Jetting opinions

[steelelc]

HI everyone got my US import gsx 750 et running the other day after picking it up its still got the american spec jets in the carbs attached a graph of the difference in the jetting 

whats everyone reckon ? was running really lean the other day, a lot better now but still lean on the 1st cylinder, 

noticed the american carbs you can't adjust the conical rods. 

what would you change/ stick with 

also on the air filters everyone use standard? or a k&n in the airbox?

Cheers,

 

Tom 

[steelelc]

pilot screw was set at 1.4 turns on the american at 2.5 turns at the moment

[nightrider]

I run standard paper filters but what ever you do,  KEEP the air box!

If memory serves, that carb is a CV carb similar to the ones in the 1100. If so #3 is nonadjustable so you set the rest to that one starting with #4, then #2 and lastly #1. #1 has to be adjusted last being that it's adjuster rides on #2's adjuster (in other words, if you adjust #1 first then adjust #2 you will mess up #1's adjustments). That might be your problem.

Being that you have the US specs I would pull the carbs and verify that you have all the standard jets (if you haven't already)

1.25 to 1.5 turns out sounds like the right base setting for your pilot screws but that is the very last setting to adjust (after balancing) and don't even bother adjusting carbs until the valves have been adjusted.

 

[steelelc]

Hi mate yep balanced them that way miles better than when I got it its got the US jets in so second row do the jet needle and needle jet / pilot jet differences between the two make that much of a difference not used to jetting 4 strokes ? what do we all reckon 

 

Cheers

[Reinhoud]

Jetting has nothing to do with opinions, every bike is different, measuring is the way to go, use an Air / Fuel ratio meter for this (O2 sensor with gauge).

[nightrider]

they all effect 0 - 1/4 turn (including float height) but the best way to think of it is;

Pilot jet mainly governs 0 - 1/8 throttle

Needle Jet mainly governs 1/8 - 1/2 (ish)

Pilot screw mainly governs closed throttle (Obviously)

Unless you have modified your engine or your emulsion tubes (needle jet) are plugged or egged I'd leave them alone.

 

That's all just stuff to chew on but as Reinhoud points out no one engine has the same fuel air requirements as another so there is no magic number anyone can give you.

Just a starting point.

 

I could get into how to adjust your pilot screws but in street bikes it's not all that critical and I doubt it's going to solve your problem.

(it's stupid critical in the 2-strk Enduro/Hairscramble world I also live in)

For right now just set them at factory standard (which is a bit lean) or +1/4 turn and move on. Adjust them later when you get your hands on the equipment Reinhound mentions (which is way easier and more accurate then doing it without )

 

The next quick checks I would do is a warm compression test and the old intake boot test (spay with liquid to see if it effects idle).

That will tell you allot.

 

Also you need to know were it's lean. FWO? 1/2? 1/4?

That will also help you diagnose the problem

 

 

Edited August 14, 2016 by nightrider
grammar

[steelelc]

Cheers mate Ill give that a go and see where it is