266 issues

[reed1517]

Finally came across a nice 266xp. It ran great but now suddenly does not. Saw has great spark. It’s getting plenty of fuel to the carb. Compression test was 151. It wants to start but can’t keep the combustion going. That’s the best way I can describe it. I’ve tried pulling it over on full throttle. everything on the carb is assembled properly and was successfully pressure tested. I did a base gasket delete with a very mild woodsman port. The intake gaskets are original and seemed to be in good shape. any insights would be greatly appreciated.

 

[singinwoodwackr]

Finally came across a nice 266xp. It ran great but now suddenly does not. Saw has great spark. It’s getting plenty of fuel to the carb. Compression test was 151. It wants to start but can’t keep the combustion going. That’s the best way I can describe it. I’ve tried pulling it over on full throttle. everything on the carb is assembled properly and was successfully pressure tested. I did a base gasket delete with a very mild woodsman port. The intake gaskets are original and seemed to be in good shape. any insights would be greatly appreciated.

Short in the coil lead or ground. Bad coil wire…had that on a 346xp…

 

[xtremez]

2 questions:
it ran great before you did the base delete or after ?
Just the carb was pressure checked or did you press / vac check the whole saw ?

Quick and dirty check, shot of mix directly into the cylinder and hook up inline spark tester

 

[reed1517]

2 questions:
it ran great before you did the base delete or after ?
Just the carb was pressure checked or did you press / vac check the whole saw ?

Quick and dirty check, shot of mix directly into the cylinder and hook up inline spark tester

Before I did the delete
Just the carb.
In-line spark tester was good

 

[xtremez]

Since you had the top end off it’d be worth vac / press check on the saw. What did you use to seal the cylinder ?

 

[reed1517]

Since you had the top end off it’d be worth vac / press check on the saw. What did you use to seal the cylinder ?

Motoseal

 

[Bob Hedgecutter]

So, you had a good saw that ran good, then you played with it and now it dont?
Kind of lends itself to something you did.
How do the gaskets on the intake tract look? That wee hole lining up with the impulse gallery on both sides of the intake block?

 

[ballisticdoughnut]

Finally came across a nice 266xp. It ran great but now suddenly does not. Saw has great spark. It’s getting plenty of fuel to the carb. Compression test was 151. It wants to start but can’t keep the combustion going. That’s the best way I can describe it. I’ve tried pulling it over on full throttle. everything on the carb is assembled properly and was successfully pressure tested. I did a base gasket delete with a very mild woodsman port. The intake gaskets are original and seemed to be in good shape. any insights would be greatly appreciated.

You got compression, fuel, and spark. Sounds to me like you got weak pulse to the carb. Gotta be careful with sealant around the pulse port in the base of the cylinder. You may have partially (or mostly) blocked it with sealant. Only way to know for sure is to pull the cylinder off. They can also leak where the carb bolts up to the intake block. Gotta use the OEM oval gasket between carb and intake. The diamond shaped one in the Tillotson kits don’t completely seal around the pulse port.

 

[Oldtoolsnewproblems]

I spent two months trying to tune my 266 before I figured out the tank vent was clogged. Idled great, no power or revs when I wanted them

 

[Bob Hedgecutter]

I spent two months trying to tune my 266 before I figured out the tank vent was clogged. Idled great, no power or revs when I wanted them

Yeah, but I would consider it unusual for a tank vent to block while the saw was having the top end worked on- the impulse passage- certainly- but not the tank vent.

 

[Bob Hedgecutter]

You got compression, fuel, and spark. Sounds to me like you got weak pulse to the carb. Gotta be careful with sealant around the pulse port in the base of the cylinder. You may have partially (or mostly) blocked it with sealant. Only way to know for sure is to pull the cylinder off. They can also leak where the carb bolts up to the intake block. Gotta use the OEM oval gasket between carb and intake. The diamond shaped one in the Tillotson kits don’t completely seal around the pulse port.

Thats where I would be looking next if the intake gaskets were installed properly- liquid gasket sealer blocking the impulse from the case to intake.

 

[Cantdog]

I concur with the to much sealer goob in the wrong place theory.....easy to do....

 

[Oldtoolsnewproblems]

I think cleaning the saw clogged the vent, either stuff moving around it solvent getting in there. It was right after a top end rebuild that I had the issue and it drive me nuts m

 

[reed1517]

Thats where I would be looking next if the intake gaskets were installed properly- liquid gasket sealer blocking the impulse from the case to intake.

The impulse hole was unobstructed

 

[Bob Hedgecutter]

The impulse hole was unobstructed View attachment 1079352

Yep looks pretty clean all around now- apart from the overspill around the edges.
So how about the intake gaskets?

 

[cookies]

pull the intake, muffler and carb apart looking for silicone...put it back together with anew spark plug and pressure test it.

 

[Squareground3691]

Sounds more and more with impulse line from crank case to carb being somewhat blocked either holes aren’t lined up properly possibly, or bad sealing ,

 

[Oldtoolsnewproblems]

If you dribble a little gas into the carb will it run for a second or no?

 

[reed1517]

If you dribble a little gas into the carb will it run for a second or no?

No.

 

[reed1517]

No.

There’s a tiny bit of smoke coming out the muffler. It wants to keep firing but can’t. I checked multiple times, The impulse is unobstructed.