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

[Oren]

The spark ignition happens at the top of the compression stroke TDC (valves closed). When fuel/air is compressed and fired piston drops to BDC ready for the exhaust stroke (valves open). No?

[M.A. Stewart]

Doesn't a teenage boy become a "two stroke", and a teenage girl a "four stroke", when coupled?

[Steve B]

"Oren" wrote .

No. Spark happens, piston travels to bottom, on the upstroke, the exhaust valve opens, piston comes up, pushes out spent gas, at TDC, intake valve opens, piston drops pulling in air, comes up on compression stroke, and a few degrees BTDC, fires again. One spark per two full revolutions of crank.

Steve

[Oren]

The four strokes of a four stroke engine in living ASCII art

I still call the compression stroke the power stroke --even if firing at BTDC or TDC. I think we get it.

[Stormin Mormon]

The engines I've serviced, the camshaft rotates once for each rotation of the crank shaft. A "stroke" is the motion of the piston, either up or down. I think the confusion may be lingering.

[Stormin Mormon]

Four stroke fires, every second rotation of the crank shaft. You described it pretty much the way I was taught. Same with your description of two stroke.

[Stormin Mormon]

Of course, the same term can refer to different meanings. I think your meaning is also correct.

[Stormin Mormon]

Worth noting. There are actually two sparks, per fire. One spark is at TDC when the gasses are compressed. The second spark is also at TDC at the end of the exhaust stroke. The second spark is wasted, but does no damage.

[Stormin Mormon]

Thanks for the link, that's fun.

If you want to talk with other mechanics, it would be wise to call the compression and power strokes different things. The compression stroke is the one before the power stroke.

Intake Compression Power Exhaust

(in that order)

[M.A. Stewart]

Simple small four stroke engines (lawnmowers etc.) spark every crank revolution. The spark is usually triggered by the crankshaft on small four stroke engines. Larger four stroke engines (automobiles) spark every second crank revolution per cylinder. The spark is usually triggered by the camshaft on large four stroke engines. The camshaft rotates at half the speed of the crankshaft.

[hls]

Yeah, that is what Cuhulin was talking about with his 6 stroke situation.. It gets that way when you get old.

[hls]

Maybe.. You still get twice as many power strokes with a two stroke cycle engine as you do with a four stroke cycle engine, RPM being the same.

[slovenianwood]

I have a Model 358 352180 18" Crapsman chainsaw too and it will not even po p with primer. I have worked on small engines for years and this is the fir st one that stumped me this bad. I did find they had the primer hoses on ba ckwards and I corrected that but it has spark, compression and fuel and it should at least pop. The one last thing to check is the key in the flywheel . If that is sheared the least bit, it will not fire. If that is okay, the saw goes in the dumpster on trash day! I should know better than to buy new Crapsman power tools ..gas or electric!! They have gone way down hill sinc e the old days!!

[bob_villain]

On Wednesday, April 27, 2016 at 4:08:58 PM UTC-5, [e-mail] wrote :

pop with primer. I have worked on small engines for years and this is the f irst one that stumped me this bad. I did find they had the primer hoses on backwards and I corrected that but it has spark, compression and fuel and i t should at least pop. The one last thing to check is the key in the flywhe el. If that is sheared the least bit, it will not fire. If that is okay, th e saw goes in the dumpster on trash day! I should know better than to buy n ew Crapsman power tools ..gas or electric!! They have gone way down hill si nce the old days!!

...I've never heard of a sheared key on a saw. Try a minute spray of carb c leaner down the throat of the cab...to see if it will pop. If it pops, get a carb rebuilding kit for it.

[Paintedcow]

There is a fuel filter in the gas tank. Check it...

[hrhofmann]

You say there is a spark, in the spark plug, or just from the wire going to the spark plug. Have you tried a new spark plug, they do crap out especially in 2-stroke engines which is what I believe you have in your saw.

[gfretwell]

You can get a carburetor for less than $30 and that will fix most of these hard to start, won't run problems.

[Terry Coombs]

I suspect he's fighting an extremely lean condition . Kalifornistan has them set the damn things so lean they'll barely run , the cure is to open up the low and high speed needle valves a bit . The problem is that "they" don't want you to do that , so they make the adjustment screws so you need a special tool to adjust them . My solution (Ryobi weedeater) was to use my dremel with a cutoff wheel to cut a slot for a regular screwdriver in the head . Runs swell now ... but I still can't get the neighbor's Stihl to run right ...

[rolandturner077]

[trader_4]

Yeah, and then tell the friend that you can't fiddle with those carb screws without having the proper keyed tool which isn't so easy to get. And those screws are probably behind plastic caps that once removed, will make it obvious that you screwed with it, so they may not take it back. It's an old thread, but if i got a "new" chainsaw and it's hard to start, I would take it back.