Jetting

[HighCountry]

Hi i am in middle of build on my 79 GS550E and was wondering if anyone could suggest a base line setting for jetting, I know K&N suggests a jetting for their pods but i am going a step farther, this is where it gets tricky, i am using a part of the standard exhaust down to muffler then about 6 inches of stainless from collector to a Couple of Dime City Shorties slightly slanted up and i dont have a clue how to compensate for jetting, I am going from an #80 to a 92.5 do i need to go more with this type of exhaust. suggestions? Thanks

 

[mydlyfkryzis]

Not trying to be snarky (but it happens) , but do you really think there is a handbook out there that says : this exhaust with this airfilter on this engine with these carburetors and these engine modifications are these particular jets?

You did something you say is unique, yet you think there might be someone who knows what jets you need?

You have to do plug chops, or exhaust O2 sensors, or even better, a dyno with a wideband O2 sensor. then you can dial it in.

No shortcuts on carb rejetting.

Does the engine run well without the mods? If you aren't starting with a properly running engine, it is even going to be harder to get it to run right with all the changes.

I am sure someone here will venture a guess (it has to be a guess) but in the end, you will be doing, at the minimum, plug chops.

Sometimes the changes make you run rich, not lean.... So good luck, pick a place to start, and run the bike, check the plugs, adjust as necessary.

 

[HighCountry]

First of all i understand there isnt a book for this, i was just asking if anyone had done something like this to get a baseline to start that is all sorry i asked!!!!

 

[mydlyfkryzis]

Wasn't excoriating you....Just your expectations are high...K&N gave you a starting point. Start there.

Question...was the carburetion right before the changes? Were the plugs nice and tan?

Does your bike run well before you make the changes?

Your question is not invalid, we just don't have enough information....

Lot's of 'Depends" in any answer.

You may find the bike runs too rich after your mods....or too lean....no telling.

Are you running stock carburetors?

 

[Sonreir]

For nearly any modification (aside from massive changes in displacement or maybe forced induction), your baseline is stock jetting. If you're just making intake and exhaust changes to a four stroke, you're not going to go so lean that you'll damage anything.