Technical Discussion Topics related to Technical Issues

Carby Jetting

Old 01-28-2006, 10:47 PM
  #1  
Senior Member
SuperSport
Thread Starter
 
shayne's Avatar
 
Join Date: Dec 2005
Location: Sunshine Coast, Australia
Posts: 963
shayne is on a distinguished road
Carby Jetting

Hi guys.

One thing that as been puzzling me is the reason for running a larger jet size in the rear cylinder. I will be jetting shortly and have been giving it some thought.

Common reason seems to be that the rear cylinder runs hotter. But if it is because of it being hotter it would need a smaller jet not a larger one. Higher temp, lower air density and a smaller jet, just like being at altitude with lower air density. If it was COOLER it would use a larger jet.

This is my understanding of jetting. Have I forgotten something?

Does anyone know what is happening with this cylinder?

One thought of mine is that it is due to the fact that the cylinders have different length intake trumpets, and therefore the airspeed will differ between cylinders.

What do you think guys?
shayne is offline  
Old 01-29-2006, 08:14 AM
  #2  
Senior Member
SuperSport
 
Join Date: Mar 2005
Location: Laurel, MD
Posts: 758
jschmidt
It's because of less cooling in the rear cylinder.

You're making a leap of logic. Cooler air is more dense and can accept more fuel.

But hotter engines require a somewhat richer mixture to avoid detonation.
jschmidt is offline  
Old 01-29-2006, 02:19 PM
  #3  
Senior Member
SuperSport
Thread Starter
 
shayne's Avatar
 
Join Date: Dec 2005
Location: Sunshine Coast, Australia
Posts: 963
shayne is on a distinguished road
Re: Carby Jetting

Thanks jschmidt.

I was thinking about intake temperature, not cylinder temp. Makes sense now you have pointed it out. Thank you.

I new there had to be a good reason!

Is this cooling difference due to airflow over the moving vehicle, or due to something in the cooling system?

The reason I ask is that when it comes to dyno tuning, if it is due to airflow, it might not show up in a static enverinment. Will you notice this on the dyno, or is it only seat of the pants tuning that it will show up?
shayne is offline  
Old 01-29-2006, 02:29 PM
  #4  
Senior Member
SuperSport
 
Join Date: Mar 2005
Location: Laurel, MD
Posts: 758
jschmidt
It's purely because it is blocked by the front one. All v-twins experience this to some degree.

It's just proper jetting. It would be a rare person who could ascribe a fueling error to a particular cylinder. It shouldn't notably change a dyno run, particularly if there is a fan.
jschmidt is offline  
Old 01-29-2006, 02:47 PM
  #5  
Senior Member
SuperSport
Thread Starter
 
shayne's Avatar
 
Join Date: Dec 2005
Location: Sunshine Coast, Australia
Posts: 963
shayne is on a distinguished road
Re: Carby Jetting

Righto, thanks. I will remeber that when I get it back together and it's time for a tune.

Cheers,
Shayne
shayne is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
Galaxieman
Technical Discussion
3
05-07-2007 06:45 PM
FRANKSVTR
Modifications - Performance
2
03-31-2007 05:12 PM
cliby
Modifications - Performance
10
03-30-2007 11:57 PM
redlinetech
Modifications - Performance
8
03-16-2007 04:34 PM
Shawn Torpey
Technical Discussion
4
03-09-2007 08:54 PM


Thread Tools
Search this Thread
Quick Reply: Carby Jetting


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.