Stihl 660 carb issue

[jacob22]

I'm trying to tune my 660, the problem I'm having is the h needle. I started with a full tank of fuel, new air filter and fuel filter. I turned the h needle all the way in and backed it out a full turn. With a tach it's not is over 15000 rpm which is way too high. When I richen it up it doesn't seem to affect it much. I can get it to 4 stroke but after a few seconds it shoots back up over 15,000 rpm. Any ideas?

 

[Ozhoo]

Is this an aftermarket carb? What's the history on the saw? Have you done a pressure & vacuum test?

 

[cus_deluxe]

Clean that carb and check ur fuel line is what i would do first.

 

[jacob22]

Oem carb, I put a kit in a few years ago. I don't have a pressure or vacuum tester. What's a good tester to get? I recently replaced the intake boot it was torn and had light scoring on intake side of piston. Haven't checked compression yet.

 

[jacob22]

I'm thinking maybe I should get a pressure and vacuum tester and at least rebuild the top end. Assuming there's not a leak somewhere. Could the carb be bad?

 

[Ozhoo]

Since you just replaced the intake, I'd focus my attention there to start but as mentioned go over the fuel system. It's either not getting enough fuel or getting too much air.

- Not enough fuel could be a clogged fuel filter, pinched or leaky fuel line. Clogged inlet filter on the carb or hard/weak fuel pump diaphragm. Dirty carb, etc...
- Excess air most often comes from intake boots or crank seals but could come from a faulty base gasket.

A Might Vac MV8500 is pretty much the best bang for the buck. Look around for deals.

 

[jacob22]

Ok thanks is anything else needed in addition to the mityvac to check for leaks

 

[ZeroJunk]

I had one wandering up a couple of weeks ago and it was a cracked fuel line.

But, as everybody has said, anywhere that it can get extra air is a suspect.