Spuds Porting and Tuning Thread

[MattyF]

Eddy can you stick as many pics as possible up of the 560 port work up when you do it.

Can't see any thing on AS in pics to give me an idea of what's needed to come off.

 

What's people's thoughts on polishing ports as well ? Is it possible the fuel side may benefit from being rougher ?

[Eddy_t]

Eddy can you stick as many pics as possible up of the 560 port work up when you do it.

Can't see any thing on AS in pics to give me an idea of what's needed to come off.

 

What's people's thoughts on polishing ports as well ? Is it possible the fuel side may benefit from being rougher ?

 

 

I will try, I'm not particularly good at remembering photos...

 

As for polished, the Americans do it a lot, but I'm lazy and don't bother to get it to a mirror finish, just smooth it out.

[peatff]

What's people's thoughts on polishing ports as well ? Is it possible the fuel side may benefit from being rougher ?

 

On a 4 stroke with longer inlet ports it is thought by some that a rougher finish may benefit the fuel atomisation but on the short distance that the fuel is travelling in the ports on a two stroke I can't see it making any difference whether they are polished or left a bit rougher. Just my view though no science behind it and if anyone has a dyno that is able to pick up minute variations in power there may be some evidence somewhere on the net.

[spudulike]

I've always thought you boffins had made up the "Venturi effect" as an in joke to confuse is regular thickos.

 

That analogy explained it in perfect laymans term, cheers!

 

I believe that was me who came up with that theory first when my ported 346XP four stroked at well under one turn out on the H screw. I then found other machines doing the same and logic says, more flow in the carb choke means more venturi effect and greater pull on the fuel in the metering section.

 

Not sure I have ever seen anyone else mention it but the theory is basic physics and Eddies experiment backs it up in a simple practical experiment.

 

I don't tend to write down rubbish, just fact from what I find:thumbup:

[adw]

Surley more power means more fuel, auto tune only has one jet into both high and low and will only allow so much fuel in, it also has a govenor, i am not so sure porting is going to increase power just alter the power curve, still i would like to hear your findings.

[Eddy_t]

Surley more power means more fuel, auto tune only has one jet into both high and low and will only allow so much fuel in, it also has a govenor, i am not so sure porting is going to increase power just alter the power curve, still i would like to hear your findings.

 

 

It has been done already! The reason I'm porting now is the warranty is about to expire.

 

The air flow draws the fuel out, it isn't sprayed out, the needles (or valves) restrict the flow of fuel to the jets.

Increased air flow sucks more fuel out because it creates a higher negative pressure behind the jet and naturally the vacuum needs to be filled.

Yes more power uses more fuel, but the carb controls this via a very simple set of rules: engine speed is too high (lean) -> add more fuel (richen mix)

Engine speed too slow (rich) -> add less fuel (lean mix)

 

That's how the autotune managed to keep saws with massive air leaks running for so long.

[wyk]

I've always thought you boffins had made up the "Venturi effect" as an in joke to confuse is regular thickos.

 

That analogy explained it in perfect laymans term, cheers!

 

That's why you want to piss in to a crosswind. Just not TOO much of a crosswind.

[Joe Newton]

That's why you want to piss in to a crosswind. Just not TOO much of a crosswind.

 

 

Another great analogy you lot make learning fun!

[wyk]

Surley more power means more fuel, auto tune only has one jet into both high and low and will only allow so much fuel in, it also has a govenor, i am not so sure porting is going to increase power just alter the power curve, still i would like to hear your findings.

 

There is no governor in AT or MTronic saws. Technically, no rev limiter either. The electronics control the solenoids. See Eddy's post.

 

As for power, if there was none to gain, why would we bother?

 

The last 261CM I ported was 42% faster with the bar buried in wood.

The last 241CM I did was 30% faster.

Hell, even just modding the muffler on the 261, you get huge gains.

 

I work with huge trees all day long, processing for furniture or firewood, on a large estate. Ain't got no time for hauling around a 660 or 880. My back is old, but my arms are young, too. This ported 044 is a god send:

 

[adw]

I need to check if it has a ignition govenor, i thought it did, by the way i do understand all the principles of how a carb works, even the compensator on the carb. I need to speak to my auto tune specialist to see just how it will react with a ported cylinder,