(First Post) porting help

[HYPERSAWS]

If you do it right you should easily hit 15000 with a 372 75cc oem piston cylinder

 

[Redfin]

How are you measuring your transfers? At 104 you are definately needing some more bd.

 

[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.

I tried it with the feeler gauge and got 111 with the .010 and 116.5 with the .020. that would make my exhaust 104.5. I also did it the way most people do it and got 100 this time. At 100 I can slide a .0038 feeler gauge through the space and when I turn the crank the feeler gauge stops the piston at 99. Which one is correct?

 

[Ronie]

If you do it right you should easily hit 15000 with a 372 75cc oem piston cylinder

That would be nice. I wish I had a xpw top end, the one I'm using is a no name 52mm cylinder. I do have a new oem 50mm that I could put on it but I don't want to cut on it until I know what I'm doing.

 

[Deets066]

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

View attachment 177301

Instead of looking from outside the exhaust port, try looking through the plug hole. It’s seems more definate.

Also, your port numbers don’t really dictate rpm. That’s more carburation.
Advance the timing as stated before and see how it does. Don’t be afraid to lean it out a bit.

 

[Ronie]

Well I put the saw back together. I went to reset the carb to one turn out and noticed that the high was only 1/2 turn out, as rich as it was I would say that the carb needs a rebuild or at the least the needle valve needs adjusted. I'll try a different carb on it tomorrow and see if that helps it out. If I can't get the rpm up I'll just move on to the next cylinder. After doing some reading on the aftermarket big bore cylinders I think the exhaust is around 104.

 

[Ronie]

Instead of looking from outside the exhaust port, try looking through the plug hole. It’s seems more definate.

Also, your port numbers don’t really dictate rpm. That’s more carburation.
Advance the timing as stated before and see how it does. Don’t be afraid to lean it out a bit.

That is a great idea, I'll give that a try.

 

[Ronie]

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

I'll try that before I give up on it, thanks

 

[drf256]

Well I put the saw back together. I went to reset the carb to one turn out and noticed that the high was only 1/2 turn out, as rich as it was I would say that the carb needs a rebuild or at the least the needle valve needs adjusted. I'll try a different carb on it tomorrow and see if that helps it out. If I can't get the rpm up I'll just move on to the next cylinder. After doing some reading on the aftermarket big bore cylinders I think the exhaust is around 104.

You seem pretty adept at what you’re doing, so I’m imagining the limiters are gone if initially equiped? I’m not familiar with the model like the others.

What’s your airfilter setup like? Usually ported saws need the H needle out more than the standard 1 turn because more power takes more fuel to make. If your airbox isn’t open enough or your filter is restricted, that would cause less rpm and a Needle that’s already set lean. I’ve had restrictive filters do just what your saw is doing. I made the mistake of oiling a flocked filter at one point, that was like putting tape over the inlet.

Things that will limit RPM at a normal tune are:

Airflow restrictions
Too much compression
Too much heat
Bad ignition

Try one run with no airfilter and airbox open. See where she 4 strokes out of wood that way, and where your H needle tunes.

 

[Ronie]

You seem pretty adept at what you’re doing, so I’m imagining the limiters are gone if initially equiped? I’m not familiar with the model like the others.

What’s your airfilter setup like? Usually ported saws need the H needle out more than the standard 1 turn because more power takes more fuel to make. If your airbox isn’t open enough or your filter is restricted, that would cause less rpm and a Needle that’s already set lean. I’ve had restrictive filters do just what your saw is doing. I made the mistake of oiling a flocked filter at one point, that was like putting tape over the inlet.

Things that will limit RPM at a normal tune are:

Airflow restrictions
Too much compression
Too much heat
Bad ignition

Try one run with no airfilter and airbox open. See where she 4 strokes out of wood that way, and where your H needle tunes.

Thanks for the tips. The limiters are off and it has a new oem air filter. I'll give it a try with the filter off and the air box open and see how it does.

 

[huskyboy]

I’m betting the am cylinder has something to do with the issues

 

[Deets066]

I’m betting the am cylinder has something to do with the issues

I didn’t really see any issues in the vid.

1/2 turn out on the screw and only 13,000 seems off though.

 

[Moparmyway]

Can you video the saw at wide open throttle without any load ?

Yup, a good 5 second piss rev for us please ?

I don’t hear any 4 stroking happening in your video

My suggestion is to open the high 2 full turns, hit WOT, (ought to be so blubbering fat) and tighten the H untill you have 13,800 rpm.

Then video another piss rev for us please

Better yet, the whole procedure from above, on video, could let us all know how to advise further.

 

[HYPERSAWS]

What carb is on there.? I'm thinking it's the am cylinder as well, my work partner recently sold a stock oem 375 with unlimited coil and it was turning at 14400

 

[Ronie]

Can you video the saw at wide open throttle without any load ?

Yup, a good 5 second piss rev for us please ?

I don’t hear any 4 stroking happening in your video

My suggestion is to open the high 2 full turns, hit WOT, (ought to be so blubbering fat) and tighten the H untill you have 13,800 rpm.

Then video another piss rev for us please

Better yet, the whole procedure from above, on video, could let us all know how to advise further.

I'll try and get a video up in a little bit.

 

[Ronie]

What carb is on there.? I'm thinking it's the am cylinder as well, my work partner recently sold a stock oem 375 with unlimited coil and it was turning at 14400

I think your right, I've been searching the forums and haven't found any high rpm am 372 big bore saws.

 

[drf256]

The 1/2 out H needle, if the carb is stock/functional/unmodified means you're not moving air.

What is your Elevation?

Don't be overly concerned with free RPM, it's rpm in the cut that matters. I've had saws that 4 stroked fat at 15k be faster in the cut tuned cold to 13,500.

 

[HYPERSAWS]

What's the ring clearence?

 

[Ronie]

I had a few minutes this morning so I changed out the carb to a Zama clone carb, they look alot smaller than the HD 12. At one turn out on the high side it was turning 13,800, so I turned it in a hair and I hit the rev limiter, I thought it was unlimited. I left it there and made aprox 15 cuts and checked the plug. I think it looks good, nice and brown. I'm going to put a kit in the oem carb and see if it can do better. I'm also going to swap out the coil.

 

[Ronie]

What's the ring clearence?

I didn't check it.