Ignition Coil Or Gas Issue, I think

[lone wolf]

Replace the fuel lines too
Could be as simple as a fuel line with a crack or pinhole in it

Pressure test them.

 

[Isidro]

Replace the fuel lines too
Could be as simple as a fuel line with a crack or pinhole in it

I put a vacuum on the fuel line and it held. the line looked really good. I do have an extra fuel line so I might just change it out. Today I am going to focus on pressure testing the saw body, sealing off the carb and muffler. I got to rule that out as the cause for no back pressure to the carb. There is not enough suck to move fuel into the carb while it is running. I do have a leak somewhere that I got to find. At this point I can not let that saw "win" Might end up with a total rebuild which could equal the cost of a new saw but I will learn a lot and it will keep my out of the bars.

 

[lone wolf]

I put a vacuum on the fuel line and it held. the line looked really good. I do have an extra fuel line so I might just change it out. Today I am going to focus on pressure testing the saw body, sealing off the carb and muffler. I got to rule that out as the cause for no back pressure to the carb. There is not enough suck to move fuel into the carb while it is running. I do have a leak somewhere that I got to find. At this point I can not let that saw "win" Might end up with a total rebuild which could equal the cost of a new saw but I will learn a lot and it will keep my out of the bars.

Vac test the impulse port or line and see if it shakes the needle back and forth while pulling it over .

 

[a. palmer jr.]

ok, will do tomorrow. Thank you

I have one to do tomorrow also.

 

[Isidro]

You should not see any activity in the purge bulb once the engine starts. Are you sure it is hooked up right? It is supposed to suck fuel out of the carb and dump it back into the tank. If there is any confusion about the purge, just eliminate it by pulling the purge line off the carb, plug the end of the line with a piece of nail and then push it back on the carb fitting. It's only there to make starting quicker and has no affect on how the engine runs.

Today I pressure tested the saw's body. Blocked the carb side and the muffler side. The pressure is holding at 10 psi for over an hour now. That is good news. Right now all signs point to the impulse lines and connections. Will wait for my new part and then update.

Tony

 

[Isidro]

I have one to do tomorrow also.

good luck

 

[Old2stroke]

I got to rule that out as the cause for no back pressure to the carb. There is not enough suck to move fuel into the carb while it is running.

Not sure what you are thinking is supposed to be happening here. Back pressure to a carb???

 

[Chevboy0167]

This is the carb flange to cylinder connection. That small tube is the impulse tube. It must free of any blockage from one end to the other. Also check for any pin holes or cracks. Pressure and vacuum testing this tube is the best way.

 

[Isidro]

Not sure what you are thinking is supposed to be happening here. Back pressure to a carb???

Yes, I am expecting back pressure to the carb. I do not see any, the saw starts but does not stay running.

 

[Isidro]

This is the carb flange to cylinder connection. That small tube is the impulse tube. It must free of any blockage from one end to the other. Also check for any pin holes or cracks. Pressure and vacuum testing this tube is the best way.

This is the carb flange to cylinder connection. That small tube is the impulse tube. It must free of any blockage from one end to the other. Also check for any pin holes or cracks. Pressure and vacuum testing this tube is the best way.

I order the part that you attached in your reply. I have check my existing unit and I find no leaks when I put a vacuum on that small hose. I think the carb connection to the line is weak and/or the surface to surface connection on the other end of the line is not "seating" well enough to support a vacuum so no fuel is being sucked into the carb. Hopefully, the new part will eliminate either or both those problems and the saw stays running. If not I am really challenged as to what is causing my problem.

Thank you for responding to my posts, I need all the help I can get.
Tony

 

[dboyd351]

Not sure what you are thinking is supposed to be happening here. Back pressure to a carb???

You are not looking for constant pressure back to the carburetor
what you want is a pulse signal - when the piston moves up It sucks a vacuum on the impulse tube and when the piston moves down it pushes of pressure wave into the tube
This back-and-forth pressure causes the rubber diaphragm in the carburetor to pump fuel which is what keeps your saw running

 

[lone wolf]

You are not looking for constant pressure back to the carburetor
what you want is a pulse signal - when the piston moves up It sucks a vacuum on the impulse tube and when the piston moves down it pushes of pressure wave into the tube
This back-and-forth pressure causes the rubber diaphragm in the carburetor to pump fuel which is what keeps your saw running

Yup just put a vac tester on it and it should flutter back and forth.

 

[Isidro]

You are not looking for constant pressure back to the carburetor
what you want is a pulse signal - when the piston moves up It sucks a vacuum on the impulse tube and when the piston moves down it pushes of pressure wave into the tube
This back-and-forth pressure causes the rubber diaphragm in the carburetor to pump fuel which is what keeps your saw running

I agree, will check for that movement with gauge and let you know. Thank you

 

[Isidro]

Yup just put a vac tester on it and it should flutter back and forth.

Yup just put a vac tester on it and it should flutter back and forth.

I still need to hock up a vac tester and see if I get back and forth movement. Tomorrow I am going fishing but I got the rest of the week to check that out. I will let you know what I find out. Thank you, Tony

 

[Isidro]

I installed a new flange and the problem still exist. Monday I am going to focus on the spark and coil. I do not think there is any more I can do related to the fuel delivery system

Wish me luck, Tony

 

[Isidro]

I hope I made a break through. I have no spark at high RPMs. I do have a constant spark at low RPMs. I order a new OEM coil which I hope solves my very frustrating problem. I ran to the ground every gas related component on my saw and nothing. I pulled the pull cord off, connected a trouble light to the spark plug, ran the saw with a drill, and got spark at low RPMs but not at high RPMs. Sure hope a new coil solves my problem. We shall see.

Again, thank you for all your help, Tony

 

[Isidro]

Received and installed the new coil. The saw started right up and remained running. Just need to adjust the carb. I am confident I, we, got my problem solved. The free saw was still a great deal and now I have a few extra parts that in the end were not the issue or bad. I did have a bad coil which I tossed.

Thank you and everyone who waded to help solve my saw issue. Learned a lot and had fun doing it.

Tony

 

[Old2stroke]

Thanks for getting back to us with the solution, too often we never know if any of our advice helped. That's strange behavior for a coil so kind of put it on the "not likely" list, but with the electronic package in modern coils, strange things do happen. Good on you for sticking with it.

 

[cdahl383]

Old thread but useful. I’m going through the same thing with one of my old saws right now. Running goofy and stalling out. Went through the fuel system completely, no air leaks after new crank seals, new points and condenser, etc. Down to replacing the coil now. Hope that’s what my issue is as well.

Thanks for updating this thread with an actual conclusion and solution to the problem.

 

[cookies]

I had 2 saws last year whoop my sorry buttt doing this exact same thing
husky 435, ran 30 seconds and shutoff.. pto crank bearing, crank seals and the case (cylinder seals against the plastic case) were all bad from overheating

Stihl 029 saw had a long rough life would stumble, run lean after 2 minutes
vac tested bad crank seals, replaced them and the bearings and the damn thing was doing the same plus acting lean
replaced coil and plug and the sob started shutting off! set down for 10 minutes in frustration, removed air filter before starting...it would pee a thin hair of fuel from the carb nipple. The fuel hose was leaking! replaced it and it ran like new. I was so mad at that damn thing! everything was bad on it from 30 years of abuse, was told it is used to cut branches on rivers from a boat and they ended up swimming for it more than once!