Author Topic: 1974 Yamaha DT100A Project  (Read 273 times)

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Offline Diablo007

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1974 Yamaha DT100A Project
« on: April 04, 2021, 03:37:49 AM »
So...this was purchased as an engine donor for a YSR project.  Popular opinion is that it should be brought back to roadworthiness.

I should have taken pictures of it before we pulled it down.  It was on a shelf about 4.5' off the ground.  Just tall enough to have motorcycles under it and on top of it.  When I first met my friend the bikes on top were 2 Montessa's, a Saracin, Yamaha DT250 (GYT kit, built to Kenny Roberts specs), 1974 Yamaha DT100A, TZ250 with 350 cylinders and pistons (original parts are in the shop), and a TA125.  Sorry don't know the years of the Montessa's, Saracin, DT250, TZ or TA. The TZ has been sold, took less than a week after we pulled it down and took pics.  The DT100A is obviously the one in the title of the post.  The rest are up for grabs.  Make a (reasonable) offer.  Shipping is from Hawaii.

I've attached pics of the DT100A as it was when I brought it home, as well as pics with missing parts that were found in the shop installed.  The ignition and left hand switch aren't correct but I can rewire to work.

The bike was well abused before my friend rescued it.  Just look at the pic of the oil pump side and you'll get an idea of the flywheel/magneto side.  As far as I can tell the left hand flywheel and countershaft sprocket covers had been removed to fit a shift lever not meant for the motorcycle.  The shifter wouldn't fit after I put the covers on...

I have the lenses for the front blinkers, the rear blinkers, taillight, and headlight.  As of right now I haven't found the oil tank or headlight ears.  A stock exhaust would be nicer, but not necessary.
2 stroke junkie:
1973 Yamaha RD350 (a bitsa); 1974 Yamaha DT125A; 1975 Yamaha RD350B; 1983 Suzuki RG250 (YamaGamma project); 1984 Yamaha RZ350; 1987 Yamaha YSR50T; and an RD200 café racer project has just been proposed... :D

Offline Diablo007

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Re: 1974 Yamaha DT100A Project
« Reply #1 on: April 04, 2021, 03:46:01 AM »
Pic of the left side...
2 stroke junkie:
1973 Yamaha RD350 (a bitsa); 1974 Yamaha DT125A; 1975 Yamaha RD350B; 1983 Suzuki RG250 (YamaGamma project); 1984 Yamaha RZ350; 1987 Yamaha YSR50T; and an RD200 café racer project has just been proposed... :D

Offline Dvsrd

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Re: 1974 Yamaha DT100A Project
« Reply #2 on: April 04, 2021, 06:48:57 AM »
I just love the look of those 70s dirtbikes. Brand or size doesn't matter. DT50 or XL350, they all look great. Until the triangular tanks became the norm....

Online soonerbillz

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Re: 1974 Yamaha DT100A Project
« Reply #3 on: April 04, 2021, 09:10:30 AM »
Yep.. definitely a cool bike.. I have a 75 DT100 in my barn I'll get to one day I hope.

Offline Diablo007

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Re: 1974 Yamaha DT100A Project
« Reply #4 on: April 05, 2021, 03:17:38 AM »
^^^^

Nice, and you have more to start with :)

Took the carb apart today.  It's in amazing shape considering it's sat for at least 20 years.  That's when my friend bought the building and started moving things in.  The shape the motorcycle was in tells me it probably sat for years before my friend bought it.  In any case the carb had some sediment in it, but no corrosions or pitting on the inside, or outside for that matter.  Probably because they were running premix.  There was still oil residue inside so everything was still lubed.

Anyone have experience with an oil pump that's been disconnected?  I'm wondering if it will still work after having had both lines disconnected.  If it had been me I probably would have removed everything, or at the very least left the oil feed from the tank and plugged it, and left the banjo to the cylinder alone.  I can probably find another in the shop but if this one is salvageable that would be much easier.  Do I just run oil to the pump and see if it pumps?  I know there's a banjo bolt in the box of old oil pumps so if it's easier to just swap it out I can go that route, if I can find the correct pump.
2 stroke junkie:
1973 Yamaha RD350 (a bitsa); 1974 Yamaha DT125A; 1975 Yamaha RD350B; 1983 Suzuki RG250 (YamaGamma project); 1984 Yamaha RZ350; 1987 Yamaha YSR50T; and an RD200 café racer project has just been proposed... :D

Offline John Ritter

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Re: 1974 Yamaha DT100A Project
« Reply #5 on: April 05, 2021, 09:37:09 AM »
If you are interested in upgrading I know I have a stock 1974 MX100 head, might even have a stock MX100 cylinder but would have to make sure. We have experience with the 74/75 MX100. Jemco who was in TX and now new owner in KY made an excellent pipe for them.

Online soonerbillz

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Re: 1974 Yamaha DT100A Project
« Reply #6 on: April 05, 2021, 12:47:33 PM »
If you are interested in upgrading I know I have a stock 1974 MX100 head, might even have a stock MX100 cylinder but would have to make sure. We have experience with the 74/75 MX100. Jemco who was in TX and now new owner in KY made an excellent pipe for them.

John,
 Who is the new owner of Jemco and is it still call the same name?


i had a custom pipe made for my Cr years ago by them.. yes good stuff.
« Last Edit: April 05, 2021, 12:49:40 PM by soonerbillz »

Online soonerbillz

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Re: 1974 Yamaha DT100A Project
« Reply #7 on: April 05, 2021, 12:50:19 PM »
Never mind John. I just found them on the web.

Offline Diablo007

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Re: 1974 Yamaha DT100A Project
« Reply #8 on: April 07, 2021, 05:54:09 PM »
What would the benefit be of changing to an MX100 cylinder and head?  Does the cylinder support the oil pump?  If I spend the time and money to bring this project back to ride on the streetl I don't want to run premix.

Thanks for the info regarding exhaust pipes.  If I can get everything to work (oil injection, fit the electronics necessary for street use, etc.) with the pipe that's on it I'll keep it.  If not I'll think about what I want to do about exhaust.  I have added the JEMCO website to my favorites as they might come in handy for other projects.
2 stroke junkie:
1973 Yamaha RD350 (a bitsa); 1974 Yamaha DT125A; 1975 Yamaha RD350B; 1983 Suzuki RG250 (YamaGamma project); 1984 Yamaha RZ350; 1987 Yamaha YSR50T; and an RD200 café racer project has just been proposed... :D

Offline Diablo007

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Re: 1974 Yamaha DT100A Project
« Reply #9 on: April 08, 2021, 02:36:36 AM »
A complete electronic ignition kit is available for this motorcycle; HPI part number 210k072 (part number is from HPI, I emailed them directly).  treatland.tv can bring it in, $250 shipped to Hawaii.  May be cheaper to the States.  Once I have an idea of what's necessary and the costs to get it back on the street I'll decide if it's worth it or not.
2 stroke junkie:
1973 Yamaha RD350 (a bitsa); 1974 Yamaha DT125A; 1975 Yamaha RD350B; 1983 Suzuki RG250 (YamaGamma project); 1984 Yamaha RZ350; 1987 Yamaha YSR50T; and an RD200 café racer project has just been proposed... :D

Online soonerbillz

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Re: 1974 Yamaha DT100A Project
« Reply #10 on: April 08, 2021, 09:24:06 AM »
A complete electronic ignition kit is available for this motorcycle; HPI part number 210k072 (part number is from HPI, I emailed them directly).  treatland.tv can bring it in, $250 shipped to Hawaii.  May be cheaper to the States.  Once I have an idea of what's necessary and the costs to get it back on the street I'll decide if it's worth it or not.

The early 100cc Yamaha enduros are getting a lot of attention over the last few years. There is a FB group that is dedicated to them that you may like. I have besides the one I shared above a couple more. A 72 & a 73 LT.  I hope you get yours back in shape.

Offline Diablo007

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Re: 1974 Yamaha DT100A Project
« Reply #11 on: April 09, 2021, 12:53:45 AM »
@soonerbillz

We also have a '74 DT125A that is almost completely stock.  Found in the same friend's shop.  That is by far my favorite of the motorcycles we have now.  It starts the day on a good note (pun intended) and no matter how the work day went I smile on the way home :D

Here are some pics from the day I was finally allowed to pull it out, give it a quick clean, and take pics.
2 stroke junkie:
1973 Yamaha RD350 (a bitsa); 1974 Yamaha DT125A; 1975 Yamaha RD350B; 1983 Suzuki RG250 (YamaGamma project); 1984 Yamaha RZ350; 1987 Yamaha YSR50T; and an RD200 café racer project has just been proposed... :D

Online soonerbillz

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Re: 1974 Yamaha DT100A Project
« Reply #12 on: April 09, 2021, 07:16:27 AM »
^^^^

Nice, and you have more to start with :)

Took the carb apart today.  It's in amazing shape considering it's sat for at least 20 years.  That's when my friend bought the building and started moving things in.  The shape the motorcycle was in tells me it probably sat for years before my friend bought it.  In any case the carb had some sediment in it, but no corrosions or pitting on the inside, or outside for that matter.  Probably because they were running premix.  There was still oil residue inside so everything was still lubed.

Anyone have experience with an oil pump that's been disconnected?  I'm wondering if it will still work after having had both lines disconnected.  If it had been me I probably would have removed everything, or at the very least left the oil feed from the tank and plugged it, and left the banjo to the cylinder alone.  I can probably find another in the shop but if this one is salvageable that would be much easier.  Do I just run oil to the pump and see if it pumps?  I know there's a banjo bolt in the box of old oil pumps so if it's easier to just swap it out I can go that route, if I can find the correct pump.

There is a fellow on FB called "Yamaha Enduro". The fellow is a expert in these bikes and if you send the pump to him he will return it to you like brand new. Plus he also stocks lots of other enduro parts and stuff.

Offline Diablo007

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Re: 1974 Yamaha DT100A Project
« Reply #13 on: April 09, 2021, 02:43:22 PM »
Thanks for the info!
2 stroke junkie:
1973 Yamaha RD350 (a bitsa); 1974 Yamaha DT125A; 1975 Yamaha RD350B; 1983 Suzuki RG250 (YamaGamma project); 1984 Yamaha RZ350; 1987 Yamaha YSR50T; and an RD200 café racer project has just been proposed... :D

Offline Diablo007

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Re: 1974 Yamaha DT100A Project
« Reply #14 on: April 12, 2021, 01:47:59 AM »
Found a NOS flywheel in the shop yesterday.  Shows some age but it's in much better shape than the one the bike had originally.  The only difference I can find is the original has what appears to be 'D-1' stamp while the one I found in the shop has a stamp of 'E-12'.  The rest of the markings are the same.

I've attached pictures of the original and the NOS one after it was cleaned up.  Thinking I'll hold off on ordering the HPI ignition for now.

Also thinking about running DT125 forks as there are more options regarding upgrades.
2 stroke junkie:
1973 Yamaha RD350 (a bitsa); 1974 Yamaha DT125A; 1975 Yamaha RD350B; 1983 Suzuki RG250 (YamaGamma project); 1984 Yamaha RZ350; 1987 Yamaha YSR50T; and an RD200 café racer project has just been proposed... :D