Modding a 7900

[drmiller100]

Not a pro Anything. Thanks

so are you a welfare case, or a trust fund baby, or???????????

 

[Lakeside53]

Surely there something in the middle or we're all screwed (except for the trust fund guys)!

 

[manual]

so are you a welfare case, or a trust fund baby, or???????????

Easy now That won't get you anywhere.

How about what you did with your carb After the wash test

 

[sawinredneck]

How much Andy?

More than I care to admit

 

[Freakingstang]

Easy now That won't get you anywhere.

How about what you did with your carb After the wash test

Thanks dude. I was going to respond, but it would not be nice. I'll have to suck it up and let it go.

 

[Four Paws]

you guys DO know how to read wash, right??????

I think it would be a BIG help if you would post pictures of your piston after your test. Then, explain to those who don't understand how to read wash what to look for, how to diagnose jetting from reading wash.

 

[vegaome]

drmiller100,

Now are you fixin to make some corrolations betwen what and how a man earns his income and mechanical knowledge? Do take it easy.

v/r

Mike

 

[manual]

Freak try this

 

[sawinredneck]

Sorry, NOT A PRO WELDER. lol.

Not a pro Anything. Thanks

Now don't sell yourself short Doc!!!! Reading you're posts and talking to you, you seem like a heck of a good wrench, and are learning the ropes of saw building quite nicely and quickly!!! I still LOVE firing up the 046 and chopping up stuff!!!
Andy

 

[Freakingstang]

At least I know how to take a pic....

 

[drmiller100]

I think it would be a BIG help if you would post pictures of your piston after your test. Then, explain to those who don't understand how to read wash what to look for, how to diagnose jetting from reading wash.

http://www.pwctoday.com/archive/index.php/t-62483.html

this has a good writeup on it all. the pics are really good as well. There are a few caveats though.

Looking at the "correct" pic.
I sled in the mountains, and I think a little extra gasoline is pretty cheap insurance, so what they call "correct" i call too lean. Too me, their correct is right on the extreme ragged edge of blown up. It would be PERFECT for racing conditions. But if we add a litttle more fuel, it will run within 3 percent as good, and give you more margin. When you have more margin, the top of the piston will be cleaner where the transfers are.

More caveats. If it is STUPID rich, gas will wash all carbon away. If you get detonation, it will rattle the carbon away pretty quick. if it is too lean, bad gas, etc, you can get detonation. if it is too lean, a lot of times it will burn the carbon off the top of the piston, but it will have a cooked, i've been hot look. When this happens, remove the piston, replace it as she is wounded and you can crack skirts. On these pistoins, you will find significant burned oil black stuff underneath the piston, which is the easiest way to know if she got hot, or she got hot with detonation.

Detonation very bad.

 

[drmiller100]

At least I know how to take a pic....

on freak's piston, that is WILD. The top of the pic to me looks like the intake should on these should. but the ring gap is at the bottom.

I've never seen a ring gap on the exhaust side of the piston. it makes no sense to me. Do you have the ring rotated around?

In any case, that is too rich. It is consistently too rich as well. The wash (cool gas WASHES carbon away) is too big. The piston is in NO danger of melting, but free performance could be had by leaning down the big end slightly.

Some people would be "happy" with that jetting, but you can easily and SAFELY lean it down slightly in incremental steps.

FWIW, it takes 5-15 minutes of run time to build carbon depending on type of oil and gas.

 

[04ultra]

1. Get new spark plug, but don't put it in yet.
2. Warm up saw to operating temp on old plug.
3. Install new plug.
4. Accellerate with throttle pinned.
5. When you hit the top , hit the kill switch
6. Remove the spark plug .
7. Hold the new plug in a vise and use a hacksaw to cut the threads
away from the center electrode.
8. You should see a brown 2mm "smoke ring" at the base of the
white center electrode if the main jets are dialed in perfect.
9. if the smoke ring is darker than chocolate brown or taller
than 2mm, you're rich on the mains, but if it revs clean to full
throttle, you can leave it there and be on the rich side.
10. If the smoke ring is smaller than 2mm or lighter than chocolate
brown, you're lean on the mains, go up a size and try again.

.

 

[drmiller100]

drmiller100,

Now are you fixin to make some corrolations betwen what and how a man earns his income and mechanical knowledge? Do take it easy.

v/r

Mike

Currently I'm a professional firewood deliovery guy in the winter, and professional landscaper in the summer. At one time in my life I was a professional computer support person.

I know professional ditch diggers. I know professional mothers, professional fathers, and I've talked on the internet to a couple of professional saw modification guys.

I believe you can be professional at whatever you do to make a living.

saw mods are a new hobby for me. mebbe that is what freak meant.

 

[Freakingstang]

on freak's piston, that is WILD. The top of the pic to me looks like the intake should on these should. but the ring gap is at the bottom.

I've never seen a ring gap on the exhaust side of the piston. it makes no sense to me. Do you have the ring rotated around?

In any case, that is too rich. It is consistently too rich as well. The wash (cool gas WASHES carbon away) is too big. The piston is in NO danger of melting, but free performance could be had by leaning down the big end slightly.

Some people would be "happy" with that jetting, but you can easily and SAFELY lean it down slightly in incremental steps.

FWIW, it takes 5-15 minutes of run time to build carbon depending on type of oil and gas.

Ring was broke. Good eye. the broken gap is at the exh side of the pic.

It was set rich, as it was intended to be a mill saw. The piston was a "new" piston with approximately 2 hours run time on it at differant carb settings.

 

[drmiller100]

1. Get new spark plug, but don't put it in yet.
2. Warm up motor to operating temp on old plug.
3. Install new plug.
4. Accellerate with throttle pinned.
5. When you hit the top , hit the kill switch
6


Oh my. I have no doubt this works on some saws. But I wonder if this is going to work on all saws. In particualr, as saws start getting cleaner epa wise, squish starts working, and more saws have rev limiters this method will have less consistency I would think.

As an example, what happens if we run a slightly hotter plug? what happens if we get a batch of gasoline where the residues burn at a hotter temp?

also, personally, I really don't care how my saw runs at WOT under no load. It won't cut wood without the chain in teh wood.
I think I'm most likely to burn down at WOT cutting a big log, so I think you should jet your saw correctly for that condition.

I'm new to saws, and I'm for sure willing to listen and learn the logic on this technique though.

 

[drmiller100]

Ring was broke. Good eye. the broken gap is at the exh side of the pic.

It was set rich, as it was intended to be a mill saw. The piston was a "new" piston with approximately 2 hours run time on it at differant carb settings.

ok, for a milling saw where you shoudl be VERY worried about heat, I could totally see that jetting.

so hard to tell on teh picture. is the top outer edge of the piston shiney?????? does it have little hen pecks around the outer edge????

what does the exhaust side look like?

 

[Freakingstang]

Currently I'm a professional firewood deliovery guy in the winter, and professional landscaper in the summer. At one time in my life I was a professional computer support person.

I know professional ditch diggers. I know professional mothers, professional fathers, and I've talked on the internet to a couple of professional saw modification guys.

I believe you can be professional at whatever you do to make a living.

saw mods are a new hobby for me. mebbe that is what freak meant.

Well, in that case my current job makes me a pro in the following areas:

Pro diesel eng mechanic, pro electrician, pro broom pusher, pro cable humper, pro lawn maitence guy, pro tree trimmer, pro commercial truck driver (3/4 ton pickup), pro customer service relations guy, pro paperwork filler-outer, pro snow plower, pro bullchitter, pro computer desk jockey, pro whatever it takes to get it done-guy.

 

[Cut4fun]

Dont stop now, I am enjoying the reading.

 

[Freakingstang]

ok, for a milling saw where you shoudl be VERY worried about heat, I could totally see that jetting.

so hard to tell on teh picture. is the top outer edge of the piston shiney?????? does it have little hen pecks around the outer edge????

what does the exhaust side look like?

Don't make a mountain out of a molehill.

that piston was broken in that pic. It was an aftermarket piston that gave way when the clutch was removed. The shiny spots on the intake crown is from the light reflection on the workbench. No hen Pecks. Just he lighting