Will a chainsaw run without the Exhaust/Muffler?

[CFOD]

To further add...

Have you verified the choke butterfly works.
The H and L jets are at factory settings.
Why no muffler? Some motors like to see some back pressure, not sure if needed with your motor.
Piston installed correctly in the right direction.
Tried old coil for elimination.
Proper sparkplug, gapped correctly.
Do you have a decompression valve, if so not stuck open.
Check timing to see if flywheel key is not sheared.

List can go on and on......

Yes
Yes
I have an exhaust now, used from ebay
Yes
Yes
Yes
Don't know what a decompression valve is
Not sure how to check timing

 

[CFOD]

New piston, carb rebuild and coil, what was the reason you did this work? Was it a running saw or dead for a reason that is carried foward to now.
Carb rebuilt properly with impulse hose connected?
Vacume or pressure leaks?
You should do a proper compression test to see how the piston and rings are sealing.
When you can confirm your repairs you can move forward with other possibilities.

I received the saw not working, had been sat in a shed for many many years, with a few parts missing. Piston was basically missing a chunk so obviously needed replacing but cylinder was in decent condition surprisingly. Can you link me to a guide showing how to do a 'proper' compression test please?

 

[ammoaddict]

I received the saw not working, had been sat in a shed for many many years, with a few parts missing. Piston was basically missing a chunk so obviously needed replacing but cylinder was in decent condition surprisingly. Can you link me to a guide showing how to do a 'proper' compression test please?

Did you put a new ring on the new piston?

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[ammoaddict]

Yes
Yes
I have an exhaust now, used from ebay
Yes
Yes
Yes
Don't know what a decompression valve is
Not sure how to check timing

It probably does not have a decomp valve, bigger saws have them to release some of the compression to make them easier to pull over.

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[CFOD]

Did you put a new ring on the new piston?

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Yeah, of course . And I lined the gap up with the key, and it's not on upside down

 

[giver]

When the piston is at top dead center where are the magnets on the flywheel

 

[giver]

Where do they line up in relation to the case

 

[CFOD]

Where do they line up in relation to the case

Oh, I'll go and check!

 

[ammoaddict]

Yeah, of course . And I lined the gap up with the key, and it's not on upside down

I figured you did, just trying to cover all the bases. It's hard to do diagnose without pictures or see the saw.

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[CFOD]

Where do they line up in relation to the case

This is the flywheel and magnets when the piston is fully extended, just starting to touch the magnet (in green) as it fully extends

 

[giver]

The timing should be good then and if you spray brake cleaner in the spark plug hole it won't even fire?

 

[CFOD]

The timing should be good then and if you spray brake cleaner in the spark plug hole it won't even fire?

Havent tried break cleaner, have tried a teaspoon of 2 stroke mix and im getting nothing. Will try break cleaner tomorrow

 

[giver]

This engine turns counter clockwisethe magnets should be just past not " just starting to touch" are you some how turning the engine backwards? And if not it must be a compression problem

 

[CFOD]

This engine turns counter clockwisethe magnets should be just past not " just starting to touch" are you some how turning the engine backwards? And if not it must be a compression problem

Magnets just go past the ignition coil as the pison goes down. Can you give me any info on compression testing?

 

[PV Hiker]

I thinking the flywheel spins counterclockwise also. Take the nut off the flywheel and look at the shear key if it is still lined up. Since you said the piston had a chunk taken out it could have stopped the motor and sheared the key.

 

[OldMontanaPhart]

I'm just an ol' hack with very little saw motor expertise but a partially sheared key was my first thought, having had that experience before. Had one on a B&S tiller that drove me nuts until I discovered that it was sheared JUUUUST enough to throw the timing off to the point it would not start...

 

[Okie]

Can you answer this question? If a man is talking and there is no woman around to hear him, is he still wrong?

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If I answer your question and woman cannot hear me, the answer is YES. always wrong.
AND if you are talking to yourself, it's OK to answer yourself, BUT when you ask yourself to repeat what you just said, YOU HAVE A PROBLEM.

 

[Okie]

Just some basics:
Now about your question running the saw W/O a muffler.
Yes, you can, BUT just don't run it while cutting any wood or getting it around dirt,
because it also sucks in at the muffler port.
When it starts running and gives promise re-install the muffler and use a gasket.

Just leave the muffler off and see if you can run the piston down enough to dump about 1/2 small spoon of MIXED gas on top of the piston, gently bring the piston up and crank with a wide open throttle and no choke if the existing plug is not wet. If you do not get a promise pop after about 5 pulls you usually have a ign issue. Look at your plug for spark while cranking over with the plug out and grounded good. Try replacing the plug with new, gapped properly. If no go check for timing or weak spark.
If the plug is WET before you start flogging it, let the saw set for about 12 hours with a new plug and try with minimum of choke.
Some saws will flood easily and if it's flooded crank with the throttle wide open and no choke, takes several good STRONG pulls on the rope usually.
I also usually leave the bar and chain off when working on a saws block or if having starting issues after a major take apart.
Make sure the air gap is correct at the magneto and if the flywheel magnet or magneto has been chewed on scrubbing each other you have a suspect magnet/magneto.
I did not read all of the replies to your post so disregard any duplicate info.

 

[Henry E]

I am new to fixing saws. So take this with a grain of salt.

A no tool test of compression is to hold the saw by the starter rope and see how long it takes for the rope to pull out while the saw lowers to the floor.
It should either not lower or is should lower over many seconds. If it lowers quickly or in less then 10 seconds your compression is too low.

You only need 1/4 teaspoon in the cylinder to get it to start. More then that will flood it.

 

[Okie]

I am new to fixing saws. So take this with a grain of salt.

A no tool test of compression is to hold the saw by the starter rope and see how long it takes for the rope to pull out while the saw lowers to the floor.
It should either not lower or is should lower over many seconds. If it lowers quickly or in less then 10 seconds your compression is too low.

You only need 1/4 teaspoon in the cylinder to get it to start. More then that will flood it.

Henry E:
yep, just a little dab of prime at first test.
That seems to be a fair test for chainsaw compression just to see if it MIGHT start. I usually just pull the rope slow up to just right at the compression and get a feel for hard it is to pull through the compression.
BUT:
One I won't ever forget:
A guy brought me two Stihl MS170 chainsaws not running. I pulled one through slow and felt compression. Picked up the other and it would fall when holding the rope handle. I told him that it's got low compression and a parts saw, might can take two and make one.
Long story short, rebuilt the carb on first one, it ran good.
Give the weak compression one a shot of gas into the carb throat, pulled twice and it started and idled for little bit. Removed muffler and looked at the piston and looked great. Long story short, after carb re-build on it ran as good and strong and cut great under load as the first saw.
I told the guy that if the easy crank one quit, don't bring it back to me for repairing just use it for parts. Seen him few months later and he said both saws still running and cutting firewood good.
I never did check compression on either saw, I have two good accurate chainsaw compression gauges but rarely use them unless a saw is hard to start or won't start and the compression feels weak.
Summary: I try not to assume anything and if it's doing it's job good I let it be.