Ignition Coil Or Gas Issue, I think

[Old2stroke]

With most purge bulbs, the shortest nipple on the bulb is the suction one and it should go to the nipple on the carb. The longer nipple on the bulb should return fuel to the tank and the line from it is usually terminated just inside the top of the tank. There are 2 one-way check valves built into the purge base and they keep fuel moving in only one direction, if they are hooked up backwards, the purge bulb won't pump fuel and the check valves will be pointing in the wrong direction, allowing air from the top of the tank (above the fuel level) to be sucked into the carb. It sounds like yours is hooked up right so I don't understand why there would be air bubbles in it when running. When you press the bulb, can you feel fuel being squished through it and can you see fuel coming out of the return line to the tank? Are you sure the purge bulb is connected to the right fitting on the carb and not to the main fuel supply fitting (the one nearest the pump cover with one central screw) that should have the supply line with the filter connected to it?
I'm suggesting that if you have a problem with the purge, just eliminate the purge, it isn't needed. The easiest way to do this is to remove the purge line from the carb and plug the fitting on the carb and the easiest way to plug it is to get a 1" piece of fuel line, plug one end of it with a piece of nail and push the other end onto the carb purge fitting.

 

[Isidro]

Yes, when I press the bulb I can feel fuel being squished through it. I have not check to see if there is fuel coming out of the return line into the tank. I will check that first thing Friday morning.

First I will check for fuel coming out the line and back into the tank. Then I am going to eliminate/remove the purge line from the purge bulb and plug it but still leave it connected to the carb. I will let you know what happens some time Friday.

Again, thanks for staying with me on issues with my 450. I truly appreciate your advice. I am not cheap enough to buy the right parts when needed but cheap enough not to take the saw into our local small engine shop.

 

[Old2stroke]

Yes, when I press the bulb I can feel fuel being squished through it. I have not check to see if there is fuel coming out of the return line into the tank. I will check that first thing Friday morning.

First I will check for fuel coming out the line and back into the tank. Then I am going to eliminate/remove the purge line from the purge bulb and plug it but still leave it connected to the carb. I will let you know what happens some time Friday.

Again, thanks for staying with me on issues with my 450. I truly appreciate your advice. I am not cheap enough to buy the right parts when needed but cheap enough not to take the saw into our local small engine shop.

You probably don't have a problem with the purge. There is always some air in the bulb and when the engine is started the vibration shakes up the air and makes bubbles that appear to be moving just because of the vibration.
If the engine starts reliably, you have to get it to run at idle long enough to give you time to do some adjusting of the idle mix (L) and the throttle stop screw (speed adjust). Forget the "proper" settings, back the L screw out at least 2 turns and screw the speed adjust screw in at least 2 turns. When the engine starts, it should run too rich and so fast that the chain spins, you can then start to narrow in on the right settings without the damn thing quitting on you. Leave the H screw set at 1 and 1/2 turn out and concentrate on getting a consistent idle.

 

[Isidro]

Ok, I am working through all your recommendations, still have a few to go. It will be interesting on what I find. I agree, it might not be the purge bulb but I will bypass it on one of my efforts and see what happens. Last item will be the L and H screws. I will back them way out, at least 2 turns and then go from there.

Again, thank you and have a safe and fun 4th of July.

I will be in touch, Tony

 

[Isidro]

Not good news, but making progress. The saw still starts up right away but it dies just like before. I have blocked off the purge bulb, put on a new spark plug properly gapped, back the H and L screws out 2 turns and more, increase the idle, and prayed. The only thing connected to the carb I have not checked is the impulse line system. There is a nipple at the bottom of the carb that goes through the flange and into the pipe assy. Its not like my old Stihl 031 and 032 which have a tube connecting to the bottom of the carb and dead ends into the lower main body of the saw. I have not completely inspected my 450 saw's impulse line connections. Everything else related to the fuel and the carburetor has been checked out and/or replaced.

I am sure I address all your comments. As always I am game for more advise and welcome it.

I feel I should move on the coil which checked out ok and maybe buy a new one. Sometimes the coil will check on good on a multimeter but only produces spark intermittently. OEM coils are not that expensive. I do know that the kill switch system is not shorting out the saw. Once I engage it the saw will not start, then I change its position and the saw starts and run for a little while.

Tony

 

[Old2stroke]

Not good news, but making progress. The saw still starts up right away but it dies just like before. I have blocked off the purge bulb, put on a new spark plug properly gapped, back the H and L screws out 2 turns and more, increase the idle, and prayed. The only thing connected to the carb I have not checked is the impulse line system. There is a nipple at the bottom of the carb that goes through the flange and into the pipe assy. Its not like my old Stihl 031 and 032 which have a tube connecting to the bottom of the carb and dead ends into the lower main body of the saw. I have not completely inspected my 450 saw's impulse line connections. Everything else related to the fuel and the carburetor has been checked out and/or replaced.

I am sure I address all your comments. As always I am game for more advise and welcome it.

I feel I should move on the coil which checked out ok and maybe buy a new one. Sometimes the coil will check on good on a multimeter but only produces spark intermittently. OEM coils are not that expensive. I do know that the kill switch system is not shorting out the saw. Once I engage it the saw will not start, then I change its position and the saw starts and run for a little while.

Tony

If that coil is an electronic module, due to the semiconductor package that controls the primary current, there is no valid test you can perform on the primary of the coil with a multimeter. Before getting sidetracked by an unlikely coil fault, you should concentrate on verifying that the impulse that operates the fuel pump is actually getting to the carb. A quick check is to pull the impulse line off the carb and squirt a drop of oil down the line and see that it bumps up and down as you pull the engine over. If the line isn't transparent, just connect a short piece of clear tubing to it. An engine will start with no impulse signal as the choke will operate to fill the fuel chamber in the carb but once the engine is running and the choke is off, it won't continue to run very long with no fuel pump to keep the chamber filled.

 

[Isidro]

Ok, thanks for my new assignment, I am on it. And thank you for the insight on my electronic module coil. I did not know that about there being no valid test.

I will keep you posted, Tony

 

[Isidro]

Ok, I got a transparent line connected to the impulse line, put some oil down it, and pulled the engine over. The oil in the line which I could see clearly did not bumps up and down as I pulled the engine over. There was only a slight rise and fall, ever so slightly. In time the oil did drained down and back into the engine. There was no real up and down oil movement in the clear tube while pulling on the started cord.

The impulse line connects to the bottom of the carb but on the other end it attaches to a plastic plate. Then on the back side of the plate there is an opening that is ringed with a gasket that seals both the impulse line opening and above that carb barrel opening to the cylinder opening. There are a lot of flat surfaces that press on the gasket unit to make, hopefully, a good seal. This saw does not have a impulse line from the carb to a port, hole, in the lower section of the cylinder like other saws. The plastic plate with a gasket that really makes the seal. Both the impulse line and the gasket looked very good. I put a very little amount, a film, of industrial silicone on the gasket.

I installed a new cylinder, piston, and rings. There is compression but clearly the cylinder, piston, and rings have not completely seated yet. To me it does not seem to be sucking hard enough to move gas into the carb. But I have never tried something like this so I have no reference point. I could just buy a new plastic plate with the gasket imbedded into it. It is call the intake inlet pipe manifold and its less than $10.00. The impulse line, two rubber boots, gasket, and plate make up this unit.

Ever grateful, Tony

 

[Isidro]

And I checked, there is no blockage in the impulse line either within the carb or into the crank case.

Tony

 

[billyboy]

Not good news, but making progress. The saw still starts up right away but it dies just like before. I have blocked off the purge bulb, put on a new spark plug properly gapped, back the H and L screws out 2 turns and more, increase the idle, and prayed. The only thing connected to the carb I have not checked is the impulse line system. There is a nipple at the bottom of the carb that goes through the flange and into the pipe assy. Its not like my old Stihl 031 and 032 which have a tube connecting to the bottom of the carb and dead ends into the lower main body of the saw. I have not completely inspected my 450 saw's impulse line connections. Everything else related to the fuel and the carburetor has been checked out and/or replaced.

I am sure I address all your comments. As always I am game for more advise and welcome it.

I feel I should move on the coil which checked out ok and maybe buy a new one. Sometimes the coil will check on good on a multimeter but only produces spark intermittently. OEM coils are not that expensive. I do know that the kill switch system is not shorting out the saw. Once I engage it the saw will not start, then I change its position and the saw starts and run for a little while.

Tony

Not good news, but making progress. The saw still starts up right away but it dies just like before. I have blocked off the purge bulb, put on a new spark plug properly gapped, back the H and L screws out 2 turns and more, increase the idle, and prayed. The only thing connected to the carb I have not checked is the impulse line system. There is a nipple at the bottom of the carb that goes through the flange and into the pipe assy. Its not like my old Stihl 031 and 032 which have a tube connecting to the bottom of the carb and dead ends into the lower main body of the saw. I have not completely inspected my 450 saw's impulse line connections. Everything else related to the fuel and the carburetor has been checked out and/or replaced.

I am sure I address all your comments. As always I am game for more advise and welcome it.

I feel I should move on the coil which checked out ok and maybe buy a new one. Sometimes the coil will check on good on a multimeter but only produces spark intermittently. OEM coils are not that expensive. I do know that the kill switch system is not shorting out the saw. Once I engage it the saw will not start, then I change its position and the saw starts and run for a little while.

Tony

 

[Old2stroke]

And I checked, there is no blockage in the impulse line either within the carb or into the crank case.

Tony

You are on the right track, there MUST be a strong positive and negative pulse coming from the impulse line to operate the fuel pump, sounds like a serious air leak somewhere in the path from the crankcase to the carb.

 

[Isidro]

Yes, I agree there got to be a strong positive and negative pulse. I am going to order a new plate which comes with a impulse line and a new gasket. Also I am going to check and make sure the surface of the cylinder is smooth.

What do think about putting some high temp non-hardening gasket material around the plate gasket, the part that interfaces with the cylinder, just a thin film?

 

[Isidro]

I should pressure test the crankcase body? What are the chance of a leaky cylinder gasket or main bearing and seal? The saw has only been lightly use by a homeowner for some tree clearly after a storm. But he sad it never ran very well or over time did not run at all. That is why he gave it to me.

 

[stihltech]

Without a pressure and vacuum test you are only guessing.

 

[Isidro]

yes, good point. I still need to do both a pressure and a vacuum test to assure my lower body does not have a leak

Thank you, Tony

 

[a. palmer jr.]

Do the pressure test first, it's the easiest and doesn't require much equipment..

 

[Isidro]

ok, will do tomorrow. Thank you

 

[cookies]

This model may have the goofy intake boot/gasket that the impulse section often fails/collapses blocking the impulse off. Pull the carb and intake to inspect the intake gasket/boot

 

[dboyd351]

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

 

[Isidro]

This model may have the goofy intake boot/gasket that the impulse section often fails/collapses blocking the impulse off. Pull the carb and intake to inspect the intake gasket/boot

I agree, I have inspected, put a vacuum on it, the impulse line and it has no leaks but I not sure about it collapsing. This impulse line at the cylinder end is a surface to surface fit, yes there is a gasket around it and its part of the carb plate which is in my option a weak connection. I order a new plate unit which comes with an impulse line and new boots for the carb and choke. I will keep you posted on the out come.

Thank you for responds, Tony