760 dual 38 carb turning

[Patty14]

I have a ported 760 with a b-pipe. It’s got dual 38s. Came with a 135m 70p. That seems basically stock for sea level. I’m riding between 2k-5k ft. What do you all recommend for setup. I ride freestyle so want it to be snappy on the low end. Thanks!

 

[bowsdelux]

760 run with 44's not 38's

 

[camper357]

760 run with 44's n

You sure helped him out.

 

[Storbeck]

Your meeting is already as close as anybody on the Internet can get you and very likely within a jet size of where your want it.

 

[Storbeck]

Ah, well I didn't see the thing about elevation. You're probably close for sea level, so probably a little rich for 5k feet.

 

[Patty14]

Ah, well I didn't see the thing about elevation. You're probably close for sea level, so probably a little rich for 5k feet.

The ski ripped down at sea level, but once I got it home and hit the lake is had zero low end snap.

 

[WFO Speedracer]

The ski ripped down at sea level, but once I got it home and hit the lake is had zero low end snap.

Thay's not going to all be in the jetting , you will need to raise the compression also with that high of an elevation.

 

[kevbo]

Probably also bore the nozzle or bend the impeller some.

 

[wmazz]

What is the impeller and pitch?

Where are you riding at? It makes a difference if your lake is
a cool 65 deg @~5000' it may be close to the physical altitude.
But if it is a warmer temp during the summer, your lake may
have a higher corrected altitude during the summer.

Other factors that effect the corrected altitude is if the lake
is near a typical high pressure area in the upper atmosphere,
or if a "heat dome" that sometimes effects the weather is driving
temps up.


Bill M.

 

[wmazz]

What is the impeller and pitch?

Where are you riding at? It makes a difference if your lake is
a cool 65 deg @~5000' it may be close to the physical altitude.
But if it is a warmer temp during the summer, your lake may
have a higher corrected altitude during the summer.

Other factors that effect the corrected altitude is if the lake
is near a typical high pressure area in the upper atmosphere,
or if a "heat dome" that sometimes effects the weather is driving
temps up.


Bill M.

As altitude increases the engine will loose approximately 3% of
its horsepower/1000rpm. So if your lake at 5000' remains a cool
65 deg, you will loose 15% of your horsepower that is needed
to turn your impeller. But if the lake's corrected altitude is 7500'
you will lose 22.5% of your horsepower and an impeller change
would be a really good idea. HP==Speed, HP==Impeller size.

In racing, an impeller change at 4500 is a good strategy. But it
maybe more practical to bore the nozzle.

As altitude increases you loose compression and the carburetion
gets richer because there is less air. You can compensate for these
changes, but you will still loose some HP even if you make some
basic altitude changes.

Another consideration to increase acceleration is the jetting. You
could modify your jet specs to: 130 main, 90 low, 1.5 needle and
seat, 115gr spring, 1/2 low (pilot) screw, 1/8 front high screw, 5/8
rear high screw (replace the gaskets). The 90, 1.5, and 115gr are a
set.


Bill M.

You might be tempted to install Boyesen dual stage reeds. They
will give you an increase in acceleration, but they will also cause
a drop in peak HP.