. At which point, the throttle closes due to high RPM, and the cycle starts again.
The other thread you started had a good bit of info. But, since it's still a problem, let's review some theory.
The governor uses some RPM related force to pull against a spring. That spring holds the throttle open. The governor closes the throttle (against spring pressure) as the RPM increases. Simple.
If, you were to replace the spring with an infinitely long spring, the governor would not function. Even if the spring pressure was the same!
Here is why: As the spring stretches, the force required to stretch it more, increases. The "less linear" the spring is, the more governor control it has. BUT, the less accurate the RPM control is, loaded v unloaded.
For example: a generator must maintain 3600RPM-60HZ. At no load, it's probably 61HZ and full load 59HZ. That's a function of the spring length! There is no easy way to maintain exactly 60HZ without electronics. If you take that governor spring and simply reduce the number of coils, you increase the rate of "rise". The generator can still be adjusted to 60HZ. But, no load will equal 62HZ and full load will be 58. HOWEVER, the governor will be less likely to hunt, and will maintain better control over frequency-RPM swings as loads are added and removed.
Also, "IF" you are using fuel with Ethanol, it's probably a touch lean.
ditto: you have a dirty carb or an air leak
I can't understand why people always blame the governor for a surging issue before blaming the carburetor. A governor in an engine like a Kawasaki is a mechanical governor and will last the life of the engine. Kawasaki is so confident of their governors that they don't even offer it has a separate replacement part; you have to order the whole lower case of the engine to get a new governor.
Originally Posted By: Merkava_4
I can't understand why people always blame the governor for a surging issue before blaming the carburetor. A governor in an engine like a Kawasaki is a mechanical governor and will last the life of the engine. Kawasaki is so confident of their governors that they don't even offer it has a separate replacement part; you have to order the whole lower case of the engine to get a new governor.
Please understand, I'm not blaming the governor. It's just a very simplified description of governor theory. Something to keep in mind when troubleshooting a problem like this.
It's very likely that the engine is too lean. Resulting in hysteresis. However, it's also possible that the governor was designed to maintain RPM very close to the set point (by having a very linear spring rate) Resulting in an engine that is sensitive to surge if any little thing is wrong.
I can't understand why people always blame the governor for a surging issue before blaming the carburetor. A governor in an engine like a Kawasaki is a mechanical governor and will last the life of the engine. Kawasaki is so confident of their governors that they don't even offer it has a separate replacement part; you have to order the whole lower case of the engine to get a new governor.
Please understand, I'm not blaming the governor. It's just a very simplified description of governor theory. Something to keep in mind when troubleshooting a problem like this.
It's very likely that the engine is too lean. Resulting in hysteresis. However, it's also possible that the governor was designed to maintain RPM very close to the set point (by having a very linear spring rate) Resulting in an engine that is sensitive to surge if any little thing is wrong.
Originally Posted By: Merkava_4
I can't understand why people always blame the governor for a surging issue before blaming the carburetor.
Amen to that Merk.
In almost all instances, the governor is doing exactly what it supposed to, but in these cases, it's chasing the engine RPM all over the place because of a fuel/air ratio problem.
I too would price a mail-order replacement carb and intake manifold gasket.
Or try removing, disassembling and cleaning the carb is so inclined.
I can't understand why people always blame the governor for a surging issue before blaming the carburetor.
Amen to that Merk.
In almost all instances, the governor is doing exactly what it supposed to, but in these cases, it's chasing the engine RPM all over the place because of a fuel/air ratio problem.
I too would price a mail-order replacement carb and intake manifold gasket.
Or try removing, disassembling and cleaning the carb is so inclined.
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