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TOPIC: 1973 DT3 250 Rich across the board - Now moving on to alternative float levels

1973 DT3 250 Rich across the board - Now moving on to alternative float levels 11 Oct 2019 19:45 #11

  • Snglsmkr
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Have you tried running it without the air filter in place? It is likely the Uni is more restrictive than stock making the stock jetting overly rich.

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1973 DT3 250 Rich across the board - Now moving on to alternative float levels 11 Oct 2019 20:07 #12

  • liferbiker
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12mm would increase fuel in bowl. I have a 73 (motor) in my bike & I've seen the 14.1, that I tried first, saw a 15.1 somewhere else and am using this. It's pretty snappy & starts hauling the mail about 4300, only went redline a few times so far (been on street mostly) as was seating rings, but now I gotta back off so as not to hit anyone in traffic. I need a larger pilot jet, as it needs choke a couple min now weather is colder, holds steady smooth& accelerates smoothly. I recently put the correct needle jet and needle in it (as bike is a 70, but motor is a 73) and after chasing carb issues a little discovered 70 has fatter NJ and goofy needle. got correct from jets r us & even though slide cutout 70 spec is a half larger (leaner tip in) @ 4500' where I am it works fine. So, try float @ 15.1mm, make sure the sealing o ring on jet holder good snug fit as bowl slides on & play w/needle clip positions, make sure points in good shape & timing spot on & it'll be a runner again. Added note; measurments are NOT taken from bowl gasket surface as w/most others, settings are measured from jet holder mounting surface down to float arms, & check other side of arm as well. Floats do float, right? just checking.

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Last Edit: by liferbiker.

1973 DT3 250 Rich across the board - Now moving on to alternative float levels 12 Oct 2019 08:23 #13

  • MarkT
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Float arm parallel to float gasket surface with needle just closed... not compressing spring if you have a spring loaded needle.

Then fix the issue. Air Filter and o-ring are most likely. Restricted exhaust also possible. Ignition timing or condenser that is starting to fail can make it seem rich.

Also, make sure you are getting it warmed up well and then running it hard. Could simply just be "loaded up".

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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

1973 DT3 250 Rich across the board - Now moving on to alternative float levels 12 Oct 2019 10:58 #14

  • denisj
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Snglsmkr wrote: Have you tried running it without the air filter in place? It is likely the Uni is more restrictive than stock making the stock jetting overly rich.


That was my first thought. Not a difference. Runs same with or without
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Denis J

1973 DT3 250 Rich across the board - Now moving on to alternative float levels 12 Oct 2019 11:02 #15

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I am looking into the needle jet and emulsion tube. I’ll post pics when I get back to the shop. I think it’s incorrect
In the box of spares I got from the original owner the spare Carb is a 32 from an RT. Maybe he swapped the needle jet assy and maybe they are different.

Thanks for checking, I am measuring from the jet holder. The arms for the floats are 12mm from it now resulting in the floats being pushed closer to the bottom of the bowl. The arms are not horizontal because of it.
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Denis J

1973 DT3 250 Rich across the board - Now moving on to alternative float levels 12 Oct 2019 11:05 #16

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It does take a long time for the cylinder to get hot. I can idle it for 5-6 min before it feels warm/hot. My CT1 is warm in 1-2 min. Different engine totally but still..

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Denis J

1973 DT3 250 Rich across the board - Now moving on to alternative float levels 12 Oct 2019 13:17 #17

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I'll just say it. It's not a good idea to "tune" with float level. Your choice though.

I was not talking about how long it takes to warm up at idle. It's a two stroke and they can get "loaded up"... especially if you've been letting it sit around and idle for extended periods. Once that happens it won't run clean until it gets ridden "aggressively" a little while. Might not be it but easy stuff is the best place to start.

Smart on checking the jetting... a lot of times people install the jets out of "carb kits" and they are usually total crap. Use only genuine Mikuni jets with the "square inside the corner of a square" marking.

Mikuni Manifold adapter is part number VM28-200k

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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

1973 DT3 250 Rich across the board - Now moving on to alternative float levels 12 Oct 2019 13:28 #18

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Thanks for the tip
Ive been using the float level as a diagnosis instead of a tune. I am scared of damaging this thing so running tests are strictly controlled
I am very much leani g toward a carb swap. Thanks for the part number on the intake.

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Denis J

1973 DT3 250 Rich across the board - Now moving on to alternative float levels 12 Oct 2019 15:21 #19

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Could try totaly blocking off the bottom of the needle jet--emulsion tube just to eliminate everything except choke jet & idle mixture jet. Or screw a main jet straight into the needle jet as a test except threads different i think. only saying that to totaly eliminate anything to do with that troublesome Oring into the bowl. I run a 360 32 on my piston port 250 with no trouble. Not got a slide out of something else with the slot on wrong side so cutaway to the motor instead of to the rear. Air bleed to the E/tube blocked with crumbled air filter, that makes them go rich mid range. Needle not set on top of plate in slide instead of retained under. Sorry, not read it all as heading out door--Till Later. Oh, choke completely closed as have had the plastic cap sit on top & hole it just off the seat. Otherwise exhaust restricted in the spark arrestor down deep in the tail bit.

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1973 DT3 250 Rich across the board - Now moving on to alternative float levels 12 Oct 2019 16:34 #20

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Check your Needle and Needle jet are correct .
Needle jet will be an N-8 , and needle is a 5DP7 set on clip # 3 .
These do wear , but they would have to be pretty badly worn to create
as big a problem as you've described , and would be worse at smaller throttle
positions than wide open .
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