McCulloch Chain Saws

Arborist Forum

Help Support Arborist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
20190505_074809.jpg
Fixed a couple gas caps today based on the posts of the guys on this forum, the poulan duck bill slipped over the brass tube and instead of fuel line I tried o-rings, the black one worked the orange one is for fuel injection and was alittle stiff.
Thanks guys.
 
What's the difference between a 1-71 and a 1-72

Sent from my SM-G920V using Tapatalk
 
Sent from my SM-G920V using Tapatalk[/QUOTE]



Sent from my SM-G920V using Tapatalk
 
This is a 1-71 with a 1-72 cover on it can anyone tell me the difference between the 2 just curious
3d21b33b9d1959c029d7a8f9863ac21a.jpg


Sent from my SM-G920V using Tapatalk
 
20190505_091119.jpg I took this 10-10 to work with me today (I'm the Maintenance supervisor of a state park),to cut some popular trees and to clear a lake shore bank. I rebuilt the carb and installed a new duckbill in the cap. After dropping some 8-10" trees and bucking them up the saw started running rich and flooded out mabye 30min of use ,so I peeked under the air filter and could see a fairly steady flow of gas filling the carb.
It was pretty warm here this morning and with the new duckbill she's not sweating out horsepower from the fuel cap any more. After work I started the saw up at home and she ran great.
Could I have the needle seated to light in the carb or could the duckbill be doing too good of a job in the hot southern sun?
Suggestions are welcome.
 
The fuel caps were equipped with a spring under the duckbill valve and the intent was that excess pressure in the fuel tank would "pop off".

DSC01069.JPG

It is possible that your O-ring repair doesn't allow any pressure to escape and so the pressure in the tank becomes excessive forcing the metering needle to unseat. Next time you are running the saw try opening the cap and venting the pressure, see if that reduces the tendency to flood the carburetor.

Mark
 
Now - a problem of my own, or really a problem with Kevin's (2 broke2ride) 7-10.

I decided to give it one last attempt, stripped it down to the short block and rechecked both pressure and vacuum. There is a slight pressure leak through the compression release, and it was still burping out through the automatic oil pump. I replaced the automatic oil pump with a used one from the attic and that cured the pressure leak there so there was just a blip, blip, blip of bubbles coming from the vent port of the compression release. I pumped the vacuum up to 20" Hg (out of the water now just in case you were wondering...) and it would very slowly bleed down, less than 1" per minute. I did put some heavy oil around the seals and it didn't change at all. I am not sure but I suspect the vacuum leak may have been through the compression release port as well. I had replaced both crankshaft seals when I worked on it last time and I believe they are still quite effective.

I didn't want to take any chances so I replaced both gaskets on either side of each of the insulators between the cylinder and the fuel tank/airbox as well as between the airbox and the carburetor and even changed out the insulators just in case one had a crack or chip that I could not detect. I went so far as to scrape the mounting surfaces on the block and the air box to insure there were no irregularities affecting the ability of the gaskets to seal.

The saw will start, run up at full throttle, but will not operate with the throttle at idle position. I fired up my 7-10 to make sure all was O.K. then switched the carburetor into Kevin's. The only way to get it to idle was to run the idle speed screw all the way in (mine had the idle speed control in the carburetor) and lean it was down. I don't think it was actually running on the idle circuit but the throttle is open far enough to pull through the main jet as I could turn the idle adjust screw all the way in with either carburetor and the saw keeps running, until it dies...then I had to choke it one pull and it would restart and repeat the scenario. As the saw continued to warm up the idle became even more erratic, seeming to lean out and speed up, then appeared to get rich and flood out

On the previous attempt I did install new points, a different condenser, and even changed the flywheel as Poge had suggested with no effect whatsoever. When I tested it Saturday morning it would certainly run at full throttle and cut pretty well, but would never operate reliably at idle.

The only thing I have not changed is the piston itself. Looking at the IPL's I see than serial numbers with the 10 prefix had a different part number (69030 as opposed to 85239 in all the other late model 70 cc saws) which is a thick ring piston.

Kevin - did the piston you changed out look like the one on the left or the one on the right???

IMG_0175 (640x480).jpg

IMG_0173 (640x480).jpg

IMG_0176 (640x480).jpg

Makes me wonder if the porting is different based on the piston and we have the wrong piston in yours?

Mark
 
Mark, could it be the pulse circuit? At an idle there is not enough to work the pump but as the saw goes full throttle it is passing enough to pump enough fuel to run it? Maybe a defect in the block or something like that. Or maybe a piece of an old gasket or gasket sealer or even carbon, or maybe not lining up somehow where it was replaced with the wrong isolator somewhere along the line. Or maybe you are on to something with the piston maybe covering the case end of the pulse port somehow. Too bad there is no way to monitor that pulse. One could make a meter if one would react fast enough. It would half to be electronic to react that fast but with one vacuum and one pressure sensor one could take an old spacer and drill a hole in it and bring out a barb fitting to hook to the sensors. Just my ramblings. Thinking about the spacer or insulator between the tank and cylinder, could it have a crack in the pulse hole and causing it to not function properly?

Just my thoughts

Brian
 
Cath Cornwellto Vintage Chainsaw Collectors Corner (Buy, Sell, Trade, Discuss)

Hi everyone just wanted to let everyone know im going to list my dad Bob Cornwell's bp399t on ebay which i believe is the best engine in his collection. No time wasters. This is for the serious collector. The only one in australia, prestine condition and is still in the original box it came in! Reasonable offers for the right price will be considered.

59553578_1247298105439406_9123182230934388736_n.jpg


60048003_1247298128772737_6930206392414371840_n.jpg


Brian
 
Back
Top