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Ok guys, I been working on my mac 250 this week and am kind of stuck on the HL carb. I have taken it apart several times now and reset the needle valve lever to the top of the seat. It starts and runs very roughly, always loosing low end tune. The low side ends up being about 2-3 turns out, and according to my semi-accurate tach, gets to 5.5k rpms max and that is only when the high jet is turned all the way in. Up until this past week, those were the settings I found the saw with and have not gotten it to run better with any other. Thoughts? It really runs weird, and won't hold any sort of a tune. Running infinitely rich as there is an excess amount of fuel dripping out of the carb into the air box. I tried looking for some the HL carb rebuild kit threads, but all of the ones I found either were lost in the hack or when the file sharing site went bonkers. I could probably do some more testing to determine the problem, but I'm getting slightly annoyed at this point, and am hoping this will be easier.
 
It sounds like the high adjust is not shutting down as far as it should. You cleaned the carb, what did you use to clean it? What carb is it? Some of the walbro carbs have a check valve in the delivery system of the main and if this is damaged or stuck I bet it would act like you are describing.

Brian
 
The carb is a HL63G. I cleaned it just like I do every other carb, bit of carb cleaner and light compressed air. Where is the check valve you speak of? Looked closely when I had apart and never saw anything.
 
On the walbro's it is built into the body of the carb. I am unfamiliar with the carb that is on your saw. Not sure if it has this or not. Being as old as this carb is, it may need a more aggressive cleaning than you are used to. Old gas can gum things up and can be very hard to get clean.

Brian
 
Brian Thacker said:
On the walbro's it is built into the body of the carb. I am unfamiliar with the carb that is on your saw. Not sure if it has this or not. Being as old as this carb is, it may need a more aggressive cleaning than you are used to. Old gas can gum things up and can be very hard to get clean.

Brian
Click to expand...
Based upon how much the saw was used, I don't think it ever saw more than a couple of tanks of fuel no later than in the mid 60s and has been sitting ever since. The carb looked beautiful when I took it apart which is why I'm confused.
 
Pressure testing the carburetor is a good place to start. The metering needle is all aluminum and there is a rubber seat. It is possible that the needle has a flaw (corroded) or the seat is shot.

What is the compression for the saw? A lot of spit back in the carburetor could be from worn rings or a sloppy cylinder allowing excessive blow by.

Mark
 
heimannm said:
Pressure testing the carburetor is a good place to start. The metering needle is all aluminum and there is a rubber seat. It is possible that the needle has a flaw (corroded) or the seat is shot.

What is the compression for the saw? A lot of spit back in the carburetor could be from worn rings or a sloppy cylinder allowing excessive blow by.

Mark
Click to expand...
I will have to pressure test the carb for sure. I don't have a reliable way to check the compression (wrong gauge), and seeing as the saw is extremely low hours, and I could still being able to see most of the machining marks on the piston, it should be fine compression wise. I figure the spitback is due to so much excess fuel from the carb. Pressure testing carb is up next.
 
Mac&Homelite said:
Ok guys, I been working on my mac 250 this week and am kind of stuck on the HL carb. I have taken it apart several times now and reset the needle valve lever to the top of the seat. It starts and runs very roughly, always loosing low end tune. The low side ends up being about 2-3 turns out, and according to my semi-accurate tach, gets to 5.5k rpms max and that is only when the high jet is turned all the way in. Up until this past week, those were the settings I found the saw with and have not gotten it to run better with any other. Thoughts? It really runs weird, and won't hold any sort of a tune. Running infinitely rich as there is an excess amount of fuel dripping out of the carb into the air box. I tried looking for some the HL carb rebuild kit threads, but all of the ones I found either were lost in the hack or when the file sharing site went bonkers. I could probably do some more testing to determine the problem, but I'm getting slightly annoyed at this point, and am hoping this will be easier.
Click to expand...

If you do need a Tillison HL63 carb rebuild kit you might be able to get them from Stihl (if you have a decent dealer in your area). Some of the older cut-off saws used HL carbs. Part number is 0000 007 1057. But one sticker on the bag I have has a "A" after the number so you might have to have them run both. Price was $30 about 6 yrs ago. Hope this helps you out.
 
I went back into the Tilly HL63 carb tonight and looked over everything. Never pressure tested it as it was getting late and I was feeling lazy. I determined that I must have been bending the wrong end of the metering lever earlier and that what was causing everything to go wonky for me. Will hopefully test tomorrow and report back with success. Worst case is that it still doesn't work and I install the carb kit that I had bought with my other parts for the saw.
 
For anyone interested, I went ahead and ordered a quantity of the full wrap handles for the 10 Series rigid mount saws. I had them make it 2" wider on the left hand side to provide some additional clearance for the starter on LH start models.

This is a direct bolt on replacement for RH start saws and LH start saws with the older type of clutch cover. I will see if the later style of clutch cover can be modified to work with the full wrap and still maintain its structural integrity.

Evidently all of my photos are on the computer at home, for now I will plagiarize a few of Pete's on a 7-10 so you get the idea. The "aftermarket" handles are a bit more squared off like the ones on the CP, SP, and PM anti-vibe saws.

IMG_1400.JPG

IMG_1408.JPG

Mark
 
Has anyone ever ported a large frame mac engine? I have a 1-72 w/ a removable head that needs a rebuild and was thinking that while I had it apart I could do some grinding.

What sorts of things do people do on them? open up the exhaust? raise the transfers? Or are the engines good enough from factory that significant gains can't really be made? I see lots of porting threads on new saws but nothing for the old ones.
 
ML12 said:
Has anyone ever ported a large frame mac engine? I have a 1-72 w/ a removable head that needs a rebuild and was thinking that while I had it apart I could do some grinding.

What sorts of things do people do on them? open up the exhaust? raise the transfers? Or are the engines good enough from factory that significant gains can't really be made? I see lots of porting threads on new saws but nothing for the old ones.
Click to expand...

The kart folks could probably advise - lots of black magic done on MAC kart motors. I don't have a clue of whether any of it worked or not. Ron
 
Been getting ready for the Baraboo Steam and Gas show, plan on running some more saws this year. Ran my Super Pro 81E, Super Pro 125, Super 550, and 1-62 today. Broke the starter rope on the 1-62, and had to put a new sprocket on the S550. Also plan on running a 890 I just got, decent shape, rebuilt the flatback carb (successfully), just waiting on some 'new' old chain ;)
 

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