Stihl 026 problems after repair

[sawlog1992]

I hope y'all can help me out with this problem. I have an 026 that I have put a Chinese P&C on. Cold compression is 120 pounds. I put a new carb (again Chinese), plug, fuel line and filter on the saw and it only started when I dribbled a little fuel onto the air filter. Once started, it ran fine. I even cut a couple of 4" trees and a few other pieces of firewood with it. Two days (and after about half a tank) of fuel, the saw will start only with the "prime". It responds well to throttling for about 2 minutes. Then it quits, it restarts with prime and runs for only a few seconds. to me it seems like a fuel issue, but I don't know what to check for. Does anyone have any suggestions?

 

[pioneerguy600]

The Chinese carbs are no longer plug and play, one often needs to be a carb specialist to make them work correctly, recently been a rash of non working AM carbs.

 

[Wood Doctor]

Sounds like it might be running lean on the low end and is fuel starved. Try opening up the low speed setscrew an eighth turn and increase the idle a tad. Just a WAG, but likely a starting point for you.

 

[sawlog1992]

a WAG? Well, the last 27 years of my life have been a WAG, so one more is worth a try! Thanks.

 

[pioneerguy600]

Tell us a little more and we may be able to help you get it working, where are the mixture screws set at, like how many turns out now from lightly seated. What condition the fuel lines,filter and impulse line is, have they been checked closely for cracks and tight fitting to the carb and engine barb?

 

[Ozhoo]

Additionally check that the flap inside the air filter is closing on choke. Is it an aftermarket filter? What about the fuel line? Aftermarket lines are known to be too long and kinking. What tank vent are you running?

 

[sawlog1992]

mixture screws: H 2 turns, L 1 3/4 turns
fuel lines and filter: New, no cracks, no kinks
impulse line: old, removed, checked for cracks, reinstalled
air filter: Stihl
tank vent: is the old style, tall, black plastic piece with the screw in the top. https://i.ebayimg.com/images/g/bW4AAOSwo4pYg7bk/s-l300.jpg

Is the screw in the vent meant to be adjusted?

Thanks to all for the help.

 

[pioneerguy600]

mixture screws: H 2 turns, L 1 3/4 turns
fuel lines and filter: New, no cracks, no kinks
impulse line: old, removed, checked for cracks, reinstalled
air filter: Stihl
tank vent: is the old style, tall, black plastic piece with the screw in the top. https://i.ebayimg.com/images/g/bW4AAOSwo4pYg7bk/s-l300.jpg

Is the screw in the vent meant to be adjusted?

Thanks to all for the help.

Metering screws on an 026 should be set at 1 turn out on both H and L to start with, most tune in just a bit less than one turn out, often about 3/4 turn on L and closer to 1 for the H. The tall black vent requires no adjustment, the screw just acts like a grub screw in a piece of line, the threads let air pass slowly around then, there is actually two screws in the tall black vent, one inside and on on top.

 

[Wood Doctor]

I should also say that 120 psi compression is bare bones for a Stihl professional-grade engine. Crank the saw a couple of times cold. Does the saw then hold up if you grab it by the pull cord handle and let it go? Or, does it fall down under its own weight? If it falls, you have low compression and that means it will not be a runner without installing a new top end.

 

[sawlog1992]

I'll try that, Wood Doctor, but I was thought I read elsewhere on the site that new p&c's had to be run for a few tanks for the rings to seat. Seems that I am to expect (hope) for a 10-15 psi increase. Is that correct?

 

[HarleyT]

Why don't you put the original carb back on?

 

[pioneerguy600]

I should also say that 120 psi compression is bare bones for a Stihl professional-grade engine. Crank the saw a couple of times cold. Does the saw then hold up if you grab it by the pull cord handle and let it go? Or, does it fall down under its own weight? If it falls, you have low compression and that means it will not be a runner without installing a new top end.

A lot of he AM P&C sets don`t make very good compression mostly due to the excessive squish area, seen many that was only making 130 lb , however compression can be increased by either deleting the base gasket or using a thin one and sealant or go whole hawg and cut the base some.

 

[sawlog1992]

I haven't abandoned the project, in fact, I have pulled the cylinder off for a do-over. I also managed to strip the decompression hole. Looks like a helicoil is in my future.While I am this far, I am going to order and replace the impulse line and intake boot. Thanks for all the help. I will post back with updates

 

[sawlog1992]

Just as a follow-up. The saw is back running. I bought a plug for the decompression hole, helicoiled a cylinder bolt hole that the threads broke out of, reduced squish, and readjusted the carburetor. Compression is now about 145 psi. It will crank after a bajillion pulls without prime, or on the second pull with about 4 drops of mix on the filter. Thanks to all y'all for the help.

 

[Okie]

It will crank after a bajillion pulls without prime.

Might take couple of bazillions if it were ran out of gas. Helps build muscle cranking mass. Sounds more like some of the Poulans I've encountered. I prime them through the muffler.

So either the choke is not working properly or the carb has a weak pump or carb also receiving a weak pulse???

Did you try the original carb?

You callin it good enough for ya?

 

[sawlog1992]

I can't find my original carb.

May be a weak pulse. Anyway easy way check that? Or just replace the impulse line?

The bazillion pulls are only requisite when it's cold.

Not sure if its good enough for me yet, lol

 

[HarleyT]

Look at the choke.

 

[Wood Doctor]

Look at the choke.

Good point. The choke flap may not be closing and thus not setting up the pumping action needed to draw the required fuel into the carb. This is typical because of the reliance on the air filter to supply the choke. I've often thought that was a goofy design and it's not even easy to tell if it's working right.