2 MS260's 1 good 1bad!!

[Turner Saw]

I recently built 2 Stihl MS260 saws. One for a friend with a tree service and one for me. Both mildly ported and muffler modded. Both have OEM 44.7 cylinders. Two saws same build. The one for the tree service I built first. He loves it. Mine is a totally different story. No throttle response and it flat out dies when it gets in the cut. I thought maybe I may have made a mistake when I ran the timing numbers so for the heck of it I put a stock piston and cylinder on it and changed the intake and fuel and impulse lines while it was apart to be safe. The saw also has new crank bearings and seals. With the stock cylinder I have the same problem! Tried another carb and it didn't help. I can't find an air leak, what am I missing?

 

[RI Chevy]

Maybe the coil?

 

[Turner Saw]

When I first built the saw I did a spark test and it looked good. I'll definitely revisit it though. At this point I'm willing to try anything!

 

[jk14]

OEM fuel line? Aftermarket lines are known to collapse when taxed. How about the spark arrestor screen has that been checked? I'd also try running it without an air filter and see what happens, the choke flap could be pulling closed. Is the carb a known good carb? I'd toss a fresh plug in it for the hell of it. Tank vent possibly.

Just a few ideas. Good luck.

 

[Turner Saw]

OEM fuel line and impulse line. I rebuilt the OEM carb and I tried an aftermarket carb just to rule it out but the OEM carb is ok. Haven't tried it without the air filter. One thing I noticed tonight was the fuel tank was pressurized. I installed a new OEM vent and it's still pushing fuel at the vent and releases it when I open the cap

 

[huskihl]

OEM fuel line and impulse line. I rebuilt the OEM carb and I tried an aftermarket carb just to rule it out but the OEM carb is ok. Haven't tried it without the air filter. One thing I noticed tonight was the fuel tank was pressurized. I installed a new OEM vent and it's still pushing fuel at the vent and releases it when I open the cap

It’s supposed to have some pressure. EPA thing not wanting them venting directly

 

[Nutball]

Maybe the ignition coil is retarded. Try a different one.

Test compression, maybe the decomp plug is bad or 44mm rings were used?

 

[Turner Saw]

Decomp is plugged. I'm going to try another coil. Easy enough to try.

 

[drf256]

Run once without airfilter please. Won’t cost you a thing. Like JK said above, the flap is notorious for being pulled closed. I’ve seen guys go as far as a full rebuild with case split to chase this problem.

Coils are usually all or none, and they fail when hot. Swap out plug either way, asses for change. Make sure the crankshaft key didn’t shear as well.

 

[Basher]

If I am forced to run an AM air filter on these saws they get some dremel work first to get that flap sitting further back away from the carb body. The springs I have seen in them were very strong but others complain of some having weak springs. I have yet to come across a weak spring in an OEM filter but there is always a chance one might.

 

[huskihl]

If I am forced to run an AM air filter on these saws they get some dremel work first to get that flap sitting further back away from the carb body. The springs I have seen in them were very strong but others complain of some having weak springs. I have yet to come across a weak spring in an OEM filter but there is always a chance one might.

I’ve only had an 024 do it once I ported it. Could be the age. Or maybe the springs were weaker on the earlier models

 

[kneedeepinsaws]

Others have suggested your coil, easy place to start. If you can swap it out with your buddy and see.

Falling flat on its face in the cut tells me a fuel delivery problem.
Have you checked out the impulse line, does it have any rtv in it from the cylinder head seal?
Finally check your metering lever and its corresponding parts.

i dont know about your stihl, but i had a husky where the intake block was installed upside down. ive also seen gaskets and diaphragms installed in the wrong order for the metering lever side of the carb.

 

[Flying_Dutchman]

Run once without airfilter please. Won’t cost you a thing. Like JK said above, the flap is notorious for being pulled closed. I’ve seen guys go as far as a full rebuild with case split to chase this problem.

Coils are usually all or none, and they fail when hot. Swap out plug either way, asses for change. Make sure the crankshaft key didn’t shear as well.

A few years back I had an ms460 sheer the flywheel key, and it had these symptoms pretty much exactly. So I second the check out the key idea. Ever since then, I've always used a torque wrench and blue loctite to put flywheels back on [emoji1787]

Sent from my moto g(7) power using Tapatalk

 

[Turner Saw]

Run once without airfilter please. Won’t cost you a thing. Like JK said above, the flap is notorious for being pulled closed. I’ve seen guys go as far as a full rebuild with case split to chase this problem.

Coils are usually all or none, and they fail when hot. Swap out plug either way, asses for change. Make sure the crankshaft key didn’t shear as well.[/QUOTE

It was the air filter! Unbelievable! I wish I would have asked you guys before I tore everything apart!! Oh well at least I have all new OEM fuel lines now. Soon to be getting an OEM air filter!!!

 

[Turner Saw]

I ran the saw without the air filter and it cuts great!

 

[huskihl]

I ran the saw without the air filter and it cuts great!

The engineer that designed that choke probably got his degree from the same school as Phillips, Slotted, and Allen

 

[drf256]

I’ve only had an 024 do it once I ported it. Could be the age. Or maybe the springs were weaker on the earlier models

You’re not that old Kev. Sorry to hear your spring got weak buddy.