New to porting

[Shane¹]

I ended up putting the 6421 top end back on first. It has a little fuel spitting back into the intake and seems like I lost a lot of low adjustment range is this normal or did I do something wrong? Did I make the intake too low?

 

[Ronie]

What numbers did you use for the 6421?

 

[Shane¹]

I did exhaust at 102 intake at 75 and transfers at 130. I started my running saw today and watched it it looked the same in the intake so I took it out and made some cuts and some adjustments I think I was just tuning it really funny to try to get the spray back down and not just adjusting it like I normally do I think it is ok now. Need to swap out the decompression valve because to won't start with it pushed

 

[MemphisMechanic]

It’s spitting back into the intake boot with the intake at just 75 degrees? I’ve never touched a Dolmar saw but that doesn’t sound right. Usually you can take them all the way to 80ish on a Stihl or Husky without issue.

 

[Shane¹]

It’s spitting back into the intake boot with the intake at just 75 degrees? I’ve never touched a Dolmar saw but that doesn’t sound right. Usually you can take them all the way to 80ish on a Stihl or Husky without issue.

I think I just may have been over thinking it. My stock saw does the same thing and it runs perfect now that I just stopped worrying about it and set the carb right

 

[Shane¹]

Why when porting do a lot of guys cut the squish band and the base to get to the same finish numbers as if they just cut one or the other? Does cutting both put numbers in a better position to start or make ports a better size?

 

[Ketchup]

Why when porting do a lot of guys cut the squish band and the base to get to the same finish numbers as if they just cut one or the other? Does cutting both put numbers in a better position to start or make ports a better size?

Cutting a deeper base cut and a band cut to set squish will get you more compression than just cutting the base down to set squish.

A band cut reduces the volume of the combustion chamber. More band cut = smaller chamber = more compression. But it has to have a tight squish, so you have to cut the base to make up for what you took out of the band.

There are limits. Drop the base too far and the exhaust will free port. Often your intake will be too low as well. Reduce the combustion chamber too much and you risk detonation.

 

[NateSaw]

Look up part one the exhaust port and start ther.


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That series has helped me a lot.

 

[NateSaw]

My stock numbers came out to intake 78 exhaust 105 and transfers were 127-130. The squish measured a little weird because of some flash at the top of the cylinder I got .019-.026. Plan is to take the exhaust up to 98 or 99 clean up transfers and widen intake and exhaust. Going to try to find a way to sand the top of the band even and remeasure squish first

Use the old piston with sticky sandpaper. But you'll have to sand the base to drop the cylinder back down to raise compression. Compression makes torque.

 

[NateSaw]

Cut base. Not sand.