Jet questions and a few answers

It took a lot of research and measuring & going round in circles to sort out the replacement jets on my KZ305 and some new mains for my Z750E with a 4 into 1 pipe.

The 305 runs Keihin CV 32 carbs & the 750 runs CV 34's
Pilot jet both bikes #35 on JetsRUs they are called 3M and only come in #38 size (that would be the right size if you were to run pods & 4-1)



This is where it gets a little confusing. Both these carbs have a Primary Main jet & a Secondary Main Jet
The Primary Main Jet on both bikes is #62.
On my 305 I have pods so I've ordered 2 sizes up #68
On the 750 it has a 4 - 1 pipe so again 2 sizes up #68




The Secondary Main Jet on the 305 stock is #85, my mechanic changed those out to a #95 & #96 (must have been what ever he had lying around I guess - thanks for nothin!)
Stock on the 750 is #125




I just watched this you tube video where the guy says he just put in #145 main jets. That sounds like he's changed the Secondary mains not the primary.

So my question is this. Have I got it wrong should I be increasing the primary or secondary main jets when I follow the jetting guide below?




BTW I just ordered my jets from PJMotorsports because Jets R Us are a pain in the ass for international buyers. Get with the program dicks, there's a whole world of Motorcycle lovers outside the US!
I really hope I haven't ordered the wrong stuff cos it's a PITA to get stuff down to NZ!

Dont know about your 305 but when I had K&N pods on my 1980 KZ750 E1 I started with primary 62 and secondary 135 and it ran pretty good. Then I went up to 70 and 140 and it ran better so I suspect you should be going up on both primary and secondary jets to somewhere in that ball park. I left the pilots alone. I also have 4 into 1 exhaust

If you have a standard airbox on the 750 and are just going to a 4 into 1 which is my current setup then 62 (is that stock ?) on the primary and 130 on the secondary works for me
Hope that helps
Those 38 pilots look interesting but at $13US each are a bit pricey when I factor in exchange rate to Canadian etc

I'm using 137.5 mains on my 750R1, pods and 4-1. It was running fine, but recently changing the pipe for a less restrictive and louder one I was advised to go bigger by a carb specialist who looked it up for me.

Plugs looking a little lean but it runs really nice, not had it WOT yet.

Dear Rustyhama:

Do you have you #35 slow pilot jets on hand? Can you measure them to check if they are exactly the same as JetRUs 3M?

Rustyhama wrote: It took a lot of research and measuring & going round in circles to sort out the replacement jets on my KZ305 and some new mains for my Z750E with a 4 into 1 pipe.

The 305 runs Keihin CV 32 carbs & the 750 runs CV 34's
Pilot jet both bikes #35 on JetsRUs they are called 3M and only come in #38 size (that would be the right size if you were to run pods & 4-1)

Attachment Pilot.png not found

This is where it gets a little confusing. Both these carbs have a Primary Main jet & a Secondary Main Jet
The Primary Main Jet on both bikes is #62.
On my 305 I have pods so I've ordered 2 sizes up #68
On the 750 it has a 4 - 1 pipe so again 2 sizes up #68

Attachment PrimaryMain.png not found

The Secondary Main Jet on the 305 stock is #85, my mechanic changed those out to a #95 & #96 (must have been what ever he had lying around I guess - thanks for nothin!)
Stock on the 750 is #125

Attachment SecondaryMain.png not found

I just watched this you tube video where the guy says he just put in #145 main jets. That sounds like he's changed the Secondary mains not the primary.

So my question is this. Have I got it wrong should I be increasing the primary or secondary main jets when I follow the jetting guide below?

Attachment SimpleJettingGuide.png not found

BTW I just ordered my jets from PJMotorsports because Jets R Us are a pain in the ass for international buyers. Get with the program dicks, there's a whole world of Motorcycle lovers outside the US!
I really hope I haven't ordered the wrong stuff cos it's a PITA to get stuff down to NZ!

If I caught him doing that to my Z1 cold, I'd make him go GACK. :evil: Moron.
Steve

Wow... what a dick..

Tyrell Corp wrote: I'm using 137.5 mains on my 750R1, pods and 4-1. It was running fine, but recently changing the pipe for a less restrictive and louder one I was advised to go bigger by a carb specialist who looked it up for me.

Plugs looking a little lean but it runs really nice, not had it WOT yet.

So you changed the Secondary mains from #125 to #137.5
Does this mean you did not change the primary mains?
If this is the case then I've ordered the wrong jets.

Ok, I'm slowly answering my own questions here. Some clarifications... What I've been calling the Secondary Main Jet (as per the manual & parts list) is the jet thats screws into the needle jet the the needle slides up & down within.
Below is my Z750 carb



So here I go answering my own questions again. Feel free to correct me if I go wrong.
According to this diagram, anyone who's interested in their carbs has seen this, right? What this tells me is if I change my Primary Main from #62 to #68 as proposed that is going to effect me from about 1/2 to WOT, if I change the Secondary Main (Needle Jet) 2 sizes that will effect me from before 1/4 right through to past 3/4 throttle. I don't spend much, if any, time at WOT so it make sense to change the Secondary mains or Needle Jets.
Best to go back to PJ Motorsports to see if I can change my order. Lucky for me they are in Portland and that's where my parcel is being consolidated, so that's a win...

undiablo wrote: Dear Rustyhama:

Do you have you #35 slow pilot jets on hand? Can you measure them to check if they are exactly the same as JetRUs 3M?

I just checked, my #35 pilot jets are exactly the dimensions as shown.

Thanks! Certainly good news for al kz750 keihin CV34 owners!

Do you have the link to those jets in PJMotorsports?

In my experience, with a wideband O2 analyzer, the needle and needle jet have most of their affect in the lower throttle position ranges. The most affect is where the needle's first taper starts to get near the mouth of the needle jet. That is where the needle has the greatest affect, and the main jet just barely starts to have any affect. As the throttle opens more, the needle's affect gradually drops off as the main jet affect gradually starts to take over.

Here is the perceived affect I get on the 550, which is a simple (manual slide), but the needle versus main holds more or less for most carbs.

CV carbs will have several other factors, like spring tension on the diaphragm, air jets, etc. On Keihin piston CV's, the air jets were one of the things I adjusted, but they may be fixed on the diaphragm type CV's.

The throttle cutaway can be ignored unless you can actually get different cutaways. But usually you can play with the needle instead. The main purpose of the cutaway is ensure there is no vacuum at the needle jet when the slide is closed all the way. By exposing the needle jet to the intake air, the needle jet has atmospheric pressure (instead of vacuum) to prevent fuel from siphoning up the main passage. That way you can fine tune the idle using the idle mixture screws.

Ignore the needle straight diameter unless you are comparing two different needles with different diameter shafts.

Ignore the needle taper unless you are comparing two different taper needles.

Ignore the throttle stop as that is only for manual slides.

On the 550, the air screw and pilot have no affect in the upper throttle positions, but that may be different on your carbs as you indicated.

Is the chart with the blue circles supposed to be for a 750? It is way off compared to what my service manual says. It is more or less the same as what Loudhvx posted. Are you sure it is correct? A pilot that goes all the way to WOT sounds strange.