Mastermind meets the Dolmar 7900

[AUSSIE1]

I figure one of the limits on power of the 7900 is the dinky 17mm carb. Probably why Andy made the emphasis on intake duration.

I've got four C3M carbs sitting here and I just might try butchering one up to see if I can open it up to 18-19mm. If it worked, I could use it on my 365BB, but it would also work on the 7900. Sure wish I had a lathe, using the Dremel is gonna be down right ugly.

Mount your carb in a cordless drill.

Bolt....washer.....carb......washer.....nut.....drill!

 

[Terry Syd]

Hmm, I've got a cheap Chinese drill press ($80) that I might chuck it up in, then stick the Dremel up inside while its spinning and hog it out - bush engineering at its finest.

Crikey Al, I'm actually thinking of doing this!

 

[AUSSIE1]

Hmm, I've got a cheap Chinese drill press ($80) that I might chuck it up in, then stick the Dremel up inside while its spinning and hog it out - bush engineering at its finest.

Crikey Al, I'm actually thinking of doing this!

Chainsaw file with the end cut off will remove plenty. You could lay down the drill press.

Be careful you don't go too far and pop into ports. I did and it took awhile to find it. Just pressurise the carb under water. If you do pop through, nail polish is a great sealer.

 

[Terry Syd]

Convert the choke valve to a throttle valve, then take some tin and make a bigger choke valve - yep, it's do-able.

Poor Randy, he'll come back to his build thread and find a bunch of Aussies have been crapping on while he was sleeping.

 

[385XP]

If I recall correctly the Walbro HD 12 carb that came on the 372 will bolt right in as well, not sure about the venturi size though.

I think you might be on to something with the walbro carbs. I beleve all the issuses ive had with the 7900 not want to restart when warm is a result of the zama carb. I may give the 7900s another try when they become available again.

 

[porsche965]

Should be a good thread. Subscribed.

 

[o8f150]

Here's a few pics of a build I'm working on.

This is a nice clean saw. It had a Chinese top end and only 140psi...

We're gonna fix that though.

New OEM 79cc jug and new light weight slab sided piston.....yeah baby!!!

It look to me like the designers wanted to try to do something to help the small case size on this saw. There's lots of potential here IMHO.

I'll cut the squish band flat and build a popup in this one.

That's it for now. A bunch of work showed up here today for one of my local guys that held me up a bit. We'll get back on it in the AM though.

looks like it should be a smoking saw when you are done,, what the hell am i saying,,any saw that you have built has been a smoking saw,,but i bet that pos dolmar won't keep up with my 372

 

[deye223]

Subscribed

 

[deye223]

looks like it should be a smoking saw when you are done,, what the hell am i saying,,any saw that you have built has been a smoking saw,,but i bet that pos dolmar won't keep up with my 372

opcorn:

 

[blsnelling]

I don't know how he does it, but Copsey can build a 7900 that will smoke a 372. Seeing is believing. Typical porting numbers go out the window with the 7900.

 

[Mastermind]

Looks like a fine test subject. I'd say it's an 05 or 06 model. The oil lines will be black and the filter cover won't have the prefilter mesh screen. She will likely leak oil with the old black lines, but as long as it oils the bar properly it's fine. I personally haven't seen any performance difference with the HD filter. Don't go crazy with your porting numbers, blow down is your friend as well as intake duration.

Have fun with the build.

I checked numbers on the new top end last night. It will end up with 162 duration after machining the jug. It has 30 degrees blowdown now. :msp_w00t:

I'm curious to see how it works out for you. All of the good builders that I know say they can get more out of a 440 and a 372 than they can out of a 7900.

Well I'm out.... :msp_sad:

looks like it should be a smoking saw when you are done,, what the hell am i saying,,any saw that you have built has been a smoking saw,,but i bet that pos dolmar won't keep up with my 372

Speaking of your 372......I'll box it up today. It's pushing 175psi and is very strong. I've ran several tanks of fuel through it and really like the way it turned out. I do apologize for having it so long, though I did get some great info out of it and the other one I built along with it.

 

[Mastermind]

I don't know how he does it, but Copsey can build a 7900 that will smoke a 372. Seeing is believing. Typical porting numbers go out the window with the 7900.

It's the elbow grease. He has a special blend that is Dolmar approved. :msp_wink:

 

[bigredd]

That is definately the 7900 I sold to a fellow AS Member. Very interested in seeing how it turns out.

 

[8433jeff]

I love this channel.

 

[importjunk]

Subscribed

 

[c5rulz]

Call me ears.opcorn:

 

[cutmaster]

Yea Man!

I don't know how he does it, but Copsey can build a 7900 that will smoke a 372. Seeing is believing. Typical porting numbers go out the window with the 7900.

I gotta get a hold of EC ( Copsey ) again myself, I want him to build up all 26 of our PS7900's!
Brad, if you can't reach Copsey for the next 3 months it's your own fault, you sent me to him in the first place! Gotta get through all this court B.S. first though

 

[russhd1997]

Another Dolmar porting thread. You got my interest. opcorn:

 

[timmcat]

Where's the next report?opcorn:

 

[Mastermind]

Where's the next report?opcorn:

I've been tuning on my lathe all damn day. :msp_mad:

Cheap Chinese bastards....... I feel sooooo dirty.

I'm replacing the slides on the carriage and polishing the ways and jibs. The little buggers can be very accurate, but some serious tuning must be done.