Killed my Dolmar :(

[loganj01]

I went to help a guy drop and cut up a large red oak yesterday. He showed up with a Stihl MS250 with a 16" bar...this tree was at least 30" in diameter. Anyway, I started sawing it with my Dolmar 7900 because I didn't want to wait the half hour or so it was going to take him to drop it with the little saw. As usual, the Dolmar went thru it like a hot knife through soft butter...until it made a little pop and quit. It refused to start or even hit again and I could tell it didn't have the compression it had before. Tore it down last night to find the piston all scorched at the exhaust port. I can only guess that it was running too lean although the limiters were still on the carb...it's only about a month out of warranty. I had a big bore kit from Baileys that I bought and then decided not to use. I installed this on the saw last night and got it running again. I cut the limiters off the high speed screw while I had it apart. I adjusted it rich enough that it had a noticeable burble at WOT...I was almost afraid to run it at all! I sawed up a load of poplar this morning and it performed well. Now I can't get it started. It's always been hard to start...especially if you ever run it out of gas. It's like it loses it's prime. I did read the article on tuning but nothing I do seems to make this saw run right. Do you think it's possible that it has an air leak somewhere? I really love this saw and I know it's a high quality machine. That makes it much more frustrating. It was kinda funny this afternoon...I have a Dolmar, a Stihl, and a Husky sitting here and the only thing that would crank and run was grandpas old Mac 10-10. Anyone got ideas? I'm only a "weekend" saw mechanic so it'll have to be written in stupid so I can follow along....

 

[NORMZILLA44]

Even with limiter caps on if over a little time they are lean I have found you can still burn a saw up, limiter caps or not. My 044 Started mild scoring I think the same exhaust side. It started out acting weird wouldnt throtle up that was awhile ago. It was the fuel line, but the mild scoring came from me having it slightly lean. How is the compression now with the big bore kit? When I first got my 2101 we had to chase a few things around thanks to help with guys on thise site, and my saw shop. We found that my trouble on the 2101 was a crank seal. It was weird I brought it into the saw shop they tuned it for me, we log tested it all kinds of stuff, ran sweet. A couple days after it did a 180, and thats when they found the bad crank seal. Air leaks can do funny things. How is the compression when it is hot or warmed up? Low comp can also make it hard to start warm.

 

[SawTroll]

Never put a new top-end on a saw, before you have found the reason that the old one failed!

 

[Moss Man]

I sent you a PM sir.

 

[NORMZILLA44]

Very good point Sawtroll. Now it can be a can a worms, and ruin a new top end too.

 

[MCW]

There are many non carby related things that could cause this. First thing I'd look at is the possibility of a blown/leaking base gasket. My 7900 blew a base gasket about 4 months after buying it new. Leaned right out but I was lucky no damage was done.

Any chance of it being straight gassed? An error when mixing etc?

 

[w8ye]

Don't throw your 7900 cylinder away. You may be able to clean it up and with a new piston, be able to use it again some day if needed?

If there is aluminum galled onto the cylinder, you can eat the aluminum off with muriatic acid.

 

[barneyrb]

7900 is rev limited ignition and will always "burble" when hitting the rev limiter. You've more than likely torched another cylinder or are on the way to torching one.

 

[tdi-rick]

There are many non carby related things that could cause this. First thing I'd look at is the possibility of a blown/leaking base gasket. My 7900 blew a base gasket about 4 months after buying it new. Leaned right out but I was lucky no damage was done.

Any chance of it being straight gassed? An error when mixing etc?

The base gasket was my first thought too Matt, but unlikely with a newer saw as they use the metal base gasket now and the cylinder bolts are loctited in.

 

[nmurph]

What the OP thought was a burble was the saw bouncing off the limiter which can fool someone into thinking it is tuned correctly when it is actually too lean.

 

[porsche965]

......."I have a Dolmar, a Stihl, and a Husky sitting here and the only thing that would crank and run was grandpas old Mac 10-10."......

Three good brands, and none would start? That can't be a co-incidence. Check your fuel, or take it to a Dealer and have him check it. My guess would be the mix/fuel. It don't take much water in fuel to toast a piston.

 

[madhatte]

What the OP thought was a burble was the saw bouncing off the limiter which can fool someone into thinking it is tuned correctly when it is actually too lean.

This is true, and is a good reason why limited carbs and coils are a bad idea. Stupid EPA.

 

[mitch95100]

......."I have a Dolmar, a Stihl, and a Husky sitting here and the only thing that would crank and run was grandpas old Mac 10-10."......

Three good brands, and none would start? That can't be a co-incidence. Check your fuel, or take it to a Dealer and have him check it. My guess would be the mix/fuel. It don't take much water in fuel to toast a piston.

Exactly +1

 

[NORMZILLA44]

I like the idea that was stated above, about not just a coincedence, because I think he's right, you got something going on that's affecting all your'e saw's. Moisture- water in the gas would this do anything like that? Had a buddy of mine call me, he had his saw, and gas with him during the storms a couple years ago. He had a brand new 660, cant remember if it was like youre situation or if it seized, but had to rebuild it he dindt have his saw gas cap all the way tight rain water got in the gas. I liked the idea of what I heard it was lean I also think that was true, because I pulled the muffler on my 044, and had scoring starting like you mentioned, and the carb was leaned to far, and I learned something, because I thought because you had limiter caps you couldnt hurt it. Not true just takes longer.

 

[rms61moparman]

Check the Welsh plugs in that carb!!!
There are some that have gotten loose and allowed an air leak.
One well respected member here pulled the cover off his carb and the welsh plug fell out in his hand.


Mike

 

[Andyshine77]

Mike if the plug was loose the saw wouldn't idle very well at all, I doubt you'd ever get her to run long enough to burn it up.

Lets see if we can figure this one out.

First the saw is still pretty new, so it's unlikely a crank seal, and hey the saw was running strong and cutting like butter, so it's not likely an air leak. Now remember an air leak large enough to burn a saw up this fast, would have to be a pretty large air leak, and this would cause the saw to run like crap, which it wasn't.

Second. I've ran many new and used 7900's with the carb limiter still intact, and I must say the 7900 is one of the only modern saws to be tuned spot on from the factory, time and time again.

So with all that said, I'd bet your fuel was mixed incorrectly if at all, or the fuel is full of water.

 

[NORMZILLA44]

Was wondering about the water myself. I posted that to too see if anybody had input, they probably did'nt see it you mentioned it to so back up, and see what I asked, and tell me what you think, because Im curious too, and was trying to find out what water in the fuel would do?

 

[Andyshine77]

Was wondering about the water myself. I posted that to too see if anybody had input, they probably did'nt see it you mentioned it to so back up, and see what I asked, and tell me what you think, because Im curious too, and was trying to find out what water in the fuel would do?

Well it only takes a little bit of water to cause serious issues. Now I've seen some old saws run a long time with really bad fuel, but loose tolerances and low rpm's helped there. This really sounds like straight fuel was used, or close to it.

 

[NORMZILLA44]

Wow, too bad good saw down. Some people give me a hard time, because Im so weird about my mix. I only run super, same gas company, and my stihl oil every time. I mix it myself, and only use my saw gas nobody else's, when I mix it I put gas in the bottle shake it up, and dump in the can, and make sure I get all the oil. Even with all those steps I take it could still happen to any of us. Thats uskc about his saw, but like somebody said about more than a coincedience if it was the gas that would explain it with all the saws.

 

[tdi-rick]

Wow, too bad good saw down. Some people give me a hard time, because Im so weird about my mix. I only run super, same gas company, and my stihl oil every time. I mix it myself, and only use my saw gas nobody else's, when I mix it I put gas in the bottle shake it up, and dump in the can, and make sure I get all the oil. Even with all those steps I take it could still happen to any of us. Thats uskc about his saw, but like somebody said about more than a coincedience if it was the gas that would explain it with all the saws.

Norm, that's normal behaviour as far as I'm concerned