Jonsereds Saw line-up/ 90 question

[aroy1234]

Hello all,

Pictured is two of my late grandfathers saws, (621 and 90) and my own 70e that I recently purchased a town over from where I live. The 621 and 70e run superb after rebuilding the carburetors and constantly picking Cantdogs brain (Thanks Cantdog). I recently picked up the 90 from my uncle. He has not used it in many years, telling me that the saw shut off after finishing a cut on a tree. I didn’t try to fire the saw up, instead dove straight into pulling the carb apart. Upon opening it up, I found there was a solid 1/4” of sawdust blocking the screen. Well now I know why it shut off. Let the carb soak and blew all the passages out with air, replaced the fuel filter, and put fresh fuel in the tank. When I went to start the saw, I noticed it would only want to run with the decompression valve pushed in. As soon as I would let go of the valve the saw would die. I removed the valve and burnt off any carbon/cleaned it up and reinstalled it. Has anyone ever ran into something like this before? For reference, I have the low and high screw both set about 1-1/4 turns out.

 

[Cantdog]

Hello all,

Pictured is two of my late grandfathers saws, (621 and 90) and my own 70e that I recently purchased a town over from where I live. The 621 and 70e run superb after rebuilding the carburetors and constantly picking Cantdogs brain (Thanks Cantdog). I recently picked up the 90 from my uncle. He has not used it in many years, telling me that the saw shut off after finishing a cut on a tree. I didn’t try to fire the saw up, instead dove straight into pulling the carb apart. Upon opening it up, I found there was a solid 1/4” of sawdust blocking the screen. Well now I know why it shut off. Let the carb soak and blew all the passages out with air, replaced the fuel filter, and put fresh fuel in the tank. When I went to start the saw, I noticed it would only want to run with the decompression valve pushed in. As soon as I would let go of the valve the saw would die. I removed the valve and burnt off any carbon/cleaned it up and reinstalled it. Has anyone ever ran into something like this before? For reference, I have the low and high screw both set about 1-1/4 turns out.

Did it run normal after you decarbonized the valve?

 

[aroy1234]

Did it run normal after you decarbonized the valve?

No, it did not change anything. Are these valves designed to stay depressed until the compression builds when the saw starts? Because the valve does not stay down unless you hold your finger on it. Attached is a video to show.

 

[Cantdog]

It is supposed to stay down when starting and pop up when it starts..... so something is a miss...

 

[Cantdog]

Take it out and plug the hole and see how it runs

 

[aroy1234]

Take it out and plug the hole and see how it runs

I will source a plug of the correct size and give it a shot. Unfortunately since I wasn’t able to start it before rebuilding the carburetor I do not have a baseline as to where I’m at besides the decompression valve, but it perplexes me how it seemed to want to run with the valve depressed. I’m assuming since the 90 uses the same Tillotson carb as the 621 and 70e that the baseline set point is about 1 turn out on both the L and H screws? I will say that this saw has crazy compression, just about ripped my arm out of my socket trying to get it started. Guess I just have to work out the kinks!

 

[Cantdog]

Yep start up carb settings are the same. That is a puzzler......sounds like it somehow got assembled backwards or something. The 90's do have big compression....the 80's do as well. My 80 pulls a consistant 238lbs and always has every time I tested it. You're up in class with these saws of starting a kick start only Harley......bring it up on compression and give it your best shot!!! Kickbacks can be pretty stunning.....guess that's why the 90 was the first to get the conventional decompression valve.......the 111S had one earlier but was a different rig all together.......you actually had to turn that one off by rotating the button manually.......it didn't pop off like all the rest.

 

[J D]

Could the timing be out?