MS440 BB lack of power/breaking up

[CWME]

Hard to explain what it sounds like other that to say the exhaust tone is not steady and it breaks up under load. I had to be careful with the load I put on the saw before a loss of power occured. I also noticed that it will cut out and die at idle now.

I was thinking this could be an issue with the coil? The BB kit has at least 15 tanks of fuel on it probably more.

I am going to pull the muffler to make sure it isn't burning up. I had it set a little rich and it had been running fine. My cousin borrowed it last week and complained when he returned it that it was cutting out at idle.

I gave him my mix and made sure he knew to run only that. I run 91 octane w/ Stihl ultra mix.

Any ideas?

 

[woodyman]

Hard to explain.

Any ideas?

I only know a couple rules for my saws and number 1 is you don't loan out your saws because 90% of the time when they are brought back the way they run is hard to explain.You need to buy a WildThing to loan out.If I did loan my saws out I would be part of the loan.

 

[guff]

i have a philosophy on saws and lending them out as well.....i once loaned my 272 to a guy and gave him the oil to mix with the gas and told him exactly what to do....he brought the saw back and gave me my full bottles of oil.....said he had a buddy who all ready had gas mixed up............weedeater brand oil, #### from the dollar store or those gas station bottles arent the same as my brand of choice...he'll never take another saw.....he hurt my baby and i hope he dies!!!

 

[sawbid]

I would check for air leaks. Under load the vacuum increases and may allow more air to get suck in from any leaks. Run a vacuum test on it if you can...or I could be way off!!

 

[CWME]

I only know a couple rules for my saws and number 1 is you don't loan out your saws because 90% of the time when they are brought back the way they run is hard to explain.You need to buy a WildThing to loan out.If I did loan my saws out I would be part of the loan.

Valid point for the guy next door but my cousin has been running saws as long as I have. He stopped running the saw when he thought it wasn't right. Doubt he could have done anything to cause the issue. He was runing my fuel to boot. The saw was rode hard and put up wet when i got it. Been putting her back together a piece at a time.

 

[CWME]

Pulled the mufler and everything looks mint. It has a nice light brown color all over the inside of the mufler. Not burning it up at least.

I have been looking for the stuff to put together a vac test kit. Haven't got there yet.

 

[oscar4883]

Pulled the mufler and everything looks mint. It has a nice light brown color all over the inside of the mufler. Not burning it up at least.

How did the piston look though? If it is not racing at all it might not be an airleak. Kinda sounds like it is starving for fuel. Does it break up all the time or only when hot? The problem sounds like it started to happen suddenly. Maybe some junk got into the carb and is causing it to starve for fuel. When it cuts out at wot does it die or just sputter? Whe it dies at idle next time check for spark. I kinda think there is a fuel issue though. At the very least pull the carb and spray some cleaner through the needle holes. See what happens. If not it might be a good idea to re-build the carb and replace the fuel line and filter.

 

[woodyman]

How did the piston look though? If it is not racing at all it might not be an airleak. Kinda sounds like it is starving for fuel. Does it break up all the time or only when hot? The problem sounds like it started to happen suddenly. Maybe some junk got into the carb and is causing it to starve for fuel. When it cuts out at wot does it die or just sputter? Whe it dies at idle next time check for spark. I kinda think there is a fuel issue though. At the very least pull the carb and spray some cleaner through the needle holes. See what happens. If not it might be a good idea to re-build the carb and replace the fuel line and filter.

If everything is tight and you have spark alot of times thats all you need to do,replace lines and rebuild carb.I did have one many years ago that needed a coil.

 

[splitpost]

did you recheck the mixture screws...........some people just can't leave screw slots alone ,makes ya

 

[acguy]

Loaner?

I'm sitting here wondering if I had a 441 BB; would I loan it out?

NOT!!!!

 

[CWME]

How did the piston look though? If it is not racing at all it might not be an airleak. Kinda sounds like it is starving for fuel. Does it break up all the time or only when hot? The problem sounds like it started to happen suddenly. Maybe some junk got into the carb and is causing it to starve for fuel. When it cuts out at wot does it die or just sputter? Whe it dies at idle next time check for spark. I kinda think there is a fuel issue though. At the very least pull the carb and spray some cleaner through the needle holes. See what happens. If not it might be a good idea to re-build the carb and replace the fuel line and filter.

Piston looked brand new, a little carbon on the skirt. I only ran it for about 2 mins to drop a big maple and to find out what he was talking about. Guess I would say it breaks up when hot. It sputters at WOT under heavy load.
Fires right back up when it dies at idle.

I haven't rebuilt the carb yet. I will pick up a kit for that tomorrow afternoon. It already has a new fuel line, impulse line, and filter. Installed that as cheap insurance when I put on the BB kit.

BB kit was installed due to low compression. P+C were just worn out from use no failure like running lean etc.

Should not have mentioned my cousin borrowing the saw, has nothing to do with the issue. He was just the unlucky one to be running it when this issue poped up. Gave him my brand new MS460 to finish his cutting. I trust him 100%.

 

[oscar4883]

Piston looked brand new, a little carbon on the skirt. .

Carbon on the skirt does not sound normal to me but I may be off on that. Would be simple to swap coils between your 460 and this saw to rule that out, but the breaking up and not dieing has me still thinking fuel. I would go thru the carb. Post a pic of the piston if you could. THe carbon issue has me worried some. The good thing is you have a known good saw, the 460, to swap carb/coil with to help with the diagnosis.

 

[Oldsawnut]

Depending on how rich it was set the plug could already be fouled.. Hopefully its that simple... If it was a carb with the limiters I have seen the screws move without them in.. Best of luck