GT550 J/K carb needle jet

[CAFE380]

Hello everyone ,
Im new to this site and found it out of desperation. lol .

What have is 1973 gt380.

What I am doing is .. Putting a set of 72/73 gt550 carbs on it ..Carbs are marked 34012 L , R , M

Problem .

I have a beautiful set of polished 550 carbs and I find out today that I am missing the center carb needle jet.
I removed a needle jet from 1 of the other carbs and found o-5 marked on it . I believe its a 09494-00105.

I need to find one of these .. This particular needle jet gets an extender threaded into the bottom and then the main jet installed onto the extender..

From the last 2 hours of reading I have only found 1 option.
which is purchase a Genuine mikuni needle jet 192-O-2 (SKU 003-413) $16.99 from JETSRUS . com and drill it out to o-5..

Is this even possible , is this the right jet ?

any help would be great !!!

I am in the west coast of Canada fyi

[yeadon_m]

Hi,
Try emailing Reiner in Germany at gtreiner1@aol.com
He appears to hold stock of the correct needle jet (according to his parts list for GT550 a few months old).
I've had many good parts from Reiner over the years. He is a collector / seller of rare parts. He does not maintain a website so please be patient with a fellow enthusiast!
Cheers,
Mike

[CAFE380]

Ok thanks !

I have fired an email his way

cheers

[tz375]

I checked my notes and you are correct. Those carbs used 192 O-2 on the outer pair and 192 O-5 in the center spot. They are a very short NJ and used a short jet extender/adapter.

If GT Reiner cannot supply them, check on ebay and if all else fails look at a #175 which I suspect could work but with hex jets.

[CAFE380]

Hmm I haven't come across any data that showed an o-2 @at all.. my outsides have an o5..I will look into the 175 idea.. thanks again

[tz375]

Maybe one of the GT550 owners can add something. My 72 had o-2 / o-5 / o-2 though the old specs mentions O-5 for all 1972 and P-0 for all three on a 76.

Jets R Us list the O-2 and P-0 but nothing between those two.

[yeadon_m]

My Italian GT550M carb NJs are O-9; JNs are 5DH21-4. These were NOS carbs.
My UK GT550B carb NJs are P-4; JN are 5DN1-3. Same on a UK GT550A I had and sold.
Maddening variation through the years and regions for the 550s, so IMO all you can do is experiment.
Mike

[jabcb]

Have a 72 GT550 cafe project bike, so I’m facing the same issue.

Per the 72/73 service data manual on oldjapanesebikes.com, Suzuki used a matched set.
Either:
1) NJ O-5 / JN 5DH21-3 / slide cutaway 2.5 / PJ 27.5
2) NJ O-2 / JN 5C4-3 / slide cutaway 2.0 / PJ 25

Am definitely no carb expert, but it would seem logical to go with either set.


This could also explain why some bikes have two NJ O-5 and one NJ O-2.
It worked because carbs were assembled using either set.

[Vintageman]

Per the 72/73 service data manual on oldjapanesebikes.com,

However, Specification 6, US Service bulletin has them all O-5 with 5D21-3 needle. I always thought the Bulletins were the latest update from Suz (?)....

My 73 gt550 had O-5 (I run o-6) and I have 2-3 other sets of carbs either from 72 or 73 (?) and all had O-5s and all poor condition inside

[jabcb]

US service bulletin, Specification-6, looks to be consistent.

The 72/73 service manual says:
1) the matched set with NJ O-5 is for “other markets than Europe”. (which includes the USA)
2) the matched set with NJ O-2 is for “Europe”

Given this, would seem to be reasonable that some carbs with NJ O-2 made it to the USA because of production line issues.

Maybe the important takeaway is that if you are in the USA & have a carb with NJ O-2, then the other parts should also differ.


You guys know a lot more about carbs than I do.
Will be a few months till we take my carbs apart — hopefully it will have the right parts in decent shape.

[Vintageman]

jabcb i don't disagree with your point (Never checked Europe being in USA... wouldn't think many in USA, but how in the heck would I know).

But just to mess with your mind note that USA 72-77 GT550 use the same jet needle (just different by one clip position) but, the needle jet goes from O-5 to P-4 as the years move on. Mains jets go up just one step too... clip one notch richer.. things keep getting richer. Just couple air box changes only(?) and suspect the later if anything (i doubt much) is more restrictive. It looks like this bike has been a challenge to tune. My understanding early ones 72/73 if you run high rpm and mainly off needle circuit they whole pistons ... early plugs were hotter and went a step cooler later. The missing piece (too lazy to get the facts right now , but have looked at this before) is the pilot circuit outlet hole sizes... but how much can that impact mid throttle?

I think of all the GTs/Ts the gt550 has been a jetting challenge for the the JAPs to tune??? And for me too (wth early carbs)...

It would be interesting to see how the early GT550 carb run on gt380 (This post) the later GT550 carb tune have been reported to be OK (later Gt380s) as well as using the 76/77 GT250A/B 28mm jetting setup in the the later gt550 ganged carb set.

Will the later GT550 ganged carb fit the early GT380/550 cylinder with their longer fins?

CAFE380

Did you change the rubber boots between carbs and cyls? I think the GT550 rubbers are larger and match the 28mm carbs diameter again my replies get too long

[jabcb]

A bad headache is the most likely outcome if I put a lot of effort into fully understanding these carb issues.

My gray 75 GT750 has early-model carbs, K&N pod filters & Jemco 3-into-1 exhaust.
Did have some difficulty getting the carbs setup but I think they are pretty close now. Forum advice definitely helped.

For the 72 GT550 cafe project, I’m planning on stock carbs, K&N pod filters & Jemco 3-into-1 exhaust.
Will be posting questions when the project gets further along.

[jabcb]

My carbs are also marked 34012, so I’m probably in the same boat.
The online parts manual doesn’t even list the 34012 carbs — it lists 34013, 34014 & 34015.

I did notice the comment, ”my understanding early ones 72/73 if you run high rpm and mainly off needle circuit they whole pistons ... early plugs were hotter and went a step cooler later.” That has me concerned with all of the long hills we have in my area.

I just found two NOS NJ O-5.
But I’m wondering if we should go with a later-model richer jetting.

[Vintageman]

jabcb

This is what I run.. Three left. They look rough on outside but so far all six i purchased to date have been nice inside, shinny as new, where it matters. http://www.ebay.com/itm/Suzuki-NOS-GT55 ... zd&vxp=mtr" onclick="window.open(this.href);return false;

as well the other extreme http://www.ebay.com/itm/Suzuki-1977-GT5 ... vw&vxp=mtr" onclick="window.open(this.href);return false;

I think O-6 are a very good fit for GT550.

shinny new 0-5s may be OK too... pay attention to pinging and what throttle position

P-4 bike will drown I think.

To make a short answer long ->

On my 73 (I run stock air box) and 0-5s were too lean. I run 3 into 3 chambers but I also think the short time I had the bike stock exhaust same issue but not as bad. When I bought the bike it had hole in piston and the other two almost through. Bike's carbs jets were not plugged in fact very nice. Suspected crank seals leak, but not the case. The original owner toured with it and i suspect he would be moving a long and back off throttle to coast. it had about 16000 miles and pre-detonation finally made its way through the pistons. I have seen other early gt550 same issues but who knows root cause

It would ping at higher RPMS > 5000 rpms only just off idle say 1/16 - 1/8 throttle . This was noticed when you sped up using most throttle to get there and then backed off to cruise/relax. Very popular scenario for me open road riding. Making the Pilot jets couple steps helped the issue sbut engine drowned during in town riding. Raising clip (2 notched) got rid of it but very poor gas mileage. From what I could see the taper of the needle jet did come into play until after 1/16 throttle so why at last notch. The Original O-5s were not perfect but not too bad (must be perfect!!!)

I reamed the 0-5 to about an 0-9 (only standard hand reamer I could find next size up from O-5 and no issues but only 30- 31 mpg was the best. People following behind me were dying off from fumes or trying to pass me on double line putting as all in danger, or just run me down

I think a P-0 or P-4 would have drowned it real bad. I think a slide cut of 2.0 versus 2.5 would have worked too with fresh 0-5s, but no way could i find that. Did not matter if I run 87, 91 or 93 octane, Didn't matter if timing a little a few degrees more retarded. Running the B8ES instead of B7ES would not fix it either

With these "new" 0-6 in place everything else is set back to stock, won't ping and 50 mpg last I cruised 65-70 mph on I 91 hills of Vermont.

In your case I don't think pods will affect 1/16 - 1/8 throttle but it probably with after that where the more opening the more the impact. You may just need to run 4th clip and bigger mains.

[jabcb]

Thanks for the info.

I bought the last three O-6 per your first link.
I typically run ethanol-free 91 octane. Will use fine-wire plugs — probably B8EGV.

My gray 75 GT750 has early-model carbs + pod filters + Jemco 3-into-1 exhaust. Ended up increasing pilots a smidgen & mains a good bit. Am using main jets that a forum member suggested.

The GT550 will be stock expect for pod filters + Jemco 3-into-1 exhaust. Will be asking for jet suggestions when the project reaches that point.