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?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.
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.If you do it right you should easily hit 15000 with a 372 75cc oem piston cylinder
Instead of looking from outside the exhaust port, try looking through the plug hole. It’s seems more definate.
That is a great idea, I'll give that a try.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.
I'll try that before I give up on it, thanksThis with half the key width shaved for timing should get you a good running saw
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.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.
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.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.
I'll try and get a video up in a little bit.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 think your right, I've been searching the forums and haven't found any high rpm am 372 big bore saws.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 didn't check it.What's the ring clearence?