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Old 01-20-2010, 10:41 AM
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Default dt 175 help

I found a bad rubber washer in the carb and now fire up first kick but when trying to run throught the gears it backfires past half throttle .. any ideas .. I thought timing but when I take off left cover it looks like greek to me.
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Old 01-20-2010, 02:18 PM
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Might be Jetting. Or it could be the High speed coil or CDI or Main coil.

Start off with jetting, seeing as how your original problem appears to have been an air leak. Try running with the choke on. If the problem subsides, your runnin too lean. If it gets worse, it might be too rich.

Wait, what washer did you replace in the carb?
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Old 01-20-2010, 02:27 PM
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thet bike used to run then was parked .. the rubber ring was on the needle valve where it seats into the bowl. I can play with it in the morning but dont think it mattered if the choke was out, where is the high speed coil? and what does the cdi do? Prior to fixing this ring I couldnt get it past a quarter throttle once in gear but in nuetral I could rev it from idle to full with no hesitation.
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Old 01-21-2010, 08:09 AM
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Well, first off, lets stick with jetting for now seeing as how a change in the carb made a change in performance.
I see you are in colorado. Is the weather very cold? The reason I ask is the colder the air temp the more dense the air and therefore the leaner the fuel mixture.
Let us know how the Choke run works and we can go from there.

To answer your other questions, I automatically thought your bike is a late 70s model so I thought you would have that ignition system. In that system there are two coils that feed charge to the CDI (Capacitive Discharge Ignition). One coil (larger of the two) supplies power at low speeds and the other smaller coil give a bit more juice for higher speeds.(I got a interesting story on that if you are interested) These coils are located behind the flywheel.

If I got the model year wrong things might be a bit different.
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Old 01-22-2010, 04:07 PM
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ok so just to clarify its a 78 dt 175 with mikuni carb the oil injector has been plugged .. so I tried it today fired right up first kick so i put it in gear and headed down the road it sputtered as i made it to about half throttle then started its popping so i opened the choke and it died. I then preceded to try to start it and at the end of every other kicked it popped or backfired but sounds more like a pop to me. it tried to start after about 15 trys but would not completely start so I then had a great time pushing it home. I'm so confused now .. yesterday I took apart the flywheel and inspected the points I cleaned it all up and ran some fine grit sandpaper over the end of the coils and magnets they had some residue on em and cleaned up what I think is the advance that was on the flywheel side tucked into the magnets, I felt confident in how it looked so put it all back toghether and it fired right up I thought i had it but was too cold to try, but dissapointment waited till now to show its ugly face. I'm soo lost with this little motor I have knowledge in cars and some common sense that tells me this shouldnt be this hard for me to figure out but I guess a tiny 2-stroke is tougher than I thought,
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Old 01-22-2010, 04:51 PM
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Quote:
Originally Posted by thatdamnabe View Post
.. yesterday I took apart the flywheel and inspected the points I cleaned it all up and ran some fine grit sandpaper over the end of the coils and magnets they had some residue on em and cleaned up what I think is the advance that was on the flywheel side tucked into the magnets,,
There shouldn't be "points" on a 78 DT 175, nor should the be a centrifical advance. You should see..


4 and 5 are your low and high speed coils, 6 is you lighting coil and 10 is you pulse coil.

I had a similar problem after putting in two remanufactured coils from Ricky Stator. As it turned out the problem cleared after the wire between coil 5 and the CDI were disconnected. (This may not be the case with your bike)

Sorry about the choke method, that usually helps figure out if its a jetting problem.

Last edited by VAL; 01-22-2010 at 05:03 PM.
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Old 01-22-2010, 07:49 PM
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ok so is this the same as the schematic





and this is what I thought was an advance



and this is a level picture is my carb too tilted if so how in the world do i fix that



when I took this off I noticed gas inside on the bottom i think you can see it in the pic of the carb what you think can this be the problem?
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Old 01-22-2010, 08:40 PM
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Good luck I have a 1972 175 ct2 that did the same thing to me several years ago. Now its been collecting dust in the shed since about 1999. I will keep tabs on this topic to see if you ever got it fixed and what the problem was. Some day I wanna get it back running it was a blast to ride.
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Old 01-23-2010, 08:23 AM
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Ok, we got a couple of issues going on here. Lets start with the latest revelation. The gas in the flywheel area is an indication of a bad crank seal. Dont worry , they can be replaced without taking the motor apart. If this one is leaking its SOP to replace both at the same time. If you are leaking gas, then you are also leaking air when running, which makes the fuel mixture too lean, and could be the cause of the original problem, but before you do anything in the jetting or timing departments, these seals need to be changed.

Second, I dont think you have a 78 dt. It looks like you have the older point and advance setup for your ignition 76 was the last year that Yamaha had that type of magneto/point set up.
This is the 1975-1976 DT

This is the 1978 DT

There is a gap in 77 as far as model, dont know if they stopped for a year or just sold 76s as 77. Any hooo, you can see the difference in the motor with the radial fins and CDI ignition.

Do you have a manual for the bike?

Last edited by VAL; 01-24-2010 at 08:57 AM.
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Old 01-25-2010, 01:14 PM
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Wow your good .. so the title states 78 but I thought you took a picture of my bike in someone elses garage, my bike must be a 75-76 its exactly the same as the pic minus a dent in my tank. So I dont have a manual is there somewhere I can learn how to fix these seals? I'm gonna call around and see if I can find those seals for a 75-76 instead of a 78.
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Old 01-25-2010, 01:28 PM
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Here is a pic of the 76 mag and points


So that kinda seals the deal with the model year

the 78 looks like this








: Left Seal:


OIL SEAL,SD-TYPE 358444-001 $6.26



Right Seal

OIL SEAL,SW-TYPE 305988-001 $6.26


If you cant get them local, BikeBandit.com can.

Double check your model number on your title. is it DT 175 C?

Last edited by VAL; 01-25-2010 at 01:34 PM.
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Old 01-25-2010, 01:33 PM
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title says dt1 but vin is a 443123640 not sure if i can find the true year with that number .. so do i do both if so .. how?
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Old 01-25-2010, 01:48 PM
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I think you are missing some numbers, I beleive the 70s to 1981 had 13 digits and after that they went to 17.

Take a look at the engine number. Might be stamped on the clutch cover or near the shifter.
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Old 01-25-2010, 02:02 PM
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That's the right number stamped behind the forks and on the clutch cover
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Old 01-25-2010, 04:06 PM
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OK I found it. Its a 1975

[Only registered and activated users can see links. ]


It looks like there wasnt any changes in basic design and I checked the part numbers for the seals and they are the same.

So I am wondering if you and I suffer from the same eye condition. If I dont wear my glasses, a 5 looks allot like a 8.

Last edited by VAL; 01-25-2010 at 04:11 PM.
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