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Prinzy carb help

12 Jun 2019 21:44
Mothersbaugh
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Prinzy carb help #1
Mothersbaugh, here, helping Prinzy out with his 71 DT250 carb, I believe it is. I can't open the repair manual in the tech library, nor can I download it. I tried Partzilla, but they have too many jet sizes listed. The carb had a 230 main in it; what should be in it? And it has either a 25 or a 45 in the pilot hole; what should that be? The 45 is one of those 2-inch long suckers, and the 25 is a non-Mikuni part. I have Mikuni pilots in everything from a 10 to a 40, and in the main jet sizes, I have Mikunis from a 130 up through a 230. I'll fix him up with a pair of new Mikunis in the factory sizes, if someone can tell me what that bike needs.

Also, what needle jet? The old one is a Mikuni 4L6, and the replacement, which isn't the same shape at all, if my eyes are seeing it right, is a bastard brand Y11. I'm going to clean the Mikuni and put it back in.

Damn these Keyster kits! They're a pain in the keister!
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12 Jun 2019 22:15
Mothersbaugh
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Prinzy carb help #2
While I am awaiting a response, I'll add more, here. The carb was not at all clean, Prinzy, my good man. Here are the parts on which I found deposits:
the slide
the float pin
the slide spring
the slide retainer (which was also in upside down)
the idle screw and the air screw
the main jet and its holder
the floats
the float bowl
the top of the float bowl

There was a large chunk o debris in the 25 pilot that was in the carb.
The nozzle into which the needle slips had 5 of 5 holes along its length plugged with gunk.
There were two rubber rings inside the screw-on cap.
The new float bowl gasket was not installed; the old one is crushed pretty thin, though it was not leaking. I'm going to install the newer, thicker gasket.
The float level was low at 19mm. At least, I think that's low. Correct me if I'm wrong, as I can't get to the repair manual in the tech library.

My prediction is that when I send it back, Prinzy, you'll install it and take off like a bat out of Hades, as my father used to say.

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12 Jun 2019 22:42
MarkT
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Prinzy carb help #3
Probably the needle that is a 4L2? Needle jet is important to remove from carb body to clean and is always a single letter followed by single number.

Here's the chart from the Yamaha manual I have.



Yamaha also had "revised" jetting specs for several models... I have an old book here someplace that lists them. I'll see if I can find it.

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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12 Jun 2019 22:55
MarkT
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Prinzy carb help #4
The Yamaha manual is showing what my other book says is the revised specs

MJ = 160
NJ = 02
Slide Needle = 5D1 (clip 3 from top)
Slide = 2.5
PJ = 35
Float level 15.1mm (I find arm level to gasket surface is good)

If you don't have the right slide needle and needle jet, all bets are off. Carb might work but could require a completely different main jet at the very least. I can look and see if I have a 5D1 needle but you'll have to check the needle jet to make sure it's an O2

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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12 Jun 2019 22:56 12 Jun 2019 22:59 by Mothersbaugh.
Mothersbaugh
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Prinzy carb help #5
Thanks! Well, according to that chart, the needle isn't even close. It is definitely a 4L6, but I'll look again when it comes out of the Berryman's, where it is soaking away just now. I used a ten-power jeweler's loupe to read all the numbers.
So we should have a 160 main and a 35 pilot. And I knew the float level was off. Thanks, there, too.
Also, this chart says the slide cutaway should be a 2.5, and there's a 2.0 in it. Yeesh! Probably can tune around that, though...
And, yes; I do have the nozzle/needle out of the carb body. That's how I can see that all 5 holes have bungs in them.:Ugh

Thanks, Mark!

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13 Jun 2019 01:26
Mothersbaugh
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Prinzy carb help #6
Yes. Both are confirmed: 02 needle jet, and the needle is a 4L6.
Any idea what the one marked Y11 might be? Is that Keyster's version of the 5D1?

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13 Jun 2019 04:38 13 Jun 2019 04:54 by Prinzy.
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Prinzy carb help #7
Wow what a mess. I admit I didn’t get real involved in it. It’s off of a ct3 remember. We’re both in the Ag industry And with the year we’re having it’s hard to keep focus on stuff that takes patience lol
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13 Jun 2019 07:15 13 Jun 2019 07:43 by Mothersbaugh.
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Prinzy carb help #8
CT-3. Good to know!! When I did a search with your name, the only thing coming up was the DT-1E. This will make a big difference in the jetting, and maybe also the needle jet!
Here's the chart for the 175's; that, I do have. And it shows we are very close. Main jet 230, pilot 25, slide cutaway 2.0. Needle is still not right, but the needle jet is right at 06. That's how I'll assemble it; the needle is easy enough to change if you want to try both of them in succession and see which works better.


About to post some pictures. Good for everyone who's not cleaned a carb before to see!!
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13 Jun 2019 07:49
Mothersbaugh
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Prinzy carb help #9
Before and after on the carb body, upper and lower. My thought here is that if you can see all that snow out in the open, imagine what's lurking inside all the smaller passages that you can't see. Soak it and clean it enough to get all the external crap, and you'll probably get all the internal crap as well.
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13 Jun 2019 07:53
Mothersbaugh
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Prinzy carb help #10
Some of the other metals parts crawling with deposits. The main jet holder I had to soak 3 times to get all the deposits off/out.
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