isacguy
You serious Clark?
So I have used Arboristsite in the past to help with my troubles, and I love coming here when I'm out of ideas to get some help from the collective mind of this amazing place. Having said that I am a little stumped..... I'm one of those guys that hates clogging up sites with posts, so I try to avoid it. I am however at my wit's end with this saw.
I have a MS390 donor saw that needed an engine. It was blown up, and once I got my hands on another one that a tree had fallen on, I thought I was in business. The guy said it ran great, I checked the compression and the piston looked great through the port. I pulled everything apart, cleaned it, rebuilt the carb. Fired it up, tuned the carb and it ran great. Put a 20" bar with a 3/8 x 7 sprocket on and a sharp chain, and this thing fell all over it face. So.....I replace the impulse line, and fuel line, fuel pickup, air filter, and spark plug. No dice, same issue. So then I pull the muffler off and mod it, to make more room for power, I then re tune the carb with a tachometer, still no power. It can't even cut through a 6" hackberry branch. The saw has strong compression, over 155psi for a stock home owner's saw wasn't bad in my opinion. I pulled the carb off and pulled the welch plugs this time, and put it in the ultrasonic cleaner with heat. Still no difference at all. I've played with the carb all day, I've looked and seen where there were all kinds of troubles from other guys, but it doesn't seem to be the issue I have. I finally broke down and bought a leak down testing kit, and the thing holds pressure and vacuum within specs everywhere, BUT it does blow tiny soap bubbles on the flywheel side during the pressure test, so small that it doesn't even register on the needle. I just found out what the soft seal, and the 2 drivers I need will cost from the dealer. Needless to say, I was pretty unhappy ($66.42). Could a little pinhole like that cause it lose so much vacuum that it has no power? I mean it has less power than a MS170. A MS390 should have no problem with this B&C setup, I don't understand what the problem is. It idles great, accelerates great, it doesn't pop, or have erratic idle, or anything else that I would feel would cause it to have any problems, it just has no power at all when you get into the cut after 2 seconds. Any other ideas? I have an old non EPA carb I thought about trying out, but I just don't think it is pulling vacuum hard enough under a load, regardless of the carburetor.
I have a MS390 donor saw that needed an engine. It was blown up, and once I got my hands on another one that a tree had fallen on, I thought I was in business. The guy said it ran great, I checked the compression and the piston looked great through the port. I pulled everything apart, cleaned it, rebuilt the carb. Fired it up, tuned the carb and it ran great. Put a 20" bar with a 3/8 x 7 sprocket on and a sharp chain, and this thing fell all over it face. So.....I replace the impulse line, and fuel line, fuel pickup, air filter, and spark plug. No dice, same issue. So then I pull the muffler off and mod it, to make more room for power, I then re tune the carb with a tachometer, still no power. It can't even cut through a 6" hackberry branch. The saw has strong compression, over 155psi for a stock home owner's saw wasn't bad in my opinion. I pulled the carb off and pulled the welch plugs this time, and put it in the ultrasonic cleaner with heat. Still no difference at all. I've played with the carb all day, I've looked and seen where there were all kinds of troubles from other guys, but it doesn't seem to be the issue I have. I finally broke down and bought a leak down testing kit, and the thing holds pressure and vacuum within specs everywhere, BUT it does blow tiny soap bubbles on the flywheel side during the pressure test, so small that it doesn't even register on the needle. I just found out what the soft seal, and the 2 drivers I need will cost from the dealer. Needless to say, I was pretty unhappy ($66.42). Could a little pinhole like that cause it lose so much vacuum that it has no power? I mean it has less power than a MS170. A MS390 should have no problem with this B&C setup, I don't understand what the problem is. It idles great, accelerates great, it doesn't pop, or have erratic idle, or anything else that I would feel would cause it to have any problems, it just has no power at all when you get into the cut after 2 seconds. Any other ideas? I have an old non EPA carb I thought about trying out, but I just don't think it is pulling vacuum hard enough under a load, regardless of the carburetor.
