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searching for needle jets

Posted: Fri Jun 10, 2016 10:16 am
by markush
Hello everyone!
I'm searching a replacement for no longer available needle jets Mikuni series 172 for GT250A- and GT550-carburetors.
There are series 169 mentioned as suitable:
https://www.jetsrus.com/a_jets_by_carbu ... mikuni.htm
Can anyone confirm this?
Or other ideas?

Re: searching for needle jets

Posted: Fri Jun 10, 2016 10:19 pm
by Vintageman
I know they say that but not completely true. The 169 series shoulder is 1mm shorter than 172. So is it will set 1mm lower in carb. Some, as I tried to shim it 1mm up, be careful the air hole may not line up and be partially blocked by carb body.

So next time I would just let it set 1mm lower and raise clip on needle to next higher position (which is also 1mm) so all is well. the shroud will set a little lower but can't see that really being a significant issue given how tall it is, I have not tried this latter statement but would with no worries. What else can you do. And you get a nice fresh needle jet which is so important.

Re: searching for needle jets

Posted: Fri Jun 10, 2016 10:43 pm
by tz375
I have seen that comment but they are different. 169 is a Primary type that takes hex jets and has a 1.5mm flange where it sits in the bore. 172 is 1mm longer than a 169 and has a 2.5mm flange (mounting ring). I think a 172 takes round jets but I'm not 100% sure of that.

So a 169 could be used in place of a 172 but would sit slightly (1mm) low in the bore.

#182 is the same height as a 172 and has the same 2.5mm flange but is designed to take hex jets. I suspect that they will be closer than 169s.

Re: searching for needle jets

Posted: Sat Jun 11, 2016 2:05 am
by PaulD
Have you tried Crusin Image? They seem to supply kits for most bikes, I've had full kits for both my GT750J and T500 and they work a treat. I even bought a set of emulsion tubes (jet tubes) for both bikes as mine where chewed up by a previous owner.

Re: searching for needle jets

Posted: Sat Jun 11, 2016 8:01 am
by Vintageman
tz375 wrote:#182 is the same height as a 172 and has the same 2.5mm flange but is designed to take hex jets. I suspect that they will be closer than 169s.
If Tz375 is correct (some dimensions) the 182 is the way to go :up: The fact it takes Hex jets versus round, well you can cross hex to round for proper flow or cross thread a round into the Hex threads. There is a paper by the respected board member that agrees with me... others don't, Oh well, works for me for years.

I tried matching a hex to round in my case there was no direct flow match... had to go higher or lower. I did both and still not correct... hmm, those jets are a very different design... put the proper mikuni round and all was as it should be. If you are modifying you bike then I suppose it won't matter where you start Hex or round.

The good news is you have options to get a nice shinny needle jet

Re: searching for needle jets

Posted: Sun Jun 12, 2016 2:33 am
by markush
Hello!

The #182 I had already found at http://3cyl.com/mraxl/partid/carb/jetid/jetid.htm but you cannot be sure that informations on web pages are always error-free. That is why I asked here if anyone already has installed other needle jets.
The use of "large hex"-Jets should be no problem. There are the conversions tables "round reverse"<>"large Hex" to get a starting point.

@PaulD: He has been asked by a friend of mine about the type and size of needle jets in his repair kits:
Answer: "There is not size on the jets. So, I can't confirm how many sizes. sorry kind regards"
:? not very helpful

bye
Markus