What fuel jets did you move up to?

Hey fellow Yamaha luvrs!

I have an '82 650J and the pipes were changed to a 4 into 1 setup with a Vance and Hines exhaust pipe. The PO installed #118 main fuel jets but did not touch the pilot fuel jets. They are still the stock #40 pilot fuel jets and at the moment I'm not getting color on my plugs until 5 turns out. NOTE: Carbs and passages have been cleaned thoroughly with carb cleaner/air compressor/boiled in lemon juice for 1.5 hours each... then cleaned, re-cleaned and re-cleaned... and then cleaned 6 more times!

Did yall change your pilot fuel jets to a larger size when changing your exhaust system? Let's here what you did and how it worked!

 

What kind of intake setup, stock airbox or pods? I don't know what the stock pilot jet is. If the #40 pilot is the stock size then it should work with th 4 to 1 exhaust and a stock airbox. If you are running pods then you can try one size larger. Jets and pods is a trial and error process in jetting to get it right.

 

Hey mlew. I was hoping we could get some members to post their jetting numbers so we can sort out some of their trial and error findings. I believe that would help us all greatly!

The intake setup is stock...stock airbox and NO pods. The #40 pilot jet is the stock size but the PO beefed up the main fuel jet to a massive #118. I believe #110 is the "stock" main fuel jet. So you see, i'm drawing extra fuel through the main but the pilot hasn't been enlarged. I was thinking this could be my issue with the pilot screw not "rich-ening" up the mixture until 5 turns out.

 

My XS1100 is running a 4 to 1 exhaust with a K&N filter. Pilot jets are stock, mains are two sizes larger than stock.
The XJ1100 is running stock exhaust with a K&N filter. Stock pilots and one size up on the mains.

With your setup I would try stock pilots and one or two sizes up on mains. Jets come in sizes 110, 112.5, 115, 117.5 120, and so on.

 

At 5 Turns Out you are already well past where the Orifice is Wide Open.

Re-Jet.
Get a hotter Pilot Fuel Jet.
(Hang-on to the OLD Jet)
Run the Hotter Jet.
If you get the desired results from the Standard sized larger Jet. OK

If the Standard next-sized Jet is too Rich ... alter the OLD Jet.

Buy some Number Drills and up the size of the Old Jet one number at a time.

 

83 750 seca mac 4/1 pipe and i settled on 122.5 mains stock pilots
no snorkel in the air box and some pot scrubbers in the muffler
when you think your close but maybe the next size might be too much
that snorkel in the air box can add some lean(mostly mid to top end)
and the muffler packing can add some rich(again mid to top end)
i think mine could still be better but it's real close and i'am tired of pulling the carbs
i'am finding the 4/1's added mid range and the 7 to 9 kick just blended in
does that sound right?

 

Thanks guys! This is great info. Let's keep the numbers coming! Rick, I love your proposal. Polock, Thanks for the muffler packing tip on richening up the mixture. I'm not sure what you meant by, "...and the 7 to 9 kick just blended in" meant though.

What jets and mods are my XJ Brothers running and how's your baby running?

 

bump

 

-82 XJ750 Maxim
-4-1 header/exhaust
-K&N box air filter
-124 mains
-dynojet fuel needles and drilled slides


Plugs are perfect shade of brown during summer @ 3 turns out fuel mix screw.
During colder weather 3.75 turns out does the trick.