Needle Jet for GT550

[H2RICK]

As an option, I think if I could buy a a used set of used O-8 needle jets I could have them reamed to a P-2 size.

This may be your only option. With ALL the paperwork I've collected over the years, I have not ever found a chart from ANYONE telling me which style/number of needle jet fits which carb. Mikuni, of course, HAS the info....but they're not telling anyone.
One nice piece of info I've found lately, though, is at motorcyclecarbs.com which has a very nice chart of the actual bore sizes of the various needle jets.
If you decide on the bore-job then that chart will be a great help to you.

[tz375]

I must have missed something. It is so simple to pop out the needle jet. remove the main jet and washer, remove the slide and tap the jet up with a wood dowel.

if you do have to drill/ream out the needle jets, fortunately the sizes are well documented all over the net.
O-8 2.640
P-0 2.650 difference 2 sizes = 0.01mm diameter
P-1 2.655 each size difference = 0.005mm
P-2 2.660 Each even number change is 2 sizes = 0.010mm
P-3 2.665
P-4 2.670 etc

For some reason, my notes say O-5 with 5DH21-3 for 73, P-O with 5DH21-4 on 74. replaced by P-8 and 5FL14 for 76-77 but I can't tell you where that data came from, so I can't vouch for its accuracy.

BTW, O-8 to P-2 is a 16% increase in annular area with stock needle, dropping to 3% difference wide open. Flow rates are not quite the same as areas and fuel flow is slightly less again, but it's indicative of the size of the change at 1/4 throttle.

[Suzukidave]

i dont know if this helps any http://www.3cyl.com/mraxl/gt/manuals/gt ... 550-40.htm" onclick="window.open(this.href);return false;

[tz375]

Thanks Dave.

The "standard" needle jet for that size carb is a #169 which was also fitted to the R5 Yamaha with the same sized carbs. It's possible that Mikuni made a special nozzle for this bike, but a 169 will probably fit.

It will be interesting to actually find out what needle series are fitted to the different years of 550. We know that the later ones are a #172 from the set Vintageman stripped, so we eagerly await someone pulling a jet out of an early type carb.

[Vintageman]

Yes if anyone has easy access to the early separate GT550 carb and can look at needle jet numbers would be awesome.

I have parts set of GT550 later model ganged style carbs and stamped on needle jet is 172. The 169s I bought may fit this later style. Even here, there are subtle differences though between 172 and 169. I have not checked this for sure for not what I am running. I could if someone needs to know.

When I got these 169s I took the carbs of my 73 GT550 and when I got the needle jet out, it was much shorter (It must be shorter than the later model ganged carbs?? Why I am asking the question for I think earlier is different). I did not spend much time for no way it was going to work. So I put it back together. At that time I upped the Pilot jet and hoped that would do it. The Pilot helps but not the right spot and drowns the idle area which is used quite a bit why riding or going slow in traffic.

I also noted that even though you raise the slide, the taper of the needle does not come into play until maybe 20% open. Well above the ping spot. So that’s why raising needle does not help solve my issue fully either.

This issue is very subtle, not major. I would say if you drive you won’t see it often, But, I know where it is and how to hit and psychologically that make riding not so enjoyable for me. I believe this is why later GT550 upped it size. Also, on-line OEM parts schematics shows there were optional needle jets and throttle valves offered for the early model. I don’t think anything wrong with my bike other than chambers amplifies this lean issue.

So I think I needed either a different throttle valve cut (2.0 instead of 2.5, or larger needle jet

I have Yamaha R5 and DS7 carbs. I see that the Throttle valve is a 2.0 cut! I am going to pull a slide out of the GT550 (2.5 cut) and one from an R5 Carb and see if the same style. I'll let you know if so.

I may just have to but another set of GT550 carbs. My other research is to see if I can hand ream an O-8 needle to P2 size… only .001" more! 2.66mm is the size I believe.

Thanks

[tz375]

I understand all of the above and agree that's the appropriate approach.

No one else seems to have a set of carbs they feel like stripping, so I'm guessing that you will have to pull one of your needle jets out of the carbs on your bike.

You said that the needle jets are much shorter than the #169 which is surprising since that jet fits a 28mm spigot carb. Yamaha used three or 4 different nozzles on the R5 through RD400 series but they are all the same height.

Is there any chance that your bike has 24mm GT380 carbs by any chance?
Are the stock needles shorter in the body or do they have a shorter spray tube?

a #169 is 38.15mm tall and 46.3mm overall to the top of the spray tube +/-0.1mm.

[Vintageman]

I hope someone who has a carb off the bike would strip. It is easy low risk. In my case all my carbs are on my bike and really don’t want to go through that again unless I have a plan... it runs very well, but…
It does it do it cold maybe I'll try B8SE. AS we know that never fixes pinging but whatever
But I bet I will have to if no else does.
I may just buy a spare set, so if I play around like crazy reaming Needle jet or machining a new slide cut I can fail without having to punish myself

I believe my carbs are correct. I will check again. I have a gt380 with ganged carbs and much smaller bore size
Today i quickly strip an R5 carb. The Needle Jet is 182 O-0, This is much more of a perfect match with the 172 series from late model GT550. Each about 1.885" long
Only difference is the keying pin slot towards bottom. It is longer on the R5 so should fit in later GT550, Not sure about other way around.

The 169 is shorter. It will go in the later gt550. But when it shoulder rests in the carb venturi bottom the orifice for needle will be lower than the 172 or 182. I bet it will be like raising the needle 6-7 slot positions only if it had that many. It is not the same as 182 or 172. The 169s I bought are true Mikuni parts for they have the square in a square icon. Stamped 169

Also the Throttle valve round slide in R5 is a 2.0 cut. It starts to fits into the my 73 gt550 single carb (so must be a 28mm carb), but the guide pin slot is small not larger as my OEM one so only goes down so far . Also its overall height is much shorter, but that may not have been an issue if slot was correct.
I know the Needle jet in my 73 gt550 were shorter. I was trying to see if there was a way I could machine off bottom end of the new 169s to match and re-tap for main jet. But I would have had to cut the bottom shoulder and beyond. That much

Heah, another option if i can make some kind of shim. Or maybe it just don’t matter if no shoulder for jet and washer will hold it centered Too bad I have other things in life that need my attention.
Come on somebody. If you have a single GT550 carb, take off bowl, remove main jet and pop out that needle jet.

[Vintageman]

Dang! your are all correct, it is published

http://www.ozebook.com/compendium/techb ... %206-9.pdf" onclick="window.open(this.href);return false;
0-5 not 0-8. Where did I ever get O-8? I got it here

http://www.babbittsonline.com/suzuki-mo ... uki/GT550_(1973" onclick="window.open(this.href);return false;)/CARBURETOR_(GT55OK)/021160001/56021160008.

So maybe Suzuki foun dthe 0-8 was better fit than the O-5.

What a jump in 1974 with p-0 and 4th clip... wonder why, just because of air box change? the 72/73 has a very large filter and low restriction airbox as I see it.

If someone does not have one carb and checks needle jet in a few days, I will pull mine off again

Thanks

[tz375]

Interesting isn't it. That R5 carb probably has the wrong needle jet. #182 is for the slightly smaller 26mm carb. I took a #169 out of an R5 carb and a 182 out of a 26mm SUNDCO supplied carbs and they are very similar but 1mm different in length.

BTW you can fit a slightly shorter NJ with no issues as long as the main jet has enough threads left to screw in properly. A needle jet is located by the top collar and the bottom is just a reasonably tight fit in the lower section. Some needle jets have a thinner or thicker top locating ring or flange. Most are 2mm thick.

Let's see what is actually fitted in those 73 carbs and then we'll all know. I did ask a friend of mine to pull an older 550 carb apart and he has said he would do that tomorrow evening if nothing else comes up.

[Vintageman]

Tz375.

You must be correct; I may have checked a DS7 carbs and not the R5. All were in the same parts box. Sorry

Yes the 169 has a short top locating ring. If the 169 NJ when installed reaches as far as the 172 into bowl, then NJ needle orifice is too low. But what you say is that it will not, meaning the NJ orifice height will be the same for the needle jet won’t go as far into the bowl. It looked to me that that would not be the case.

You must again be right for all data says 169/172 are the same and I don't want to mislead anyone.

Thanks for having someone look. I also broke down and bought a set of used carbs off ebay for $60.00 He said they were in good shape inside as well with no water damage. So I have spares incase.

Thanks. And sorry for confusion. I am learning a lot and did not know as much as I thought I did.

[tz375]

I am learning a lot and did not know as much as I thought I did. That should be true for all of us. The more I learn, the more I realize that I don't know.

I also went back and looked at the 182 and 169 and you are correct. The 182 has a 2.5mm thick flange compared to the 169 with a 1.5mm flange. If you were to insert a 169 where the 182 came out, it would indeed be sitting 1mm too low. It would be possible to machine a 1.0mm thin washer to use a 169 in a carb designed for 182's but that would cost more than the replacement jet, unless you could do it yourself.

A quick email this morning said #192, so I asked him to measure the thing to be sure. 192 is supposedly used in a 26mm flange mount carb.

[tz375]

And the answer is #192 O-5 and it's 8mm shorter than a 169... That is one short arsed jet. I mean vertically challenged.

Overall length 38.5mm, 1.5mm flange, 30.0mm to the top of the flange (retaining ring).

[Vintageman]

Tz375.


Thanks.

I see that the 192 is still offered, but I only see size O-2 then skips to P-0. I was thinking maybe 0-8 like Suzuki website shows for the 73 GT550 size.

Maybe P-0 ok if i put clip back to 3rd pos or 2nd pos from top and put pilot jet back to 27.5 or even 25 like the later model gt550.

What do you think?

Looks like I jump gun on those spare set of carbs. Oh well. Also made a mistake thinking NJ was a 172/169 without verifying.

I'll just print more money

[tz375]

That's what copiers are for !.......................

If the carbs you bought had good NJ's then you could be OK to drill/ream them out to the size you want, or get a set of P-0 and try them. That's a pretty big jump though.

If you have spare needles, you could machine down the top section by .001" or so to get the same effect.

You don't want to see what I have had to do with needles over the years.

[BlkY2k]

Ive got a set of carbs here off my 72, what exactlly are you looking for? Mine are vm-28sc