3120 runs without spark!!!!!!!

[AUSSIE1]

A mate has rebuilt a 3120 with an aftermaket cyl kit, nil base gasket @ .025 squish.
Can't get idle down, so tries to kill it by the switch and yep, she keeps running!
I'm calling crank seals/air leak.
He bought this saw with crook P&C.

 

[andrethegiant70]

It has spark. Even when you don't want it. You have a busted on/off switch or you have a continuity problem between the switch and the case.

 

[brncreeper]

Yep, either a bad switch or possibly a bad coil.

I've got a 372 unlimited coil from Bailey's on my bench that did what you described.

 

[madhatte]

Agreed with the above. My old 036 PRO won't shut off properly sometimes, even after wiggling the switch. Usually I kill it by pushing in the decomp.

 

[AUSSIE1]

Yes.
Got all this by phone.
Anyone know which side the low is on as he says it's not marked?

Thanks guy's.

 

[AUSSIE1]

Nope, he reckons he pulls the plug lead and it still runs! :jawdrop:
I think he should do a pressure test.

 

[madhatte]

Nope, he reckons he pulls the plug lead and it still runs!

Whoah. I've never heard of a modern 2-stroke engine dieselling before. I'll be interested to see how this turns out.

 

[wigglesworth]

Nope, he reckons he pulls the plug lead and it still runs! :jawdrop:
I think he should do a pressure test.

sounds like it has a bad hot spot, causing it to deisel. He better check the squish. How much comp?

 

[barneyrb]

He's got a piece of carbon that is getting hot enough to act as a glow plug.

 

[madhatte]

He's got a piece of carbon that is getting hot enough to act as a glow plug.

^
That makes sense.

 

[AUSSIE1]

sounds like it has a bad hot spot, causing it to deisel. He better check the squish. How much comp?

Don't know the comp Wiggs as I don't think he has a comp gauge.
There is certainly something igniting that fuel though.

Yeah recheck squish, pressure test might be a good start.

 

[AUSSIE1]

He's got a piece of carbon that is getting hot enough to act as a glow plug.

Sounds like it does doesn't it, but it's all new only started for the first time.
Apart from a possible high comp issue, there is still the issue of can't get the saw down to an exceptable idle.

 

[brncreeper]

Nope, he reckons he pulls the plug lead and it still runs! :jawdrop:
I think he should do a pressure test.

With just plane gas and 2 stroke oil that's not possible.
A little too much Nitro Methane perhaps?

 

[AUSSIE1]

With just plane gas and 2 stroke oil that's not possible.
A little too much Nitro Methane perhaps?

First I've heard of it.

 

[rbmopar]

Dieseling two stroke

I had an old Arctic Cat Pantera 500 snowmobile that I was riding wide open down the middle of a gravel road after an ice storm put about an inch of ice down. I made it a little over a mile when the belt exploded, and the motor kept running at about 5000 rpm with the kill switch off. I got it to stop on the ice and pulled the spark plug leads off and it kept on running. I had to put my hand over the carb to kill it. In this case I think the whole piston was the hot spot because both pistons were melted when I took it apart. I've sure never had this happen on a saw though.

Randy

 

[barneyrb]

Sounds like it does doesn't it, but it's all new only started for the first time.
Apart from a possible high comp issue, there is still the issue of can't get the saw down to an exceptable idle.

I didn't catch the new part.....alum burr, trash in plug, etc...

 

[AUSSIE1]

I didn't catch the new part.....alum burr, trash in plug, etc...

New cyl and piston kit.

 

[wigglesworth]

I didn't catch the new part.....alum burr, trash in plug, etc...

:agree2: Yep...hot spot somewhere.

 

[AUSSIE1]

:agree2: Yep...hot spot somewhere.

Yeah, a few tests before a tear down is probably in order.

 

[alpinecrick]

I had an old Arctic Cat Pantera 500 snowmobile that I was riding wide open down the middle of a gravel road after an ice storm put about an inch of ice down. I made it a little over a mile when the belt exploded, and the motor kept running at about 5000 rpm with the kill switch off. I got it to stop on the ice and pulled the spark plug leads off and it kept on running. I had to put my hand over the carb to kill it. In this case I think the whole piston was the hot spot because both pistons were melted when I took it apart. I've sure never had this happen on a saw though.

Randy

Dang--and I was happy just to get those Panteras started..........



Casey