Spuds Porting and Tuning Thread

[spudulike]

I have ported it as you know, and it sucks more air through, hence a richer mixture, so, by my reckoning I can sort this by fitting a carb with a larger diameter centre (dunno what it's called) as this will suck less fuel out, allowing a bit more adjustment

 

 

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Mine runs a H screw setting of around 3/4 turn - it is normal, no need for a bigger carb, the extra flow through the carb pulls up a lot more fuel through the high speed circuit as the venturi effect of the carb is greater because of the flow!

[wisecobandit]

Is that a Zama el42 carb Eddy? They aren't so good as the walbros on the 357. The zamas also wont 4 stroke most of the time however rich you set them for some reason. Most of the tuners "overseas" swap them out for walbros.

 

Yup your right on the 385, if you can source the x torq 372 carb its about 2mm bigger.

[Eddy_t]

Mine runs a H screw setting of around 3/4 turn - it is normal, no need for a bigger carb, the extra flow through the carb pulls up a lot more fuel through the high speed circuit as the venturi effect of the carb is greater because of the flow!

 

 

But would not a larger bore decrease air velocity, which draws more fuel?

 

 

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[Stubby]

But would not a larger bore decrease air velocity, which draws more fuel?

 

 

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A larger bore will decrease velocity unless its pulled in by a larger piston/engine. There must be an optimum ratio for carb bore size against piston bore and stroke . ?

[spudulike]

Been porting a 372XP today, took a while to clean it up but is coming along well. Unfortunately the clutch side seal failed the vacuum check so needs replacing - just as well I found it as it would have gone pop in a short while:thumbdown:

[div_h]

Been porting a 372XP today, took a while to clean it up but is coming along well. Unfortunately the clutch side seal failed the vacuum check so needs replacing - just as well I found it as it would have gone pop in a short while:thumbdown:

 

On the exhausts on a 346 what do you do with the old outlet when out weld a pipe in?

[spudulike]

But would not a larger bore decrease air velocity, which draws more fuel?

 

 

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No, a smaller bore will inrease velocity and increase the draw on the fuel. I have ported a few of these saws now and not needed to go to the lengths you are looking at going to.

 

The carb can only deliver the amount of fuel/air it is designed to deliver so if the engine is radically modified, it may benefit from a larger bore carb but I have found that mine is verging on dark brown and is pulling 15,000rpm!

 

I reckon you will open a bag of worms if you do this - I have heard of some tuners opening the carb bore up!

[spudulike]

On the exhausts on a 346 what do you do with the old outlet when out weld a pipe in?

 

I open the existing hole in the exhaust up - it is a simple mod on this saw!

[div_h]

I open the existing hole in the exhaust up - it is a simple mod on this saw!

 

Ah is that the angled up thing? Can't really explain it:blushing: I put a pipe in mine today, might have to purchase a new 1 before you get it

[spudulike]

A larger bore will decrease velocity unless its pulled in by a larger piston/engine. There must be an optimum ratio for carb bore size against piston bore and stroke . ?

 

Quite correct, generally the standard carb will suffice for a woods ported saw and I would only come away from this if I were engineering something quite radical!

 

I do have a bit of software that calculates all the variables but it gets a bit complex and isn't that conclusive!