Sportfury70
ArboristSite Operative
I don't need a Cummins either, but WANT is a powerful motivator..
I would not fuss with it as a first go. Try learning on some AM cheapy cylinders, not a $200 one.
Trust me, a first timer will make a 7900 run worse. Brad Snelling has a bunch of info on them. Part of why they run so well is because the transfers are narrow keeping the fuel atomized. Learn on a cheap aftermarket cylinder before you go to work on a $200 one you will probably make run worse. My 6401/7910 hybrid has a .22 thou squish with the base gasket. Do a muffler mod and research a lot more before hacking them up. They are so tight from the factory there is not a lot of room for the first timer to improve outside of the muffler.I understand why you would say this, but I'm no noob. I promise I won't ruin it LOL. I've polished my share of cylinder heads and fitted more beaver tails than I can count. Most days I do some form of metal work either as a hobby or through my job.
I'll probably give the existing cylinder a massage just to get a feel for it.
I'm looking to do a moderate port job on this saw, pretty much by just widening and polishing the ports a bit, and smoothing the transfers. Nothing extreme.
Just looking for tips from folks who have been in these saws so I have an idea of how far I want to take a moderate woods port.
Trust me, a first timer will make a 7900 run worse. Brad Snelling has a bunch of info on them. Part of why they run so well is because the transfers are narrow keeping the fuel atomized. Learn on a cheap aftermarket cylinder before you go to work on a $200 one you will probably make run worse. My 6401/7910 hybrid has a .22 thou squish with the base gasket. Do a muffler mod and research a lot more before hacking them up. They are so tight from the factory there is not a lot of room for the first timer to improve outside of the muffler.
Really Tenderfoot, I appreciate your concern, but I didn't ask whether I should do it or not. I asked what to look out for while porting this saw.
Are you saying that a mild port job isn't worth it? I've done lots of research, and all the posts (here and elsewhere) show decking the cylinder, removing the squishband, raising and lowering ports, and other advanced things. I'm not interested in that, just some basic port work.
Even if I don't enlarge the ports, I have a hard time imagining that simply polishing and gasket matching won't be of some benefit.
If I wreck a new cylinder it's on me, not you, so feel free to impart some wisdom that will make this just a bit stronger than stock.
Exactly. They made a lot of changes over production that took away the 'easy' mods. The most recent cylinder run is the best for power apprarently, as is the old style muffler the 6401s have. From what I gather that combination runs stronger then the original 7900s due to the updates to try and offset the SLR mufflers.Ahhh now I'm starting to smell what your cooking. Kinda like putting an intake and exhaust on a bimmer. Doesn't really do much but sound different and waste money.
I haven't seen that thread, I'll give it a read. Thanks man.
Good luck. I re-read that thread and apparently with a stock 7900 a muffler mod only makes it louder. I fiddled with a few saws over my time, but realized in the real world, filing makes me cut faster. I would bet money that your saw will be pretty close to mine without doing anything. I was considering all the porting and fussing, but once I actually ran it I was happy. Without doing anything it can keep up with a husky 390 until it has a buried 28 in bar, and then you only notice with a stop watch.Sounds like I'm already starting with the winning combination then.
So MM, and I'll measure squish to see about the gasket. Hopefully it's like yours and has just the right squish with the gasket.
Thanks for your patience buddy, hope to have some test and tune vids after the swap in the next few weeks.
Maybe to you. I think a $30 part is too much to ruin with my own incompetence!Without machine with and a degree wheel you will find some gains but just enough to make you want more and that's how it begins.
Everybody has to start somewhere and everybody,no matter how experienced was a rookie at some point.
Parts are cheap and the only way to learn is to do it.
Read all you can and I'll do the best I can to answer your questions if you have any.
Considering it was YOUR saw that started my obsession with this blue monster, this seems like one of those things you just don't pass up.I'll do your machine work if you send me the cylinder and squish.
My bb is 100 126-128 80 200lbs.
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