"RPM" Limited carbs....

[weimedog]

So is there really such a thing? I have a 272, with a carb from something else I think, that has this little check ball spring arrangement. No matter what I do it won't go past 12,000. Are the two things related? (The spring-check ball device on the carb & the 12,000RMP max) If so, what is the best way to disable that device on the carb? Can u fill it with epoxy? Maybe remove the spring and put in a solid spacer instead?

 

[Ambull]

How would the carb know how fast the saw is running? The only item that would "know" is the ignition. Any simple rev limited engine I have seen does it by cutting out the ignition. The better systems with just skip a spark every now and then, so there is not a complete loss of power.

 

[Cliff R]

My 181 is supposed to have a governed carburetor on it, but it runs flawlessly with plenty of rpms in the cut so I've never messed with disabling this feature.....Cliff

 

[mtngun]

How would the carb know how fast the saw is running?

It senses the vacuum pulses. The spring and ball have a natural resonant frequency. When the pulses hit the resonant frequency, the spring no longer holds the ball against the seat.

If you can access the seat, you can disable the carb governer by sealing the orifice with a gasket. I wouldn't use epoxy, since it could find its way into places where you don't want it to go.

 

[pioneerguy600]

When the engine reaches 12000 RPM does it still pull smoothly? If it sounds rough like its bouncing or fourstroking then it has a rev limited coil. If it pulls smoothly but just won`t go any faster it likely has a governed carb. The brass jet/governor can be pushed out, clean the insides of it good and a drop of solder will close it for good, reinstall it back in its bore. You will then need to retune your carb on the saw, best to do it with the fourstroke, clean up in the cut method.

Pioneerguy600

 

[weimedog]

Thanks! (U see this Motomedik!!!)

It run real strong there and doesn't get rough until I'm ridiculously lean so that's falls into the carb limiting class. I looked thru my box of Tillotson's and realized I have quite a few! So I'll go thru and mod them to disable those limiting jets/

 

[AZLOGGER]

It senses the vacuum pulses. The spring and ball have a natural resonant frequency. When the pulses hit the resonant frequency, the spring no longer holds the ball against the seat.

If you can access the seat, you can disable the carb governer by sealing the orifice with a gasket. I wouldn't use epoxy, since it could find its way into places where you don't want it to go.

mtngun:
Pretty good description on the way the governor works.

weimedog:
The carb you are describing is the carb used on the 272K cuttoff saws, and yes it it will limit the saw to 12,000 RPM's, if you want to disable it, you will have to remove the governor and place something behind it (a small gasket or a small piece of aluminum foil will work), be sure and use some type of sealant on the threads when you re-install it (nail polish or blue or red loctite will work), after the modification re-adjust the carb and put it to the wood.
I have done this many times to my old saws back in the days, mainly the Pioneers P51, P52, P61 and etc.

Hope this helps you solve your problem.

 

[Cliff R]

So the basic mod needed to eliminate the fuel controlled governor is to seal off the port where the check ball seats?.....Cliff

 

[CGC4200]

sounds a lot like a high speed governor valve

Modified Mark has posted a similar fix for the Tillotson HS 176A used
on Poulan 5200's on the Poulan thread. I have a 5400, probably uses
the same carburetor, kitted it about three years ago, if I had been aware
of the issue, I would have "fixed" it then.

 

[stihl86]

The "governor" dumps MORE fuel into the venturi when the engine hit the resonance point. It doesn't restrict flow at all.
So, if you have a problem with it, your symptom would usually, be a rich condition.

 

[pioneerguy600]

The "governor" dumps MORE fuel into the venturi when the engine hit the resonance point. It doesn't restrict flow at all.
So, if you have a problem with it, your symptom would usually, be a rich condition.

Thats right, it dumps in fuel to limit RPM and the result is a rich running saw at WOT. ..By eliminating it the engine relies on the fuel the carb jets supply, if the engine is then tuned by adjusting the carb it would most likely be able to go past 12000 and possibly reach 13500 without running lean.

Pioneerguy600

 

[Wildman1024]

I'm pretty sure Mark uses a hole punch and a thin aluminum pie baking tray. He punches out a little piece of aluminum and it fits nice between the gov screw and the carb blocking it off. makes a great non permanent fix.

I use an old welch plug trimmed to fit...also works well. I tried the epoxy route one time and it was a mega fail. Mark saw the results of that.

 

[troutfisher]

I use a little dab of J-B Weld to disable them.

 

[Modifiedmark]

It senses the vacuum pulses. The spring and ball have a natural resonant frequency. When the pulses hit the resonant frequency, the spring no longer holds the ball against the seat.

If you can access the seat, you can disable the carb governer by sealing the orifice with a gasket. I wouldn't use epoxy, since it could find its way into places where you don't want it to go.

The info that I have states that the governor is operated by vibrations.

The fuel inlet for the governor itself is a small hole near the inlet needle and I'm not sure you would get much pulse there.

From the 2100 workshop manual.

"Speed governor

The purpose of the governor is to limit the engine
speed in order to protect vital parts like the crankshaft
and ignition system from excessive stresses.
We therefore advise most strongly against any interference
designed to render it inoperative. When the
saw IS run under no-load conditions, the engine
speed IS limited to 10,500 r/min as the governor
comes into operation.

The steel ball and spring in the governor are so devised
that vibrations in the carburettor at a certain
engine speed cause the steel ball to open the fuel
outlet. An excessively rich mixture IS then obtained
and the engine begins to four-stroke, the speed
drops and the vibrations decrease. The steel ball
then closes the outlet, the engine speed increase
and the process IS repeated.

 

[Modifiedmark]

I'm pretty sure Mark uses a hole punch and a thin aluminum pie baking tray. He punches out a little piece of aluminum and it fits nice between the gov screw and the carb blocking it off. makes a great non permanent fix.

I use an old welch plug trimmed to fit...also works well. I tried the epoxy route one time and it was a mega fail. Mark saw the results of that.

Rick, you told on yourself, my lips were sealed on that one! LOL It was quite a mess though and ruined a perfectly good carb body.

Your right though thats exactly how I block them off. It's quick, easy, effective and non permanent. One thing I learned though is to pull the copper sealing ring out and put the aluminum disk against the carb body and put the ring on top of it to let the governor tighten and turn on it instead of the aluminum disk to keep from tearing it.

I use a little dab of J-B Weld to disable them.

Look above the JB weld can be a bad idea.

Just because the carb has a governor does not automatically mean it needs to be disabled. You just have to know that the carb needs to be set in the wood, you cannot just wind it up full speed with no load to adjust the high side.

What got me going on these was chasing a couple that were defective and its easier to block a bad one off then to find new ones. The ones that I had that were bad would not allow maybe 4000-5000 rpms without flooding out.

Also, Tilliotson is not the only ones to use a governor like that, some Walbros also used the same type setup.

 

[albert]

You could plug it or just tune it in a cut. Unless it's heavily ported it not goimg to run more than 10k in the wood.

 

[albert]

I only plug them off if the spring gets weak and the valve dumps fuel at too low of a rpm.

 

[Wildman1024]

Rick, you told on yourself, my lips were sealed on that one! LOL It was quite a mess though and ruined a perfectly good carb body.

Your right though thats exactly how I block them off. It's quick, easy, effective and non permanent. One thing I learned though is to pull the copper sealing ring out and put the aluminum disk against the carb body and put the ring on top of it to let the governor tighten and turn on it instead of the aluminum disk to keep from tearing it.




Look above the JB weld can be a bad idea.

Just because the carb has a governor does not automatically mean it needs to be disabled. You just have to know that the carb needs to be set in the wood, you cannot just wind it up full speed with no load to adjust the high side.

What got me going on these was chasing a couple that were defective and its easier to block a bad one off then to find new ones. The ones that I had that were bad would not allow maybe 4000-5000 rpms without flooding out.

Also, Tilliotson is not the only ones to use a governor like that, some Walbros also used the same type setup.

I guess I did tell on myself now didn't I. It was a learning experience! JB Weld and Carb Governor = NO DICE!

 

[stihl86]

Thats right, it dumps in fuel to limit RPM and the result is a rich running saw at WOT. ..By eliminating it the engine relies on the fuel the carb jets supply, if the engine is then tuned by adjusting the carb it would most likely be able to go past 12000 and possibly reach 13500 without running lean.

Pioneerguy600

I'm aware of what it does, but increases in RPM don't always equal increases in horsepower.

 

[weimedog]

I'm aware of what it does, but increases in RPM don't always equal increases in horsepower.

no..