srcarr52
We can't stop here, this is bat country.
Good point... could be cold seizing.
5 gallons I think is somewhere between 15-20 tanks... that is a lot of run time and many fill ups for someone to put raw fuel in or to mess up on the ratio.
Mastermind meets the Dolmar 7900
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Good point... could be cold seizing.
5 gallons I think is somewhere between 15-20 tanks... that is a lot of run time and many fill ups for someone to put raw fuel in or to mess up on the ratio.
Srcarr, it's the exhaust side, arrow points to muffler as does the ring gap.
Unless all these I purchased were put together during OctoberFest!:msp_confused:
nmurph
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How are you tuning these saws?
Jacob,
we do use a steel 55 gallon drum.
We use Husqvarna XP Professional Performance 2 Cycle Oil mixed at 48:1
with Sunoco 260 GTX unleaded - no oxygenates and no metallic additives.
1 Gallon Husqvarna XP Professional Performance 2 Cycle Oil
added to 48 Gallons of Sunoco 260 GTX unleaded.
srcarr52
We can't stop here, this is bat country.
The locator pin is in the middle of the exhaust port? That sounds like a wonderful way to snag a ring.
Brad,
no never - we always start the saws in the sawmill shop, it's about 50 degrees in there without the heat on, my 2 sons and I always start the morning out like this:
We have breakfast, while my wife makes our lunches for the day we go out into the sawmill, check the saws out, fill them up with fuel and bar oil, sharpen the chains, the cut up slabwoord ( the thin bark left over from the sawmill from the day before ) push it all outside with the skidsteer, then I use my big bucket loader and dump it all across the road where people snatch it up like it's money.
Then it's back in the house to get our lunches then we head out into the woods, - resharpen the chains, fill everything back up start the saws for 5 to 10 minutes while I hollar at the boys as to what I need each of them to do, then we cut trees down until we can't move, then I jump in the skidder to clear the area while my boys continue cutting.
Here is the strangest thing:
The first Dolmar I blew up, while my 2 sons continued to run their Husqvarna 372XP's.
Same bar oil, same gas mix, same everything.
This saw is the second PS 7900 to blow up, my youngest son used this on.
I went back to using my Husqvarna 395XP, my oldest running his Husqvarna 372XP.
Again, fueled and oiled from the same containers, everything the same.
The only common thing here that I can see is Husqvarna vs Dolmar.
I am not in anyway shape or form bashing Dolmar!
I am stating the facts to all of you to help myself out here, I made a large purchase of 7900's this past fall and I'm asking for you all to help me figure out what is going on with these Dolmar Saws.
Steve
nmurph
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You do realize that these saws have a limited coil? Four stroking at WOT sounds like you are hitting the limiter. They will do this and still be too lean.
Dan_IN_MN
Addicted to ArboristSite
I'm not sure if this is a red flag or not....Are you mixing the whole 55 gallons all at once? Is this a common thing to do? What is the chance of the oil settling over time or not being mixed thoroughly with the gas? Where are you in located in MN?
thomas1
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Holy thread derail, Batman! 
Mastermind
Work Saw Specialist
Derail away. 
I just hope you figure out what has been killing your saws. What nmurph said about the limited coil is what my money's on. I just ran a stock one that was bouncing off of the limiter badly.
I'm almost done with the first 7900 with two more to go. Everything that could happen to slow a day up has happened here today. My wife's van took a crap, local guys have been in and out all day, the phone has been ringing off the hook.............I'll get done someday.
I just hope you figure out what has been killing your saws. What nmurph said about the limited coil is what my money's on. I just ran a stock one that was bouncing off of the limiter badly.
I'm almost done with the first 7900 with two more to go. Everything that could happen to slow a day up has happened here today. My wife's van took a crap, local guys have been in and out all day, the phone has been ringing off the hook.............I'll get done someday.
Since this was the second 7900 that we were using we were now aware the first saw had a problem the we never could find out " why "
This saw I thought we had tuned up rich and perfect, the original hole on the muffler seemed small for a 79cc saw, it was a 14mm hole, I opened up that same hole to 17mm.
Then pulled the caps off the carb, band new out of the box I turned out both carb adjustment screws out 1/2 turn each, I put a tach on it and revved it lightly to 6751 rpm, once the saw was hot I turned it off and adjusted the I started the saw and adjusted the dle speed to 2500 rpm, I then turned the low speed carb screw in until it started to surge. I then backed that screw out until the engine started to load up. I split the difference between the lean and rich setting, say 2 o'clock was lean and 10 o'clock was rich, I ended up at 12 o'clock, I then went out about 1/8 turn and re-adjusted my idle speed to 2500 rpm. I then went to WOT and hit the kill switch, tach said 13,884, I backed out the high speed screw 1/4 turn, started the saw and went to WOT and hit the kill switch, tach said 11,414 rpm, it sounded great at that point, I then started the saw with the tach still attached and started a cut through a 15" dia red oak log, I dug it in slightly and hit the kill switch, tach said 8112 RPM. I pulled the spark plug and it looked rich, I replaced the spark plug with a new one, made 4 cuts and pulled the spark plug again, it looked rich.
This is how I left it until it blew......
I am no pro saw tuner, so if I did anything wrong here please let me know, I tune all my saws this same way and have for roughly the last 15 years, ever since I bumped into a chainsaw tach!!
Steve
o8f150
Tree Freak
Holy thread derail, Batman!
thats what i was thinking
11,400 is WAY too rich for a 7900. You need to get the saw good and warm. Start rich. Have someone else hold the tach. Go WOT and lean it out until you see 13,500 or until it bumps the rev limiter. From there, you'll have to tune it in the wood. It should run perfectly clean in the cut, but slightly 4-stroke when you let off the load. However, as already mentioned, it's VERY easy to think it's 4-stroking when it's actually hitting the limiter. This is why I despise rev limited coils and one reason that I just can't fall in love with a 7900. That, and the fact that they look like an AMC Pacer!!!
Brad that that amc pacer shoy was like adagger to the heart
Even in the right colors
Brad, 13,500 RPM is where the first one was set at, and that saw looks just like this one.....11,400 is WAY too rich for a 7900. You need to get the saw good and warm. Start rich. Have someone else hold the tach. Go WOT and lean it out until you see 13,500 or until it bumps the rev limiter. From there, you'll have to tune it in the wood. It should run perfectly clean in the cut, but slightly 4-stroke when you let off the load. However, as already mentioned, it's VERY easy to think it's 4-stroking when it's actually hitting the limiter. This is why I despise rev limited coils and one reason that I just can't fall in love with a 7900. That, and the fact that they look like an AMC Pacer!!!
I'm willing to try the EC unlimited coil trick - but if the next 7900 end up like these 2 - I'm going to dump the rest off on ebay and run to the hills!
A Pacer, c'mon Brad, A Pacer?? Dude that's gonna hurt for weeks on end!!!
Ahhhh!!!!
Steve
Hedgerow
HACK
Brad??? Why have you not found your way around that stupid coil yet???
Get busy you slacker!!!:msp_sneaky:
Get busy you slacker!!!:msp_sneaky:
The truth hurts sometimes:hmm3grin2orange:
Yes, I did it once. Not worth the hassles. If I were to run another, I'd probably stick with the stock coil and just tune in the cut.
