Mac 640 From Brian

[SkwerI]

Jay, I'd bet that the person who installed the washers wrong had no prior experience working on any chainsaw and was just trying to figure it out. I'd suspect that whatever is preventing this saw from running is a direct result of somebody putting it together incorrectly.

 

[woodworkingboy]

Likely scenario you describe, skwel. An air leak won't remedy anything, unless the air filter was never cleaned and they at least got it to start with the washers in there, but highly unlikely.

 

[GASoline71]

The primer pump was just stuck. I broke it loose with a little light pressure after I pulled the carb out.

Saw runs... but won't stay runnin'. It runs longer than it would with just a shot of fuel into the carb. So it is gettin' fuel. But there is a fuel leak at the carb somewhere. Either the primer pump is leaking, or whoever messed with the carb didn't tighten the lower fuel pump diaphram screws... not sure... will have to pull carb back out to check. So it starts to fill the carb/airfilter chamber with fuel while runnin'. It was almost a 1/2" deep when I shut it off... almost suckin' it back into the carb throat.

I am hoping I don't have to find a carb kit for this carb. They (the kits) are gettin' as rare as hens teeth.

Anyways... it does run, and will be a good saw to tinker with. Thanks again Brian.

Gary

 

[Al Smith]

That flat back carb has a big enough metering diaphragm to run a small motorcycle . If it is a tad stiff try lifting the fuel lever just a tad bit but not too much else that thing will flood in a heart beat .

Once you get it to stay running that diaphragm might limber back up again ,you never know .

I've got one and only one of those carbs on a 250 .I must have dissasembled that peckerwood a half dozen times before I got it right .

 

[woodworkingboy]

Excuse the thread distraction....

Al, do you know of a way to allow a bit more fuel to come out of the carburetor into the cylinder? I have a 242xp that I modded, and bumped the rpms up to 14,500, still with good four stroking. It runs great, but there is a slight hesitation at one point as it climbs up to the peak revs, I think short on fuel. A larger carb would be awesome, if I could find one that would fit. Any ideas to tweak the current one?

Thanks!

 

[Al Smith]

Hmm ,could be several things . I doubt you are over running the carb so that's out .

It could be the transfers aren't allowing enough transfer .They say you need the increased area in the transfers for sustained high speed .To be quite honest about it I have no idea how much of an increase you would need .

Try a tad more fatter on the low needle and see what that does . There is a transitional period as the r's increase where the fuel comes from both needles until the pressure drop is great enough to suck it out of the front jet which is the high speed .

Due to the fact the engine 4 stroke cackles I would say the high speed is putting out enough fuel .

Now ,talking about old Macs .I have the same thing on the old 650 geardrive .That engine sings for an old reed valver .However running nearly open exhaust I have the low speed too rich else it won't idle .The result of that is as the r's come up it does just the opposite as it has to burn off the rich mixture before it can come up to speed . A little hesitation ,no big deal on an antique .

 

[woodworkingboy]

Good idea on fattening up the low speed a tad, worth a try. Thanks.

 

[GASoline71]

Here is the monster with the bar and .404 chain mounted. I did the Tilly HL carb swap to get rid of the Mac "Flatback". It was a bitch getting the sprocket off to flip it over. But I got 'er done. Need to get some files for the .404 chain. It's pretty dull. Vids will be soon!

Gary

 

[SkwerI]

Cool deal, Gary. Was the old .404 chain different than the .404 you buy today? Because the .404 chain on my MS880 uses a 3/16" file, same as 3/8" chain.


oops, I meant 7/32" file.

 

[MasterBlaster]

Slice and dice!

 

[Al Smith]

It might be chipper chain B. That would be the only difference, same file size .

 

[GASoline71]

Been so long since I filed a .404 chain I wasn't sure. Hell if it takes the same as my 3/8" chain... I gots all kinds of files. But it was spittin' nothin' but dust when I tried to make a cut with it.

Gary

 

[Al Smith]

The picture looks like chipper but it's hard to tell .If it is sharpen that stuff all the way down to the tie strap and on soft green stuff it will pull fluffy chips about 2 to 4 inchs long .Looks weird .Rolls them up and spits them out like a wood planer .

 

[woodworkingboy]

Probably the older chain had longer cutters, before the days when it occurred that they could gyp you. I have some have inch chain with cutters that are awesome long.

 

[Ax-Man]

Glad you got it running Gary. I have to diagree with Brian on the file size. I think he made a typing error. If the cutters are anywhere close to new or have only been sharpened a few times the file size is 7/32 th's for .404. This will also work for 3/8ths pitch. About the only time you need a 3/16th's file is when the cutters are about half gone or more. 3/16th's is for .325.

For years a 7/32th's file was used for .404 and 3/8th's on Sthil chain. Now they recommend the 13/64th's for 3/8th's. Brian made a comment awhile back on this little detail. I have to agree with what he said that it is just a marketing thing to get you to buy those 13/64th's files from Sthil. A difference of a 64th's of an inch isn't going to amount to a big difference when it comes to filing a saw chain.

 

[woodworkingboy]

I disagree with Larry who agrees with Brian...

Angles on cutter faces for saw blades are pretty critical for less resistance cutting and clearance that also ties in with heat dissipation, they have it worked out what is optimal. I must assume it's the same for chains. That being said, once you have hand filed a time or two, the file sits lower or higher in relation to the top of the cutter, so I doubt the file size is that critical as the hook angle is going to vary anyway, unless you can file like a robot. Basically I agree too, but only because of the degree of variable that results from hand filing, I guess I'm saying. It gets down to how technical you want to be.

 

[SkwerI]

You're absolutely correct, Larry. I had a brain fart and typed the wrong size.

 

[Al Smith]

Assuming that chain GAS has on that thing is chipper ,it doesn't have much back taper on the tooth . I suppose you could use a smaller file when it gets worn about half way back but I doubt it would help much .

What you would end up with is a smaller gullet that would not hold the amount of chip and it wouldn't cut as fast as a deep one .

I've said before that the chipper was all we had in these parts until some time in the 80's when semi chisel and full chisel appeared .Might sound odd but this is farm country and not timber country .

Of course chipper won't cut as fast as chisel but it's more forgiving about kissing the dirt etc .We got by for years with it but then again we just didn't know any better .

 

[Cut4fun]

Cool deal, Gary. Was the old .404 chain different than the .404 you buy today? Because the .404 chain on my MS880 uses a 3/16" file, same as 3/8" chain.

Thats strange 3/16 , even my 404 stihl file is 7/32 like my 3/8 chain file, for my stihl, oregon, carlton 404 chains.


Never mind I see some else caught it and corrected it too. Brian even said mistake posting wrong info.

 

[GASoline71]

My 7/32" files fit fine... but it's gonna take a little filing to get into the gullet.

Gary

 

[Ax-Man]

Hope your file is sharp that chain needs quite a bit of filing. Is that Homelite chain ?? I see an H in the cutter.

 

[Al Smith]

You could hit it a lick with a Dremel then go back over it with a file if you wanted to .. I can't remember off hand the depth gauges /rakers but 30 thou kind of sticks in my mind .BTW it's 35 thou on 1/2" chipper .You get it sharp that thing will cut .

 

[woodworkingboy]

That is one dirty chain. Give it a kerosene bath and make it purdy again!

 

[Ax-Man]

.035 thou on a depth gauge. WOW!!! It will definately cut. The chips will look like they came from a block plane. I lowered the depth gauges on my 088 with .404 once to .030 once. Never again. It cut fast enough but was way toooo aggresive for me especially for a big saw like that. It took a couple of filings to get it to settle down.

 

[Al Smith]

I was incorrect on that .404 chipper .I just retrieved a NOS loop of 1/2" chipper from my garage still in the Homelite box .404 chipper is in fact 25 thou and 1/2" is indeed 35 thou as per directions on that box .

It would most likely be best to keep it at that 25 thou but keep in mind it's a geardrive saw and will have lugging power like a yoke of oxen .