(First Post) porting help

[Czed]

Thanks, I paid $29 on Amazon. It's a 372 wrap on a 372 tank dyed black.
View attachment 177253

Yeah I've got 7 of those
The johnny wraps are pricey.

 

[srcarr52]

As it stands now the numbers are, exhaust 101, intake 81 and transfers 121. It has a HD 12 carb. Unlimited coil.

What BB kit is this? I've never seen a 372BB cast with over 150 ex duration (105 opening) and you haven't ground on the port roof at all. So I think your numbers are a little suspect. I wouldn't run more intake duration than exhaust.

I can't tell by the pictures if you did, but when you cut the base remember to cut the skirt extension. It could be bottoming out on the case before the gasket surface touches.

 

[Ronie]

What BB kit is this? I've never seen a 372BB cast with over 150 ex duration (105 opening) and you haven't ground on the port roof at all. So I think your numbers are a little suspect. I wouldn't run more intake duration than exhaust.

I can't tell by the pictures if you did, but when you cut the base remember to cut the skirt extension. It could be bottoming out on the case before the gasket surface touches.

I'm not sure of the brand, white box? The numbers are right, I've had the wheel on there three times and got the same numbers. I've also checked the exhaust two different ways. The normal way setting up the wheel using a piston stop and starting at zero when the exhaust opens. Same number both ways. I cut around .017 off the base and cut the cylinder skirt also.

 

[Ronie]

Made a new muffler. The pipe is a little over 1".

 

[srcarr52]

I'm not sure of the brand, white box? The numbers are right, I've had the wheel on there three times and got the same numbers. I've also checked the exhaust two different ways. The normal way setting up the wheel using a piston stop and starting at zero when the exhaust opens. Same number both ways. I cut around .017 off the base and cut the cylinder skirt also.

Do you have a dial caliper? To get 101 opening on the exhaust with 0.020" squish the port roof should be 0.960" from the squish band.

 

[Ronie]

Do you have a dial caliper? To get 101 opening on the exhaust with 0.020" squish the port roof should be 0.960" from the squish band.

I have a caliper. I havn't pulled the cylinder off yet but will measure it as soon as I do. As soon as I finish my coffee I'm going to pull it off.

 

[Ronie]

What BB kit is this? I've never seen a 372BB cast with over 150 ex duration (105 opening) and you haven't ground on the port roof at all. So I think your numbers are a little suspect. I wouldn't run more intake duration than exhaust.

I can't tell by the pictures if you did, but when you cut the base remember to cut the skirt extension. It could be bottoming out on the case before the gasket surface touches.

My numbers could be wrong if I'm not doing the exhaust right. I'm taking the number the pointer is on right when I see the first bit of light.

 

[Ronie]

I pulled the cylinder off and the top of the piston is very black and the crankcase is wet. The whole problem maybe because it needed lean out. I can't really hear a saw four stroke when the rpm are up, I can only hear it when the tone is low. That maybe why all my saws end up around 13,000 rpm.

 

[Ronie]

gasket on the cylinder

 

[Ronie]

Do you have a dial caliper? To get 101 opening on the exhaust with 0.020" squish the port roof should be 0.960" from the squish band.

I measured it and I got .990 and the squish is .017

 

[srcarr52]

I measured it and I got .990 and the squish is .017

That puts you at 152 duration, 104 opening, more inline with what I would expect. I normally expect 1 deg opening error between the mathematical way and reading the port opening on a wheel, make sure your not letting the port chamfer put too much error into your reading.

 

[EvilRoySlade]

That puts you at 152 duration, 104 opening, more inline with what I would expect. I normally expect 1 deg opening error between the mathematical way and reading the port opening on a wheel, make sure your not letting the port chamfer put too much error into your reading.

“You’re”, that time it mattered.

 

[Ronie]

That puts you at 152 duration, 104 opening, more inline with what I would expect. I normally expect 1 deg opening error between the mathematical way and reading the port opening on a wheel, make sure your not letting the port chamfer put too much error into your reading.

Ok, the pic is how I've been reading it.

 

[BGE541]

As it stands now the numbers are, exhaust 101, intake 81 and transfers 121. It has a HD 12 carb. Unlimited coil.

This with half the key width shaved for timing should get you a good running saw

 

[srcarr52]

“You’re”, that time it mattered.

GFY!

 

[srcarr52]

Ok, the pic is how I've been reading it.

View attachment 177301

You might be reading some of the chamfer.

I've heard of peoples methods of removing error like putting a piece of paper in the port till it touches. The best method I've heard is taking two wheel readings with a 0.020" and a 0.010" feeler gauge in the port; then the real opening is the 0.010" reading minus the difference between the two.

So, I think you might need to add a bit more exhaust duration and try to flatten the entrance of at least the exhaust side transfers.

Also, you may want to unshroud the lowers. Mark the piston at BDC and then match the lowers to the piston shape.

 

[Ronie]

You might be reading some of the chamfer.

I've heard of peoples methods of removing error like putting a piece of paper in the port till it touches. The best method I've heard is taking two wheel readings with a 0.020" and a 0.010" feeler gauge in the port; then the real opening is the 0.010" reading minus the difference between the two.

So, I think you might need to add a bit more exhaust duration and try to flatten the entrance of at least the exhaust side transfers.

Also, you may want to unshroud the lowers. Mark the piston at BDC and then match the lowers to the piston shape.

Thanks for the tip. I'll give the feeler gauges a try and see if I'm off.

 

[HYPERSAWS]

How many rpms are you looking for?

 

[Ronie]

How many rpms are you looking for?

Around 14,000 would be nice.

 

[HYPERSAWS]

I would go with scarr52 about the exhaust..