Flat spot and pop

[Fatherwheels]

I put away a Makita EA4300, I had the muffler gutted.
I cut an hour with it in a log pile, Two months ago, I cleaned it up
and was in the process of running it dry, I noted what looked like a spray of fuel
coming from the exhaust as I cycled it, I let it idle until I heard it die a little.
Empitied out the bar oil for storage, and decided to screw in the low needle a shade,
so I could test how it responded and whether there was still a mist which could have been unbrunt fuel
from the muffler on next start up.

Two months passed, I decided to try some Aspen, it’s the 50:1 premix.
Fuelled and oiled, saw almost started on third pull on choke, and died again,
off with choke and two pulls later she fired up.
I let it warm, 15 seconds passed, great throttle response to mid way, which was all I asked for
as I let the saw come up to temperature, 30 seconds idling, checked response, response was good
to a point, then quite a flat spot, let saw warm more with some slow to 3/4 revs, but flat spot is there,
let some more heat build up, flat spot there as I sneaked up the revs, I can pass flat spot by holding
throttle to the stop, it still flat spots / dips, but will go on to where I wouldn’t want to pass or hold at outside
a cut.
Also noteworthy is the saw pops on deceleration from full throttle, this was why I had the low set out more
in the first place, it wasn’t to get more response off idle, and I had the high set to four stroke.

I only changed the low to see if it was playing a part in what I saw as being raw fuel coming out the muffler,
which I saw none of this time, am wondering if the raw fuel I previously saw was due to idling as I waited to
empty the carb I would every so often increase the revs to speed the process up.

Now, even as is, this saw has a wicked off idle response, so, should I again richen the low, to stop the popping
on deceleration and ride past the flat spot, which coincidently also kicks in with real authority when I pass the flat spot,
or am I missing something and it’s the high side I need to tweak, I don’t think it is, but I have often been wrong,

Any advise very welcome, thanks.

 

[Fatherwheels]

Anyone care to comment, lots of these saws about.

 

[farmguywithasaw]

I would richen it back up so it accelerates smoothly. Could be you opened up the muffler to much. I like the area of my opening no more than half of the area of the port on my saws. A muffler opened to far will run lean. The more open the more fuel you need as it flows more air but also you lose some of the charge to scavenging. You lose more the more you open it

 

[Fatherwheels]

I would richen it back up so it accelerates smoothly. Could be you opened up the muffler to much. I like the area of my opening no more than half of the area of the port on my saws. A muffler opened to far will run lean. The more open the more fuel you need as it flows more air but also you lose some of the charge to scavenging. You lose more the more you open it

Your the first to say it, but I agree, the muffler is too open for a non ported saw.
I did not open the main outlet though, and left the spark screen in place.
I have two of them, both bought and muffler modded at the same time.

I only removed the cat from the first one, didn’t adjust carb, it runs well and four strokes
out of cut, stops fours stroking in cut and will immediately four stroke again when weight comes off.

Second one I removed cat and the large plate the cat is attached to, had to adjust the low to get it
to transition between low and high and not pop on deceleration, the high I also had to richen
to keep the saw from revving too high, it was difficult to get the high right, am guessing it was
because the low was leaning out on me and needed a hair more fuel.

I will open the low again, and tune it in the wood, if it’s putting un burnt fuel out, then I will
have to put the plate I removed back in, minus cat of course.

Thanks for posting

 

[computeruser]

If you didn’t open the muffler outlet beyond stock dimensions, then it isn’t “too open” for a non ported saw.
The problem is you fiddled with the carb adjustments without reason or a plan, and now you need to get it back to a proper state of tune.

 

[Fatherwheels]

If you didn’t open the muffler outlet beyond stock dimensions, then it isn’t “too open” for a non ported saw.
The problem is you fiddled with the carb adjustments without reason or a plan, and now you need to get it back to a proper state of tune.

The cab is in the exact place I got it when it came, before the muffler mod, I had to open the low to get it to
rev without the flat spot, this resulted in seeing a mist of un burnt fuel out the muffler, I have a tach and its set correctly to the factory spec.
Turning the carb back to factory spec is why the saw has a flat spot, I can easily get rid of that, by putting the low back to where I had it, its marked accurately
on the saw casing and I used a degree wheel to make the adjustment, all so I could readjust to original spec.

Right off the bat, both saws are the same, both new, both ran differently from new, one was way more wicked than the other, the wicked one
is the one I am working on, it has the cat and retaining plate removed, the other one I only cut the tacks of weld off and removed the central
cat piece, it did not need any carb adjustment.

No I did not open the stock outlet under the spark screen, its already bigger than what I see on much bigger saws.
The saw with the plate still in it has way more back pressure, as the exhaust fumes have to hit a steel plate first,
that directs them down and out to where the cat was waiting, so far it looks like this is a better recipe for a non
ported engine.

 

[sean donato]

I personally wouldnt worry about a little splurge out the exhaust. Rather not have the annoying lean pop on deceleration. I normally shoot for 50% on non ported saws and 70% on ported saws (%of exhaust area). I doubt you've opened it up too much.

 

[computeruser]

A degree wheel for carb screw settings? Marking screw positions? You are overthinking this. Way overthinking this.

 

[Fatherwheels]

A degree wheel for carb screw settings? Marking screw positions? You are overthinking this. Way overthinking this.

OK, first you say I had no plan and was fiddling, now your criticizing my thinking for actually having a plan, and taking simple
steps so I could revert to factory settings, whats wrong with you.

 

[Fatherwheels]

I personally wouldnt worry about a little splurge out the exhaust. Rather not have the annoying lean pop on deceleration. I normally shoot for 50% on non ported saws and 70% on ported saws (%of exhaust area). I doubt you've opened it up too much.

Thanks Sean, I think there is a slight lack of back pressure, the first muffler mod has the plate left in there,
the fumes have to hit it head on, then they are deflected down and out through the space where the cat sat,
then up and out the top of the muffler, slightly more back pressure would resolve my issue, I knew from how well
the first saw ran, that the obvious lack of back pressure from removing the complete plate in the second saw
would likely cause a slight disagreement with how things would flow.

 

[sean donato]

Wont hurt to toss the plate back in and see how it runs.

 

[Vintage Engine Repairs]

Hi Whinbush,

I’d suggest going back to basics, clean air filter, chain tensioned, fresh fuel, new fuel filter, tune the saw and then upload a video here of the issue and share where your carb screws are sitting.

So much can so easily get lost in translation and interpretation, both your end and ours and I find uploading a video has helped me many times in the past when I was struggling with issues.

There maybe an issue you’re unknowingly jumping over that could be involved too.

Don’t worry about degree wheels for the carb adjustment screwdriver or marking positions unless it helps you from stepping on your own toes. There is nothing wrong with doing either so opt for whatever you’re most comfortable with.
Set the screws to factory and go through the recommended tuning procedure. The chaps here will help you with fine tuning it if that’s a difficulty too. I still bug a few on here with videos of me tuning my saws and getting affirmation / feedback.

I look forward to hearing the video and the responses shared.

Warm regards, Tom

 

[Fatherwheels]

Hi Whinbush,

I’d suggest going back to basics, clean air filter, chain tensioned, fresh fuel, new fuel filter, tune the saw and then upload a video here of the issue and share where your carb screws are sitting.

So much can so easily get lost in translation and interpretation, both your end and ours and I find uploading a video has helped me many times in the past when I was struggling with issues.

There maybe an issue you’re unknowingly jumping over that could be involved too.

Don’t worry about degree wheels for the carb adjustment screwdriver or marking positions unless it helps you from stepping on your own toes. Just set the screws to factory and go through the recommended procedure. The chaps here will help you with fine tuning it if that’s a difficulty too.

I look forward to hearing the video and the responses shared.

Warm regards, Tom

Thanks Tom
I have new fuel in there, that canned premix / aspen2, air filter spotless, chain spot on, oiling and right tension,
am just going to take out the low a smidge to stop the popping, if this works out I will do some cuts and
monitor for wasted fuel out the exhaust, I may well be ok, and the spray I noted may have been picked up from
idling as I waited on the carb to empty for storage.

 

[Fatherwheels]

Wont hurt to toss the plate back in and see how it runs.

I still have it, tomorrow I will cut the cat from it.

 

[Vintage Engine Repairs]

Thanks Tom
I have new fuel in there, that canned premix / aspen2, air filter spotless, chain spot on, oiling and right tension,
am just going to take out the low a smidge to stop the popping, if this works out I will do some cuts and
monitor for wasted fuel out the exhaust, I may well be ok, and the spray I noted may have been picked up from
idling as I waited on the carb to empty for storage.

That’s great, my muffler spits 2t out too when it’s cold especially, until I get the thing hot and in the cut. I run my saws on the richer side. Now the guts have been removed from your muffler there isn’t anything to stop the oils from exiting directly.
Pop it in some wood for 10 mins and work it hard, get it hot, and see how it sounds and acts then

Warm regards, Tom