poor top end power...

gsxrg · Post by **gsxrg** » Tue May 12, 2009 4:52 am

In need of the experts help.
I have the following parts on a arnada (sym)
72cc corsa bore
ct crome mani
28 kehin carb (with air box)
v8 pipe
7.4 to 1 gears
I have checked compression (135psi).
I have replaced the ign coil.
changed jets over and over.
The bike runs smooth, idle great, and get good gas mileage.
I just has poor power at top end.
What Should I check next!
Any help would really help.
Thanks

bakaracer · Post by **bakaracer** » Tue May 12, 2009 5:04 am

What is it doing on topend?

gsxrg · Post by **gsxrg** » Tue May 12, 2009 12:48 pm

when at full throttle or 1/2 throttle very little differance. There is more noise at full but dont have the power like before. When I first installed all the parts. I would go about 60mph. now I am lucky to get to 52-53mph.

Wheelman-111 · Post by **Wheelman-111** » Tue May 12, 2009 1:02 pm

Greetings:

Sometimes it can be hard to differentiate between outright lack of power and just incorrect variator weights. Your setup sounds like it should rev sky-high. Usually that means a loss of midrange oomph.

Perhaps just drop 6 grams from the variator and see if you like it better?

bakaracer · Post by **bakaracer** » Tue May 12, 2009 3:53 pm

also check the belt and make sure its not worn out.stock belt width is 15.5mm,if its less than 14.5mm you need to change it.

Post by **noiseguy** » Tue May 12, 2009 9:06 pm

Is that 28mm carb a bit large for his setup? The "no difference between 1/2 and full throttle" makes me wonder if there's not enough air velocity in the setup.

gsxrg · Post by **gsxrg** » Tue May 12, 2009 11:13 pm

Thanks everyone.
Just figured it out. (after 3 weeks).
The compresson is low when it warms up. (down to 120psi)
I was checking compresson when the engine was cold.
checked a know good bike with the same engine and he had 140 psi.
Time for a new piston!!!!

Thanks again for the help.

burnt_toast · Post by **burnt_toast** » Wed May 13, 2009 11:02 am

still decent compression..

I'd bet on lighter weights and different pipe

maddog · Post by **maddog** » Thu May 14, 2009 3:08 am

if you live on the rock as i do you should not be posting any problems

Arnadanoob · Post by **Arnadanoob** » Wed May 20, 2009 11:23 pm

noiseguy wrote:Is that 28mm carb a bit large for his setup? The "no difference between 1/2 and full throttle" makes me wonder if there's not enough air velocity in the setup.

28mm isn't the textbook ideal size for a 72cc but the Hawaii guys use them all the time with no issues.

The compression pressure isn't that bad, I'd look at what's already been suggested (belt wear) and check the weights in the front pulley. The OP said V8 pipe, I'm assuming Typhoon which isn't a high rev pipe. If I knew how many grams he's running in the variator I can usually figure out what the true issue is.

The questions I need to know to provide a real answer is:

1. What oil is he running? Castor, AMSOIL, etc.

2. What oil ratio? 32:1 50:1 ?

3. How much weights in the front pulley?

4. What jets is he using for pilot and main? Position of needle clip?

5. What center spring is he using? 1000/1500/2000 ?

gsxrg · Post by **gsxrg** » Fri May 22, 2009 4:35 am

I am running caster 927 at 40 to 1.
my weights are 7g and 7.5g (3 each)
my jets is at 52 pilot (1.75 turn out for the mixture screw)
my main jet is a 130.
clutch is a kelly med with the green springs
the center spring is 1500.

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