Ignition Coil Or Gas Issue, I think

[Isidro]

Hello,

I have a Husqvarna 450, lightly used. It starts and run for a "short" while and then dies. Short being defined as 5 to 10 seconds. It idles a short time but once you touch the throttle it dies. I have replaced the carb, replaced the purge ball, gas filter, checked and/or replaced all the rubber hoses. Started the saw with the saw tank cap off, not easy I might add. I have checked the resistance on the coil and its good. I have spark. I have not checked the main seals for leaks, that is next but I am doing a lot prior to going there.

I put a spark plug light on the spark plug and then start the saw. I have spark. After all that I have done the saw still acts like it is flooding once to use the throttle. Just prior to stalling but still running the spark light goes off and the engine stalls. So this is my question - does my issue point to a fuel problem or an electrical problem? It is sort of like the chicken and the egg. What comes first gas not getting to the carb and the engine stops, or no spark from the coil and the engine stops. Gas or electrical, chicken or egg. Coils for this saw are easy to get and not that expensive but prior to making another purchase I thought I would come to my favor place for chainsaw enlightenment.

Now, I could be wrong all my entire line of thinking but I am ready for that. I have stopped crying so just break it to me gently.

Thanks in advance, Tony

 

[av8or3]

I don’t believe your throttle is connected in any way to the coil (ignition) . Barring mechanical interference that might ground the kill switch wire. You have a fuel related problem. The press/vac test you proposed is a good idea. If it passes the press/vac test toss the carb and get another.

 

[Backstage]

If it’s sparking, it’s probably not electric? Check plug gap though. Also remove plug and pull the starter cord while it’s in contact with the cylinder.

He says new carb. Makes me think way out of tune. Try also pulling the tank vent completely off.

 

[Brufab]

Carb leak possibly,

 

[Old2stroke]

When it quits, is the plug wet or dry? Do you have to use the choke every time to get it running? If so, it sounds like the fuel pump is not working, check how the impulse signal gets from the crankcase to the carb.

 

[Isidro]

I don’t believe your throttle is connected in any way to the coil (ignition) . Barring mechanical interference that might ground the kill switch wire. You have a fuel related problem. The press/vac test you proposed is a good idea. If it passes the press/vac test toss the carb and get another.

Thank you for responding. I will work through your suggestions and keep you updated

 

[Isidro]

If it’s sparking, it’s probably not electric? Check plug gap though. Also remove plug and pull the starter cord while it’s in contact with the cylinder.

He says new carb. Makes me think way out of tune. Try also pulling the tank vent completely off.

I have not conferred the plug gap, I will check that first thing tomorrow morning. I did take the tank vent completely off, just did not make that clear in my original post. Thank you, I will keep you posted.

 

[Isidro]

I don’t believe your throttle is connected in any way to the coil (ignition) . Barring mechanical interference that might ground the kill switch wire. You have a fuel related problem. The press/vac test you proposed is a good idea. If it passes the press/vac test toss the carb and get another.

I will soon investigate a press/vac leak. Not looking forward to that effort. Great suggestion regarding the kill switch wire. I need to look closer into that. Thank you, Tony

 

[rupedoggy]

I don't think it is flooding. I think it is going lean. You have not said anything about adjusting the carb or cleaning the small screen inside the carb. speaking of screens is the exhaust screen clear?

 

[John Stryker]

Try a brand new spark plug. It worked for my saw last week when it did this, and the old plug looked fine but obviously it wasn't.

 

[Isidro]

When it quits, is the plug wet or dry? Do you have to use the choke every time to get it running? If so, it sounds like the fuel pump is not working, check how the impulse signal gets from the crankcase to the carb.

The plug is dry. I use the choke every time. Once the engine rolls over I take the choke off and then one or two pulls the engine starts. I will check on the impulse signal pathway. I am not sure. I think once the carb is in place the connection is made, but not sure.

Also, another interesting thing. Once the engine starts and you watch the purge ball there are a lot of bubbles in the chamber. Is that normal? I thought it would just suck gas but air is getting in there too.

 

[Isidro]

Hello,

I have a Husqvarna 450, lightly used. It starts and run for a "short" while and then dies. Short being defined as 5 to 10 seconds. It idles a short time but once you touch the throttle it dies. I have replaced the carb, replaced the purge ball, gas filter, checked and/or replaced all the rubber hoses. Started the saw with the saw tank cap off, not easy I might add. I have checked the resistance on the coil and its good. I have spark. I have not checked the main seals for leaks, that is next but I am doing a lot prior to going there.

I put a spark plug light on the spark plug and then start the saw. I have spark. After all that I have done the saw still acts like it is flooding once to use the throttle. Just prior to stalling but still running the spark light goes off and the engine stalls. So this is my question - does my issue point to a fuel problem or an electrical problem? It is sort of like the chicken and the egg. What comes first gas not getting to the carb and the engine stops, or no spark from the coil and the engine stops. Gas or electrical, chicken or egg. Coils for this saw are easy to get and not that expensive but prior to making another purchase I thought I would come to my favor place for chainsaw enlightenment.

Now, I could be wrong all my entire line of thinking but I am ready for that. I have stopped crying so just break it to me gently.

Thanks in advance, Tony

Additional information to my original post. Another interesting thing to me. Once the engine starts and you watch the purge ball there are a lot of bubbles in the chamber. Is that normal? I thought it would just suck gas but air is getting in there too.

 

[Isidro]

Try a brand new spark plug. It worked for my saw last week when it did this, and the old plug looked fine but obviously it wasn't.

Will do, thank you

 

[Isidro]

I don't think it is flooding. I think it is going lean. You have not said anything about adjusting the carb or cleaning the small screen inside the carb. speaking of screens is the exhaust screen clear?

I adjusted the carb, 1 and 1/4 turn out on both the high and low screws. I just check the spark screen on the muffler. It is surprising clear. I installed a new carb so I have not taking the carb apart to check anything inside it. Not yet any how.

Also, another interesting thing. Once the engine starts and you watch the purge ball there are a lot of bubbles in the chamber. Is that normal? I thought it would just suck gas but air is getting in there too.

 

[Isidro]

Try a brand new spark plug. It worked for my saw last week when it did this, and the old plug looked fine but obviously it wasn't.

I will try a new plug. Thankfully, I am getting a lot of great feed back so I am making changes as I receive info but later today I will get back running the saw to see what happens.

thank you

 

[rupedoggy]

1 1/4 is an initial setting but not necessarily correct in all cases. Turn the high speed to 1 3/4 and try that. You can always go back if no change

 

[Isidro]

Ok, I will go to 1 3/4 and let you know how it goes. Thank you

 

[Smitty Smithsonite]

Like others have mentioned, it sounds to me like a mixture problem. The low speed screw setting is critical for starting and idling. That's always the one I start on first.

Not only because you have to, but it also affects the mixture slightly at higher RPM / throttle settings. All circuits overlap from smallest (L) to largest (H). In other words, at full throttle, you're still getting fuel from the low / pilot circuit mixing in with the high circuit in the venturi. If you lean the low circuit out after the high / main circuit is set correctly, the high circuit will become leaner.

In a situation like this, I will start at a baseline, like 1-1/4 turns out then go out (richer) in 1/4 turn increments until it starts. If it still won't start, I go the other way ... but 9 times out of 10, more fuel is the answer.

 

[Old2stroke]

I adjusted the carb, 1 and 1/4 turn out on both the high and low screws. I just check the spark screen on the muffler. It is surprising clear. I installed a new carb so I have not taking the carb apart to check anything inside it. Not yet any how.

Also, another interesting thing. Once the engine starts and you watch the purge ball there are a lot of bubbles in the chamber. Is that normal? I thought it would just suck gas but air is getting in there too.

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.

 

[Isidro]

Thank you, the short answer is NO, now I am not sure I hocked up the purge bulb correctly. Can I also just switch the two lines around on the purge bulb and start the saw? If I did screw up the install and once corrected I should not see any bubbles in the purge bulb unit? If I still see bubbles then I must an air leak somewhere but where?

It is not clear to me when you say "....plug the end of the line with a piece of nail and then push it back on the carb fitting." It is not clear to me which hose I plug and which one to redirect. Maybe to get it simplified for me; is the purge line the longer of the two lines on the purge bulb and it connects to the longer nipple of the two on the purge bulb? In the part list for the 450 that hose is called the "return hose" and terminates in the gas tank. The short hose from the carb to the purge bulb connect to the shorter nipple on the purge bulb. Right or wrong that is the way I have things connected now and I get bubbles in the purge bulb while the saw is running. Sorry I am struggling so.

Again, thank you for taking the time to respond to my issues, Tony