How do you "tune up" a hard-to-start Craftsman 18" chainsaw

Do you recall the color of the spark? A yellow/orange is a weak spark (bad plug gap or weak ignition).

A bright blue color with a loud "snap snap" is what to look for.

Oh oh. I read warnings about running two strokes too rich or at wide-open throttle. I run it at full throttle all the time (if I don't, it stalls). Is that bad?

Anyway, I figured I'd better google for Poulan carb adjustment procedures:

BTW, I learned in this video that the low and high have H and L stamped on them. Will look for that first.

Bluish yellow. No snapping sound though.

Am watching this video to learn how to adjust the carb:

Doh. I just realized the "L", "H", and "T" embossed on the cover that I first removed indicated the low, high, and ... hmmm ... I guess "throttle" adjustment screws?

Both the "L" and the "H" pin are NOT screws. Clearly they are not designed to be adjusted. Again, this may be a California (smog) thing. To discourage you from touching them, there is a point instead of a screw slot; and they have a housing around them just so you can't easily get to them.

The "T" screw is easy to get to, even with all the covers on as there is a slot in the plastic to allow access. Do you think the "T" is for throttle?

It is not easy to see the crack in the line. Several models of chainsaws have had the problem, and it is not at all unusual from them to go bad within a year.

But the bottom line is to be sure you have fuel and spark, and if either is missing, you have to work backward to locate the problem. Remember the basics...you have to have spark (hot and at the right time), fuel, and compression to have the engine run.

Grand Daddy taught me to check for the color of the spark. A yellow/orange is a weak plug, gap or ignition. Change the gap on the plug first and try again.

A bright blue, that snaps is a strong spark.

(like a gas stove - blue flames are hotter than orange flames)

It was a no go when I tried to start it just now. No catching at all.

If the spark is yellow mostly, how do I get it to be blue? I'll buy a new plug, but, how do I fix a weak ignition?

I just realized that just before it stopped running, it ran really really fast. Of course, I had protective headgear on, but, even then, thinking back, it was running really fast.

I wonder ...

I wonder if I blew the rings somehow.

When I put my finger over the hole after removing the spark plug, and pulled the starter cord, there was only a small puff. Noticeable. But small.

Do you think compression might be the problem?

All small engines have had a solid state/coils for years now. The timing is set by the flywheel key and usually not adjustable. They are usually pretty trouble free. What you can do is squirt some carb cleaner into the carb throat and that should get it to start for just a second maybe two. If it does and you know you are getting gas to the carb then you will have to clean the carburetor. The metering holes are very very small and it doesn't take much to clog them. One side of the carb is the fuel pump. The other side meters the gas to the engine. First I'd spray a little carb cleaner or a little gasoline into the carb and make sure the engine will start and run just a bit. Then the carburetor cleaning. Since it's only a year old the gaskets and diaphragms ought to still be good. The metering holes and jets are very small (emissions control) two strokes are considered dirty burning and the carburetors are made so you can't over richen the mixture which is what you really need at times. Anyway I've gotten small engines to run by priming them directly with gasoline or carb cleaner even WD 40 sprayed into the carburetor throat and if you can just get it to "pop" and run sometimes that will be enough to get things working enough to continue running. The screw that was backed out 8 turns probably doesn't matter since the carbs are now fixed with such metering holes. You will have to make sure those are clear when you have the carb apart spray carb cleaner into all the little holes and use compressed air to blow them out, there is a small screen also but those are usually not the problem. Old fuel is usually the problem it coats things with varnish and gum. You might get this thing running yet. Some of the youtube videos are very helpful.

If the T is for throttle - that may just fix your idle problem.

Is that the screw with the spring? When adjusting a screw, on the carb, count the number of turns it takes to seat the screw. Not tight, but just seated.

Back the screw out shy or past the number you wrote down.

Get it running and adjust a second time...

I would close the gap about the thickness of a match-book cover, trying to get a snappy blue spark.

Try closing the gap a bit.

Oh, when you test a spark plug like this and ground it to the block - always make sure you have a shinny surface. Use good metal and not a painted surface.

Find us the online manual/link for the engine.

You can always try the compressed air trick. If it won't run on compressed air, there could be an internal problem with the piston and rings.

TDD

Be more definitive. Did it puff past you finger/thumb, regardless of how hard you pressed to stop it? If so, that's enough compression.

nb

This is an excellent treatise. It explains a lot, e.g., why I can't find the L and H carb screws (they're pinned apparently). And why the T screw didn't do anything useful.

BTW, I tried to "listen" for the snap of the spark across the gap but you just can't hear it because of the noise made while you're pulling the starter so that snap test will always fail. But, I can "see" the spark easily so I'm gonna assume it's the air:fuel ratio.

I guess it's time to take the carb apart. I have MAF cleaner in stock (xylene) but not carb cleaner, so, I'll have to stop off at the store about

I didn't want to say this but I totally didn't get the compressed air trick. How are you going to COMPRESS the air in the spark plug hole and keep it there? The second you remove the air gun, the air will blow out the open spark plug hole. And, even then, with no spark plug, what's gonna ignite the mixture inside?

I just didn't understnad it at all? Sorry.

No. I could easily hold my thumb on the hole. It puffed like the way you would blow a fly off your wrist.

Of course, it's only a 40cc engine ... so I'm not sure how much compression it should have.

It will have enough to be unequivocably noticeable. Now, this doesnt always mean rings.

All reciprocating (piston) engines are basically air pumps. The characteristics of a two cycle engine allow you to run it on compressed air. You hook an air hose to the spark plug hole, feed it with a steady supply of compressed air, pull the starter cord and the engine will run on the compressed air. The pressurized air is taking the place of the explosion of fuel/air to push the piston down. A two cycle engine exhausts every time the piston goes down which is why the compressed air can be used to run it. When I check a two cycle motor with air, I stick a rubber blow gun tip into the spark plug hole and hold it there. I don't run it for hours, just a minute or so in order to test the ignition for spark output and make sure there are no problems with piston and rings. It's not rocket surgery. 8-)

TDD