High Quality Chainsaw Bars Husqvarna Toys Hockfire Saws

McCulloch 39, no throttle response, help?

LAWN BOY

Pothole
Local time
2:58 PM
User ID
28603
Joined
Feb 27, 2024
Messages
1,883
Reaction score
5,214
Location
Merrill, WI
Country flag
I recently got a McCulloch 39 that sat many years. I cleaned the fuel tank which had old fuel in it. Gave it a drink down and it fired up and idled a little. The next day(today) I gassed it up with 32:1 which I’m told will be fine with modern quality 2 stroke oil and it fired up on its own 5th pull and would idle then die, longest idle was 8 seconds, a few times. An hour later I go back out and it’s slowly fixing itself as it now idles just fine for as long as I want it to. The throttle trigger doesn’t have much wiggle tho and it does nothing. I don’t see anything broken or missing, but then again I don’t have much experience with this series of McCulloch saws yet. Any ideas? I applied some WD40 to the linkages but that did nothing.
 

heimannm

Here For The Long Haul!
GoldMember
Local time
4:58 PM
User ID
714
Joined
Jan 28, 2016
Messages
3,393
Reaction score
23,559
Location
Dike, Iowa
Country flag
The throttle rod (red line) must be connected to the throttle trigger. When the trigger is squeezed the rod operates a lever in the back of the carburetor rotating the linkage (circled in green) to move the throttle plate, and also allows the fuel control rod (blue arrow) to open.

20200229_120814.jpg

Here the throttle plate is installed.

20200229_120930.jpg

As the throttle opens, the fuel control rod also moves allowing more fuel. The high speed adjustment (lever on top of the carburetor) allows the throttle to open more or less, and thus controls the high speed fuel flow.

The low speed adjustment is the screw on the bottom of the carburetor.

20200229_115714.jpg

Mark
 

heimannm

Here For The Long Haul!
GoldMember
Local time
4:58 PM
User ID
714
Joined
Jan 28, 2016
Messages
3,393
Reaction score
23,559
Location
Dike, Iowa
Country flag
Keep in mind that the fuel pump is located in the bottom of the fuel tank, and the filter is a large felt wick in the bottom of the tank. If the saw was left setting with fuel and it all evaporated, the wick may be plugged with varnish. Your description of idling longer as is sets sounds like either the diaphragm is limbering up, or some varnish is dissolving out of the wick.

Mark
 

LAWN BOY

Pothole
Local time
2:58 PM
User ID
28603
Joined
Feb 27, 2024
Messages
1,883
Reaction score
5,214
Location
Merrill, WI
Country flag
Keep in mind that the fuel pump is located in the bottom of the fuel tank, and the filter is a large felt wick in the bottom of the tank. If the saw was left setting with fuel and it all evaporated, the wick may be plugged with varnish. Your description of idling longer as is sets sounds like either the diaphragm is limbering up, or some varnish is dissolving out of the wick.

Mark
Thanks for all the info. The old fuel was still present and hadn’t evaporated.
 
Top