brass plug

[booger1286]

rebuilt the carb on jonsered 920 and i was just wandering if anyone could tell me what the brass plug is under the choke lever on the carb i put the carb back on but i cant seem to get it to idle low enough dont think this is the problem but just wanted to know what its purpose is thanks

 

[Man of $tihl]

i'm not real familiar with the 920 but i think that is the carb limiter?

 

[Modifiedmark]

It is the high speed governor.

 

[booger1286]

ok

It is the high speed governor.

what should i do with it? i just put it back in tight. can i bypass it or something?

 

[galde]

Is it threaded and was it sealed with a red adhesive? If it is indeed a governor to limit max RPM, then by tightening it beyond the factory setting, you will raise the RPM at which it kicks in. These things worked by resonating at a preset RPM. At resonamce, a ball in a seat would jiggle out of the seat and allow fuel to bypass the jets in the carb and dump directly into the carb throat, thereby flooding the saw. Any means of plugging this chanel will disable the governor.

 

[booger1286]

governor

Is it threaded and was it sealed with a red adhesive? If it is indeed a governor to limit max RPM, then by tightening it beyond the factory setting, you will raise the RPM at which it kicks in. These things worked by resonating at a preset RPM. At resonamce, a ball in a seat would jiggle out of the seat and allow fuel to bypass the jets in the carb and dump directly into the carb throat, thereby flooding the saw. Any means of plugging this chanel will disable the governor.

yes it was threaded and sealed will this by chance be why it is idling too high thanks

 

[Modifiedmark]

then by tightening it beyond the factory setting, you will raise the RPM at which it kicks in.

Please explain this to me would you please?

The governor is flat on the bottom and seals in the bottom of the well against a copper gasket. Once its tight, its tight, no further tightening will make a difference.

If not tight it could let fuel seep past the governor and flood the engine.

I'm serious, I don't understand your statment.

yes it was threaded and sealed will this by chance be why it is idling too high thanks

Probably not.

 

[booger1286]

idle

abybody have an idea of why this thing is idling too high? i can take the idle screw all the wat out and it is still too fast.

 

[Modifiedmark]

abybody have an idea of why this thing is idling too high? i can take the idle screw all the wat out and it is still too fast.

Might be a air leak. I'm not really that up on that particular saw though.

 

[booger1286]

governor

thanks for all if the info. i see how the gov works now, i cut a piece of aluminum to fit and put it in there and while i was at it found that the brass disc on the choke had the edges broken off that stopped it from flipping completely around which im hoping is my high idle problem.

 

[galde]

Please explain this to me would you please?

The governor is flat on the bottom and seals in the bottom of the well against a copper gasket. Once its tight, its tight, no further tightening will make a difference.

If not tight it could let fuel seep past the governor and flood the engine.

I'm serious, I don't understand your statment.

Probably not.

The brass plug pushes on a spring which in turn pushes on the ball in the seat. It is the spring compression that regulates the RPM where resonance occurs.
The factory setting was made to limit RPM to prevent over-revving at WOT when at no load. The governor was not meant to be tampered with by the user. If the threaded plug is backed out, then the RPM at which it resonates (and floods the saw) is lowered. Over-tightening the plug will raise the RPM that causes resonance. Beyond a certain amount of over-tightening, the governor is effectively disabled, since the saw will max out by itself. Many older saws were at risk of coming apart when over-revved, that's why the carb governors were used.

 

[Modifiedmark]

The brass plug pushes on a spring which in turn pushes on the ball in the seat. It is the spring compression that regulates the RPM where resonance occurs.
The factory setting was made to limit RPM to prevent over-revving at WOT when at no load. The governor was not meant to be tampered with by the user. If the threaded plug is backed out, then the RPM at which it resonates (and floods the saw) is lowered. Over-tightening the plug will raise the RPM that causes resonance. Beyond a certain amount of over-tightening, the governor is effectively disabled, since the saw will max out by itself. Many older saws were at risk of coming apart when over-revved, that's why the carb governors were used.

I'm sorry, I'm thinking were not thinking about the same thing. I'm thinking Tillotson governors. HS and HL style.

There is no adjustment on them that I have ever seen. Like I said they sit flat into the well and there is no mechanical way to make any difference by how much you tighten them that I can tell.

The service manuals make no mention of it or any torque specification on it either. There are different part numbers for the different governors for different model carbs though, and I figured the reason for that was they would open differently.

If you can explain to me how mechanically they change by changing the torque on them when there installed, I'm all ears.

I just cannot agree till then.

 

[galde]

If you can explain to me how mechanically they change by changing the torque on them when there installed, I'm all ears.

I just cannot agree till then.

I am thinking Walbro models with governors. The valve that "leaks" fuel into the carb throat at a predetermined RPM consists of a check ball held against a seat by a spring whose compression is controlled by how far a threaded brass plug is screwed into the carb body. It isn't a matter of torque, but rather the spring compression that tells the check ball when to "leak" and thus limit RPM. I think the system is crude and can be expected to change with age. As the spring weakens with fatigue or other causes, the RPM of resonance will decrease, requiring recalibration of the brass plug -- which would be very hard to do IMHO. I mostly disable these carb governors by plugging the channel with JB Weld. I never run the old saws at WOT unless in a log.

 

[Modifiedmark]

I am thinking Walbro models with governors. The valve that "leaks" fuel into the carb throat at a predetermined RPM consists of a check ball held against a seat by a spring whose compression is controlled by how far a threaded brass plug is screwed into the carb body. It isn't a matter of torque, but rather the spring compression that tells the check ball when to "leak" and thus limit RPM. I think the system is crude and can be expected to change with age. As the spring weakens with fatigue or other causes, the RPM of resonance will decrease, requiring recalibration of the brass plug -- which would be very hard to do IMHO. I mostly disable these carb governors by plugging the channel with JB Weld. I never run the old saws at WOT unless in a log.

I have only done a Walbro or two with the governors so I will not comment much on them, I think they were in a WJ or WY or something but at a glance and by my feeble memory I thought they were basically the same as the Tillotsons.

I understand what your trying to say about compressing the spring and it changing the pressure on the ball and seat but like I said the ones I'm talking about you cannot change the spring pressure by screwing it in or out farther.

The matter of torque is the act of tightening the screw in governor tighter and is what I was referring to.

I have seen first had the carbs with JB weld used to disable the governor, and it was a ruined mess. The JB weld had oozed into the venturi and up into the metering chamber and actually stuck the needle valve.

The best way to disable them is to block them off with a thin piece of aluminum.

I thank your for your imput but like I said I have not seen a adjustable governor yet. Please post one up for us to see will you?

The original posters carb should probably be a Tillotson HS and like I said no matter how tight you install the governor it will not affect the governors performance as far as I have ever seen.

So no matter the others Walbro etc, they don't actually apply to this posters question.

 

[galde]

I have only done a Walbro or two with the governors so I will not comment much on them, I think they were in a WJ or WY or something but at a glance and by my feeble memory I thought they were basically the same as the Tillotsons.

I understand what your trying to say about compressing the spring and it changing the pressure on the ball and seat but like I said the ones I'm talking about you cannot change the spring pressure by screwing it in or out farther.

The matter of torque is the act of tightening the screw in governor tighter and is what I was referring to.

I have seen first had the carbs with JB weld used to disable the governor, and it was a ruined mess. The JB weld had oozed into the venturi and up into the metering chamber and actually stuck the needle valve.

The best way to disable them is to block them off with a thin piece of aluminum.

I thank your for your imput but like I said I have not seen a adjustable governor yet. Please post one up for us to see will you?

The original posters carb should probably be a Tillotson HS and like I said no matter how tight you install the governor it will not affect the governors performance as far as I have ever seen.

So no matter the others Walbro etc, they don't actually apply to this posters question.

The manuals for these carbs say that the governor installation is done at the factory and is "tuned" for each specific saw, and the plug threads are sealed. They ar not meant to be tampered with, so if the brass plug is adjusted then the governor most likely can not be restored by the user.
I know what you mean with problems created by sloppy JB Weld applications. When applied with skill and care it can be very effective in many repair situations.

 

[Modifiedmark]

The manuals for these carbs say that the governor installation is done at the factory and is "tuned" for each specific saw, and the plug threads are sealed. They ar not meant to be tampered with, so if the brass plug is adjusted then the governor most likely can not be restored by the user.
I know what you mean with problems created by sloppy JB Weld applications. When applied with skill and care it can be very effective in many repair situations.

Yes I'm sure they are "tuned" for each specific saw, I said that different carbs used different part numbered governors.

I'm pretty sure that is the "tuned" part and yes the threads are sealed no doubt, but like I said, the governors cannot be "adjusted", they bottom out in the well on a copper gasket.

Not saying that all are the same but untill I see one that is different, then I'm satisfied with my beliefs.

Please point me to a different one!

 

[galde]

Mark, thanks for your patience and perserverance. You are absolutely correct. To jog my foggy memory, I went to my junk collection and removed the governors from a Tillotson and a Walbro carb. Just as you say, the governors are self-contained brass plugs with the check ball and spring built into the threaded plug. The sealant on the plug threads is not there to lock in an adjustment as I had mistakenly assumed, but rather to seal the threads against leakage. The plugs indeed bottom out against a copper gasket.

 

[cpr]

I have nothing to ad. However I appreciate the spirited, gentlemanly debate that contributed to me learning something. Thanks and hats off to you both.

 

[Modifiedmark]

Mark, thanks for your patience and perserverance. You are absolutely correct. To jog my foggy memory, I went to my junk collection and removed the governors from a Tillotson and a Walbro carb. Just as you say, the governors are self-contained brass plugs with the check ball and spring built into the threaded plug. The sealant on the plug threads is not there to lock in an adjustment as I had mistakenly assumed, but rather to seal the threads against leakage. The plugs indeed bottom out against a copper gasket.

You had me doubting myself for just a minute, I thought I might have missed something and you actually made me think about it which is good.

I have nothing to ad. However I appreciate the spirited, gentlemanly debate that contributed to me learning something. Thanks and hats off to you both.

Why thank you.

 

[rms61moparman]

Mark is pretty sharp on those old carbs, he has probably done 25 or more in the last year.


Mike