Saw either stays revved coming off the throttle or sputters.

[sliceoflife]

Bought a super XL as wont start but did in the past. Put some gas in it and started right up. So pleasant surprise. Trying to get it running 100% now...

Idles great... but If I rev it up... when I let off the throttle it will occasionally do one of two things:


1. Keeps the revs up, chain spinning... not as high as WOT, but definitely higher than it tends to idle.
2. Go back to idle properly then after a few seconds sputter out.

Of course 50% of the time or better it does:

3. Works as intended, goes back to idle and idles fine.


Some issue with the fuel line/filter (or possibly carb/fuel pump diaphragm) or the throttle linkage maybe? Any other guesses?

 

[lohan808]

Rebuild the carb it's going to be rough from age. I would also suggest looking for air leaks. Great saw though.

 

[sliceoflife]

There's a thousand and one carb rebuild kits that claim for super XL's on Amazon, but they all also claim they're for 33-42cc saws... got a model number for the correct rebuild kit so I can be sure?

It's an SDC carb.

Thinking this is the kit?

https://www.amazon.com/AUMEL-Carbur...t+homelite+super+xl+sdc&qid=1685550349&sr=8-4

 

[ericm979]

What you describe sounds like the low speed is lean. I'd try tuning the carb (if you haven't already) before taking it apart. And its always smart to check the throttle linkage as you don't want it hanging up at WFO.

 

[sliceoflife]

Linkage is good, checked it real quick when I looked for carb ID...

Low is set very lean... maybe 0.8 turns CCW from seated. I tuned it that way to minimize the Idle throttle needed after playing around with a few different positions. If I richen up the L adjustment, I have to give it more Idle throttle to keep it idling. Is that the right course of action?

Best way to describe it is it feels like how it idles is inconsistent. It'll be idling beautifully, I'll give it a few revs and it'll come back and idle with revs quite high... then I'll rev it again and it may come back down in revs at idle but start sputtering. No rhyme or reason. Rotating the saw doesn't seem to affect it; so I think that makes air leak less likely?

So one time I'll tune in the saw and have it idling good; then when I go to use it the next time; I'll start it, rev it and it'll be idling at high revs... so I'll reduce the Idle throttle until it idles smooth again... then when I run it a bit, and let off throttle; it'll start to die... so I'll increase idle throttle until it's idling well again... and repeat.


Now if it's an air leak, what's the best way to diagnose and fix?

I will say; just letting the saw sit; the idle is consistent. It doesn't rev up and down UNLESS I give it some throttle... that seems to trigger something that changes the idle when I let off the throttle.

 

[KostasVolos]

To me sounds like a dry/wrapped metering diaphragm .

-Pump and metering diaphragms and their gaskets should be replaced.
-The carb should be cleaned with a carb spray ( passages ,needle,jets).
-Needle should be inspected for good sealing .
-The fuel filter should be replaced with a new, clean one.
-The fuel line should be inspected for cracks or other wear.
-The fuel tank vent should also be inspected .

 

[lohan808]

Air leak checks can be found using brake cleaner sprayed on while saw is idling. Focus on the intake areas, bearing seal spots, impulse line and there are no shortage of threads here for more details. You can buy a pressure/ vacuum test kit if you want to spend the dough. It is a good tool to have.