Ms660 big bore. Yeah I know.

[MG porting]

Mine was .018 in stock form

What's it sitting at now or do you still have it?

 

[MG porting]

Sand a bit from band, or run .016 if it’s on the money.

I’ve heard from reliable sources that some old 066 left the factory at .017.

Epoxy the intake and start with classic numbers, 100/120/80. See what you think.

It's right at .016 darn thing runs pretty darn good I'll most likely leave the transfers where there at but was going to raise the intake to see how it will do.

 

[drf256]

I’ve never had any problems with oem decomp valves. In fact, I prefer them.

The small air leak people talk about them having is incomprehensible to me in so far as how it would cause engine harm. It’s above the crankcase.

Once the saws get to around 75cc, I prefer the “smart” button. My need to show off my strength faded 20 years ago for me. In fact, if anyone wants to start a big saw for me I’m more than happy to let them, thank you very much.

It’s generally not the compression or cc that bites ya, it’s the saw firing before TDC. The decomp allows you to get more speed with your pull and not get bitten as often or quickly.

Even on 60cc saws, a decomp that’s there is nice for initial startup after a build with an oiled cylinder. It makes the starter mechanism happier for sure. After that, I never touch it. The saws start better without it being depressed.

 

[Deets066]

What's it sitting at now or do you still have it?

Still have it. It’s my 066 work saw jug. I had it on the race saw while my other jug was getting re-done. It’s been machined at least 3 times now, somewhere between .070 and .080 off the base. Squish remains at .018

 

[mdavlee]

I’ve never had any problems with oem decomp valves. In fact, I prefer them.

The small air leak people talk about them having is incomprehensible to me in so far as how it would cause engine harm. It’s above the crankcase.

Once the saws get to around 75cc, I prefer the “smart” button. My need to show off my strength faded 20 years ago for me. In fact, if anyone wants to start a big saw for me I’m more than happy to let them, thank you very much.

It’s generally not the compression or cc that bites ya, it’s the saw firing before TDC. The decomp allows you to get more speed with your pull and not get bitten as often or quickly.

Even on 60cc saws, a decomp that’s there is nice for initial startup after a build with an oiled cylinder. It makes the starter mechanism happier for sure. After that, I never touch it. The saws start better without it being depressed.

I bought a scored 394. Decomp killed it. Only place it leaked. They ran it long enough that the decomp sucked enough extra air in that it scored but didn’t lock up

 

[huskihl]

I bought a scored 394. Decomp killed it. Only place it leaked. They ran it long enough that the decomp sucked enough extra air in that it scored but didn’t lock up

I get what you're saying. But the saw wouldn't have been four stroking then either. So it wouldn't have been really any different than a cracked impulse line or fuel line. Or slight air leak from somewhere else

 

[mdavlee]

I get what you're saying. But the saw wouldn't have been four stroking then either. So it wouldn't have been really any different than a cracked impulse line or fuel line. Or slight air leak from somewhere else

That’s true. It’s the only one I’ve ever heard of actually failing from the decomp leaking

 

[drf256]

How do you know it wasnt run at too high of an RPM and also, the decomp leaked?

 

[MG porting]

I’ve never had any problems with oem decomp valves. In fact, I prefer them.

The small air leak people talk about them having is incomprehensible to me in so far as how it would cause engine harm. It’s above the crankcase.

Once the saws get to around 75cc, I prefer the “smart” button. My need to show off my strength faded 20 years ago for me. In fact, if anyone wants to start a big saw for me I’m more than happy to let them, thank you very much.

It’s generally not the compression or cc that bites ya, it’s the saw firing before TDC. The decomp allows you to get more speed with your pull and not get bitten as often or quickly.

Even on 60cc saws, a decomp that’s there is nice for initial startup after a build with an oiled cylinder. It makes the starter mechanism happier for sure. After that, I never touch it. The saws start better without it being depressed.

Maybe when I get old I might get smart enough to put a decomp on my Saw's.lol

 

[MG porting]

Still have it. It’s my 066 work saw jug. I had it on the race saw while my other jug was getting re-done. It’s been machined at least 3 times now, somewhere between .070 and .080 off the base. Squish remains at .018

I might take a little off the squish band while I got the jug off to build up the intake but it's happy where everything is at now but never know it might gain a little more poop.lol

 

[MG porting]

Well I had a chance to go and do some fun work on my experiment saw I didn't get to take pictures for the reason I had a short time to get what I wanted to do before I needed to get back on another saw. Now remember this saw without a bass gasket it was .015 - 016 so not getting a bass gasket for it I made one out of printers paper shhhh. Stoled it from the little woman. It was perfect .010 so then I had to take some off the bass a little bit to get the squish at .021 I'm a little more at ease with that. The saw still runs strong so I'll leave it as is ive got a few Saw's that will be put against it here next month and I'm thinking there's one in the group that's going to put the spank on it but it could suprise me.

 

[Nutball]

Yeah, that high heat JB weld is useless. It's like it shrunk while it dried/hardened, and just looked terrible. I was able to pop it out of the exhaust port on the 2 cylinders I tried it in. I think you can mix it and use as much as you need, then re mix it when needed again. It is like powdered steel in some liquid, and it just separated out after a while. Keeping the cap on the bottle should keep the stuff good even though it is useless.

 

[rogue60]

A leaking decomp will never suck in air it's impossible isin't it?.
When is there a strong vacuum above the pistion that it pulls air in through the decomp? I don't get it.

 

[Deets066]

A leaking decomp will never suck in air it's impossible isin't it?.
When is there a strong vacuum above the pistion that it pulls air in through the decomp? I don't get it.

Just ATDC?

 

[rogue60]

Just ATDC?

If piston rings are above exhaust port moving up or down (compression going up and expanding combustion going down) it's always positive pressures with engine running.
I can't see when exhaust or transfers are open at any timing there is ever a way a negitve pressure could pull air in through the decomp it's impossible lol
Does a negitve pressure vacuum ever happen above the piston top in the cycle of the engine?
Sure 4T's will pull air in through a leaking decomp but I can't work out how a 2T chainsaw ever could what am I missing? lol