McCulloch Chain Saws

[Yokosukadweller]

Question to the forumites: My CP/SP 70 saw has a fuel supply issue. I am trying to chase it down now. When firing up normally it starts for a second and then dies. I just opened the carb top and put in a teaspoon of fuel. It immediately started at first pull and idled (too high albeit), but it idled for 6-7 secs until the fuel was used. Doesn't that mean it is the fuel line rather than the carb that is the issue? Or still I have to rebuild that carb? What do you think.

Thanks.

 

[vinnywv]

Likely culprit is the fuel pump diaphragm. Id rebuild the carb. Meaning replace all the gaskets and diaphragms in the carb. Id not replace the welch plugs. Id leave the meter alone too. Just the gaskets and diaphragms. Itll likely pull fuel after that. Sounds like its not able to pull fuel. They get stiff over time. If they cant move then you get no fuel.

 

[Yokosukadweller]

Likely culprit is the fuel pump diaphragm. Id rebuild the carb. Meaning replace all the gaskets and diaphragms in the carb. Id not replace the welch plugs. Id leave the meter alone too. Just the gaskets and diaphragms. Itll likely pull fuel after that. Sounds like its not able to pull fuel. They get stiff over time. If they cant move then you get no fuel.

Thank you @vinnywv , meanwhile I tried with another fuel cap (if the initial one was faulty), and I have checked the fuel line - nothing there. So yes I will to ahead and replace gaskets and diaphragms as you advise.

 

[mogulmasher]

Good call trying a different fuel cap as most have melted/blocked cap vents. Trying running it with cap loose just to be sure since almost any cap with some age to it will not be functioning.

 

[heimannm]

I always remove the metering lever and metering needle and make sure the fuel passage is open. It is not uncommon for the metering needle to be stuck in the closed position if the saw has been setting long enough for the fuel to evaporate and leave a varnish residue behind. Removing the needle also provides a good opportunity to examine the tip more closely to check for any damage that could leak to leakage issues.

While you have the carburetor apart, spray some carburetor cleaner through the fuel passages on the fuel pump side to make sure there are no blockages. I always like to remove the H and L needles as well and spray some carburetor cleaner through each opening to verify that the passages are open to the venturi.

Mark

 

[Yokosukadweller]

Thanks for the info and tips, definitely sounds like I will be rebuilding my first chainsaw carburetor soon.

 

[matt_lamb_160]

Interesting Kevin - the saw appears to have 400 stamped in the block, lined out, and 450 below. Not remarkable the the model changed in production, but I have never heard of a 400 before. Obviously your new saw is quite rare and unique and probable worth $15,000.

Mark

Mine must be rare too, because it is marked the exact same way... haha.

 

[vinnywv]

Uh oh....2 of them now. Price has dropped due to market flooding. Haaahaaa

 

[Syncop8r]

I take it this starter handle isn't original? It looks different to what's in the IPL.

View attachment 901903

I realized I have a couple of parts 610s I could borrow a starter handle from as a temporary replacement.

I would like to find an original (or close to) handle for it one day though. The IPL lists the handle as #62190 and the insert as #62191 for '60s 2-10s and #62190A / #62191A for '70s ones.
A search for #62190 on ebay brings up similar-looking starter handles with numbers like:

#87851 https://www.ebay.com/itm/164938633626?hash=item26671bd19a:g:7CkAAOSwGTRg3ahA
and https://www.ebay.com/itm/193440875214?hash=item2d09f982ce:g:RPUAAOSwLmxep0iH
#91255 https://www.ebay.com/itm/255027549281?hash=item3b60d39461:g:GHEAAOSwTxlg09gP
No number https://www.ebay.com/itm/173807899372?hash=item2877c212ec:g:xp4AAOSwfchccLMR
No number https://www.ebay.com/itm/154349510207?hash=item23eff29e3f:g:yWMAAOSw-IlgOpSQ

I'm wondering if any of these are identical to the original (having never seen it)?

 

[PogoInTheWoods]

Doesn't that mean it is the fuel line rather than the carb that is the issue?

Could very well be an issue with the pulse line (or passages) between the crankcase/cylinder base and the tank housing. It provides the pulses required by the pump diaphragm in the carb to draw fuel from the tank. May be loose, kinked, broken, missing..., or barbs blocked/passage at the intake assembly possibly obstructed by incorrect gasket orientation. A spring is typically located inside the hose to keep it from kinking. I didn't notice the barb on your newly painted handle, so I presume you removed it and are aware of the hose.

With the carb removed, you can easily test for pulse by putting a little oil or grease at the carb mount/intake pulse passage to see if it is drawn in or pulsed outward when pulling over the saw. If it is, you at least know the path is clear, though there could still be a leak in the hose or at either barb fitting location. A strong pulse should be fairly obvious. (The spark plug needs to be installed for obtaining enough internal case pressure/vacuum to create an adequate pulse.)

 

[GoBigRed]

I have a question for the Mac folks with experience using the tillotson HL carbs

a while back I picked up an older 250 and a 1-43. The 43 was seized so I parted it out and used some for the 250. The 250 was super clean but would not spark. After a coil swap and ignition chip instal it sparked great. Cleaned the carb and installed a kit as well. After to pulling the starter to get gas to the carb it fired. Choke off and she idled. Made some carb adjustments and the idle circuits holds great and she purrs. To get the high side revving I had to turn in the jet needle all the way. That seems odd. Then I noticed fuel starting to accumulate inside the housing for the carb. Looking a little further it seems the carb is spitting fuel out the intake and pooling gas inside the housing. Definitely more than any I have seen but I’m guessing that is making the high side run fat and also making fine tuning on the low side a challenge.
What would cause this. Before the carb rebuild it would idle great for a short time and then die. I could restart it, but the result was the same and hence the rebuild.
I’m missing something and have only seen this when I ported a 10-10 and got a little aggressive on the intake port and gave it a little, okay...a lottle, too much duration. But this is bone stock and. I know I’m missing something that probably is the cause but I’m not sure what. Thought I would throw this out since I’m not experienced in the slightest with an HL carb. Or any tillotson for that matter

thanks guys. Send what you know and I’ll try it

Jay

 

[knightmax]

Got a couple of US chrome reworked blocks back from Bob J a couple weeks back. Gonna rebuild an old 850. Not worried about cosmetics so much, this one is gonna be a worker.

Fun times!

 

[knightmax]

I received this interesting tool from Frank Bierce at the PNW GTG last year and just moved it over to the museum recently for display and use. This was designed and built by someone to aid in putting the springs back in the large frame saw clutches.

View attachment 922253

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View attachment 922258

Mark

That super cool!

 

[heimannm]

Jay - It is possible the reeds or reed plate are worn enough that they are not seating/sealing properly and you are seeing some "spit back" when the charge in the crankcase is being compressed. It is also possible that the needle is damaged, wrong one, metering needle is leaking, or the metering lever is set too high; any of those conditions could potentially cause an excessively rich mixture.

Mark

 

[vinnywv]

Ive got am 850 block that was us chromed. Its a great runner. You should have no issues.

 

[Maintenance supervisor]

Got a couple of US chrome reworked blocks back for Bob J a couple weeks back. Gonna rebuild an old 850. Not worried about cosmetics so much, this one is gonna be a worker.

View attachment 922602 a couple reworked blocks back from Bob J that US chrome redid. Going to rework this 850 into strong rebuilt runner for use. Not to worked about perfect cosmetics. this ones going to work. Fun times!

If you dont mind, whats the ball park for rechroming?

 

[knightmax]

Ive got am 850 block that was us chromed. Its a great runner. You should have no issues.

Any tips on prepping the cylinder. I have never prepped a new one so to speak lol. Warm water and mild dish saop with clean white cloth. then blow out with air then check with dry white cloth?

 

[knightmax]

If you dont mind, whats the ball park for rechroming?

sending to Bob J and then him sending to US chrome with NOS piston and then back to me $290ish plus the ride

 

[GoBigRed]

Jay - It is possible the reeds or reed plate are worn enough that they are not seating/sealing properly and you are seeing some "spit back" when the charge in the crankcase is being compressed. It is also possible that the needle is damaged, wrong one, metering needle is leaking, or the metering lever is set too high; any of those conditions could potentially cause an excessively rich mixture.

Mark

I did some tuning and have it almost worked out. But I just guessed on needle height when I put the new lever in. Ill go back and check that and drop it just a little bit.
Didn’t realize these old girls were reed saws. I’ll keep my fingers crossed that isn’t the issue. I’m still waiting on an IPL to arrive before I take anything too far apart or really dig in to it. I don’t mind disassemble, but the IPL give me a good reference for going back together. But if the lever does help and dig in there and inspect and clean the cage.
I’m guessing being a low rpm and low hour saw the reeds wouldn’t be beat up to much. Hopefully just a little dirt or something.
Thanks Mark. Great info to get me going. I’ll figure it out eventually, just need some guidance sometimes

 

[Yokosukadweller]

Could very well be an issue with the pulse line (or passages) between the crankcase/cylinder base and the tank housing. It provides the pulses required by the pump diaphragm in the carb to draw fuel from the tank. May be loose, kinked, broken, missing..., or barbs blocked/passage at the intake assembly possibly obstructed by incorrect gasket orientation. A spring is typically located inside the hose to keep it from kinking. I didn't notice the barb on your newly painted handle, so I presume you removed it and are aware of the hose.

With the carb removed, you can easily test for pulse by putting a little oil or grease at the carb mount/intake pulse passage to see if it is drawn in or pulsed outward when pulling over the saw. If it is, you at least know the path is clear, though there could still be a leak in the hose or at either barb fitting location. A strong pulse should be fairly obvious. (The spark plug needs to be installed for obtaining enough internal case pressure/vacuum to create an adequate pulse.)

Hi Pogo, Ok interesting. I know the pulse line is there, there is also a spring in the line. But the condition of the rubber is poor, it has surface cracks at least on the outside. I should probably replace it. I think any brand (non original) pulse line would work right? I want to test it though, so as you say, I pull the starter with the carb off and place some oil at that little hole where the carb gasket sits at the carb mount, is that right?

And then what do you mean by barb at the handle? Sorry I don't know that terminology...