help with Stihl 021

[cftuna]

My Stihl 021 will not rev up to working speed. The plug is new. the fuel is good. the carburetor has been rebuild and triple checked. the chain is not too tight. it starts easy and will run at high idle, then when you open the throttle it starts to rev up but never to working speed. the fuel line and filter are new.
What next ??????

 

[Lakeside53]

Welcome to AS...

First, some questions:

What was the reason you first rebuilt the carb? Was it because of the symptoms you describe above?

What is the compression? Exactly which carb do you have?

 

[buck futter]

also what does it sound like when you have the throttle open? is it like it is to rich or just not opening up. How is the throttle linkage? do a rope test my 025 has a lot of compression for its weight and does very well with the rope test.

let us know

Buck

 

[cftuna]

021 Stihl

Yes the new kit was put in the carb for the non rev problem the diaphram looked stretched...
The carb is a Walbro 503 and had a dry cracked fuel line, replaced new with new filter and carb kit 615-463

 

[cftuna]

When I open the throttle it goes blahhh and acts like it is to lean or sucking air.
the rope test is fine as it will hold plenty of compression

 

[cftuna]

throttle linkage is fine and works smooth....

 

[Lakeside53]

As you have no doubt figured out, the 503 has no H speed adjust screw, so...


If you think it's lean, it's probably a bad outlet valve in the carb. Doesn't sound like seals unless you have a weird one that flaps open only at moderate crank case pressure (I have just seen one do that!).

How is your L screw setting?. Is is close to 1 turn out? If for example you have it at 1.5 to 2, then you may be compensating for an air leak.

Have you verified the plug condition after holding the throttle open for a while to see if it is in fact lean or rich?


and.... check your muffler for blockage - just take out the screen to verify...

 

[cftuna]

thanks

The only thing I have not done is pull and clean muffler. I'll do that and let you know.

 

[cftuna]

THANK YOU LAKESIDE

I just pulled the muffler and the screen was totaly plug left it out and saw runs great.
this will make a great 4th July

 

[Lakeside53]

You're welcome! I see a lot of these on fixed jet carbs - they tend to run way too rich, and once the air cleaner blocks the screen starts to block, and it compounds quickly.

To clean your screen. just burn it out with propane and a squirt of compressed air.

 

[buck futter]

my 025 was rich on the hi end and that is why I went to a two screw carb. everyone on here said the worst part of the one screw carbs is that they lean out the saw to much to appease the epa, I glad someone else noticed it the same way I did.

 

[Lakeside53]

It's the same on the 026 - the singe screw version is much too rich, but on the other hand, I almost never see a melted piston with this carb!