Modding a 7900

[Lakeside53]

Thanks ultra. That's what I get for trying to help out....:deadhorse:

Stihl an ugly color for a saw opcorn:

 

[spacemule]

Stihl an ugly color for a saw opcorn:

What are you talking about? I happen to like sky blue pink.

 

[04ultra]

What are you talking about? I happen to like sky blue pink.

Space the pink is you....




.

 

[drmiller100]

The added scoop has weld spatter on it. (right side) lots of it, was done with a flux core welder...

The left is the stock scoop, with a brown tint. It might look black, but the saw is not running rich. It was when i got it though (used), the spark screen was almost plugged shut....


Yes, screwing the carb in leans them out. Have you figured how to get past the limiters on the jets yet?

Be careful of the rev limiter, you set it on the limiter, you'll burn it up in big wood.

hmmm. So is it bad when all that flux stuff goes back down inside the engine???

I haven't drilled out the main jets yet. I am a little curious how much to drill it. Any suggestions???? The little screw thingy had a casting imperfection on it that I trimmed up with my dremel.

On the rev limiter. Does the rev limiter change under load??? I am a little curious how I'd burn it up in big wood. I haven't really cut much the 28 inch bar won't go through.

I did upgrade to an 8 tooth driver. We haven't run it a full day yet. Any guesses what will happen?????

 

[Freakingstang]

hmmm. So is it bad when all that flux stuff goes back down inside the engine???

I haven't drilled out the main jets yet. I am a little curious how much to drill it. Any suggestions???? The little screw thingy had a casting imperfection on it that I trimmed up with my dremel.

On the rev limiter. Does the rev limiter change under load??? I am a little curious how I'd burn it up in big wood. I haven't really cut much the 28 inch bar won't go through.

I did upgrade to an 8 tooth driver. We haven't run it a full day yet. Any guesses what will happen?????

it's like beating a dead horse....

It isn't flux stuff. it is weld spatter, part of the weld spray that sticks on surrounding metal. i suppose it would be very bad if i was a complete moron to weld it while on the saw, right beside the gas tank of all things, and run the risk of weld spatter getting inside the piston/cylinder. it was welded while the muffler halves were apart. And before you ask, yes they come apart. It is a PITA and i don't recommend it... lol.

The muffler had to be taken off to remove the baffle..... That is when the holes were enlarged and the scoop welded. before the halves were put back together. Everything was cleaned on the inside. including the excess carbon from the rich setting. I could have cared less if there was carbon soot on the outside....


The limiter does not change. it limits the coil at 13,5K. if you have it set on the limiter out of the wood, it is too lean and will sieze when you get it into some big wood that creates more load on the engine, thus requiring more fuel that isn't there The rev limiter doesn't tell the carb to give it more fuel in the cut, and doesn't know where the carb is set at. It doesn't care.....You can still have the saw set way to lean and not know it with the limiter. you could set the carb at 18K if the (pretend the limiter was not there), but the motor would sieze in no time, even though the limiter would kick in at 13.5K. Rev limited saws do not have the four stroke burble that other saws are set by ear. Like i said, be careful. Don't want to see you burn it up.


And you don't need to drill the jets out yet. That carb will feed quite a bit of mods before needing redrilled.

 

[Four Paws]

:deadhorse:

Ha Ha Ha - aren't you tired yet. I was exhausted back on page 2.

 

[ciscoguy01]

Your 79

Hey Stang, have you still been runnin your 7900 all week??? How's she holdin up and is it still getting stronger as you go??? I'm picking mine up this friday and wondered how you were likin' it...

 

[drmiller100]

it's like beating a dead horse....

It isn't flux stuff. it is weld spatter, part of the weld spray that sticks on surrounding metal. .


The limiter does not change. it limits the coil at 13,5K. if you have it set on the limiter out of the wood, it is too lean and will sieze when you get it into some big wood that creates more load on the engine, thus requiring more fuel that isn't there
.

So you've got all of that purty weld splatter on your muffler outlet. What happens if some of it drops back inside the muffler and goes back into the engine???

So I set the mixture by running it in a log for a few seconds. then tweak, then run, then tweak.

I am not good enough to understand what people learn from running a saw for 5 seconds at a time WOT with no load, but willing to learn.

for sure my saw makes more power at some rpm much lower then when it hits the rev limiter. to me, this means something inside is limiting it somehow.

my guess is transfers. what do you think?

 

[drmiller100]

it's too bad you guys didn't hit it off. He is really close to you. LOL

Getting very tired...nice choice of words.

only 360 miles away. Just around the corner.

the funny thing is watching you guys. I started the thread, so I don't feel really guilty about fishing you.

 

[rahtreelimbs]

for sure my saw makes more power at some rpm much lower then when it hits the rev limiter. to me, this means something inside is limiting it somehow.

my guess is transfers. what do you think?

Too much fuel!!!:bang:

 

[Freakingstang]

So you've got all of that purty weld splatter on your muffler outlet. What happens if some of it drops back inside the muffler and goes back into the engine???

First off, it is weld, it isn't going anywhere i could have ground it smooth for the carmera but... When is it going to drop backinto the engine? while it is running and blowing exhaust out the hole? I hate negative vaccums. there is a screen on it, just not in the pic. the muffler was done a year ago and has seen many hours of use with no ill effects.

So I set the mixture by running it in a log for a few seconds. then tweak, then run, then tweak.

what are you tweaking for? sound? or hitting the limiter? you don't want it on the limiter.

I am not good enough to understand what people learn from running a saw for 5 seconds at a time WOT with no load, but willing to learn.

they are listen for a burble. they call it "four stroking" it is how you set it by ear. You "tweek" it until it burbles and it is good to go. The burble will, or should if set correctly, clean up as soon as it is in the wood. Do a search on here for "four stroking"

for sure my saw makes more power at some rpm much lower then when it hits the rev limiter. to me, this means something inside is limiting it somehow.

The limiter is an act of EPA. not a tuning tool.

you will never make peak power on the limiter in this saw. Go back to the last post i wrote, i'm not doing it again. you can't make max power with too little fuel. Lean is mean, but too little will sieze. it is not like a limiter on an MSD or other RPM limiting device on a car, bike, quad, boat, etc. Those all drop spark while there is still fuel present. This coil has no idea how much is there and doesn't care. it will not rev past 13.5K period. Even if the high speed jet could be screwed completely in (and in theory still run at infinite rpm on no air and fuel mix)

my guess is transfers. what do you think?

yes, the transfers are the limiting factor on this saw.



Let me ask you this. how would your power be, or how would you tune it if there was no rev limiter

 

[sawinredneck]

Too much fuel!!!:bang:

BIG FIRE!!!!!

 

[drmiller100]

mebbe, but wash sure looks good.

can you not confirm jetting with wash???

 

[Freakingstang]

Hey Stang, have you still been runnin your 7900 all week??? How's she holdin up and is it still getting stronger as you go??? I'm picking mine up this friday and wondered how you were likin' it...

Dood, you are going to love this saw. I've seen your posts and you say you like to push the saw. You can push this thing like there is no tomorrow. No, not all week...it is dark when i get home, but she cut about 10 full cord last weekend...splitting is another story, lol. It probably 30 hours on it, stronger every minute. lol. Good choice my man, good choice. We like to see pics and vids... lol.

 

[Four Paws]

I started the thread, so I don't feel really guilty about fishing you.

I'll give you that one.

There are lots of nice folks here, with tons of knowledge - many of which are more than eager to help. However, basic carburetor/saw tuning has been covered here many times, as have muffler mods, and even some in-depth two-stroke engine theory. Your introduction was less than humble for a new guy seeking advice...had you used the Search function, perhaps the heated debate and all the eye rolling at you in this thread could have been avoided. Keep reading, think about what you are saying before you post, and post some numbers when you degree that saw in - don't forget to Search!

 

[sawinredneck]

only 360 miles away. Just around the corner.

the funny thing is watching you guys. I started the thread, so I don't feel really guilty about fishing you.

I like fish!!!

 

[04ultra]

I like fish!!!

Catfish are good ...




.

 

[Freakingstang]

Catfish are good ...




.

You like bottom feeders?



:hmm3grin2orange:

 

[spacemule]

I'll give you that one.

There are lots of nice folks here, with tons of knowledge - many of which are more than eager to help. However, basic carburetor/saw tuning has been covered here many times, as have muffler mods, and even some in-depth two-stroke engine theory. Your introduction was less than humble for a new guy seeking advice...had you used the Search function, perhaps the heated debate and all the eye rolling at you in this thread could have been avoided. Keep reading, think about what you are saying before you post, and post some numbers when you degree that saw in - don't forget to Search!

What do you want to bet he makes his saw slower. :hmm3grin2orange:

 

[sawinredneck]

Catfish are good ...




.

A little butter, sliced lemon, sliced onion and some leomon pepper. Wraped up in foil, steam on grill for about 20 mnuets. MMMMMMMMMMM.....MMMMMM.... Good!!!!!