BR550 Issues

[Roger]

I have a BR550 that's driving me nuts. The original problem is that it starts immediately after the first or second pull. Runs great for a minute or two, then instantly dies -- like someone pulled the plug wire. Pulling the cord is fruitless (no sign of life) until you wait a 10 minutes or so. Then the process repeats. After pulling the cord about 10 times or more I pulled the plug. It was dry. I squirted some two cycle into the carb throat after removing the baffle. The engine springs to life, runs great and dies.

All this convinced me I had a fuel delivery problem. So, parts cannon time: In separate efforts I replaced all the fuel lines, the primer bulb, fuel filter, rebuilt the carb, and then replaced the carb entirely, and set valve timing. Now the symptoms have changed somewhat. It still starts easily and runs great for a while, then will sometimes sputter and eventually die. Working the throttle as it's in the dying process doesn't help. Eventually it quits. BUT, I can start it again easily until the next event. If it doesn't die outright, it runs great for a time, stutters, and then recovers.

Does ANYONE have an idea about what's going on here? I should add that this blower is 11 years old, is used residentially, and has only about 100-120 hours of accumulated use. I used 89 octane fuel with Stihl 2-cycle oil for about the first half it's years, and then switched to 50:1 pre-mix, alcohol-free in the second half of its life. I treat this thing like my kid. I winterize it properly, and perform all routine maintenance.

Thanks in advance for any insights.

 

[Marshy]

Sounds like a blocked tank vent. The saw operates and draws a vacuum on the tank then starves for fuel. Try running it and when it stalls loosen the gas cap and listen for suction. You could also take the air cover/filter off and look at the fuel lines to see if any are collapsed before you open the gas tank. Then try and restart it.
Otherwise it could be a bad coil and once it warms up it dies. You can check for spark after it dies to rule that out.

Welcome to the site. Maybe you'll get more traffic of this thread was in the chainsaw section. Our all mighty moderator @Jon1212 can determine if it belongs over there.

 

[Roger]

Sounds like a blocked tank vent. The saw operates and draws a vacuum on the tank then starves for fuel. Try running it and when it stalls loosen the gas cap and listen for suction. You could also take the air cover/filter off and look at the fuel lines to see if any are collapsed before you open the gas tank. Then try and restart it.
Otherwise it could be a bad coil and once it warms up it dies. You can check for spark after it dies to rule that out.

Welcome to the site. Maybe you'll get more traffic of this thread was in the chainsaw section. Our all mighty moderator @Jon1212 can determine if it belongs over there.

Thanks for your reply, Marshy. I've been all over this problem for about the last eight weeks. I was bound to forget some things. I did suspect a vent problem and did as you proposed. There's a definite rush sound when the cap is loosened, but I can't tell if it's pressure or vacuum. To eliminate vacuum I have left the cap off, and squirted two cycle fuel into the carb. The engine springs to life and dies (even with the fuel cap off.)

And I assume (perhaps incorrectly) that a bad coil would leave a wet plug behind. This plug has never been wet, and I must have checked it dozens of times during the troubleshooting process. Finally, to cover one more base, I suspected that perhaps the impulse tube was blocked or cracked. It's pristine upon checking it. I'm frankly left with the possibility that this is a compression problem, that the crankcase can't create the vacuum necessary to service the the fuel demands of the engine. However, I don't have a leak-down tester or the fixtures necessary for those tests.

BTW, the BR550 is a Stihl backpack blower. Is this the right thread?

Thanks again.

 

[Roger]

Just to recap this long saga:

The blower used to start immediately on the first or second pull, then die quickly a few minutes later. Subsequent pulls of the starter cord had no signs of life. The plug is dry. Wait 10 minutes or so, it starts again, and the process would repeat. Now, after the parts cannon, things have improved but not corrected. The blower starts immediately and may run longer before acting up. When it does, it either just momentarily sputters (misses) while at high speed, or struggles to stay running and eventually dies. But now when it dies it can be immediately restarted with one pull of the cord. Sometimes after restarting, it will struggle to stay running. Other times, it runs fine.

I'll be ankle-deep in leaves in a couple of weeks and, if this keeps up, it's serviceable at this critical time of the year. But I'm just really perplexed that after throwing so many parts and thought at it that I don't have complete resolution.

 

[Marshy]

Oh, I wasn't picking up on the fact that it's a blower...
The carb has a fine mesh screen in it as a last chance filter for the fuel. Sounds like you should buy a rebuild kit and go through the carb. Have you done that yet?
The tank shouldn't have a vacuum in it at all. Find the vent and try to clean it.

 

[Roger]

I should have clarified initially that the BR550 is a blower. Sorry for that. But, yes, I first rebuilt the carb. The internals appeared perfect. That includes the fine mesh screen that you referenced, which was unblocked, but I replaced it just the same. When that rebuilding failed to resolve the problem I replaced the whole carb. Like I said...Parts cannon. Anyway, each repair attempt seems to have brought me a tiny step closer to resolution without actually getting there. I haven't messed with the vent since the early going, when I think I proved that it wasn't an issue. At that time I opened the cap and still couldn't start the thing until I squirted fuel in the carb throat. It ran and died again even with with the cap off. Now, after all the parts replacements, the next time it stalls I'll open the cap and verify that again.

 

[Stump Shot]

Sounds like you could have a coil going bad, check to see if it can jump about a 5mm air gap and be a nice bright blue color. If it seems puny and light in color, your coil is suspect. If it snaps a bright blue spark it should be good to go. Make sure that the stop wire isn't shorting out somewhere along the way and that the kill switch isn't malfunctioning.
There is also a metal screen in the muffler outlet, if it is plugging up, will give you troubles. If dirty take it out and use a propane torch to burn off the residue. If all this still doesn't work, go back to the fuel system and triple check your double check there.

 

[Marshy]

I've rubbed a fuel line so thin is developed a pin hole and started sucking air. If you haven't replaced the fuel lines yet check them over... Idk, maybe try a new coil.

 

[Lone Wolf]

Ohm the coil at the high tension lead and the hot contact on the body and tell me what you get.

 

[Stump Shot]

Ohm the coil at the high tension lead and the hot contact on the body and tell me what you get.

 

[Roger]

Thanks for all the recommendations. I assumed that since the plug was dry during times when the engine would not start that ignition was not a problem. Nonetheless, I'll look at spark color and strength and measure coil resistance and report back. Thanks again.

 

[Lone Wolf]

Thanks for all the recommendations. I assumed that since the plug was dry during times when the engine would not start that ignition was not a problem. Nonetheless, I'll look at spark color and strength and measure coil resistance and report back. Thanks again.

Did you try running it with the fuel cap loose to by pass the tank vent yet?

 

[Roger]

Did you try running it with the fuel cap loose to by pass the tank vent yet?

Well, each time I replace something (carb, filter, fuel line, etc.) performance improves without making it all the way to fixed. Way back when it would spontaneously die and could not be restarted without a 10-minute wait, I removed the fuel tank cap. That had no affect. Now that the blower is at least limping along I have not gone back to that test. I will, though, and let you know.

Thanks

 

[Lone Wolf]

Well, each time I replace something (carb, filter, fuel line, etc.) performance improves without making it all the way to fixed. Way back when it would spontaneously die and could not be restarted without a 10-minute wait, I removed the fuel tank cap. That had no affect. Now that the blower is at least limping along I have not gone back to that test. I will, though, and let you know.

Thanks

Coil suspect! Get the measurements and post. But also look at the spark cold run it till it dies and look at spark again.

 

[Roger]

I made two coil resistance measurements:

Coil tap to plug wire: 20.27 kΩ
Coil tap to ground: 18.18 kΩ

I checked the strength of the spark. I can't say that the color was blue, but it was a bright white and arcing at least 0.25 in. I also checked continuity of the the kill switch at the coil. No problems there.

The muffler screen is perfect. That's one of the first things I checked.

In the interest of full disclosure, and to keep everyone from chasing ghosts, I ran the blower immediately after making the above tests, and it ran fairly well. It stalled once when I went quickly from full throttle to idle, but I was able to restart it with a single pull. So, maybe its okay, or at least functional. I don't know.

Thanks

 

[Stump Shot]

I made two coil resistance measurements:

Coil tap to plug wire: 20.27 kΩ
Coil tap to ground: 18.18 kΩ

I checked the strength of the spark. I can't say that the color was blue, but it was a bright white and arcing at least 0.25 in. I also checked continuity of the the kill switch at the coil. No problems there.

The muffler screen is perfect. That's one of the first things I checked.

In the interest of full disclosure, and to keep everyone from chasing ghosts, I ran the blower immediately after making the above tests, and it ran fairly well. It stalled once when I went quickly from full throttle to idle, but I was able to restart it with a single pull. So, maybe its okay, or at least functional. I don't know.

Thanks

While I'd like to see what @Lone Wolf has to say about your ohm measurements, but usually a white, pink or even a pale light blue spark is a sign of a coil that is on its way out.

 

[Lone Wolf]

While I'd like to see what @Lone Wolf has to say about your ohm measurements, but usually a white, pink or even a pale light blue spark is a sign of a coil that is on its way out.

Now tomorrow I have to check my BR 600 blower and see.

 

[Lone Wolf]

I made two coil resistance measurements:

Coil tap to plug wire: 20.27 kΩ
Coil tap to ground: 18.18 kΩ

I checked the strength of the spark. I can't say that the color was blue, but it was a bright white and arcing at least 0.25 in. I also checked continuity of the the kill switch at the coil. No problems there.

The muffler screen is perfect. That's one of the first things I checked.

In the interest of full disclosure, and to keep everyone from chasing ghosts, I ran the blower immediately after making the above tests, and it ran fairly well. It stalled once when I went quickly from full throttle to idle, but I was able to restart it with a single pull. So, maybe its okay, or at least functional. I don't know.

Thanks

Coil problems can be intermittent.

 

[Roger]

Wow! Do you guys ever sleep? I really appreciate the fast a great responses to this problem.

I guess, as the saying goes, in for a penny in for a pound, the best approach is to buy a new coil pack. They're fairly inexpensive and would either solve the problem or eliminate ignition from the equation. Up until now I've not considered it since the plug was always dry after trying to restart this thing with many, many pulls. That's what led me down the path of fuel delivery. It might also be that there were multiple problems. I solved the fuel delivery problem by replacing everything up to and including the carb. Maybe now I'm left with a flaky coil pack as the remaining issue.

My plan is to purchase the pack and run this thing until it acts up again. Then replace it. If that doesn't work, I'm left with the jug and crank seals and I'll scrap the beast. I can't find a gap spec for the pack-to-magnet spacing. I'll perhaps use the classic business card approach or measure it before I replace it and use that gap.

Thanks again.

 

[AVB]

While I'd like to see what @Lone Wolf has to say about your ohm measurements, but usually a white, pink or even a pale light blue spark is a sign of a coil that is on its way out.

The color of the spark is dictated what is present in the air. Say you're in Hawaii (salty air) your spark will likely be bright orange due to the sodium content of the air. What matters distance it is able to jump which in direct proportion to voltage available at tip to jump to ground. Here Briggs recommend a gap .166 as good indication of good spark.

Now coil electronic spark advance do fail shifting timing to far. I would suspect if your compression and fuel delivery is good