Jetting

[Dawn]

I need your help here...

Going through the invoice of the parts that Paul ordered, I noticed that he purchased a number of jets.  Can someone give me a quick explaination as to the theory behind this?

Thanks!

Dawn   ;)

P.S.  He was working on the bike, with only 4 days to go, I didn't want to bother him.  He must stay focused.   ;D

[KBOlsen]

I'll take a stab at it..

Different size jets would be used to deliver different volumes of fuel to the carburetor under specific conditions... allowing you to fine-tune your air/fuel misture for optimal performance.  For example, if you were racing in Denver, you'd want smaller ("leaner") jetting than in St. Louis because the atmospheric composition would cause you to run "richer" (the air is thinner at higher altitudes).

From John's drag-racing days... he had a little board with every size jet made for his carburetors... and would watch barometric pressure, etc. to help tune the bike.

[Dawn]

From John's drag-racing days... he had a little board with every size jet made for his carburetors... and would watch barometric pressure, etc. to help tune the bike.

Ahh....

That's why Paul stated that we need to get a barometric pressure gauge (Paul used to drag race also).  

Is it true - the colder the day, the larger the jets and visa versa?

Dawn   :)

[sdiver68]

Colder air = more o2 per volume = larger fuel jets to provide enough fuel to burn

[TZDeSioux]

Yep.. colder it is outside.. the bigger the main jets. High relative humidity=smaller main jets
Higher the relative air density=bigger mains

I have a weather station that collects temperature, relative humidity and barometric pressure(which you have to calibrate whenever you go to a different race track) to calculate the relative air density. Once you get a perfect setup. You can record every little detail about that particular day. That is your baseline. So if the relative air density increases you go up 2 jet sizes and ride the bike to see how it runs. Then you know that if the RAD increases or decreases by a certain percentage.. you  change the changes by however many sizes. Soon enough you'll have a chart with all the correct jet sizes that match up to the RAD.

[Dawn]

Thanks for the quick lesson.  I am sure that Paul will provide more insite as we get into the season.  

Thanks again!

Dawn   :)

[Super Dave]

Production bikes like and SV, R6, etc probably won't change a whole lot with the stock air box.  Pretty consistent.  

The one thing to remember, if you have a JET KIT...

The needles probably have a different taper, so the jet that you used with the stock needle will be different than the jet you use with the jet kit needle.  Probably leaner...

[MightyDuc Racing]

Anybody know where to buy jets for Keihin flat slides?

[Super Dave]

Sudco would be the place to call.  Any dealer should be able to get them from 'em.

Always use the OEM jets (meaning Mikuni, Kehin).  They are accurate.  You can get some cheaper ones from K&L, etc., but they aren't as accurate and then you start to have problems.

(Yes, we race motorcycles... ;D)

[MightyDuc Racing]

Got my local shop looking into it for me.  Thanks for the info.  By the way, any idea how much jets cost on average?

Thanks!

[h8mondays]

The last time I bought jets I think I paid $10.00 after tax for the main and a pilot. (one each)  I don't remember their individual prices, but it isn't much regardless.

[Super_KC124]

I have a weather station that collects relative humidity  

Do you know the definition of relative humidity? ...........Never mind. :-X