Jonsered runs for 1 second

[rcw3586]

Well, go figure. I put the butchered carb back together and back in the saw. Now it fires up and runs perfectly! I'll test it on some wood but now have a brand new one inbound that I just got shipping confirmation on. I'll have a spare for next time. It's still disturbing that I never found the problem and I'm a firm believer that problems that fix themselves always come back.
Roger

 

[Old2stroke]

If that was the body check valve that you removed, saws always works more reliably without it. You will probably find that the primer bulb only sucks air now as the only reason the check valve is there is to enable the primer to function. If the choke is effective in getting the saw started without pulling it over a zillion times, you don't need the primer anyway, it's just a quicker start convenience. I disable a lot of primers by pulling the purge line off the carb, pushing a small ball bearing up the line and then sticking the line back on the carb, keeps the primer permanently out of the picture.
I'm still wondering why the vacuum test on the purge port didn't open the inlet valve, it should have as it now appears to be operating normally. When you had the carb apart, did you carefully clean the tip of the inlet valve and the seat in the carb? Might have been a sticking inlet valve. How much vacuum did you use in the test?

 

[rcw3586]

I was not able to remove the check valve. I just chewed up the edges with my pliers. I used a small piece of tubing to blow and suck on it. It was definitely working to some extent. Maybe I dislodged some debris.
The primer bulb sucks gas just fine now.
I did take extra care to clean the tip of the inlet needle and blasted a bit of compressed air around to clean up the body.
I used all the vacuum that the MityVac could muster - about 25 in Hg.
I also applied all the pressure the MityVac could muster to the inlet nipple but the hoses would blow off before the valve would open.

Anyway, I believe you were on the right track with the check valve not functioning and its at least partially working now.
Roger

 

[a. palmer jr.]

I went out and tinkered with the 025 and it's still doing the same thing. I put it aside until I get back around to it and then I'll just take the thing all apart and see what needs fixed..Right now I'm messing with something just as bad, an MS270 that won't idle. Thought I'd found the problem when I stumbled over the fact that previous mechanic forgot to hook up the impulse hose on one end but it has other problems as well. I usually get the dogs that the other saw people won't work on.

 

[Old2stroke]

Sounds like the check valve sticking shut was the main problem and it could happen again. Do you know if fuel containing alcohol was used, that's the main cause of these things going funny? If you feel like experimenting, just remove it and not bother replacing it, as I mentioned it's only there to enable the purge bulb to work and the saw should run fine without it. Not so with the main jet check valve, it is essential. To remove it, the best way is to tap and thread it for a 4-40 machine screw and use a screw threaded into it to pull it out. Do NOT try to pull it out with the tap bit, it's brittle and if you break it off in the valve you will be in more trouble, just be aware that removing it will destroy it and the purge function will no longer work.
When pressure testing the carb by blowing into the fuel inlet port, it SHOULD hold pressure up to 7-10 psi if the inlet valve is seating properly.

 

[rcw3586]

Sounds like the check valve sticking shut was the main problem and it could happen again. Do you know if fuel containing alcohol was used, that's the main cause of these things going funny? If you feel like experimenting, just remove it and not bother replacing it, as I mentioned it's only there to enable the purge bulb to work and the saw should run fine without it. Not so with the main jet check valve, it is essential. To remove it, the best way is to tap and thread it for a 4-40 machine screw and use a screw threaded into it to pull it out. Do NOT try to pull it out with the tap bit, it's brittle and if you break it off in the valve you will be in more trouble, just be aware that removing it will destroy it and the purge function will no longer work.
When pressure testing the carb by blowing into the fuel inlet port, it SHOULD hold pressure up to 7-10 psi if the inlet valve is seating properly.

I may experiment with that if/when it breaks again. I.m very curious to see what's inside that check valve and how it works. Your technique of removal will clearly destroy it. Is there any diagram on-line which shows a cross section of one? I'm a retired engineer and love to see how things work.
Ill also experiment more with that inlet valve if it fails again. I want to know everything about how these things work.
All fuel around here has 10% alcohol in it. I've been using a steady diet of it in this saw for 12 years. Unless you have a connection to aviation fuel or buy the quart cans of small engine fuel for about $10 each you're stuck using it.

 

[Old2stroke]

The check valve is real simple, there is just a small round rubbery disc held against an aperture by a sort of cage on the end of the brass fitting. The valve is normally closed but suction on the cage end will lift the disc enough to let fuel flow. Alcohol in the fuel will make the disc expand and become sticky, high air pressure will blow the disc right out of the cage. The problem with the body check valve is you can't get it out without destroying it so it can't be repaired. The main jet valve can usually be punched out without damage and some of us remove the disc, make a new one, stick it back in the valve and press the valve back into the carb. If interested, there's a thread on how to do this. For what it's worth some carbs (zama I think) make the disc out of fibrous material and they last forever.
https://www.arboristsite.com/community/threads/repairing-walbro-check-valves.269276/post-5117319

 

[rcw3586]

Great info! Thanks.

I used the saw a little today. Although it runs fine it is much harder to start now.

Roger

 

[a. palmer jr.]

I'm kinda thinking that my 021 is a tad low on compression so I'm putting it back awhile until I can order and new top end for it, probably an 025 top end. I don't think I can reliably get parts from China right now so I'm not gonna order any parts for a while...

 

[rcw3586]

Got the new Zama carb today. Dropped it in and it starts easily and runs great. Thanks for all your help!
Roger