Mccullough Timber Bear Dies after running about ten mins..please help

[mustangwagz]

Well got another saw from the neighbor..Big bulky saw, RUNS great for ten mins..then dies. Doesnt loose spark, just dies... Doesnt make sense? any ideas? i thought maybe carb..but why would it only run for 10 and shut off rather than not run at all?. Help me out guys. Thanks much!!

-Zac :chainsawguy:

 

[Mac_Muz]

Next time open the fuel filler cap and put it right back on, and see it this same even takes place again.

I assume when it quits you have to wait a while before the saw will start again.

 

[mustangwagz]

yah gotta wait about an hour?

 

[Mac_Muz]

Go run it and when it quites pop off the fuel cap and see if it starts right back up. Might be a clogged tank vent. If it is, an hour might be enough time to allow air pressure to equalize... Popping the cap open will equalize it as fast as you can put the cap back on.

 

[mustangwagz]

Excellent idea! i had a homo lite weed wacker that did that too, had like 3 other old tanks layin around with same lid on them and i replaced the lid and solved the problem.. DUH never even thought of that, prolly since it aint gotta prime on it and i couldnt see the bulb bein empty. Good idea man! ill keep ya posted!!

 

[Mac_Muz]

I am a in general engine tech for any engine, so I got no clue where the tank vent is on this specific engine or how it is set up. That part is for you to discover.

If you said i was running this saw at full rpm a long time gang cutting slab wood I would some other ideas... you didn't.

 

[wgrassel]

The tank vent for that saw is a duckbill valve on the cap itself, and is notorious for aging badly and, well, not venting.

 

[wampum]

It could possibly have a split (or hole) in the fuel line(in the tank) It will run great until the fuel gets below the split,and then it will suck air. If after it sits and you add no fuel to the tank,starts up and runs 10 more minutes this is not the problem. But if every time it quits, and you added fuel it could be that simple.

 

[mustangwagz]

ok so i tried running till it stopped, opened tank, and closed it again. Still nothing. tried without the cap, still nothing. Tried choking it and still no go.... SO i tore it apart, dumped all the gas out. plugged the end of the tank, and vaccum guaged the tank. Held vaccum for half hour, dropped 1 psi..which aint bad in my opinon..coulda been guage settling or something i suppose. Checked lines as well, still..only 1 psi drop in thirty mins... So.....next ideas? lol maybe a big hammer or a highwall? lol

 

[heimannm]

If it is not a fuel related problem, check the spark when it gets hot. Some of the older electronic coils would develop an open when hot.

Mark

 

[Old Mac Guy]

Good advice, Mark.
My first thought was "coil"...

 

[mustangwagz]

Exactly my thoughts as well..and not it..imma mechanic as well and cannot figure this thing out.. When it comes to automobiles or quads and stuff, usually no big deal. but with this particular problem..yah...i'm stumped... WHat about for example, when stuff warms up it expands...think maybe something is expanind (for example spacer between carb and head) and letting air pass between?

 

[cuznguido]

Whatever you find, I once had the very same problem with that saw. Thing was fairly new and when it ran it did fine, but never did figure it out. Finally dumped it. I do mean "dumped" it.

 

[sawman2077]

I had a saw do that. It took me 2 days to figure out that after it ran for about 15 minutes the fuel line would ca laps and when the saw was cold it would harden the line up again. Check your fuel line in the tank and if it is soft or squishy replace it and try again.