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Old 10-12-2014, 07:52 PM
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Davezilla Davezilla is offline
Motorized Bicycle Elite Member
Join Date: Mar 2014
Location: San Antonio Texas
Posts: 2,710
Default Re: Newbie questions for upgrading

I agree with HenShooter's recommendations, even tho they don't add power or speed, they do add reliability... The rejetting can add power tho if yours is running too rich or too lean, there's no size I can recommend because a lot depends on other conditions like outside temperature, altitude above sea level, and any engine mods etc will change what jet size your engine likes. Some like to solder the main jet shut then re drill and others like to have a collection of jets to swap out until they get it right... both methods work, but drilling tends to be the most accurate when one size is a bit rich and the next size down is too lean etc..

for the sprocket size, if your bike reaches top speed quickly and it feels like the engine is running out of rpm when it feels like you should be going faster, it's time to go to the next size smaller sprocket, if it accelerates sluggishly and feels like it's struggling to go faster then it needs to be geared down with the next larger sprocket. Going from a 44T to a 41T is enough for you to feel a difference, but if you live on flat land with very few hills, a 36T may do better... The way the engine is set up will also be a factor in what rear sprocket size you want, an engine with decent torque and doesn't rev past 6k rpm will do better with a small rear sprocket than a 8000 rpm screamer with less bottom end torque but good top end power.

As far as the most bang for the buck mods goes, a good expansion chamber pipe will deliver and can be tuned for more bottom end or more top end by the header length.

The stock NT carb works great with nice all around power, it's also simple and reliable, no real need to upgrade the carb unless you're looking for big power at high rpm's, then a Mikuni VM 18 or Dellorto PHBG 19 or 21mm carb work really well. They do require some tuning to get right but make good power once dialed in.

The stock CDI unit also makes good power but the weak link is the spark plug wire and boot, replace with a decent 7mm automotive wire and boot. The HD Lightning CDI is a really good choice for aftermarket.

For the cylinder head the stock one is way too small for good heat dissapation and has poor compression in stock trim, you can shave off some of the head to boost compression and power, but it still don't do much for keeping cool... The fred head, Diamond head or a Puch Hi comp head work really well here... excellent compression and much much better cooling.

A ported jug and indexed piston will make even more power and you can buy them from a few vendors in here with decent results, Fred's jug and piston combo work well and so does the Arrow ported cylinder and piston sets, or you can read up on the subject and do your own porting, Mainly cleaning up the casting flash from the transfers, widening the intake and exhaust will give noticeable results, but for more rpm and power you can alter the port timing but that's a much more in depth subject... people in here can help once you're ready to go that way.

Start off with a good pipe and maybe tune the carb, and then a better head and you'll have a nice noticeable gain, then go for a ported jug and indexed piston for the next step if the bike still isn't fast enough for you..
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