Saw bogs down in the cut

[bama]

I have a 621 Jonsered that I am working on. I have redone the seals and it pressure/vac tests good. It holds 50% pressure and vac for almost a minute. I rebuilt the carb and swapped the fuel filter with my running saw. The piston and cylinder are in great shape: so scoring at all plus new rings.

It starts great, but when I go to cut it starts out strong then acts like it is running out of fuel. I tried opening up the H screw with no effect. It idles good, but the idle setting seems to change every minute or so. Sometimes slightly faster, sometimes slightly slower.

What should I look at next? It sure acts like a fuel problem.

 

[SawTroll]

Have you checked the tank vent?

 

[mbopp]

Ditto on the tank vent. I've seen the small duckbill valve in the gas cap on Macs get gummy & not venting.

 

[bama]

No, I haven't checked the vent. I will do that today.

 

[havvey]

621

yes on fuel problem you may need a carb job. The 621 series were noted for problems on the shield between the carb and jug it sounds like an air leak. I would check the timing you can use a static light on those. :yoyo:

 

[bama]

I would check the timing you can use a static light on those.

I hate to sound ignorant, but what is a static light? I know that I need something to check timing since it can't be changed unless the flywheel is off. Is it cheap to purchase or make?


I did a pressure/vac test that included the intake boot/shield and the leakdown was acceptable, so I will look at the tank vent. It sure is posible that it could be gummed up. I would also like to check my timing since all I could do was try to put it back where the marks on the ignition plate were.

 

[retoocs555]

Does the choke stay wide open the whole time? I've seen saws where the choke will slowly wiggle closed and cut the saw out.

 

[bama]

The choke stays open and there is no play or looseness in the plate or linkage. This afternoon I will check the vent, but it could be the little aluminum check valve that the vent hose attaches to. Maybe it sticks closed. I figure I will try running it in a cut with the gas cap loosened and see if it does the same thing. Thanks, Scott.

 

[SawTroll]

.. Maybe it sticks closed. I figure I will try running it in a cut with the gas cap loosened and see if it does the same thing. Thanks, Scott.

Good idea!

 

[buck futter]

since we are kicking out ideas, a compromised ring can have enough compression to start a saw and the saw will scream but like a cross dressing dike its just got no sack.

Buck