Thread: uneven power
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Old 09-01-2015, 08:58 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: uneven power

Good advise so far, but I'll give my 2 cents worth of free power...
If the engine feels like it's lacking on top you can remove the cylinder and run 2 base gaskets, this will raise the tops of all the ports in relation to the piston, or even more importantly, crank position. This trick will add a few more degrees of transfer and exhaust duration and give a little more power up top.
Now to get back the power down low you can lap the head while you got it off, just set a sheet of 180 grit sandpaper on a flat surface like a sheet of glass... the surface needs to be perfectly flat. Next just take the head and run it over the sandpaper in circular or figure 8 motion and shave off at least 1mm (2mm if running 2 base gaskets). This will boost your compression and will give an improvement from idle to redline... if you got a compression tester, ideal compression is 135 to 150 psi (it may need 93 octane premium fuel above 15psi tho).

For the intake, the shorty intakes usually work best for mid range and top end power, but the stock shorties are rather restrictive since their opening is only 13mm, this can be opened up to about 16mm to allow all the flow from the carb, a stock nt carb has a 14mm bore and the nt speed has a 14.5mm bore. If you're running a Dellorto clone, these are usually 14mm, they perform better because they're less restrictive internally and they mix the fuel and the air a little better so they feel and act like a slightly bigger carb comparing to the nt type carbs... anyway, opening up the shorty intake to at least 14mm will unlock some more power from midrange on up.

For the exhaust, the banana pipe is a poor performer because it's "tuned" to a higher rpm than most of these engines can reach... they're also quite restrictive if you're looking for more rpm or top end power... depending on what kind of tooling you have access to and your skill set, there are other pipe options that aren't too expensive... you would also be surprised how well a straight pipe that's tuned to run best at a certain rpm can do too...
And pretty much for all pipes you can buy, if you got a dremel and some carbide burrs or grinding stones, the inlet flange on most pipes is a huge restriction since the hole is usually small and round, open this up enough to match your exhaust port outlet and this will free up a few more ponies...

Just by doing all the free mods mentioned above and in previous posts will give you a very noticeable improvement, some of the stuff I mentioned is free or really inexpensive to do except the exhaust, but doing all the free mods will free up enough to get you a good pipe... there are a few mods you can do to make a banana pipe perform but it takes some cutting and welding, if you got a welder and can weld, I can help ya out there as well as a few other members in here who know how to mod these pipes...
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