Topic: carb rejetting guidelines?

[nilsey]

i have been looking for the guidelines on choosing jet sises for various configurations (pods vs airbox, exhaust configuration etc).

I'm pretty sure i have seen it posted here and i have searched but for the life of me i can't find it.

the instructions were very mathematical, like, "add two jet sizes for pods, subtract one size for stricter exhaust" etc.

does any one know where that info is?

[Stert]

i would also like to see something like this if it is out there.

[mlinder]

I've seen this, but can say that it really depends on the bike.
These are base guidelines that may or may not work for you.

• 1 jet size for pod (K&N, Uni, generic) filter (single inside the air box)
• 1 jet size for drilling out the bottom of the air box
• 2 jet sizes for both single K&N and drilled air box
• 2 jet sizes for individual pod filters
• 2 jet sizes for 4 into 1 exhaust
• 1 pilot jet size for every 3 main jet size increase
Add up all the jet size increases and subtract one. (Remember they go in steps of 2.5 for each jet size).
Check plug spark plug colour often, sync carbs after each jet change and make sure the floats are set correctly.
Example
• Stock main jets: 102.5
• Stock pilot jets: 15
• 2 sizes for 4 into 1 exhaust
• 2 size for pod filters
• Main Jet Calculation = (2+2) - 1 = 3 size main jet increase or 102.5 + (2.5 * 3) = 110
• Pilot Jet Calculation = 1 size pilot jet increase or 15 + (2.5 * 1) = 17

[chopstar500]

What I'd love to see is a "real life" applications list. Actual owners could list their mods/etc. and give input on actual performance results.

Example:

Owner #1: 1971 CB500 with 4 into 1 Mac Exhaust, UniFilters, 105 Mains, etc... =  good overall performance.

This way we can see how other owners have dealt with rejetting after modifications.

[nilsey]

found it!

http://forums.sohc4.net/index.php?topic=28088.0

now can anyone answer me this: what is the jet size increment for a 1976 CB550K?

my specs show the main jet stock being  a size 100, with my K&N pods and my 4 into 2 exhaust what means 2 + 1 - 1 jet sizes = 2 jet sizes, so does tham mean o go up from 100 to 110?

i ask this beacuse i notice that the jets i see for sale go up from 100 to 105 then 110.

by the way, where is a good place to order carb jets?

[hapsh]

found it!

http://forums.sohc4.net/index.php?topic=28088.0

now can anyone answer me this: what is the jet size increment for a 1976 CB550K?

my specs show the main jet stock being  a size 100, with my K&N pods and my 4 into 2 exhaust what means 2 + 1 - 1 jet sizes = 2 jet sizes, so does tham mean o go up from 100 to 110?

i ask this beacuse i notice that the jets i see for sale go up from 100 to 105 then 110.

by the way, where is a good place to order carb jets?

Yep, 100-110 is two jet sizes.  I also agree that altitude is very important, I only went up one jet size to 105 with pods and 4-1, and dropped my needle clip one position because I am at 2600ft.  Also I see alot of the times people seem to think changing main jet sizes make a difference on around town riding using the lower end of the throttle.  They really don't, they only come into play when you really crack open the throttle( 3/4-WOT).  I focus on needle positions and the airscrews first.  Many times in the past when jetting I would run without ANY main jet until I got the idle/midrange airscrew/needle throttle positions figured out.

[nilsey]

Yep, 100-110 is two jet sizes.  I also agree that altitude is very important, I only went up one jet size to 105 with pods and 4-1, and dropped my needle clip one position because I am at 2600ft.  Also I see alot of the times people seem to think changing main jet sizes make a difference on around town riding using the lower end of the throttle.  They really don't, they only come into play when you really crack open the throttle( 3/4-WOT).  I focus on needle positions and the airscrews first.  Many times in the past when jetting I would run without ANY main jet until I got the idle/midrange airscrew/needle throttle positions figured out.

yep, thats exactly where i bog down, at WOT.  makes it hard to get up to spped on the expressway!

thanks for the tips!