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266xp : wrong kind of snappy throttle

davidwyby

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I suspect the hole being sloppy in the plate. If I lift slightly on the link bar, it improves. Other less worn looking carb almost does it.

oiled with 3m oil, made it worse...maybe the plastic doesn’t like that oil.
 

drf256

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Any pics of that arm? I can’t remember the setup, I just remember breaking one of those arms.
 

Xr650jkallen

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Jb weld and redrill it to the correct size.
 

davidwyby

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I would make sure the throttle shaft is tight in the the body of the carburetor. You may also need to bend the link outward a little.
Throttle shaft fit seems good. Does have quite a bit of end play, maybe .025”? Moves when rotated.
Make the wire connecting link longer?
Or bend the throttle shaft plate outward?
 

huskihl

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Any chance you have mixed parts from early vs later designs? Seems like the hole in the carb side linkage could be higher. No idea if the early vs late are even different
 

davidwyby

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@huskihl have two carbs off two 266s, 224s, one sticks and one doesn’t. The one that does is more worn. I thought I could feel a stick in the motion when cracking throttle open by hand with it out of the saw. I took the throttle blade screw out and it seemed to go away. Maybe the plate centered itself better in the bore. But back in the saw without the plate screw, no improvement. I think I’m going to pull the throttle shaft clear out and inspect. Maybe swap springs. The problem one feels like maybe it’s stiffer. Also maybe get creative with a punch and hammer and move that hole up. If I leave the left carb screw out and drop the carb a little the bind goes away. I may also swap tanks as this one has op pres lever issues anyway.
Later on today...this am gonna get work done on saw shop while it’s 93, not 117.

@Czed @jacob j. no amount of bending or tweaking on the link any which way seems to help.
 
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drf256

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It’s not binding in the saw body is it? Can you post a short vid of it happening from the same angle as you pic with the saw off?
 

davidwyby

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It’s not binding in the saw body is it? Can you post a short vid of it happening from the same angle as you pic with the saw off?
90% certain that it is not binding in the handle/tank, nor in the cases.
 

Woodslasher

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A buddy asked me to fix a 61 rancher for him, as it was putting me through hell it developed the same problem with a "sticky" linkage. One of the other problems with the saw happened to be that the carb shafts were worn out and the carb wouldn't hold pressure, so I swapped in a good used Tillotson from a parts saw I'd long sold. Once I did that the linkage problem magically disappeared and I forgot about it until this thread. So, my bet is that it is the carb.
 

MERR6267

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Edit: I just re-read your comment about new hole/weld, good stuff. Below stuff still applies in less binding situations. ;)

I just saw this one, but I had a similar issue on a 670 recently.

Try to lengthen the link bar a little by stretching it out at the bend. When the link is shortened like it is the "angle of attack" is focused near the throttle shaft. Only after enough force is placed on the system will it snap over center and go full throttle. By lengthening the rod a little, the direction of the force is then shifted slightly away from the actual pivot center (throttle shaft) and allows the direction of the force to effectively lengthen the lever arm of the throttle shaft. It's only a small percentage, but that's really all you need.

See the sketch on the right with the 2 lines and the effective arm length (red and black) at the throttle shaft. You'll notice that the black line is slightly longer (better leverage) than the red line.

Without taking all day to sketch and animate this is about the best I can get, lol.
upload_2021-7-1_10-38-0.png
 
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JohnnyBlade

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LOOKS LIKE GAS ON BRAIN OFF INSTANTLY:D
I has a saw on this chassis do the same thing, just not as bad. It was right at the beginning of the pull but would hang just a fuzz off idle. With it on the bench it seemed horrible, running in ur hands it was like the vibrations allowed it to work smoothly. I just wound up sending it! Lol! Now i see what im up against down the road, thanks David:clap2:
 

JohnnyBlade

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Edit: I just re-read your comment about new hole/weld, good stuff. Below stuff still applies in less binding situations. ;)

I just saw this one, but I had a similar issue on a 670 recently.

Try to lengthen the link bar a little by stretching it out at the bend. When the link is shortened like it is the "angle of attack" is focused near the throttle shaft. Only after enough force is placed on the system will it snap over center and go full throttle. By lengthening the rod a little, the direction of the force is then shifted slightly away from the actual pivot center (throttle shaft) and allows the direction of the force to effectively lengthen the lever arm of the throttle shaft. It's only a small percentage, but that's really all you need.

See the sketch on the right with the 2 lines and the effective arm length (red and black) at the throttle shaft. You'll notice that the black line is slightly longer (better leverage) than the red line.

Without taking all day to sketch and animate this is about the best I can get, lol.
View attachment 300262
So this makes sense to me. Now to figure out y its happening. Im gonna guess from holding the saw wide open throughout its life. We also know there isnt a saw that hits the carb stop and the trigger bottoms at precisely the same time. So there is always extra pressure on that throttle rod beyond what its designed for. Ill bet over time the bend in the rod actually develops some memory and that changes that center point like u described.
Just my guess:D
 

davidwyby

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I tried quite a bit of lengthening the link, didn’t help much if at all.
 

huskihl

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Wonder if you have a mix of different case/intake block/carb/shafts from early vs later runs of 162 through 272 platforms. Like on some models, the idle screw access being in the case vs in the cover. Just thinking that if the hole in the carb linkage were 1/16” up or forward that it wouldn’t snap forward like it does. Maybe loosen all the carb/block bolts and rotate the carb up on the left side and retighten the bolts
 

davidwyby

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Took it out to run it a bit today. 20” BnC that was too grabby for noodling. I like the saw, seems to have good power. But on the second cut, I noticed that when I applied pressure, the RPM came up by itself. I think it’s from me fooling with the linkage, maybe bad AV mounts, hopefully not air leak.
 

Ronie

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Have you tried shortening the rod as much as you can and still get full throttle, it seems like the more in line you can get the throttle arm the less down force you would be putting on that pivot point and the smoother it would be? I've had a bunch of those and it's common for them to have a little snap when you first pull the trigger.
 
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