I have a ryobi 720r gas trimmer, and a mcculloch 2116av chainsaw. Both are
giving me the exact same problem. The following is as complete a
description as I can come up with:


Spark arrestors:
The ryobi has had the spark arrestor burned clean with a propane torch,
however I can't see it, as it's integral to the carb and not removable. I,
of course, removed the muffler from the engine for this procedure.

The saw has had the arrestor removed for the moment, though it looks in good
shape.


Air filters:
Both have had the air filters cleaned thoroughly.


Spark Plugs:
Both are running new plugs, purchased based on the plug recommendation
sheets at the local hardware store.


Fuel/oil mixtu
I admit I'm cheating by using a husqvarna 50:1 2-stroke mixture even though
the ryobi calls for 32:1, and the mculloch calls for 40:1 (I also have a
husqvarna saw that calls for 50:1, but it's not giving me any trouble (big
surprise)).

Before attempting to use this mixture in all three motors, I spoke with a
logging equipment supplier about mixtures, and his advice was to mix for
what the oil tells you, not the motor, as the oils have gotten so much
better, bla bla friggin' bla bla.

I'm using freshly purchased 94 octane fuel (as in purchased today, and put
into both machines prior to trying to get them to run a little better).


Carburetors:
Both use Zama carburetors, though I think the models are different. Both
have had the diaphragms replaced. The ryobi carb has limiting caps on the
low speed/high speed screws, the mcculloch does not.

The saw allows adjustments when the air cleaner is in place, the ryobi
initially did not. Ryobi doesn't make the mixture and idle adjustment
screws accessible with the air cleaner and cover over the carb installed. I
drilled three holes in the cover over the carb so I could insert a screw
driver and make adjustments to the idle, low-speed and high speed
mixtures when the air cleaner is in place.


The problem:
Both motors exhibit the same problem, regardless of how meticulously I
attempt to tune the mixtures for low and high speed. Both have their idles
set a little high, or they won't run. Both will either bog severely, or die
if I just pull the trigger hard to fully open, even after letting things
warm up well. If I ease them up to high rpm, they seem to have lots of
power, but sometimes when I let go of the throttle, both will return to idle
for between 5 and 10 seconds, then start to idle lower and rougher, then
stall.

The high idle on the trimmer doesn't bother me too much, but it would be
nice if it would idle a little lower, and the chainsaw is still not idling
high enough to move the chain, other than the odd little jump. The
Husqvarna, OTOH, idles lower, and responds like a race engine, no bogging,
no hesitation, just lots and lots of power.

Is there something I need to do to the mixture screws, like removing and
cleaning, that might account for the trouble? How does one remove the
limiting caps from the ryobi carb? Zama's web site just says you have to
destroy the caps to get them off, but you shouldn't ever need to because if
you leave things in the limited range set by the caps, things will never go
wrong. I'm quite skeptical about this, as it looks like something Murphy
would have a field-day with.

Is this possibly a fuel starvation problem? A hint that this may be the
case is that when I move the choke to mid range on the trimmer, it seems to
hesitate less, regardless of whether or not it's warmed up. I didn't try
this on the saw. Both the trimmer and saw have the little ezstart bubble
that you pump before starting, and I can see that in both cases they're full
of fuel when the engines are running, and when they stall.

Both of these pieces of equipment are a few years old, and I usually remove
the fuel and run them dry in the fall for storage through the winter.

Does anybody have any further suggestions?

Oops, that paragraph on Spark arrestors should read:


Spark arrestors:
The ryobi has had the spark arrestor burned clean with a propane torch,
however I can't see it, as it's integral to the muffler and not removable.
I, of course removed the muffler from the engine for this procedure.

The saw has had the arrestor removed for the moment, though it looks in good
shape.


Also, is this the best place to post a question like this?

I have been having the same problems. If you need instructions on how to set your carburetor, email me @ .