TOPIC:

Patton wrote:

Injected wrote: ...He tried raising and lowering the needle and running huge pilot jets with no improvement... he tried 2 sizes richer needle jet and it cured his problem... it was way too lean in the midrange....

six862m6 wrote: So he actually had to change out the needles instead of just moving them up a notch or two?.. I THINK the needle size is ok....

For RS34 carb, am thinking there are available several different size needle jets as well as several different size jet needles.

Good Fortune!

Yes that is true. and im sure u know but others may not, a bigger needle jet will give u more fuel at an equal rate through the mid section. a new needle will offer dif tapers to tailor the mid section to your needs.
Injected's friend changed the jet not the needle.

He changed the Jet Needles #33 - you can only change so much until you have to change the matching
part which is #37 Needle Jet (sometimes called a bleed pipe)the main jet screws into the bottom of this jet.


If you look at item #33 under a loop you will see it has about 3 different tapers along its length - it is a very precise metering rod and small changes make huge difference in fuel feed.

Mikuni puts recommendations on there web site as a starting point - a baseline reference... from what I have heard motors running less than 1200cc will almost always require 34's... 36's would be required over 1200cc with a big valve ported head and big cams... running the 36's just because Mikuni recommends it might be a backwards step because your motor does not require the air that those carbs are capable of flowing.

Check the search function for posts with RS34 - there is valuable information in there.

There are a lot of variables to take into account other than engine size... the most important thing the carb is looking for is air/fuel... the head is the bottleneck between the pistons and the carbs - if you have giant carbs and a big bore but the head is stock, the head will dictate how much air it needs to operate effectively... I hope this sheds some light on your situation.

Injected wrote: He changed the Jet Needles #33 - you can only change so much until you have to change the matching
part which is #37 Needle Jet (sometimes called a bleed pipe)the main jet screws into the bottom of this jet.

Attachment RSexplviewLG.gif not found

If you look at item #33 under a loop you will see it has about 3 different tapers along its length - it is a very precise metering rod and small changes make huge difference in fuel feed.

Mikuni puts recommendations on there web site as a starting point - a baseline reference... from what I have heard motors running less than 1200cc will almost always require 34's... 36's would be required over 1200cc with a big valve ported head and big cams... running the 36's just because Mikuni recommends it might be a backwards step because your motor does not require the air that those carbs are capable of flowing.

Check the search function for posts with RS34 - there is valuable information in there.

There are a lot of variables to take into account other than engine size... the most important thing the carb is looking for is air/fuel... the head is the bottleneck between the pistons and the carbs - if you have giant carbs and a big bore but the head is stock, the head will dictate how much air it needs to operate effectively... I hope this sheds some light on your situation.

X2 if you can't figure what the next richer needle is call Sudco they can help you out.

Injected wrote: He changed the Jet Needles #33 - you can only change so much until you have to change the matching
part which is #37 Needle Jet (sometimes called a bleed pipe)the main jet screws into the bottom of this jet.

Attachment RSexplviewLG.gif not found

If you look at item #33 under a loop you will see it has about 3 different tapers along its length - it is a very precise metering rod and small changes make huge difference in fuel feed.

Mikuni puts recommendations on there web site as a starting point - a baseline reference... from what I have heard motors running less than 1200cc will almost always require 34's... 36's would be required over 1200cc with a big valve ported head and big cams... running the 36's just because Mikuni recommends it might be a backwards step because your motor does not require the air that those carbs are capable of flowing.

Check the search function for posts with RS34 - there is valuable information in there.

There are a lot of variables to take into account other than engine size... the most important thing the carb is looking for is air/fuel... the head is the bottleneck between the pistons and the carbs - if you have giant carbs and a big bore but the head is stock, the head will dictate how much air it needs to operate effectively... I hope this sheds some light on your situation.

Sorry for the confusion, u had said needle jet earlier.

Do u know what size needle , he ordered?

Andy-

I do fully agree with you that regardless of identical specs that jetting will end up being slightly different for any two bikes. You might only get it close on one bike using identical carb settings as the other bike that runs perfect even if everything else is identical as well.

All-
My only surprise about upping the size of the needle jets in the one example is that they had to up the needle jet size for a relatively stock engine with only a header and pod filters. (BTW, I'm the one that started this confusion, I initially read "Jet Needle" instead of "Needle Jet" which is what Injected originally listed) I didn't say it was wrong... just surprising, you know? Anyway, all my jets should be here either today or tomorrow. I will be doing a lot more testing out once they are, provided the damn weather cooperates somewhat. The jets I ordered are all the large round style, which is correct for these carbs though as mentioned earlier that the small round style are interchangable with the same flow ratings (They are both Mikuni brand obviously).

Sorry - I don't post here too often... I can ask my buddy what needles sizes he ordered - one thing he did bitch about was how much $$ it was to swap them out...

I am only offering up this example because I read in your post about a WOT bog on some RS34's - I rode the bike when it was like this and it was very unpredictable... almost dangerous.

If I can help you or anyone with this example its worth the time.

The guy who owns said bike is an ex Kawasaki service mechanic (1978-82) - so he rode and tuned a lot of 900s when people were converting from air boxes and stock pipes to pods and headers... they use to throw the stock pipes that customers didn't want in a trailer and take them to the dump at the end of the month!!!

Anyways he knows his way around these motors... he tunes by ColorTune and plug chops - old school.



Pic without the air box

I checked with buddy and he said that the RS34's come standard with a #9DZHO1 jet needle which is the leanest they list for the RS series... he is using the #9DZH04 which is 2 sizes richer. The standard needle jet is a #P4... The tech at Mikuni said that if that needle was not rich enough he would be required to go to a #P5 (richer) needle jet and its matching leanest jet needle. He first started changing out the pilots jets as he had extras on hand... he went as big as #25's,but once he changed the needles he went back to the standard #17.5's... mains remained constant at 122's.

The jet needle accounts for throttle settings from 1/4-3/4, so that is half the throttle input...
they are special on the RS because they have two distinct tapered sections which I believe could result in more of a "tune up" window.

Sorry for the lingo confusion... I casually just use needle, bleed pipe, and main/pilot - that's all I have ever know.

This solved a particular issue for someone - I just wanted to pass it along if you think it could be of any use... I think he mentioned it was around $60 to swap them out!

I'll put my .02 in since I have RS34's also. I have an 1105 kit in mine and the carbs are set with 135 mains,17.5 pilots and slot #3 on the needles. Has a little hesitation till around 2500 and then runs like mad all the way to 10,000rpms. Cruises right along with no problems,but I am running a 37 tooth sprocket also. Oh also,they are 1/4 turn out on the idles. It does seem to run a little rich,but the plugs do look ok. Hope this helps. Good luck with it. Plus I live in S. Indiana near KY.

Injected wrote: I checked with buddy and he said that the RS34's come standard with a #9DZHO1 jet needle which is the leanest they list for the RS series... he is using the #9DZH04 which is 2 sizes richer. The standard needle jet is a #P4... The tech at Mikuni said that if that needle was not rich enough he would be required to go to a #P5 (richer) needle jet and its matching leanest jet needle. He first started changing out the pilots jets as he had extras on hand... he went as big as #25's,but once he changed the needles he went back to the standard #17.5's... mains remained constant at 122's.

The jet needle accounts for throttle settings from 1/4-3/4, so that is half the throttle input...
they are special on the RS because they have two distinct tapered sections which I believe could result in more of a "tune up" window.

Sorry for the lingo confusion... I casually just use needle, bleed pipe, and main/pilot - that's all I have ever know.

This solved a particular issue for someone - I just wanted to pass it along if you think it could be of any use... I think he mentioned it was around $60 to swap them out!

Can u help me understand this. u are calling the needle and jet the same thing so i need clarification. did he change both the needle and emulsion tube or just the needle?
is there are range of needles that match the tube, and if that is not enough fuel u would then increase to the next size tube and its smallest matching needle?
as u know, i have a small low end bog, so this is of great interest to me. i have not the resources to tackle an air box like his, but it would be worth trying some dif jetting.
Did he do this before or after he added the airbox ?
Thanks
M

RS34 Parts & Tunning Manual:

RS34 Parts & Tunning Manual

Follow the HS series for tuning, pretty much the same...

HS Series Tuning

mark1122 wrote:

Injected wrote: I checked with buddy and he said that the RS34's come standard with a #9DZHO1 jet needle which is the leanest they list for the RS series... he is using the #9DZH04 which is 2 sizes richer. The standard needle jet is a #P4... The tech at Mikuni said that if that needle was not rich enough he would be required to go to a #P5 (richer) needle jet and its matching leanest jet needle. He first started changing out the pilots jets as he had extras on hand... he went as big as #25's,but once he changed the needles he went back to the standard #17.5's... mains remained constant at 122's.

The jet needle accounts for throttle settings from 1/4-3/4, so that is half the throttle input...
they are special on the RS because they have two distinct tapered sections which I believe could result in more of a "tune up" window.

Sorry for the lingo confusion... I casually just use needle, bleed pipe, and main/pilot - that's all I have ever know.

This solved a particular issue for someone - I just wanted to pass it along if you think it could be of any use... I think he mentioned it was around $60 to swap them out!

Can u help me understand this. u are calling the needle and jet the same thing so i need clarification.(No-I pointed it out the # in the exploded view) did he change both the needle and emulsion tube or just the needle?(just the needle)
is there are range of needles that match the tube(Yes), and if that is not enough fuel u would then increase to the next size tube and its smallest matching needle?(Yes - all info is available in Sudcos Mikuni catalouge - pg126-7 pg129-30)
as u know, i have a small low end bog, so this is of great interest to me. i have not the resources to tackle an air box like his, but it would be worth trying some dif jetting.
Did he do this before or after he added the airbox ? (He figured it out when the pods were still on but he had already started the air box... the box ended up making it run even better, but it might have not been necessary - he called Mikuni and Winners Circle about the needles)
(He had a stock air box on his bike from a 82 KZ750 (one with 34's) and it fit - he said it could be adapted to work with the RS34's, but it looked ugly to him)
Thanks
M

I have a j motor 1100 with 34s on it. Mine is currently 125 main with 17.5 pilot. clip on #3. works ok but I think my pilot is still just a little lean waitng to buy expensive jets after I install 83 gpz head.moving my clip 1 spot did make quite a difference.maybe just play with that and see how it works out.