McCulloch Chain Saws

[heimannm]

2 broke - should go out in the mail tomorrow if I remember to put one in an envelop tonight. I agree with Chris in that I believe it is a carburetor problem. I have a 621 Jonsered that acts the same way, if you keep going for 5 to 10 minutes it finally picks up and runs as it should. That saw mostly sits on the shelf so I have not bothered to go through the carburetor.

Mark

 

[2broke2ride]

I agree, I think I've covered my bases as far as air leaks go. What am I looking for under the Welch plug? Is there a serviceable part under there or am I just looking to clean out any blockage?

 

[heimannm]

The 440 is an older saw and should have the sintered metal "capillary seal". It may take several attempts with carburetor cleaner to make sure it is open through and through. It looks just like the sintered metal breather in the fuel cap on many of the later model large frame saws. Bad photo but the only one I could find.



FWIW - there is little point in vacuum testing a reed valve saw since by design, the crankcase will never operate under a vacuum, the reeds make sure of that.

Not to say the crankcase should be leaky, just that it will never really see a vacuum.

I will have to disagree with Brian about running without reeds, if the reeds are missing there will be no pressure built in the crankcase to push the fuel/air charge into the cylinder and no combustion as a result. I proved this point to myself a few years ago by working on several saws at the same time and managed to put one (D-30) back together without the reeds. I ended up with extra reeds on the bench and a saw that would not fire.



Mark

 

[2broke2ride]

Thanks for the info Mark. I will report back my findings.

 

[Brian Thacker]

I stand corrected. This is a true case reed engine. Most modern 2 strokes just have reeds in the intake and a hole drilled in the side of the piston to let the fuel get into the engine quicker than waiting for the piston to get far enough up the bore to open the intake ports. With that type of setup the reeds can be removed or broken and the engine will still run but not very well as with the reeds. Have had reeds break in a race and still be able to finish the race but very low on power. On a case reed engine the are needed.
But the vacuum is still as necessary as any other 2 stroke motor. It still has to have the vacuum to draw in fuel from the carb.

 

[Brian Thacker]

Man I hate to ask this but... are you sure there is not something restricting between the intake and the exhaust. Is the reed retainer pointed away from the reeds and letting them move freely? I had a guy about two years ago bring me a Suzuki LTR450 to be moded for race. I ported and polished the intake and exhaust, put in 1mm bigger exhaust and intake valves, cams. dyna tune fuel injection tuner, after market exhaust, Bored out the throttle body and put bigger butterfly valve, 14.5:1 piston. He took it to the race that weekend and came back to my shop ranting that I had messed his motor up yada yada yada. It would not rev up either. So I started checking it and he had watched me clean airfilters and saw that on the track with all the dust I would stuff a rag into the intake to keep dust out. He had done the same but he forgot to take the rag out of the intake before he re installed the airfilter. He kind of crawled out of the shop after what he called me. He was not happy. Any way I watched the video again of your saw, when you open the throttle the pitch of the engine barley changes. You can here it kind of start to rev but level out. It really sounds like it is not flowing all the air that it can for some reason. I would think if the main jets were not flowing fuel you would hear the engine start to rev and then lean out and I would think it would quit being that lean, not enough fuel to combust. I could be wrong on that as I have never tried it but I am going to take one of my old 10-10s tomorrow and screw the high all the way in and see how it acts. My thinking is that it would get too lean and quit but I will see in the morning. I have been wrong before. It just sounds like to me that it cannot flow enough air to rev up. The only other time I have saw this was on a 4 stroke that had a CV type carb and the vacuum valve had a hole on the diaphragm and would not raise which would not let it rev up. This is a strange one. It is like the butterfly valve in the carb is not opening but you can see it move in the video.

Brian

 

[Brian Thacker]

I just thought about something. Don't know why I did not think about this before. Start the saw and open the throttle then take some carb cleaner or starting fluid, I know I hate using starting fluid on a 2 stroke but this will show if you are running lean. You will just want to dribble a very small amount into the intake and if it revs up then I bet your main is stopped up.

Brian

 

[2broke2ride]

I agree that it seems like an air flow issue. But it was doing this before i took the reed plate apart to reseal. This actually started doing this after I messed with the metering lever in the carb now that I think of it hmmmm. I've tried hitting the throttle and pushing the primer at the same time and it doesn't seem to help.
Like I said before, I can see the reeds when I remove the carb and if I pull the motor over I can see them flutter open and closed with the piston pulses.

 

[rocketnorton]

I have a micro doin same. haven't checked fw key yet. on those, easy to see its getting fuel. wont rev even w/squirt.

 

[2broke2ride]

So I decided to take the plugs out of my spare carb first to see what I was dealing with. Glad I did because I promptly destroyed the brass screen under the 1" plug. I guess I don't have a spare anymore. Oh well. I am gonna wait till I get the 1" plug then very carefully take the "good?" Carb apart and carefully clean/soak it and hopefully I can get this thing to run right. I don't really want to convert this one to a Tilly because of the different primer linkage. I think it would be a bear to hold down the choke and try to RH start this thing. Plus I don't exactly have a surplus of carbs just laying around so I would need to locate one.

 

[emf123]

OK, I think I can help a little. I have a 550 that I changed the carb to a NOS flatback with choke. So if you want to go to a Tilly, it can be done. You'll need a knob off a saw with a choke, like a 1-42 or something, some linkage, and a dremel. The handles are similar, they're just not machined out for the choke screw. Its just a little slot that locks it into place, not too bad to do. I could maybe take some pics tonight.

 

[ML12]

Picked up these saws this week. First time I bought any saws in the last 5 months.... crazy I know.





So they are a 4-30, 1-72 and what I think is a 790, but it has no decals and an engine block with no paint (replacement block?) the only number is 61209A, does anyone know what it means? It has a flatback and thin ring piston. It also has a loose (quite sloppy) bar stud, what is the best option for fixing that?

 

[2broke2ride]

OK, I think I can help a little. I have a 550 that I changed the carb to a NOS flatback with choke. So if you want to go to a Tilly, it can be done. You'll need a knob off a saw with a choke, like a 1-42 or something, some linkage, and a dremel. The handles are similar, they're just not machined out for the choke screw. Its just a little slot that locks it into place, not too bad to do. I could maybe take some pics tonight.

This doesn't have the straight round buttons. It uses square hinged buttons. That's what makes it difficult. If you watch my video, the part where I show me pulling the trigger it shows the black square oiler and primer buttons.

 

[emf123]

10-4, I watched it but forgot about that. IMO, it sounds like the metering lever is too high, but I think you double checked that. The only case I had where a saw acted like that was on a double eagle 50, zama carb. The little button on the diaphragm that contacts the metering lever was a little taller on the rebuild kit version than the original. I couldn't set the lever low enough, because then the inlet needle wouldn't open at all. My solution was to add another gasket, runs like a champ now.

 

[heimannm]

ML12 - show a photo with the front of the saw in question. A 790 would have an automatic oil pump on the top of the oil tank, can't see from your photo if there is anything there. Here is a view showing the oil pump on my 795 runner.



Mark

 

[ML12]

Thanks Mark! Its got the oil pump, and I looked up the number in the piston/cylinder cross reference chart I have and it lines up with a 790/890. I also have a nice 795.



how does drilling out the bar stud hole and adding a bushing sound? I think that might be the solution to the sloppy stud.

 

[heimannm]

Drilling it out and adding a bushing may be a workable solution. The bar studs (bolts) are pressed through the side of the oil tank and the head is supposed to be held fast by a lockplate. This is from a 440 but the tank for the 790 is exactly the same.



I have what is supposed to be a 797 in the attic with one bolt so wobbled out that I doubt it can be repaired. I have lined up another oil tank so I will be ready if I ever get a chance to work on that one.

Mark

 

[rwoods]

Okay, my MAC friends in search of 24" bars. Two left. http://m.ebay.com/itm/Mcculloch-Spr...%3A4447547115b0aa46949c01dcffffe013%7Ciid%3A3

Note the best offer and free shipping. I got my two on an offer basis. Buy them before I turn into a hoarder and buy the rest of them.

Ron

 

[PogoInTheWoods]

My SP81 had a wallowed out bar stud hole and I used JB to solve the problem. Worked perfectly to fill the space and retain the bar stud.

 

[emf123]

Okay, my MAC friends in search of 24" bars. Two left. http://m.ebay.com/itm/Mcculloch-Sprocket-Tip-Nose-Chainsaw-24-Bar-New-In-Box-P-n-86846-05-375pitch-/152498499288?hash=item23819e6ed8:g:h3cAAOSwAANY5IE0&_trkparms=pageci%3A35d9b1a0-1aed-11e7-84c3-74dbd1801ca6%7Cparentrq%3A4447547115b0aa46949c01dcffffe013%7Ciid%3A3

Note the best offer and free shipping. I got my two on an offer basis. Buy them before I turn into a hoarder and buy the rest of them.

Ron

I got my two as well, 60 each

Eric