The right jets

74yamabob · Full Member Joined: Mar 08, 2008 Posts: 24

Hey guys I'm running a two 4in K&N air filter off a 45 degree pipe to my stock carbs. My carbs are off a 73. Can anyone give me a good idea what Mods I need to make as far as jetting and adjustments to keep my bike from bnogging down when i take off. I can hear it sucking massive amounts of air.

xsjohn · Posted: March 15, 2008, 3:55 pm Post subject: Re: The right jets

Have been hearing that the 4" filters can do that.....just went through the same thing with a customer.......try just taking them off for a test run and see what happens.....???

xsjohn

74yamabob · Full Member Joined: Mar 08, 2008 Posts: 24

Thanks I'll give it a shot. So when are going to come up with the mod for eailier models?

xsjohn · Posted: March 15, 2008, 10:50 pm Post subject: Re: The right jets

Three of the best on this site are testing as we speak.......Pretty much have to ride them to get the position of the needle absolute........I can correct the cylinder temps but there is nothing like the real test......the ride......actually takes more work than one would expect........

xsjohn

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

There are no "right jets" for these. The jetting specs changed many times over the model run. Rejetting must be based on what came stock in your year carb set, not the year of the bike. Here's a chart of the stock specs for reference .....

img163.imageshack.us/i...cs1qb3.png

As you can see, the '73 carbs you're running have slightly different jetting than the original '74 set. For minor mods like yours, what's usually required is 1 to 3 steps up on the mains and maybe one up on the pilots. As you increase the main jet size, it will bleed over into the upper midrange making it too rich and causing a stumble at about 4 or 5K under heavy throttle applications. If that occurs, lower the needle to lean the midrange and correct the stumble. When you lean the midrange, that may induce a stumble or flat spot just off idle, in which case you'll need the larger pilot.

74yamabob · Full Member Joined: Mar 08, 2008 Posts: 24

Thanks I'll give it a shot

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