saw tuning 2153 and 2172

[JONSSTIHL]

Hey guys,
A little history on my 2153 this is my best starting saw. always pops on the third pull and starts on the fourth pull every time. but lately it has started bogging when I pull the tripper just after starting.
And my 2172 has always been hard to start like 10 pulls so I decided to clean them both up and tune the carbs.
2172 is stock and I think I got that one squared away at 3000 rpm idle and 13000 rpms.

The 2153 has a extra port in the muffler but otherwise stock minus the limiter caps and unlimited coil
now for my 2153. The H setting keeps moving around for me so I decided to make a couple cuts to help with the tuning. Got it set to 13900 rpm tuned the 2172 and then decided to double check the 2153 and it was turning 15000 rpm so I screwed in the H screw about half a turn and then it was turning 13000 rpm

What would make the H setting move around by 1000 rpm without turning the H screw.

 

[rupedoggy]

air leak or worn carb diaphragms

 

[JONSSTIHL]

I was thinking it may be time for a carb kit.

the saw is from 2007 and I haven't done anything to it except one fuel filter change a couple years ago and I just replaced the coil last year.

 

[JONSSTIHL]

I think I can add one more thing to your list. An empty gas tank. Decided to take a quick look at the fuel line and filter before tearing into it and I realized that the tank looks awfully empty. It is too early to test my theory but I'm pretty sure it will tune fine on a full tank.

thanks for the tips. always pays to check the simple stuff first.