Dif sized jets...

[katinvermont]

Just out of curiosity ... I have seen a number of people install different sized jets in outer cylinders vs. inner. Two questions...

1) Why would this be necessary or desireable?
2) If there is a good reason for doing this, why don't they ever do this
at the factory (at least I have never heard of it)?

Any insight appreciated. Thanks,
Chris

[md86]

Pre 98's come from the factory with 105's on #'s 1,2&4 , while # 3 gets a 110 . I've heard that having a slightly larger jet on one carb is supposed to make starting easier , while larger ones in the middle carbs are supposed to help those cylinders run a bit cooler . Just what I've read .

[The CyberPoet]

Factory jetting in different countries and markets varied for the Katana. Countries and markets which have tight idle emissions controls tend to have different jetting for the center cylinders than the outter cylinders to compensate for heating rate and expansion differences. Some countries do not test for idle emissions, but only for emissions at specific speeds (Germany comes to mind), and Kats for those markets ship with the same jets all the way across.

Cheers
=-= The CyberPoet

[bonstrosity]

I recently cleaned out my carbs and looked at all of the jets hearing this. I looked at all of the jets and they all had the same markings on them...how can you tell if one of them is different?

[The CyberPoet]

Generally, stamped into the jet is a three digit number (i.e. - 110, 130, etc), located on the side of the jet. That is the jet size.

Cheers
=-= The CyberPoet

[bonstrosity]

When I cleaned them out they all had the same numbers...is there anything wrong with this?

[The CyberPoet]

Not as long as what that three digit number represents is fueling the bike correctly and you're not getting any symptoms of poor fueling (fouled plugs, after-fires, loss of power at low throttle openings, etc). But it does mean someone else has been inside those carbs before if it's a North American model

Cheers
=-= The CyberPoet

[Court93kat]

Hey Cyber......

So what you're saying is that the middle two should have a larger jet than the outer two cylinders? If that is true, by how much larger?

[Special K]

OLD SCHOOL thinking: The inner two cylinders get smaller jets because they get hotter when running (air cooled engines, less air gets to inner cylinders), so slightly smaller jets balance out the heat. THis can be cheked with an infared heat gun pointed at the exhuast pipes where they exit the head.

NEWER SCHOOL thinking: It does not matter that much, so just go with all the same size jets.


BTW...........I installed these both ways, and it does not seem to matter that much, so I just go all the same for all 4.


COURT93:
If you want to try alternatives, I've got lots of spare jets here you can experiment with, just drop me a line.


Keith

[The CyberPoet]

So what you're saying is that the middle two should have a larger jet than the outer two cylinders? If that is true, by how much larger?

I'm with SpecialK on this one. What is needed to qualify for EPA acceptance status and what is actually best for the bike aren't always the same, and I really can't see how a 2.5 offset on the center two cylinders would make significant differences to most riders (who usually don't spend their days hovering around the idle point) in terms of performance. On the other hand, I do recall the Germans saying that their Kats tend to idle smoother and warm up quicker, so I can see how even jetting does make some sense in that sense.

Cheers
=-= The CyberPoet

[Court93kat]

OK.. here is a question that goes with this topic.

As far as jet sizes go, what is the average jet size difference between stage 1 and stage 2 jets for a 600?

[The CyberPoet]

OK.. here is a question that goes with this topic.

As far as jet sizes go, what is the average jet size difference between stage 1 and stage 2 jets for a 600?

The big difference would be the needle taper (and ability to readily shim to adjust the height), not the jets, as far as I've been able to tell...
The DynoJet kits come with a variety of jets (from #106 to #134 for the pre-98's as a combo kit for stage 1+3, and from #110 to #120 for the 98+; 98+ available as a stage 1 only). The stock jets are 115 outside cylinders, 112.5 inside cylinders for the 98+, with the US version getting a #110 main throttle valve, and the European/Canadian versions getting a #100 main throttle valve.

Cheers
=-= The CyberPoet

[Court93kat]

Thanks Cyber. Now I have an idea where I stand with the jets that I have in my carbs.

[92xjunker]

What is the oem jet size for a 92 kat 600, Just curious. Started a carb rebuild found 4 120 jets. I think they have been changed for the yoshimura 4 into one and k&N filter.
runs fine when warm, hangs @ 3000 rpm a/f screws were set @1.5 turns

[phantasm]

Set a/f to 2.5 and ditch the k&n for stock air filter