Porting

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dfw
Pictures wont show important details. Remember that a 650 wont have as much low end so raising the exhaust port also requires raising compression. A zeeltronics ignition can help with response and lower the fuel requirement. I like to clean up transfers and widen the exhaust port to 66% of the bore and raise it no more than 190 degrees open. Bend the impeller so the pipe hits quick enough, this is important and it will end up flatter than you may expect. Top rpm should be close to 7000 depending on the pipe used. You can pump them up more by widening the exhaust more and upping compression but top end life will suffer. I know that a pair of Mikuni 44s will work, never tried anything larger.
 
Pictures wont show important details. Remember that a 650 wont have as much low end so raising the exhaust port also requires raising compression. A zeeltronics ignition can help with response and lower the fuel requirement. I like to clean up transfers and widen the exhaust port to 66% of the bore and raise it no more than 190 degrees open. Bend the impeller so the pipe hits quick enough, this is important and it will end up flatter than you may expect. Top rpm should be close to 7000 depending on the pipe used. You can pump them up more by widening the exhaust more and upping compression but top end life will suffer. I know that a pair of Mikuni 44s will work, never tried anything larger.
I got a couple of cylinders and both have had some work done. Both have the exhaust cleaned up but 1 has 1 sleeve cut down (or up) to the divider and then it was kinda tear dropped only on the inside of the sleeve? I've seen that done before. So no matter what I'll have to resleeve the cylinder set so they'll match. Hopefully I can get some templates from Ericsson's? My wife isn't going to let me spend a ton change on it so I'll have to just get by or find someone who has to many parts and easy on the pockets..lol!!
Here's a pic of what I got from a guy in CA. He gave 2 set's for a $100 so there's no complaining!
I have a new 44 to use. I'm not going with duels because I don't want the headache of getting them setup. I only get to ride a few times a year so I just want to have fun sliding, diving, and normal screwing around. I raced in my younger yrs like in my early 20"s now I'm 56!
Thanks for your help and if ya come across anything please let me know.
I'm new to this forum...
 

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I did one this spring that was pretty similar to what Kevbo described. I raised both exhaust and transfer ports, was around 186/122 exhaust/transfer duration, this was in an X2. Used an R and D pipe meant for a 750 that was probably not ideal because it had a HUGE manifold (~49mm at the manifold/head pipe joint that everybody is so obsessed with), stock waterbox (even the stock cast elbow) from chamber to waterbox, I did have an oversized straight out exit though, zeeltronic, I screwed up a little when I cut the head and ended up about 170 psi (about what I was shooting for) and about .070" squish clearance (way bigger than I was shooting for), dual bn38 round body carbs that worked just fine despite everybody hating on the round bodies. I saw a best of 46mph on gps at a probably-too-high 7500 rpms, would have probably been better with a little bit smaller nozzle/steeper impeller but about then my 30 year old crank ate a crank bearing. (the rpm might have been a factor). Don't underestimate the importance of pipe chamber temp and water routing/restrictors because it made a big difference, particularly the amount of water into the stinger/waterbox made a surprisingly big difference, it always wanted less water until it was no water.

I don't have any pics but it looks like sloppy amateurish porting, so the pics wouldn't be much help. I measured out what I wanted my exhaust port height and width to be, and then just cheated my yamanube template up/down side to side to form the outline based on that height and width, this resulted in very round corners that probably gave up some performance to a more square port shape but I was okay with that. I did port the case too Just rounded off the transition from the reeds to the cylinder, the 650 cylinder actually has a fair amount of material there you can open up because the cylinder sleeves don't extend down below the cylinder casting. It's easier than a 750 or a 62t because the reeds are the same width as the crank so it's just rounding a corner not much of the "fingers" to make.

I think my strategy with the porting would be different if I was using a stock ignition without the raised rev limiter or the ability to pull back timing up top, but I dunno. I've only had the one 650 so can't say much about what to do with a stock ignition.
 
Evidently my memory is not great, it was only turning about 7250 on my best setup. Still would have liked to try a little bit smaller nozzle for a little less rpm.


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