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Carb. tuning an 075AV

Started by roughhewn, March 22, 2006, 12:37:27 PM

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roughhewn

 Hello;

   Wondering if I can get a sanity check.

   Maybe that's a bad idea.

   I have a Stihl 075AV. It's got an Alaskan II mill bolted to a 36" bar, runing a 404 chain. I've never quite had the gift of two stroke carb tuning. Wonder if anyone can help.

   I use a 40:1 mix. Saw starts fine Idles very well. If I throtlle up to quickly it'll stall. If I throttle up slowwly it'll come to speed. It runs strong, no smoke whatsoever. The exhaust is super hot. Maybe that's normal and it's just the volume of exhaust from such a large saw I'm not used to. When I stop cutting she'll always stop and then give one "pop", almost like a backfire. My suspicion is I've got it to lean. What are the clues that an experienced saw tuner will look at to make sure the engine has enough mix to keep lubricated but it's not choking out on excess fuel. Thanks gents.

leweee

just another beaver with a chainsaw &  it's never so bad that it couldn't get worse.

roughhewn

Thanks. It does help, though I was hoping there was something more concrete than sound. Makes it hard for the novice to act with confidence. The tuning guide mentions checking RPMs without a bar and chain. I don't have a tach. Should I still tune it without a bar and chain or no? Another side question is, are there any tips for holding a screwdriver on a saw that's vibrating like skateboard on gravel?

Minnesota_boy

Quick and dirty.  The saw seems to idle well but it wants to die if you "grab a handful of throttle".  Turn the idle mix screw counterclockwise just a smidge, like 1/16 turn.  Start it up and let it warm up.  Grab the throttle and see if it dies.  Does it idle well?  Keep richening the idle adjust until it won't die when you grab the throttle.  Now work it.  Still have good power?  If so, go back to work.
I eat a high-fiber diet.  Lots of sawdust!

sawguy21

Make sure the intake gaskets and the insulator block under the carb are in good shape.  The hold down nuts also need to be tight. Those old laydowns were famous for intake leaks. The 075 is a good saw for milling, tons of torque.
old age and treachery will always overcome youth and enthusiasm

roughhewn

All good stuff. Thanks guys.

I am pleased with the 075AV. I first tried milling with a Poulan Pro 335. It was so bad I learned to hew and built my workshop the oooold way. I'm 10 years older now and I'm seeing that with a proper saw, the chainsaw milling is a reasonable alternative. I'm terrified of burning the saw as the 075AV is a done deal and with a few exceptions there are no parts to be had.

twoodward15

When I tune carbs on a saw I usually have a really really good and knowledgeable friend to help out.  I usually hold the throttle and keep the saw running while he turns the screws slowly.  It seems to work better for me to run the saw because he doesn't know my saws and I don't know his.  We'll run them up and check them in wood when done.  Sometimes We'll make adjustments in the wood to see if it'll run better than no load runs.  Obviously I use the same frien everytime.  He knows what I want and when we do his saws I know what he wants.
108 ARW   NKAWTG...N      Jersey Thunder

Al_Smith

 What was already said on the low speed .On the high speed,rev the saw run the needle in ,the speed will increase.Turn the needle out until it just starts to "burble" or "4 cycle".Under power,if you did it correctly,that "burble" will disappear and just be felt as power.

Nothing to it,easy as falling off a log,so to speak. 8)

Tony_T

Once you get it dialed in and warmed up take a good cut then kill it.  Check you spark plug for coloration, sooty is too rich on high speed and no color-white too lean.

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