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Makotosun

Inherited Enduro 1975 DT125B

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Inherited Enduro 1975 DT125B was created by rfisher125

Hoping this is the correct forum to post this.

 

My daughter inherited this bike from her late grandfather. At one point it ran, but I think it's been 20 years since. It's very sentimental to her and we'd love to get it running again. Unfortunately, we know nothing about repairing motorcycles, so hoping this forum can help us out. The gas tank is full of rust. We're going to attempt cleaning and sealing it and then plan to put in an inline fuel filter. With the help of my neighbor, we disconnected the carburetor with the intent to clean it. We were hesitant to take it apart, so he threw the whole thing in an ultrasonic cleaner he has at work. It does look much better, but not sure how clean the inside is. I was going to reinstall the carb, but as I investigated things more, I noticed a number of rubber tubing lines from other parts on the bike were disconnected. With pictures, I'm hoping someone can tell me where to connect them...assuming they need to be connected?
  • Yellow tubing from transmission area. It just leads to underneath and is not connected to anything. What is its purpose?
 
  • Black tubing connected to the battery? What is its purpose? 
  • Orange tubing from oil tank? What is its purpose? This one is in rough shape so we'll probably replace it.
 
  • Carburetor lines - Both were rock hard and brittle and ran to a spot underneath the bike...same location as the yellow tubing from the transmission. I think reading online...one is an 'air breather' line and the other is an 'overflow' line? Neither were connected to anything from I can tell. We'll obviously be replacing these as well.
 

I'm guessing we should drain and refill the oil, change the spark plug, clean the air cleaner, replace transmission fluid, and maybe put in a new battery? Anything else? The tires are shot as well, but we want to get it running before we deal with those.

​​​​​​​Hoping you all can help.
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03 Jun 2023 12:18 #1

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Replied by Gr8uncleal on topic Inherited Enduro 1975 DT125B

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 from near Salisbury, UK.

Check out the Tech Library (see top toolbar) for parts and service manuals. Parts manuals can also be found online at Partzilla and CMSNL. It's only my opinion, but I find CMSNL more user friendly (see link below).

Yamaha DT125 1976 USA parts lists and schematics (cmsnl.com)

Buy a set of "JIS" screwdrivers and use these on the bike - you're less likely to chew up screw heads.

Nearly all of those are breather pipes and are in the correct position - you can replace like for like if you want.

The carb should be stripped and cleaned in the ultrasonic bath. In no particular order, unscrew the cap, remove the valve (aka slide) and needle. Then turn it upside down, unscrew the four screws on the float bowl and, keeping it upside down, lift off the float bowl (it might need some persuading if the old gasket is stuck on!). The float arm, retaining bar and needle jet can be disassembled - no screws or anything. The main jet (likely with a hexagonal head) can be removed.

Clean and re-assemble.

At EVERY stage take a photograph before you remove a part, so that you can see how it goes back together.

Behind the small cover on the left side of the engine should be a set of points - clean the faces of these with a points file, or some emery paper. Finish off by pulling a small piece of white card through the two faces, and when no black smudges show then they are clean.

That's all for the time being!
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03 Jun 2023 12:46 #2

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Replied by 1971DT250 on topic Inherited Enduro 1975 DT125B

Yes this is the place for help. We are here to help. First off I suggest you take the carb apart, the ultrasonic bath won't get the insides clean unless it is dismantled. There are several parts that should be replaced after you see what the inside looks like. The brake shoes should be replaced with newly manufactured ones. The lining can come unglued from the old ones. The clutch fiber plates might need to be replaced. The oil pump should be verified for proper operation.
Tech manuals are in the library.
Others will be along with advice.
Also the electrical system on this model is a 12V battery ignition. It needs to be functioning with a good battery. Sometimes the entire dynamo needs to be taken apart and cleaned.
 
The hours spent riding my Enduros is not deducted from my life span.
03 Jun 2023 12:55 #3

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Replied by rfisher125 on topic Inherited Enduro 1975 DT125B

A few questions on the carb clean up...
  1. I purchased this rebuild kit last Fall  Carburetor carb repair rebuild kit 73 YAMAHA AT3 125 NEW MIKUNI VM24SH - Damineding Moto . It was the only one I could find for the VM24SH model. If the parts in the kit match what's in the carb, is it ok to assume they are the correct parts and just switch them out?
  2. From a few Youtube videos I've watched, most just take it apart, spray it with Carb Cleaner and blow out all the orifices with compressed air. Is this a good way to go? I did locate this article on this forum  Basic Carburetor Cleaning (yamaha-enduros.com) . It mentions dunking the carb body in a bucket of solvent...is this necessary?
04 Jun 2023 05:32 #4

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Replied by Clegg on topic Inherited Enduro 1975 DT125B

The only thing I would use from that carb kit is the float bowl gasket and maybe the float valve. It is best to reuse all of the jets (pilot, main) and needles that are Mikuni original. Pay close attention to cleaning the jets, making sure you can see light through all of the orifices.

I use Berrymans Chem dip for carb cleaning. Disassemble the carb and put everything in the dip. It's a 1 gal can of cleaner.

Since you have access to the ultrasonic, disassemble the carb and be sure to make sure all parts are operating room clean.
1971 SL350, 1973 Bultaco Matador, 1978 XS650, 1979 MX175, 1982 XT250, 1982 GS650, 1982 CB450T HAWK, 1979 IT175, 1977 Suzuki TS185
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Last edit: 04 Jun 2023 06:09 by Clegg. Reason: sp
04 Jun 2023 06:02 #5

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Replied by MarkT on topic Inherited Enduro 1975 DT125B

The original float bowl gaskets are very good... if you are careful and don't tear or damage it, it can be reused. Aftermarket replacements are ok, but not as "durable" as original.

Don't be afraid to take carb apart... it's not difficult or tricky. Pay careful attention to cleaning tiny pilot jet. Post pictures if you get lost and there are tons of people here that will help.
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
04 Jun 2023 07:29 #6

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Replied by rfisher125 on topic Inherited Enduro 1975 DT125B

Thanks for all the prompt responses. In regard to some of the other items.... replace spark plug and battery, change the oil, clean the air filter, changes transmission oil/fluid...would you all recommend doing all of these items now vs tackling them one by one later?
04 Jun 2023 10:13 #7

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Replied by asco on topic Inherited Enduro 1975 DT125B

Find someone with 2 stroke vintage Yamaha experience. Would be my best advice since there is so much sentimental value and no experience. 12 volt systems are more complex than 6 volt bikes.

a
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1971 CT1-C (BRANDY)
1970 DT1-C (MONICA)
1972 AT2M (ZIFFLE)
1970 CT1-B (HULK)
1971 DT1E (GINA)
1970 CT1-B (CLIDE)
04 Jun 2023 10:52 #8

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Replied by MarkT on topic Inherited Enduro 1975 DT125B

Those are not bad things at all...  especially air filter. 

Shouldn't be a need to replace spark plug...  but having a couple spares is a good idea.  Make sure they are gapped 0.020 to 0.024"...  usually gap is too wide out of the box.  Also get the correct plug. NGK B8ES.   NGK stopped making some of the non-resistor plugs but many places sell an "R" plug (BR8ES) as equivalent, it's not.  Autolite still sells non-resistor (Part number 4054), or you can swap to a non-resistor spark plug cap and use the "R" plugs. 

You will need a battery for spark on that model...  and while the electric start is cool...  I wouldn't use it for the first start and until you get it to start easy.  Starter is not as robust as a "normal" starter and will drain the battery pretty quick.

It is a two stroke so the only engine oil you can change is in the autolube tank which isn't a bad idea.  The way I do it is remove the bleed screw at the pump and let it drain.  Then fill tank and let it continue to drain about half a quart or more to flush out the old oil. 

Trans oil, make sure you use something "wet clutch" rated.  Most auto parts stores have Vavoline or Castrol 10W40 motorcycle oil that is JASO MA rated for wet clutches...  usually says "safe for wet clutch" or something like that on the bottle.  You could probably wait on changing trans oil until running and you get it warmed up. 
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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Last edit: 04 Jun 2023 10:55 by MarkT.
04 Jun 2023 10:53 #9

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Replied by MarkT on topic Inherited Enduro 1975 DT125B

P.S. You don't really need to replace all the vent hoses unless missing... but if you do, critical that you route the battery vent properly.
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
04 Jun 2023 11:03 #10

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