Saw fattens up as you run it?

[Gunn]

hey guys I'm looking for idea what's causing this.

Jonsered 670
Cold start saw runs as it should for a few moments at 12.5k rpm. Then it gradually fattens up and goes from 12.5 to 11..to 8k max rpm and won't speed up.

If you lean the carb out further, itll hold rpm for a few moments but just dumps back down to a low rpm.

If you let it sit for a bit it'll rev up like it should but just fatten up again.

Air filter has no affect. I don't have a spare carb to swap out and test.

I haven't tested the tank vent, but it seems like if the vent was failing it would cause the saw to lean out right?

Could the coil be going out? It's got the 2 piece style.

Any suggestions would be most appreciated.

 

[Termitebuffet]

Have you tried another carb ?

 

[Termitebuffet]

Have you tried another carb ?

Sorry I just saw you don't have a spare .I'd try another carb or kit that one ...

 

[merc_man]

Carb is my guess too.

Sent from my SM-J320W8 using Tapatalk

 

[huskihl]

Have you counted the # of turns out on the screws? On mine, the H screw backs out on its own. Needs a stiffer spring. A carb from a 272 or 268 may be more readily available for testing. Hi idle won't work though

 

[backhoelover]

i have a saw that was doing that one time. i tested for days trying to figure it out. come to find out the seals would start leaking around 6000 rpms. i used a drill to spin the motor over. was weird

 

[BuckthornBonnie]

Ive had that issue as well. Different carb fixed it. Also changed the plug since it was fouled badly.

 

[Chainsaw Jim]

Either your high screw is rattling loose or you need a new kit in the carb.

 

[Johnmn]

Is it a recirculating tilly or does it have a tank vent? And yes these can richen out from vibration and it can happen fast. It's happened to me a couple times. I have had 5 of these saws and I have had this problem on two of them.

 

[Warped5]

I vote for a crank seal that is warming up and getting more pliable.

 

[Gunn]

It has a new kit and the carb screws were reset.

It was recently rebuilt with new seals etc. It ran good for a while until the neighbor was cutting a stump and it started doing as described.

 

[Gunn]

Is it a recirculating tilly or does it have a tank vent? And yes these can richen out from vibration and it can happen fast. It's happened to me a couple times. I have had 5 of these saws and I have had this problem on two of them.

Non recirculating on this one

 

[Chainsaw Jim]

Probably the oil tank leaking into the crankcase when it gets hot.

 

[backhoelover]

pull the muffler and then put on a spark tester and what you spark make sure it isnt cutting in about out

 

[huskihl]

Probably the oil tank leaking into the crankcase when it gets hot.

Had an 034s do that. I was running 80/90w from a drum for bar oil. There was no guessing what was wrong, given the smell. No mosquitos for awhile though

 

[Mastermind]

Has it got the brass plug on the side of the carb?

 

[Termitebuffet]

Has it got the brass plug on the side of the carb?

The governor? (I said this with a British accent )

 

[huskihl]

The governor? (I said this with a British accent )

Let's just keep politics out of this for now, mmmkaaaayyy?

 

[Termitebuffet]

Let's just keep politics out of this for now, mmmkaaaayyy?

But but Benny Hill

 

[Gunn]

it has the tilly s250a