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Post by spacebrowni on Jun 21, 2023 15:45:42 GMT -5
Hey guys i just joined this group because i have a few questions
Im starting a 2001 yamaha 3kj jog built and i camt afford a high end racing cylinder kit
I want to know if i could just bore out the 3kj cylinder and port it
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Post by 90GTVert on Jun 21, 2023 21:28:20 GMT -5
Welcome to the forum!
I don't mean this to sound rude; but if you are uncertain of this answer then it's not likely that any boring attempt would ever turn out like a high end racing cylinder kit. It would take a lot of skill to turn a stock cylinder into a true high end racing cylinder.
Boring in the first place, rarely makes sense for these small engines. To have it done properly (so the cylinder is actually straight and round) it's probably going to be at least in the $50-$100 range. Then you need a piston kit, gaskets and so on. So say you wind up with $150 in it. You could buy a Polini Sport or similar for roughly that much, which would include a matched cylinder head instead of you needing to figure that out as well.
Then there's the issue that you may or may not be able to bore the cylinder enough to go to a ~70cc. Cylinder walls could be thin, ports will be changed... it's going to be a hassle.
IMO either save up for whatever setup you're after, or just don't bother. You could wind up wasting money to learn that it's not as easy as it sounds. I'd also recommend not starting with a high end racing setup. They are a handful and not for everyone. Maybe just put a 70cc sport kit on it first. Follow that with a pipe and CVT mods if you wish to continue on the tuning journey. See how you like that before you dump thousands in a high end racing setup.
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Post by Zino on Jun 21, 2023 22:33:34 GMT -5
the jog is a great platform
It all depends on your ultimate goals an expensive race toy that will push past 60 mph or a daily rider that breaks 50 mph
if you screw up the stock bore you have a paperweight and have to buy a kit any ways
race build you will need more money to buy the supporting pieces a bigger carb to feed it and keep it cool a pipe that is matched to the port timing of the bore a variator and clutch upgrade to handle the extra power .
I just spent 1000 bucks on the supporting pieces .
They are very finicky and require constant tweaking
a sport 70cc kit is more for daily rider
very reliable and most stock parts can stay as is with small tweaks on upjetting stock carb and variator weights and clutch springs to rebalance the cvt
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Post by aeroxbud on Jun 22, 2023 14:16:10 GMT -5
Like Brent said it's not economically viable.
I have just put a new cylinder on. And the piston and gaskets for the same price as a good piston.
Go for any of the sports cylinders, and with a good exhaust you will be surprised how good it is.
The true race stuff would need considerable maintaining if used to do many miles. You need to think about that cost when buying these parts.
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