268xp throttle shaft air leak

[Avisagio]

Hi folks. Been working on a 268xp for @Normzilla. I've tried three carburetors now, one aftermarket brand new, 2 good used. Idle will fall with the clutch side up and will rev higher with the flywheel side up. This saw has a new case gasket and seals. In fact it's on its second round of seals because of the symptoms it was having. I figured I damaged the flywheel side seal the first go around so I took them out and very carefully installed another set.

Back to the carbs. I've vac'd and pressure tested and the only leak I had was at both sides of the throttle shaft. I tried o-rings but it didn't seem to help. Anyone have any specific air leak issues with this series saw? I'd appreciate any input.
Thanks, Travis

 

[Agrarian]

You say you vacuum and pressure tested. I'm assuming you are talking about the crankcase/cylinder where you block off the exhaust port and the intake port. If so, the carb throttle shaft is not in the picture so I'm confused how you found a leak there. Regardless, the throttle shaft is not designed to be air tight so there will be some small leakage there. That being said, I've replaced many Tilly throttle shafts that were very worn.

The symptoms sure sound like a seal leak. Did you spin the crankshaft while under pressure and vacuum? What level of pressures and vacuums were you using?

Did you replace the main crankshaft bearings?

 

[redline4]

268 uses an intake block, doesn't it?
Possibly warped or cracked?
@Stump Shot knows a good bit about the 2 series and may have input.

 

[Avisagio]

You say you vacuum and pressure tested. I'm assuming you are talking about the crankcase/cylinder where you block off the exhaust port and the intake port. If so, the carb throttle shaft is not in the picture so I'm confused how you found a leak there. Regardless, the throttle shaft is not designed to be air tight so there will be some small leakage there. That being said, I've replaced many Tilly throttle shafts that were very worn.

The symptoms sure sound like a seal leak. Did you spin the crankshaft while under pressure and vacuum? What level of pressures and vacuums were you using?

Did you replace the main crankshaft bearings?

I pressure tested with and without the carburetor in line. 8 psi and 15 in/hg, without the carb in line while rotating the crank. I too was convinced I damaged a seal upon installation. I've installed at least a hundred seals and only had a prolapse issue one time that was easily noticed and corrected. Using carb cleaner, while the saw is running, I can spray behind the flywheel, clutch, cylinder base and intake block and get no change. Aimed at both ends of the throttle shaft, it will kill the saw immediately. There's no axial or radial run out in the bearings. I'm leaning towards the carburetor, so I just ordered a brand new Tillotson.

 

[Agrarian]

You might remove the throttle shaft to see if it is very worn where it passes through the carb body. Replacing the shaft is a simple operation and new shafts can still be found but ensure the carb body is not also excessively worn. If doing that, you should also check the butterfly and replace it if there are flat spots, a common issue on high use carbs.

Another odd thought - have you checked the pop-off pressure of the carb, doing the test from the filter end of the fuel line? I wonder if there is a small vacuum leak in the line that gets uncovered when the saw is held in certain positions?

Please let us know if the new Tilly carb fixes the issue.

 

[Stump Shot]

268 uses an intake block, doesn't it?
Possibly warped or cracked?
@Stump Shot knows a good bit about the 2 series and may have input.

Yes, the 268 uses an intake block.

Looking like it's passed inspection we'll have to kick back and see what the new Tillotson does for it.
I can say if the shafts are worn it will give run issues, so a new carburetor may do the trick, AM carbs being hit and miss aren't reliable enough to tell the story, unfortunately.

 

[Avisagio]

Yes, the 268 uses an intake block.

Looking like it's passed inspection we'll have to kick back and see what the new Tillotson does for it.
I can say if the shafts are worn it will give run issues, so a new carburetor may do the trick, AM carbs being hit and miss aren't reliable enough to tell the story, unfortunately.

I pulled the throttle shaft and ran an o-ring the linkage side but it didn't change much. I'll update after I install the new carb. Thanks guys.

 

[Michael Rupley]

Had one like that one time. pressurized the crankcase and stuck it in a bucket of water. Bubbles from under the fuel tank. Yep a case gasket slip!

 

[Avisagio]

Had one like that one time. pressurized the crankcase and stuck it in a bucket of water. Bubbles from under the fuel tank. Yep a case gasket slip!

Interesting. I'll try this even though I don't have any discernible leaks.

 

[Normzilla]

Hi folks. Been working on a 268xp for @Normzilla. I've tried three carburetors now, one aftermarket brand new, 2 good used. Idle will fall with the clutch side up and will rev higher with the flywheel side up. This saw has a new case gasket and seals. In fact it's on its second round of seals because of the symptoms it was having. I figured I damaged the flywheel side seal the first go around so I took them out and very carefully installed another set.

Back to the carbs. I've vac'd and pressure tested and the only leak I had was at both sides of the throttle shaft. I tried o-rings but it didn't seem to help. Anyone have any specific air leak issues with this series saw? I'd appreciate any input.
Thanks, Travis

Thanks for all your hard work Amigo. Sure appreciate it.

 

[Normzilla]

The history if this saw friends, is unknown. Got it from a friend who had it gone through by a very good shop I deal with. Over a year and a half ago. Ended up going to buy it from him, my friend. None of us knew it was such a can of worms. Harry thought he had a good running saw he only used a couple times he said. Something happened to it, and it's a mystery. No idea but that thing was blown up.and then some. Brought it to Travis who has been absolutely faithful and diligent, to turn over every leaf and get this saw on the road for me. And it's been truly appreciate, as well as his talent. I knew this saw and all needed was above me. I'm not sure.if my friend is having memory stuff or dementia, who I got the saw from. But don't feel it was neglect at the shop. I think something must have happened to it while my friend Had it before me and he did.not know or remember. But it's been a mystery and old chasing of Gremlins. I'm glad it's in the right hands. Thank you Travis.

 

[Avisagio]

The history if this saw friends, is unknown. Got it from a friend who had it gone through by a very good shop I deal with. Over a year and a half ago. Ended up going to buy it from him, my friend. None of us knew it was such a can of worms. Harry thought he had a good running saw he only used a couple times he said. Something happened to it, and it's a mystery. No idea but that thing was blown up.and then some. Brought it to Travis who has been absolutely faithful and diligent, to turn over every leaf and get this saw on the road for me. And it's been truly appreciate, as well as his talent. I knew this saw and all needed was above me. I'm not sure.if my friend is having memory stuff or dementia, who I got the saw from. But don't feel it was neglect at the shop. I think something must have happened to it while my friend Had it before me and he did.not know or remember. But it's been a mystery and old chasing of Gremlins. I'm glad it's in the right hands. Thank you Travis.

The tough ones are where the valuable lessons are learned. Thanks for your patience, Norm. I'll get this thing figured out!

 

[Normzilla]

The tough ones are where the valuable lessons are learned. Thanks for your patience, Norm. I'll get this thing figured out!

Absolutely agree.