Hi. I have a Stihl BG55 that is bogging down as soon as I hit the throttle. It will barely rev up and then die. I have replaced the spark plug, carb, fuel filter, air filter and fuel lines (dumped old fuel and added new). I've also checked the spark arrestor and verified that it isn't clogged. What could this problem be? Crank seal? I feel like I'm missing something obvious.
#2
Fish
Have you tried richening up the mixture screws?
#3
PTmowerMech
With a small screw driver, open the low idle screw 1/8 turn. Give the trigger a quick squeeze and release.
I'm not an expert on this, but in small increments like this should solve your problem.
Of course if you have limiters on those H and L screws, you may not be able to adjust it to the best of its ability.
Remember, small increments.
And as I learned today, after each turn, give it about 15 seconds between turns, before squeezing the trigger.
#4
Scrubcadet10
Might need to purchase one those special tool kits on amazon if the mixture screws are those weird heads.
#5
Hammermechanicman
Just to be sure remove the spark arrestor and run it. Better?
Next remove the 2 screws that hold the muffler on and look at the piston. Is there any scoring or is it perfectly smooth?
If piston is good start it with out the muffler. Will it rev up?
If it still runs the same put muffler back on. At this point you should have good compression, clear exhaust. That leaves air fuel delivery or primary compression. Disconnect fuel line from carb and start engine and let it idle till stops. Hold throttle wide open a spray a small amount of flammable carb cleaner or premix into carb and try to start. It should fire up strong for a couple seconds. If it doesn't rev up you have a primary compression or possibly a secondary compression issue assuming you have good spark. Check spark with a spark gap tester to be sure.
If it revs up you have an air fuel delivery problem.
If you have primary or seconday compression problem it is an engine tear down. I have never put crank seals and bearing in a handheld blower but i have had customers junk them for scored piston/cylinder.
Thanks for all the suggestions. I removed the spark arrestor and started it up. It seemed to run better--now it will run for about 30 seconds at WOT and then bog down/die, and is hard to get re-started. I moved the idle speed screws as recommended and no change...any other suggestions? Seems like I'm getting closer but still not quite there.
Update--it was the GAS CAP. Not venting so choking off the carb. Runs great with the gas cap removed so there must be some vent holes that are clogged somewhere? I don't see on the gas cap itself though...any idea?
#9
StarTech
Item 4 is the fuel tank vent.
#10
Fish
The gas cap has no vent, the vent is in this pic, there were a couple different versions.
Actually the 11/23/2019 (23/11/2019 Euro format) IPL lists two different tank vents.
The 0000 350 5800 is the one I showed and then there is the 4203 350 5801 as appears below.
Or at least that is what 2019 IPL shows as the PNs.
