mac 3818 head scratcher

[SplinterPicker]

I bought a mac 3818 that the former owner said he loaned to his neighbor and it quit running. They replaced the fuel lines ? but still no fire. this is where I step in. I have replaced the internals in the carb, fuel lines primer etc. Still harder than all get out to start ... when it does. It will run for ~ 15 seconds not to full speed and definitely wont idle. I have done

reset carb to 1.5 turns out on mixture needles and no pop they were 4 turns out when I tore into the carb and thats where the best results are acheived.

Spark plug is a light chocolate color

compression test 50#, CAME UP TO 75#+ when i put oil in and rechecked

muffler screen is clear

no scoring in cylinder,examined through intake and exhaust ports

Pushed on ring through exhaust port and it did not seem to move much if at all. This was done after a 36 hr soak with PB penetrating oil.

It tried to start but that was it, tried.

When I did look at the piston / ring through exhaust port seemed to have blackish color behind ring land ???

Stuck ring ??? THIS IS WHAT I AM LEANING TROWARDS

IDEAS ? It is currently soaking with seafoam in the cylinder

Thanks in advance

 

[NSEric]

That's not enough compression to run. It may need rings.

 

[HarleyT]

Lines hooked up correctly?

 

[SplinterPicker]

That's not enough compression to run. It may need rings.

Thank you. I was afraid of that. J have another 3818 that is a Strong runner and the compression is way better. Just stumps me that it ran then stopped. I figured for the purchase price the bar and chain would be worth it. Any sites that would be recommended for rings ?

 

[SplinterPicker]

Lines hooked up correctly?

I believe so I have checked on line diagrams and will look at good running saw tomorrow.

 

[WacoDustin]

Was it straight gassed? I'm a noobie when it comes to two cycle stuff. I lean on the folks here for all my rookie questions, though I'm learning.
I'm going out on a limb (haha) and saying the last guy that had it put straight gas in it and cut with it. With those compression numbers, a stuck ring is possible. Was it used by someone who is afraid to rev it? How ugly was the old mix? I would use B12 instead of Seafoam. In my experience with 4 cycle stuff from a weed eater to 8.1 Chevy, seamfoam did nothing except cost money. You need a stronger chemical when working with stuck rings. If you suspect the carb, get a new one from eBay. They are cheapish
Dustin

 

[dougand3]

I doubt you can find OEM rings to buy. My IPL shows 32cc 35cc 38cc Macs all in one IPL. For rings, it says just buy a 38cc shortblock. So, you'll have to pull jug and measure piston diam and ring thickness..probably 1.2mm or 1.5mm. Then buy a ring that fits.

 

[SplinterPicker]

** UPDATE ** My wife came in and said the saw bit her. she hit the bar... I WANTED TO ASK ' what was moving and what was stationary ??" but alas i did not. I went and made sure the bar was well out of the walking path. She got a scratch and a bit of blood was drawn. she must have healing blood .... i went out 4 days ago and started the saw it smoked like crazy and attempted to idle. I was floored ! I have started it for the last 3 days cold with 3 pulls and it is a lot stronger than it was ! I am currently running some sea foam through and it is smoking more than normal. I have cut a 2X4 but no more. No compression test has been taken. It is still blowing my mind, all i can figure out is that the sea foam must have loosened the rings enough to staart working again ???

THANKS ALL FOR YOUR HELP

 

[a. palmer jr.]

Sounds like you might have some oil in the crankcase. You can always drain the saw of all fluids and take the sparkplug out and hang the saw so the sparkplug hole is toward the bottom. Drain the engine overnight then see how she does...

 

[Chainsaw Jim]

They are easy models to learn on, and the lesson you learn is about throwing away a worn out saw to avoid wasting time and money. These things retailed for right at $115 at true value and they're only 50 hour engines. You'll easily match its value rebuilding the carb, replacing fuel lines and filters just to find you're gonna need to eventually fix a leaking oil tank, which is prone to cracking at the threads under the cap. It's poly plastic so there won't be any quick fixes unless you already have a good one to replace it.
Funny thing is they are the least depreciating models you'll find if you don't consider rare collectibles. In good running condition these things still sell for 100-120, but the only way to make any profit is by getting enough of them free and building a good runner within one hours time.

I think this is the most I've ever typed in one post. I'm calling my doctor, lol.