One tough starting Mac 125

[cbfarmall]

Never had a saw start this hard. Only way for me to start it is to put my foot in the handle, grab the recoil with both hands and pull as hard and as fast as I can. Only behaves this way with the switch off. I checked the points and coil gap, flywheel key is intact. I may still have to set the timing back more. I'm worried about breaking things here.

My 084 will start like this if I forget to punch the decomp. I wonder if the decomp is releasing enough compression? I just replaced it and but it doesn't really seem to be doing its job. I'll be tearing the 125 down to thoroughly clean it, so I'll be looking into it further.

Chris B.

 

[ozflea]

The fine passages used by the decompressor could be blocked old mate there's a small allen headed screw that you can remove to clear the hole that accesses the cylinder but be careful from memory this is a certain size which for love or money i cannot remember it's size. As the line of relief is a 90 degree turn.

Pulling the engine over, is it easier with the decompressor in and can you hear the engine venting through the decompressor as there's quite a notable difference in compression.

Or as you said it could be the timing.

Mc Bob.

 

[cbfarmall]

Bob,

Went out and tore the 125 down to the engine. The decomp isn't venting because the passage through the cylinder isn't open. I cannot tell from here, but do you know if that passage goes straight through the cylinder? (I imagine that it is and that is the reason for the allen screw.) Looks like I may have to tear the saw all the way down. Oh well, it needs a good cleaning.

Chris B.

 

[Al Smith]

Yes it does.It is basicaly a right angle hole,thus the 10-25 allen head plugging the hole.
I'll bet that was like trying to rope start a Harley.

 

[cbfarmall]

Al,

I'm no wimp, but I tried starting that thing Sunday and my left hand and arm were sore the next day.

Wrapping the recoil handle with a rag and pulling it over with both hands was the only way to get her going. At that rate, however, parts are going to start breaking.

I'll be drilling that sucker out tomorrow.

10-25 allen??? Don't you mean 10-24?

Chris B.

 

[Al Smith]

Hmm,I guess I did one too many a thread count on the bolt.A typo.
Can you imagine trying to start a high comp 101 Mac,ugh.
I have an sp 81 that has a tedency to come off decomp,on occasion.It will nearly dislocate your shoulder.
I also have a little 6-10 that I set the points with a piece of cellophane to get max advance .That little rascal can out kick them all,and it's only 4.3 cubic inchs.

 

[cbfarmall]

Got it fixed, passage was all carboned up. Now to find the ????ed copper washer! I had a new one but lost that also, along with a bunch of spare screws. Plus the 125 needs a new wrap handle. The one on the saw seemed solid, but when I removed it I found 2 cracks.

Chris B.

 

[TimberPig]

If they're only cracks, i would think any half decent welder could TIG them up for, you, then just grind the beads down, paint and it would be good as new.