Can a chainsaw run lean if tachometer shows idle speed and high speed rpms in normal range?

[BHanes]

Manufacturers recommended rpm are good for brand new saw or fully rebuilt to spec saws, when a saw loses compression from wear and tear or gains from mod work the recommendations set by manufacturers are out of the window.

Lower compression motor might need more fuel aka opening L/H more to compensate the weaker combustion. More fuel accompanied by oil will provide better ring seal and improve power albeit sacrificing some rpms, yes always remove the limiter caps which will give you full range of adjustments

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Hey thanks again for your personal experience! Sometimes u have to screw up to learn and I appreciate you helping not to screw up the entire piston and cylinder. I got those caps off just with a pair of pliers and tuned it richer! I feel more comfortable with it now! Thanks again!

 

[Robin Wood]

Hey thanks again for your personal experience! Sometimes u have to screw up to learn and I appreciate you helping not to screw up the entire piston and cylinder. I got those caps off just with a pair of pliers and tuned it richer! I feel more comfortable with it now! Thanks again!

You're welcome
Good to hear things worked out for you

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[buzz sawyer]

Update:

Thanks to everyone for their advice and wisdom. I should have said earlier that I do tune my saws by ear but I didn’t with this one because they bought an OEM carb that came with limitir caps. In my naivety, I thought the caps are there for a reason so I shouldn’t take them off to tune it by ear. Thank all of you who set me straight on this faulty logic! The caps just pulled off easily with pliers and I tuned it to run richer, which I feel good about. I really appreciate all your help and look forward to learning more about saws on this forum!
Ben

Yes, good to hear all is well.

 

[Okie]

I did not read all of this thread but the answer to your question is
YES.
The engine can severely overheat in a loaded cut and it can heat fast due to running lean and the piston starts swelling into the cylinder and the engine starts bogging similar to a chain groove loading or clutch problem and you pull it out of the cut and try to piss rev and the engine will usually speed up and back into the cut you go and same thing again. The engine is not exceeding rpms. Too much air, not enough fuel is hitting the piston. Fuel (rich condition) is what keeps the piston cooler. The operator if not familiar with such is unaware that the block is overheating due to lean condition, maybe even thinking he has a clutch issue or carb may be starving for fuel not aware he is ruining his saw until it's too late. Replace the piston/cylinder and go again and get same results again. His vac and pressure tests were ok.
The piston skirt is eating itself due to the skirt swelling into the cylinder wall which is then producing more friction heat. Saw may even lockup and die, cord hard to pull. Let it rest (cool down) for sometimes as long as 24 hours and it starts up and ready to go again.
All seems ok out of the cut unloaded.
You need to tune the saw in the cut. If you cannot do it in the cut at least do a test of the temp in a full bar cut with a sharp chain so as the engine is loaded up good for at least 30 seconds. Small short cuts and a saw that is running lean may run for a long time before lean causes damage. It will occur (overheating due to lean) quite often in a long (30 seconds or longer) full bar cut.
Get yourself a IR thermometer and monitor the temp of the block while the saw is into a full bar cut. Take the saw out of the cut and let it cool down while running and tune the carb richer if the temp gets to 350 fast.
Make sure the cooling fins are clean.

 

[HarleyT]

When adjusting the H speed screw while running, and using a tach, you can follow the range of rpms.
As you richen the screw {left}, the engine will richen, slow, and blurb a bit.
Then as you slowly turn the screw to the right, the engine will speed up, and it will run a lot better, and you will be approaching the target rpm.
After reaching the max rpm, which will be much higher than your target rpm, and if kept turning, the rpms will start dropping. The max rpm - dropping zone is where saws die.
So the tach may be reading your target rpm, but the mixture is way too lean, so you must make sure that you stay on the rich side of the curve.
When the fuel/air mix is leaned out, so is the engine's lubrication, as that is in the fuel mix.
So the temps can/will spike quickly, so do this procedure with care!

 

[BHanes]

Lots of great info! Thanks for sharing!!