Okay Carb experts...

[celt_rock]

carbits.jpg

Okay, got this from eBay last year and never even opened it. Think it came from Cruzinimage
(or however you spell it). Anyway, the parts I got (which seem pretty standard from pictures I
find online) are different from my parts. The new parts are in the top row, the old ones are on
the bottom. For one, I don't even have a place to put the part on the top right (the small jet
with the holes). Second, the new main jet doesn't have a slot for the screw driver (though
the main jet in the first package did... this is 1 of 2). Also the float valves look completely
different. Lastly, the screw second from the right is obviously not the same size or design
as the one I removed (below it with the o-ring attached).

So my question: Do I not have the right carbs on my '75 T500 Titan? They are Mikuni carbs,
says ISO on the other side, rectangular float bowls. I'd really like to know where the jet on the
right goes! Can anyone help?

Thanks so much!

[ConnerVT]

Hate to have to tell you this, but the best place to put most of the parts from an aftermarket kit is in the trash.

I've bought two kits (from different sources), and most of the parts were worthless (or worse). The needle/seat was completely the wrong length, and made a flooded mess of my engine and garage. I've done a crude measurement of the jet needles, and they don't come close to matching either the early or late model carb needles.

I've bought genuine Mikuni float needle/seat, idle jet, and main jet from Dennis Kirk. Very reasonable price, and at USPS postal service rates.

As for the part on the far right of your picture: That's the Idle Jet, and I'm sure both of your carbs have one. From the underside of the carb, there's a small, circular tunnel opening right next to the Needle Jet (what you unscrewed the Main Jet (large round with the screwdriver slot). The Idle Jet is screwed in down there. You need a long, narrow screwdriver to get to it.

[jabcb]

Two other sources for the parts:
http://jetsrus.com
http://www.motorcyclecarbs.com

You might also find good deals for some of the parts on eBay.

[celt_rock]

Thanks for the tips, I put an already long, narrow screwdriver to my bench grinder and I now have a screwdriver
specifically made for my idle jet!

I rebuilt a carb for a Honda XL250 and in that carb the needle jet came out. Does
it not in the Mikuni? I tapped it a bit and nothing. So I've left it alone for now. But on the Honda carb the needle
jet actually had some holes along the way that needed cleaning out and the only way to do that was remove it.
I'm trying to read up more on this but my ADD has me distracted by shiny things.

Last question... how do you know when a carb part needs replacing. To look at my jet needles they appear to
be in great shape, not nicked, mishapen at all. Do people just change these after a certain amount of time? Like
bearing seals?

[ConnerVT]

Yes, the Needle jets can (and should) be removed, so they can be cleaned correctly. Like everything else in a decade-plus long neglected carb, it is probably glued in place.

With the Main Jet and washer from under the Main Jet removed, you should be able to push the Needle Jet out. An appropriate drift, and moderate persuasion, may be required the first time. Heating the mostly disassembled carb (oven, boiling water) may be of help to soften up any accumulated varnish holding the Jet in. The Needle Jet has a slot on its side, and the body has a dimple which acts as a key. This will accumulate gunk which will make it stubborn to come apart, until all is cleaned up.

As to when to replace carb parts - Metal parts which don't move (much), such as Main and Pilot Jets, screws, springs, etc., really don't need to be replaced, unless someone damages them (such as reaming out clogged jet openings). The Float Needle/Seat will eventually wear. Replace when it won't seal properly when the bowls are full.

The design of Mikuni carbs due tend to make the Jet Needle rub the inside of the Needle Jet. The needle 'floats' on the slide, vibration, and the up/down motion of the throttle, will eventually score both the needle and the jet. A strong magnifier and good lighting will allow you to inspect both the needle and the inside of the jet, to see any wear, jet out of round, etc. If worn, they should be replaced, but direct, exact replacements can be very difficult to find.

[tz375]

I rebuilt a carb for a Honda XL250 and in that carb the needle jet came out. Does
it not in the Mikuni?

Typically Keihin press the short needle jet in from below and old them in place with a screw in emulsion tube.

Mikuni typically make needle jet and emulsion tube as one part and it's located from below by the main jet and teh washer. Remove teh main jet and washer and then screw the main jet back in to protect the threads. Knock it puwards through teh slide opening with a chop stick or something similar. So, Keihin needle jets push down to remove and Mikuni press UP to remove.

[oldjapanesebikes]

John Aylor off the Triples board and occasionally here also did a couple of carburettor cleaning videos a few years ago showing a carb tear down. Part 2 covers the needle jet removal and the tool he uses. I modified an old screw driver rather than using an old jet - the key thing is to not damage the pin.

http://youtu.be/ylD17LedDPo" onclick="window.open(this.href);return false;

and

http://youtu.be/UhidQ7aTJaI" onclick="window.open(this.href);return false;

[celt_rock]

John Aylor off the Triples board and occasionally here also did a couple of carburettor cleaning videos a few years ago showing a carb tear down. Part 2 covers the needle jet removal and the tool he uses. I modified an old screw driver rather than using an old jet - the key thing is to not damage the pin.

http://youtu.be/ylD17LedDPo" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

and

http://youtu.be/UhidQ7aTJaI" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

Those are great! Sorry I didn't think to look for those before I started this.

[celt_rock]

The design of Mikuni carbs due tend to make the Jet Needle rub the inside of the Needle Jet. The needle 'floats' on the slide, vibration, and the up/down motion of the throttle, will eventually score both the needle and the jet. A strong magnifier and good lighting will allow you to inspect both the needle and the inside of the jet, to see any wear, jet out of round, etc. If worn, they should be replaced, but direct, exact replacements can be very difficult to find.

Thanks so much, you are a wealth of information! I hope that if you are up this summer that you'll consider swinging by (no 4 week Xcountry trip in my books this summer). I hope to have this all put together by then with the wiring harness all sorted. Only thing I'm missing now is a seat!

[ConnerVT]

Thanks so much, you are a wealth of information! I hope that if you are up this summer that you'll consider swinging by (no 4 week Xcountry trip in my books this summer).

Don't know how rich I am. For me, the most problematic area of my bike was the fuel system. Everything that could be messed up, was. Fuel tank, petcock, carbs, all gave me major headaches. I've had the carbs off my bike so many times, I can now remove them, tear them down, swap some brass, and have it all back together in about an hour. Just like you, I fought with it at first. Now, I probably can do it blindfolded in a dark room. Think I have my fuel issues about 95% ironed out now, enough that I (finally) felt good about going off on 150+ mile rides.

Looking forward to the warm weather eventually showing up. I'm sure to take one or two rides up to B'town this year, as I have friends who put me up on their boats for a day or two. It will be nice to meet up.

[celt_rock]

Man, I wish I had friends who would put me up on a boat!

I'm worried about the whole fuel thing myself. That'll be something for me to
sort out in warmer weather though. I took the needle jets out (one was quite
stubborn most likely due to the fact that I tried getting it out the opposite way
earlier in my tear-down thinking it was like the Honda carb I took apart last
year). One of the jets looked like it had been cleaned and greased? Weird.
The other had the whitish-green sludge varnish and spent an hour in the
Chem-dip. Clean as a whistle. I can't wait for the temperature to climb above
50 degrees so I'll feel like installing these on the bike. Heck I can't wait for the
temperature to climb about 10 degrees! (That's Fahrenheit btw).

Cheers!

[aslsmm]

my rebuild kits were worse than the bits i was trying to replace. i was not happy. "if it dosnt say keyster than it's not quality" was the slogan. i was pissed.

[Vintageman]

I have found cruzinimage (sp?) parts are waaaay off. At least the T350 was.

Keyster is OK, but they only appear to have made one kit per bike model and you have to be sure you have the right one for that model may have undergone changes. Also the machining quality is not always good, but, OK if you need a Jet Needle that is obsolete and they have the one for your year. Once I found a website that crossed keyster Jet Needle to Mic. Keyster have Yxx format. If there is no worn or corrosion spots you are OK assuming not bent.

Main jet and pilots you can get anywhere (go true Mikuni). You can still get OEM Needle Valve but $$. If yours is OK no corrosion or wear mark on needle you may be OK. Lately I have just changed these. Keyster are OK, check float height after change

Jet Needle may be obsolete. The T500 for example is but, you can swap over to shinny new 159 series instead of the 188. You need to run Hex main and just force a Round into it. If you use round the Jet needle will be pseudo tapped to that different thread and can't go back to Hex. Your call. There are table that cross hex mains to Round mains

I have known a lot of "experts", but not all check the condition of the barrel inside of the needle jet. Most look at outside and call if the hole looks round and not worn due to rubbing with Jet needle over many miles of use. But, that is usually not an issue for vintage bikes. The issue is corrosion inside the first part of the barrel the needle meters in. That area is important and machined to very tight tolerances You need a bright light an good eye (or magnifying glass) to see inside. It must be smooth if not shinny.

If the floats are brass and have obvious of corrosion, change else the will leak and be sinkers not floaters.

Those original (minus round main and pilot) parts look OK you show look OK.

Get a new Needle Jet, Float, Needle Valve, and Pilot jet if yours are not pristine. Just get a new main regardless

My 8 cents