Planning mods, need help

[mew905]

Alright so I plan on squeezing out every ounce of performance outta my motor but I gotta know some things before I do it.

#1, the crank.
I screwed up my old crank by drilling out the wrong side. If I get a new one and balance it properly (or perhaps even re-drilling my 'ruined' one to make it lighter AND balanced), what can I use in the holes to preserve or boost compression if it's not a bolt-on style? Some old school tuners said they used epoxy and cork, Jag recommends aluminum. My concern is when I fill it I dont want it to come back out again as I've heard some horror stories (high speed scooters, actually, the counter-balance fillers slide out and catch the rod at high speed).

#2 the pipe
I plan on buying a new exhaust. Would it be worth it to learn to weld (I know 0 about it) and do a torque pipe, or is there good pipes available? Those of you who have used a gutted stock exhaust and moved to an expansion/torque pipe would have particularly valuable opinions here.

#3 The carb
I plan on buying a new carb. I have a Runtong (dellorto clone, also known as the Dax RT) and noticed the inherent disadvantages of only being able to tune the jet. You can jet for high end and lose all your torque, you can jet for low end and four stroke like crazy, or meet in the middle and notice it sucks at both.
Jag now sells adapters to run Mikuni 22mm carbs and I was considering going that route. Would it be worth it? I always suspected a huge handicap on these motors is the inability to breathe properly. I didn't notice much performance moving from the stock NT to the Runtong, just that it idles a little better.

#4 Heat/the ports
I plan on re-porting all the ports to ideal timing (I'll decide what that is later) and aside from making the intake bigger (I have reeds so I cant screw the timing up), I'll also be making the exhaust wider. Doing so will also increase the heat output of the motor, I plan on going to ~30mm (62% cylinder bore) and yes, I'll round and bevel the port. However with the extra heat output, would I be exceeding safety limits? Morini's apparently handle 375 to 425 head temps daily, as well as 1100 exhaust temps. My bike (I'll get accurate measurements when the time comes) reads 175F head and 230F exhaust. That's gotta be way below the threshold, so I'm curious, what temps are other members seeing? What would you consider as safe temps? (I know I asked this all day in chat but I keep ending up having to leave before an answer is given).When I ran the bike lean last year (for a few months!) I saw around 900F on the exhaust (glowing hot enough to see the ground under it at night), no damage ever occured from it.

Please answer any questions (or as many as you feel you'd have a valuable opinion on). I'd love to hear your replies. I'm looking to have a highway worthy bike. All hardware has been changed to high grade steel, all bearings are industrial SKF rated to 30k RPM and the head is a puch head so damage shouldnt occur there. And please dont go on about how highway speeds could be unsafe on a bicycle, I just want to see if it can be done with an HT.

 

[ivan H]

Hi, I just wanted to say that a 22mm Mikuni is way too big for 1 of these China girls. I have a 66cc that is reeded with the piston properly ported for plus 5mm taken off the skirt adjacent to the intake port, with the Jugs intake lowered 5mm with a boost port added, RSE billet Hi comp head, SBP chamber, my own CDI etc & run a 16mm mikuni. 22mm will mean that u will be loosing velocity thru it & thus poor mixing & atomization. 16mm will do u fine,,, 18mm if ur pulling really hi rpm. Cheers

 

[mew905]

Hi, I just wanted to say that a 22mm Mikuni is way too big for 1 of these China girls. I have a 66cc that is reeded with the piston properly ported for plus 5mm taken off the skirt adjacent to the intake port, with the Jugs intake lowered 5mm with a boost port added, RSE billet Hi comp head, SBP chamber, my own CDI etc & run a 16mm mikuni. 22mm will mean that u will be loosing velocity thru it & thus poor mixing & atomization. 16mm will do u fine,,, 18mm if ur pulling really hi rpm. Cheers

I'll be running a full custom exhaust, high RPM's and need a large carb to compensate for it. One of these engine's major issues is breathing, with a good exhaust to haul gas into the chamber I'll need a wide throat carb. I chose the mikuni because Jag's site recommended it for its tunability (and I just recently started seeing them and Walboro carbs appearing on the forums and store sites). I've noticed my Runtong (Dellorto SHA clone) has an inherent disadvantage when it comes to tuning, and that with a richer jet you can get more low-end torque out of them (of course at the sacrifice of four-stroking at high speed). To hit 50 or even 60mph I'm going to need all the torque this thing can muster.

...That and once I figure out how to gear the motor internally and flow oil, I'll throw a turbo on.

 

[48ccbiker]

the only "velocity" difference between a 22mm and a 16mm carb happens when the 22mm is opened up far enough to be equivalent to a 16mm at WOT. So the old wives tales concerning bigger carbs mostly isnt true. A big carb runs just as good at low and mid rpm if it is jetted right. And a 69cc ported for high rpm needs at least a 20mm carb.
Widening the exh port wont increase heat output at the engine, only at the pipe. If anything it lowers head/cylinder temps because it lets the exhaust out faster. Pipe temps dont matter unless you are designing an expansion chamber.

 

[mew905]

Widening the exh port wont increase heat output at the engine, only at the pipe. If anything it lowers head/cylinder temps because it lets the exhaust out faster. Pipe temps dont matter unless you are designing an expansion chamber.

As far as I understood the wider area of the exhaust port (no matter in what direction) will increase temps because the piston makes less contact with the cool cylinder wall. Either way, my engine only produces a breezy 260F at the exhaust and 216F on the head.