Stihl 044 over revving

[DarrenS]

I've a 044 that i was fixing up, put it all back together, set carb at 1 turn out for each screw, starts fine, idles ok at approx 2400rpm but at high it's at 15,100rpm whereas it should be 13,300.
I've pressure & vacuum tested for leaks and it held up fine.
So why is it over revving?
I can turn the high screw out to 2 & 1/2 turns and it revs at 13,300 but at that it's throwing a lot of petrol mix out the back, towards the air filter, so somethings not right?

Any ideas would be appreciated.

 

[AVB]

Double check you metering lever height @ spec or lower it slightly but I have found some needs to running rich on the high is necessary sometimes to limit max rpms. Also if you lower the metering the L mixture will lean out some too so you must increase it.

 

[DarrenS]

Thanks for the reply, but when i turn the H screw out to make it richer it throws fuel out the back of the carb in to the air filter, so something is wrong,
The saw has also just had a replacement engine (chinese type but i've fitted them to other saws without this issue) Could it be running lean until the rings seat in?

 

[Fruecrue]

Did the saw fail previously to your work?

 

[Fruecrue]

Typing at same time...
Cause of previous failure?

 

[DarrenS]

Bought it in as spares or repair so history is unknown. I will check the metering lever and if that seems ok i will fit a different carb.

 

[Wonkydonkey]

What else have you done to the saw, it makes it a bit easier to diagnose. Eg China carb, some work otta the box and some don't.

Cheers

 

[DarrenS]

What else have you done to the saw, it makes it a bit easier to diagnose. Eg China carb, some work otta the box and some don't.

Cheers

All original other than chinese cylinder piston assembly, it starts easy idles ok runs nice and smooth just at 15,100 rpm rather than 13,100 rpm as stihl state.
All i have done is fit the new cylinder piston assembly and then pressure & vacuum test the crankcase (no leaks found)

 

[Fruecrue]

I would check impulse line and carb diaphragms.

 

[DarrenS]

I would check impulse line and carb diaphragms.

I would check impulse line and carb diaphragms.

I've pressure and vacuum tested the crankcase which also tests the intake manifold and the impulse line so that isn't at fault i don't think,
I did check the carb diaphragms and they looked fine, i might ultrasonic clean the carb as well tomorrow, see if that helps.

 

[Wonkydonkey]

I wonder what the timing numbers are, IE it could be a good running cylinder,
Plug colour may help
Does it sound like its 4 stroking @wot. Edit or just screamin...
Does it have torque in a cut
A vid can help..

Not sayin I'm good at diagnostics, just sayin all the possibles, and happy to learn more

 

[Fruecrue]

Impulse line could also be plugged.

 

[DarrenS]

I wonder what the timing numbers are, IE it could be a good running cylinder,
Plug colour may help
Does it sound like its 4 stroking @wot. Edit or just screamin...
Does it have torque in a cut
A vid can help..

Not sayin I'm good at diagnostics, just sayin all the possibles, and happy to learn more

Yeah i've still a lot to learn i know a lot more about the older saws, 08 s10 07 090 types.
At normal H 1 turn out it screams at 15k rpm plug colour is nice brown so not short of petrol, not too lean, then when H screwed out to 2 & 1/2 turns running at 13k rpm it gurgles nicely the plug still seems to be nice brown, not wet, but saying that most of the extra petrol is just being chucked out the back of the carb.
I'll take a video tomorrow morning so you can hear and see it run, but i've no wood to try it in,

 

[DarrenS]

Impulse line could also be plugged.

Don't think so but will check it in the morning.

 

[Wonkydonkey]

Ahh,,,,,,, fuel filter ?? Runs ok till it needs more than it can suck throu the half clogged filter, in the tank, or even the one in the carb ?

Edit, I think I'm stabing in the dark, it would not run at 13k if fuel filter was blocked and H was 2.5 turns

 

[DarrenS]

Ahh,,,,,,, fuel filter ?? Runs ok till it needs more than it can suck throu the half clogged filter, in the tank, or even the one in the carb ?

Yeah maybe, worth a check, but if it was struggling to get fuel due to blocked filter then surely by opening the H screw would not make a difference, whereas opening the H screw does give it more fuel and reduce rpm, it's just that the H screw needs be open 2.5 times more than stihl say and most of that seems to be blown back out towards the air filter.
And although it runs high at 15k it is very smooth no chugging or any signs it's short of fuel, and the plug is nice brown colour, not white which would be a sign of fuel shortage.

 

[DarrenS]

Hey everyone, don't know if anyone is watching this thread but managed to get it running better today, checked the impulse line, no fault there, check fuel filter and line, that was also ok, then ultrasonically cleaned the carb and reassembled, when pressure testing the carb there was a very small air leak, so disassembled and then oiled the gaskets in the carb, once reassembled and tested the carb held pressure nicely,
The saw then ran nice at H screw 1 turn out and almost at the 13.3k rpm speed required, a little more tuning and it seems ok, I'm guessing the air leak in the carb was allowing more air to be sucked in and running lean, or maybe there was dirt in the carb, either way it's running nice now
I'm taking it on a job tomorrow so will see what happens
Thanks for all your input on this i appreciate it.

 

[Wonkydonkey]

Carbs can finicky little things at times, good to hear you sorted it