McCulloch 250 help

[PaulS225]

Hey Everyone,

I have a McCulloch 250 with a Tillotson HL carb. I have been working on the saw fo a while and it has me stumped. I know the carb is good because I put a new carb kit in it and ran it on a Homelite c-72 to eliminate the carb as an issue. The saw has a strong spark and has a lot of compression. The reed valve looks to be in good shape as well. The cylinder wall has light scoring, but thats the only thing I can see wrong with the saw. The saw runs at idle but runs poorly when the throttle is opened up. It doesn't have that clean smooth bark when revved and looses power to the point of stalling when cutting into wood. One thing that I have noticed when trying to tune it is that the saw gets that clean rev once the high jet is turned almost all the way in but then dies because it is starved of fuel. Any suggestions will help.  

[hms11]

I'm not familiar with these saws and carbs but assuming (I know, I know) they have an impulse line to the carb from the crankcase have you checked that for splits or blockages?

[PaulS225]

No impulse line, but after studying the gas cap it's missing a duckbill valve. So I'm wondering if that's causing all of my problems.

[retiredmechanic]

It sounds like your getting to much air that is why you have to run the high in almost to zero I would check the carb Base gasket reed gaskets plenum gasket etc. and make sure the vacuum holes on the gaskets line up question; was the tillotson the original carb for that saw? sometimes also when mounting a carb the base gasket slips out of place  also sometimes the wrong gasket is sold in the kits did you check it with the old gasket and check for small cracks as well in the plenum if someone over torqued the carb at some point it might be cracked the fact that it idles smoth but wont run full throttle tells me the leak is suction draw only so high chances it being a gasket check if it also runs with the choke applied on high speed and high needle set at 1 to 1 1/2 out if it does itis certain it's a leak 

the fuel cap should not change anything mine has been missing for a year it still runs great but it is a 610 it's hard for them not to run 

you also stated minor scratching on the cyl wall so try running a little higher oil concentration in your mix just out of curiosity they might be causing a bit of blow back but doubtful 

[DennisK]

Older 200 & 250's crank seals would go bad, usually made for hard starts.