Pressure testing and ported saw question

[sILlogger]

just did a pressure test on my ported 066BB. it held 10lbs of pressure for as long as i wanted to stand there...i don't have a vacuum pump yet so a vac test will have to wait

this saw hasn't been performing up to snuff. when the piston is at TDC the exhuast port is just open out the bottom...thus letting some of the fuel charge out of the exhaust, correct? here is a pic

 

[Jacob J.]

What do you mean by up to snuff? Not enough torque band? The fact that the exhaust is open a bit when the piston is at TDC could be a factor, but not as much as if the exhaust port were 'freeported', meaning the skirt wasn't covering the port on the sides.

 

[sILlogger]

What do you mean by up to snuff? Not enough torque band? The fact that the exhaust is open a bit when the piston is at TDC could be a factor, but not as much as if the exhaust port were 'freeported', meaning the skirt wasn't covering the port on the sides.

the saw just doesn't have the power that it should...it won't stay tuned...im running a velocity stack and the carb will spit back fuel and over steady running will saturate the bottom of the grean weanie with fuel. the exhuast isn't free ported..it is closed off on both sides of the port

 

[CaseyForrest]

Happy to hear that tester is working out for you.

When you get a vac pump, all you need to do is swap the bulb with the pump. I think thats why I had the valve in there, to hold vac.

 

[Crofter]

You havent by any chance exposed the top of the piston to the intake port at BDC? also. Even stock there is very little coverage of the exhaust port bottom at TDC. The cylinder must have been lowered a fair bit. What is intake duration. That effects Base Compression too. Just with your mouth you should be able to pull enough vacumn to check if it is holding negative pressure.

 

[Four Paws]

the carb will spit back fuel and over steady running will saturate the bottom of the grean weanie with fuel.

This is often caused by a long intake duration...but not a rule. The 7900 Dolmar has a ridiculously long (by stock saw standards) intake duration. Intake harmonics play a large role here, as well.

If it is a BB kit, lots of guys don't like the way they perform. You may be one of them?!