Don't hate me Nikko
Mastermind Meets The J'Red 2188
- Thread starter Mastermind
- Start date
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Mastermind
Work Saw Specialist
Noise.
I ran one of the ones I had done that way for about 8 hours.......and I started hating that saw.
Trx250r180
Saw polisher
WHATTTT!!
I do love that mm. Does it's job and looks stock.
Jim Timber
1/4 bubble off
I realize this is an older thread but the issue of a larger carb wasn't really addressed.
When you increase the venturi diameter, you decrease the intake charge velocity given the same volume of air is passing through it but it has more space to occupy. This reduces natural supercharging (pulse wave stacking as the intake slams shut causes a high pressure zone behind the piston due to the mass of the intake charge trying to keep it's velocity), and also reduces the responsiveness of the venturi itself to correctly meter the fuel as the charge has a lower vacuum signal across the jets.
There's a big difference in having enough carb and having too much. Too much carb causes more problems than not having enough (assuming you're not so under fed as to run lean). Since these are tuned for WOT more than anything, the midrange isn't as much of an issue like it is with cars, but there's a lot of folks running 750cfm Holley's who'd be far better served with a 650 given the engine they've got it on. Being able to dial in enough fuel for a given bore diameter is likely the problem with smaller chainsaw carbs rather than them acting as some kind of restriction; but that's just a slightly educated guess as I have no experience with the little carbs beyond turning the needles.
When you increase the venturi diameter, you decrease the intake charge velocity given the same volume of air is passing through it but it has more space to occupy. This reduces natural supercharging (pulse wave stacking as the intake slams shut causes a high pressure zone behind the piston due to the mass of the intake charge trying to keep it's velocity), and also reduces the responsiveness of the venturi itself to correctly meter the fuel as the charge has a lower vacuum signal across the jets.
There's a big difference in having enough carb and having too much. Too much carb causes more problems than not having enough (assuming you're not so under fed as to run lean). Since these are tuned for WOT more than anything, the midrange isn't as much of an issue like it is with cars, but there's a lot of folks running 750cfm Holley's who'd be far better served with a 650 given the engine they've got it on. Being able to dial in enough fuel for a given bore diameter is likely the problem with smaller chainsaw carbs rather than them acting as some kind of restriction; but that's just a slightly educated guess as I have no experience with the little carbs beyond turning the needles.
Mastermind
Work Saw Specialist
That's what I've been trying to tell em.
Jim Timber
1/4 bubble off
Everything's gotta be bigger!! I did chuckle at the saws from the 80's had bigger carbs comment. They used more fuel, made less power, and turned lower RPM's in the cut - yeah, that's exactly the example we should be following... 
It's too bad having an intake stack would mean putting the air filter out in space above the piston. I bet you could see some healthy gains increasing the distance from the carb to the piston.
It's too bad having an intake stack would mean putting the air filter out in space above the piston. I bet you could see some healthy gains increasing the distance from the carb to the piston.
Mastermind
Work Saw Specialist
There are lots of things I would like to try.....but time is something I have little of.
Hedgerow
HACK
Pfffttt...
I just like it when they work right...
I just like it when they work right...
Jim Timber
1/4 bubble off
A supercharger would be fun too.
I always enjoy watching your builds Randy. Thanks for posting them.
I always enjoy watching your builds Randy. Thanks for posting them.
Mastermind
Work Saw Specialist
Hedgerow
HACK
You need to figure out how to fix them...So......when they ain't Zamas?
Mastermind
Work Saw Specialist
I've got too much on this cart to add anything else.
big t double
Addicted to ArboristSite
How is squish velocity determined
Mastermind
Work Saw Specialist
Best guessimation?
big t double
Addicted to ArboristSite
I like your style
Mastermind
Work Saw Specialist
A couple of years ago I thought I had stumbled onto something that was game changing.
I accidentally cut too much out of a squish band......and ended up with more clearance that I normally would use.
The saw still had great power.......but it seemed to idle better.
In my mind it was something worth noting, and I posted about it. Within a few minutes my buddy Dennis Cahoon was calling me on the phone.
He told me that no matter what I "thought"......I was going backward.
We had a great talk......and have since had many more.
The point I'm trying to make is that sometimes that gut feeling is way wrong. Tighter squish clearance, coupled with a flat squish band allows us to run a higher compression ratio without worrying about detonation. More compression always makes more power.
I accidentally cut too much out of a squish band......and ended up with more clearance that I normally would use.
The saw still had great power.......but it seemed to idle better.
In my mind it was something worth noting, and I posted about it. Within a few minutes my buddy Dennis Cahoon was calling me on the phone.
He told me that no matter what I "thought"......I was going backward.
We had a great talk......and have since had many more.
The point I'm trying to make is that sometimes that gut feeling is way wrong. Tighter squish clearance, coupled with a flat squish band allows us to run a higher compression ratio without worrying about detonation. More compression always makes more power.
Olesenofalaska
ArboristSite Member
Well you did this one right Randy. I think I just added a video of it. It's broken in now and wears a 24 Cannon sbp when not falling.I tried taking a video of it yesterday but the trees I have to cut right now are poplar and the saw falls through them so fast that it doesn't make sense to use the big saw.
SawTroll
Information Collector
Jon1212
Riff Raff Fart Knocker from other Forum's.
How does the 2188 compare to a 390XP?
