Mastermind Ported Dolmar 6100

[Terry Syd]

Yeah, using the term 'strato' in conjunction with the flashy videos has tended to create a mental image that is too simplified.

When I started working on my 450 Husky the strato ports opened 10 degrees longer than the intake port. Kinda like the reeds on the 6100 staying open longer than the intake port.

 

[Terry Syd]

So we are talking about increasing cylinder filling, and an appropriate increase in VE?
The mix feed is compressed in the crankcase, and the fresh air feed is just coming in at atmospheric pressure, right?

I'll have to go back to Blair's work and get the right terminology, but we are getting less dilution from the exhaust gases. We can't increase the cylinder filling like a turbo would, it would just blow out the open exhaust port.

Both the mix feed and the fresh air are coming into the crankcase at atmospheric pressure - and then both are compressed and fed into the cylinder. The 'pure air' being in the top of the transfer tunnels is the first to mix with the residual exhaust gases and to be lost out the exhaust port. If we can increase the quantity of 'pure air' we can purge more exhaust gases and leave more 'pure air' in the cylinder for the carb mixture to mix with.

 

[weedkilla]

I'll have to go back to Blair's work and get the right terminology, but we are getting less dilution from the exhaust gases. We can't increase the cylinder filling like a turbo would, it would just blow out the open exhaust port.

Both the mix feed and the fresh air are coming into the crankcase at atmospheric pressure - and then both are compressed and fed into the cylinder. The 'pure air' being in the top of the transfer tunnels is the first to mix with the residual exhaust gases and to be lost out the exhaust port. If we can increase the quantity of 'pure air' we can purge more exhaust gases and leave more 'pure air' in the cylinder for the carb mixture to mix with.

So raising the strato timing on the piston should show if there was anything to gain by playing with the reeds?
The risk is reducing the pressure difference seen by the mixed feed, that you would say is a benefit by reducing mechanical work?

 

[Terry Syd]

I just looked back at Blair's work and it is chapter 3 where he goes into scavenging ratio and scavenging efficiency.

So raising the strato timing on the piston should show if there was anything to gain by playing with the reeds?

That's a bit too simple, the reeds work by demand, not timing. A longer strato timing on say a 562 piston would bring in more air, but it would also delay the point the engine could begin to make crankcase compression. At lower rpm it might even create a blowback through the strato system.

If we could get a 6100 to get a full charge in the crankcase by the stock 71 degree ATDC piston timing, that would be the equivalent of having a strong ROTARY VALVE engine that used 71 degrees ATDC on the rotary valve - that would be a very strong running chainsaw.

 

[bryanr2]

Really appreciate how there's a "sharing" of knowledge on this site.

 

[166]

New Style



Old Style

 

[Terry Syd]

I can see they changed the inside of the boot and put in some 'dimples', but it is the back side of the reed block that may be more interesting. Here's a picture of the old reed block -

 

[David Young]

Nice explanation Terry. I think of the term overscavenge. You can blow some charge out the exhaust because it is just air and not mixed charge. Then benefit is less spent gasses in the new charge. We can flood a motor with fuel but we fight to get more air in.

I think Randy has a good point part of the usefulness of reeds is low rpm charge management.

Good stuff.

 

[CoreyB]

When did they change the intake?

 

[Terry Syd]

I think Randy has a good point part of the usefulness of reeds is low rpm charge management.

Yes, one of the benefits of reeds is that when the rpm drops below maximum delivery ratio (peak torque), the reeds can open to help prevent any charge in the cylinder from being sucked back down into the crankcase through the transfers by the rising piston.

 

[Mastermind]

I've got one issue to work out with this saw. I can't tune it so that it becomes overly rich. No matter how far out the high speed jet, it's not too fat. I can make it too lean, but not too rich.

Thoughts?

 

[Terry Syd]

Let's see the inside of the carb. The wet side may have an auxiliary jet you can drill. Failing that, we just might drill an auxiliary jet in the back of the discharge nozzle, just like the Zama carbs.

 

[Mastermind]

It will be this afternoon Terry. I'll get pics then. The bench is covered in Husqvarnas.....

 

[Terry Syd]

It's 11pm here, I'll check back in the morning.

 

[Mastermind]

It's 11pm here, I'll check back in the morning.

Ok Terry. I appreciate your input my friend.

 

[CR888]

It took me a while to work this out but here goes....Terry is really smart.

 

[P.M.P.]

After watching video a few times.I went and grabbed the MMWS 7901 and did some cuttin to keep the urg down from buying new saw.

 

[bryanr2]

After watching video a few times.I went and grabbed the MMWS 7901 and did some cuttin to keep the urg down from buying new saw.

Don't fight it.... succumb to the CAD.

 

[David Young]

I've got one issue to work out with this saw. I can't tune it so that it becomes overly rich. No matter how far out the high speed jet, it's not too fat. I can make it too lean, but not too rich.

Thoughts?

This may be a little crude. And not apply to this saw. I had a similar issue on a ms261.

I hope this make sense I took some of the plastic out of the basket that is under the filter. But only on the wet side of the carb. I went from over 2 turns to about 1 1/4

May have to drill in the carb.

 

[Mastermind]

Thanks David.......any ideas are welcome.

I didn't get to tear back into this saw yet. Had to do some work on the van this morning. I'm grinding on a pair of Huskys right now.......