Well the head is on so a photo is out. And since you asked so nice I'll try and explain. Like said you want the exhaust side cleaned up for nothing to hamper the exhaust getting out,so make it smooth, and get rid of any sharp edges.
On the intake smooth sides and roof, and a really rough bottom will cause turbulence keeping fuel moving with the air, instead of sticking to the tunnel. Same as the exhaust smooth out any sharp edges to keep the flow going to the valve. I even trim off the bottom of the valve guide, and of course lap the valves. Just like every porter does.
Now my little trick, you make the intake smaller. Yeah, smaller. There is flow and there is velocity. Biggest port doesn't do you any good if you can't get the most mixture into the combustion chamber via the valve. You have to help the flow. How? Introduce something that will speed up the flow, and actually pull it through to the valve. Think venturi effect.
I put a hump on the port floor, ahead of the valve. It squeezes the mixture and speeds it up dumping into the valve, at the same time as it speeds up it causes a vacuum on the backside pulling more of the mixture in from the carb.
Both my engines seem to like it. I had to up the jets, both idle and main, as from reading the plugs afterwards, they both were lean, and idle quality was poor. So it looked like I was getting lots of air and not enough fuel. Added more fuel and both now idle just fine, and the bikes run great. Before I had to up the idle speed to keep em running, or have the choke partially on. And they would seem to fall off at higher rpms, like they were running out of gas. Now They both will sit there and idle like a Harley, barely turning over, and I've yet to hit top end, they both just keep pulling.
No dyno to proof the change, just seat of the pants and spark plugs that show they are now in range.
As for the hump, it's one of those you have to play with to find the sweet spot, size wise. Your plugs will let you know when you hit it.
The head work was done after all the normal upgrades, header, valve springs, air filter, billet rod and flywheel, gov removed. At that time the plugs were showing a nice tan color.
So there you go, happy now? :smile:
On the intake smooth sides and roof, and a really rough bottom will cause turbulence keeping fuel moving with the air, instead of sticking to the tunnel. Same as the exhaust smooth out any sharp edges to keep the flow going to the valve. I even trim off the bottom of the valve guide, and of course lap the valves. Just like every porter does.
Now my little trick, you make the intake smaller. Yeah, smaller. There is flow and there is velocity. Biggest port doesn't do you any good if you can't get the most mixture into the combustion chamber via the valve. You have to help the flow. How? Introduce something that will speed up the flow, and actually pull it through to the valve. Think venturi effect.
I put a hump on the port floor, ahead of the valve. It squeezes the mixture and speeds it up dumping into the valve, at the same time as it speeds up it causes a vacuum on the backside pulling more of the mixture in from the carb.
Both my engines seem to like it. I had to up the jets, both idle and main, as from reading the plugs afterwards, they both were lean, and idle quality was poor. So it looked like I was getting lots of air and not enough fuel. Added more fuel and both now idle just fine, and the bikes run great. Before I had to up the idle speed to keep em running, or have the choke partially on. And they would seem to fall off at higher rpms, like they were running out of gas. Now They both will sit there and idle like a Harley, barely turning over, and I've yet to hit top end, they both just keep pulling.
No dyno to proof the change, just seat of the pants and spark plugs that show they are now in range.
As for the hump, it's one of those you have to play with to find the sweet spot, size wise. Your plugs will let you know when you hit it.
The head work was done after all the normal upgrades, header, valve springs, air filter, billet rod and flywheel, gov removed. At that time the plugs were showing a nice tan color.
So there you go, happy now? :smile:
