Author Topic: Dolmar 7900 Porting Info  (Read 3806 times)

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Offline EHP

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Re: Dolmar 7900 Porting Info
« Reply #10 on: January 05, 2012, 11:22:52 pm »
then put a wider skirted piston in it , remember some saws have a real wide skirt piston in them at these GTG's so pretty much a real racesaw , if you use the stock piston get the compression up as high as you can as that helps the 7900 alot and the higher compression works very good with the tight crankcase volume , if you raise your transfer ports to high it will boil the gas in the crankcase real bad and have less power so watch how high you raise them

Offline Mastermind

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Re: Dolmar 7900 Porting Info
« Reply #11 on: January 05, 2012, 11:30:59 pm »
I really appreciate you input on this. It's plain to see that you are no stranger to the 7900.

What piston would you recommend? And could you share a little about using a Husky coil?
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Offline EHP

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Re: Dolmar 7900 Porting Info
« Reply #12 on: January 05, 2012, 11:52:28 pm »
I have done alot of 7900's , 99% were worksaws but have built a couple race 7900's on alcohol , on muffler or pipe , Myself I would use the 272 piston as its a single ring , I have made my own 7900 wide skirt pistons but that takes me alot of time , now you will have to build a spacer plate which I know is nothing for you cause the 272 piston is taller than the 7900 piston but also with using the 272 piston you donot need to grind your crankcase as much as with a 7900 wide skirt  piston cause the skirts hit the crankcase at BDC,

No secret on the coil , its a 272 coil and retime the flywheel, , the easiest way for me to tell you how to time the coil to the flywheel is find someone that will let you time a stock 272 , Get a dial gauge in your sparkplug hole , find TDC and look at where the coil matches the flywheel magnets , transfer the coil over and start your motor at TDC and mount the flywheel to the same spot of the magnet or you can go advance the flywheel a touch over the stock 272 setup, I know most transfer the coil onto the 7900 metal part but I just use the 272 coil setup and make the holes line up

Offline Mastermind

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Re: Dolmar 7900 Porting Info
« Reply #13 on: January 06, 2012, 11:25:34 pm »
Ed I sure to enjoy you giving me the chance to learn these things from you. I'll be talking with the saw's user about how far he wants to take this build. I'll post it all here if that's ok, I'll need some help with this one.
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Offline StumpysCustoms

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Re: Dolmar 7900 Porting Info
« Reply #14 on: January 07, 2012, 12:01:24 am »
My second post & already lovein this site.  Thanks Ed for letting out some of the secrets of the 7900. ;)
I think I may be gitting a 6400 in on trade in the near future that I'll do some playin with. 
I've learned alot in just a few minutes from this thread.  Thanks fellers :-*


fixed it for you  ;)

Offline Cut4fun .

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Re: Dolmar 7900 Porting Info
« Reply #15 on: January 07, 2012, 06:32:30 am »
My second post & already lovein this site.  Thanks Eric for letting out some of the secrets of the 7900. ;)
I think I may be gitting a 6400 in on trade in the near future that I'll do some playin with. 
I've learned alot in just a few minutes from this thread.  Thanks fellers :-*

EHP is Ed Heard.  Not eric.  ;) 
REDNECK Saw Repair Getter Done

Offline EHP

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Re: Dolmar 7900 Porting Info
« Reply #16 on: January 07, 2012, 09:06:04 am »
That's a first  ;D
Funny Funny x 1 View List

Offline Mastermind

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Re: Dolmar 7900 Porting Info
« Reply #17 on: January 07, 2012, 09:56:54 am »
What you said about the tight crankcase of the 7900 got me to thinking.......

When we build these hybrids.....044/046 comes to mind. I just wonder if more blowdown would be better on these as well?

The funny thing about these two strokes is the more I learn, the less I know.  ???
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Offline man of stihl

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Re: Dolmar 7900 Porting Info
« Reply #18 on: January 07, 2012, 10:17:04 am »
I just bought a 7900 basket case, so I'll be watching this thread closely. :) Ed. When you say get the compression up as high as you can. Were talkin what? 175+?
Ron

Offline rms61moparman

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Re: Dolmar 7900 Porting Info
« Reply #19 on: January 07, 2012, 10:42:39 am »
More like 175+++

Mike

 

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