1989 Yamaha DT50 build thread

So I picked up this DT50 today with the engine locked up and no title. I figured for $450 it was my best bet at getting a complete DT50 even if it wasn't in the best of shape. I'm planning on making it a ripper and there doesn't seem to be all that much info on these so I hope this will be useful to other people rebuilding these bikes.

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Re: 1989 Yamaha DT50 build thread

Brandon Weiss (Detective brandon to you) /

Wow, super clean. You got quite the deal at 450 I think.

Re: 1989 Yamaha DT50 build thread

This bike has obviously spent a lot of it's life outside. The tank is extremely rusty but solid. It was empty when I got it so I shook it upside down to get all the big flakes out. Then I flushed it with water and compressed air, and it's currently sitting in my garage full of evaporust.

I sprayed some penetrating oil down the spark plug hole and decided to look at the carb.

Ho-ly shit. The airbox and carb look like they had birds living in it or something; I've dealt with mouse/rats nests before but the carb looks like it was full of bird shit and it's all really caked in there. Getting the float bowl off was a struggle, I had to put the carb in a vice and hammer the top half of the carb off the float. I was greeted inside by the worst corrosion I've ever seen; it was just full of this white powder shit. It's really really caked in everywhere, including the float passage. The one half of the plastic float just broke in half when I was trying to get the jet out, so I'm gonna have to replace that at least. Realistically it's looking like I'll need a new carb. But we'll see how soaking it for a couple days in carb cleaner goes.

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Re: 1989 Yamaha DT50 build thread

> Brandon Weiss (Detective brandon to you) Wrote:

> -------------------------------------------------------

> Wow, super clean. You got quite the deal at 450 I think.

Thanks! Hopefully it won't take too much to get it going but if the carb is any indication of the health of the rest of the bike I'm gonna have to drop the motor and split the cases for a full rebuild/inspection. Tires are definitely shot too but that's a non issue really.

So I got the head off and the cylinder was just full of sludge. The moisture in the picture was the penetrating oil I sprayed in earlier. I wiped out the sludge best I could and managed to free the crank by moving the entire cylinder up using screwdrivers as levers. I'm gonna let the piston soak overnight at least before I do anything drastic like start hammering on it

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Re: 1989 Yamaha DT50 build thread

Brandon Weiss (Detective brandon to you) /

Sludge makes me think coolant was leaking into the cylinder and sat?

That carb is pretty toast, I would just get a new one. Definitely water damage.

Drain the oil and see what comes out

Re: 1989 Yamaha DT50 build thread

dope deal. you definitely have your work cut out for you. keep it coming we love seeing this type of stuff

Re: 1989 Yamaha DT50 build thread

So after just one night of evaporust the tank is in amazing shape considering how bad it was. The neck of the tank is indicative of what the whole tank was like, and now it looks like there's just a few stray spots of rust here and there. You can see how bad the pitting was/is inside the tank.

The seals in the petcock looked like they were trashed so I just left the petcock on and turned it off while it soaked. The petcock leaks now, unsurprisingly. It probably wouldn't have lasted that much longer anyway, but if you're thinking about using evaporust in a tank with the petcock on keep in mind you'll probably need to replace the seals.

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Re: 1989 Yamaha DT50 build thread

Dude, that is a loooot of corrosion. Like mopedallday said, your carb is toast. In addition the the chem neutralization with evaporust, you're going to need to mechanically remove the debris. Put some bolts and nuts in the tank and shake all that crap loose so you can flush it out.

I'd be interested to see closer pics of the fairings and body. Is there any rot in the plastics or frame?

Regarding the piston being seized, WD40 might not cut it. PB plaster or another heavy duty penetrating/creeping oil might help. WD is more for water displacement (ergo "WD") and cleaning but it does a lot of stuff well enough. Best luck I've ever had was using diesel fuel (old dodge truck motor) but it took a loooong time. Also steel and cast iron so the chemistry might be different.

Good Luck!!!! Interested to see how this developes for you.(edited)

Re: 1989 Yamaha DT50 build thread

> J D Wrote:

> -------------------------------------------------------

> Dude, that is a loooot of corrosion. Like mopedallday said, your carb

> is toast. In addition the the chem neutralization with evaporust,

> you're going to need to mechanically remove the debris. Put some bolts

> and nuts in the tank and shake all that crap loose so you can flush it

> out.

>

> I'd be interested to see closer pics of the fairings and body. Is there

> any rot in the plastics or frame?

>

> Regarding the piston being seized, WD40 might not cut it. PB plaster or

> another heavy duty penetrating/creeping oil might help. WD is more for

> water displacement (ergo "WD") and cleaning but it does a lot of stuff

> well enough. Best luck I've ever had was using diesel fuel (old dodge

> truck motor) but it took a loooong time. Also steel and cast iron so

> the chemistry might be different.

>

> Good Luck!!!! Interested to see how this developes for you.

Yeah the cylinder has been soaking in PB blaster since I got it. I did shake up the tank with some nuts and bolts in it when I first got it, and I got out a concerning amount of rust. Then I flushed it with water/air/evaporust and now gas. But I mean it still holds liquid so I guess I'm good. I am probably going to have to purchase a new carb, which is gonna be like $125 unless I can find someone on here with one. Thanks!

Re: 1989 Yamaha DT50 build thread

> Nick Haber Wrote:

> -------------------------------------------------------

>I am probably going to have to purchase a new carb,

> which is gonna be like $125 unless I can find someone on here with one.

> Thanks!

I see them as low as $18.20 for clones :

Quick Google search

Re: 1989 Yamaha DT50 build thread

> P D Wrote:

> -------------------------------------------------------

> > Nick Haber Wrote:

>

> > -------------------------------------------------------

>

> >I am probably going to have to purchase a new carb,

>

> > which is gonna be like $125 unless I can find someone on here with

> one.

>

> > Thanks!

>

> I see them as low as $18.20 for clones :

>

> Quick Google search

Thanks for the heads up. Seems like those are for the air cooled versions, for some reason on these the coolant passes through the carb. I could probably just bypass the carb and run the coolant lines straight to each other.

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Re: 1989 Yamaha DT50 build thread

You can bypass that exactly like you described.

Re: 1989 Yamaha DT50 build thread

Dont get a Parma 70 cylinder. It is trash. I was running mine with a phbg and athena 50, was a solid 50mph bike, 55 on the flat. Its crazy how much better the ns50 is with only 1 more hp. The gearing on the dt really bums me out, once you drop it into 3rd, fun times are over.

Re: 1989 Yamaha DT50 build thread

> Daniel '' Wrote:

> -------------------------------------------------------

> Dont get a Parma 70 cylinder. It is trash. I was running mine with a

> phbg and athena 50, was a solid 50mph bike, 55 on the flat. Its crazy

> how much better the ns50 is with only 1 more hp. The gearing on the dt

> really bums me out, once you drop it into 3rd, fun times are over.

Good to know, I think I'm gonna order an Athena from this European website. Should only take like 2 weeks to get here. It's gonna cost me less than a Parma kit would cost from treats anyway.

Re: 1989 Yamaha DT50 build thread

So I freed up the piston by cutting down a piece of wood to fit on top the piston then hammering a railroad tie onto it. It was in better shape than I was expecting. I went to O'Reilly to pick up a hone without realizing that the pucks were too small and would get caught in the ports. I basically only honed the top of the cylinder where the rust and corrosion were since I couldn't hone past the ports. I'm gonna throw a kit on it anyway so it doesn't really matter. Pics of before/after my shit hone job

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Re: 1989 Yamaha DT50 build thread

Dirty30 Dillon /

I'm pretty sure Dos has the Athena kits.

Re: 1989 Yamaha DT50 build thread

What does the M or W by the piston arrow indicate ?

Re: 1989 Yamaha DT50 build thread

I got my athena 50 on amazon for like 180. I think there's two versions, a bridged exhaust and an oval. I had the latter and it was pretty nice. Like a more reasonable stock cylinder with a very useable mid range. Theres a Portuguese site that has 44mm dt80 cranks and the big 100cc kits. I have seen some you tube videos of a dude ripping 4th gear power wheelies on the Italkit.

Re: 1989 Yamaha DT50 build thread

> Daniel '' Wrote:

> -------------------------------------------------------

> I got my athena 50 on amazon for like 180. I think there's two versions,

> a bridged exhaust and an oval. I had the latter and it was pretty nice.

> Like a more reasonable stock cylinder with a very useable mid range.

> Theres a Portuguese site that has 44mm dt80 cranks and the big 100cc

> kits. I have seen some you tube videos of a dude ripping 4th gear power

> wheelies on the Italkit.

Yeah I saw that on Amazon (for future reference, it's much easier to find these kits if you Google "Athena 068800"). There's a British site that has them on sale for $105 but only takes mastercard for some reason. I actually haven't ordered the Athena yet cause I saw that 100cc kit and I've been considering that with a DT80 crank. It would be an absolute ripper but then it's much less of a shifty fifty ya know

> P D Wrote:

> -------------------------------------------------------

> What does the M or W by the piston arrow indicate ?

Good question, it points to the exhaust port but not sure why it's a M/W

Re: 1989 Yamaha DT50 build thread

yeah Jeff- 'river2strokes' has posted a lot of great info on some heavy duty DT50 tuning type stuff.

Re: 1989 Yamaha DT50 build thread

looks good dude! you gotta project on your hands for sure

Re: 1989 Yamaha DT50 build thread

been working on a dt50 at work, found out the ysr50 piston is the same. ysr50 and dt50 share the same connecting rod. Wiesco stocks them got a 1.0 over bore. sent cylinder for bore and hone. going to plug oil injection, most likely carb swap. another interesting thing the coolent sensor is the same as a vino 2012 and up i believe.

Re: 1989 Yamaha DT50 build thread

> Zach Riddle Wrote:

> -------------------------------------------------------

> been working on a dt50 at work, found out the ysr50 piston is the same.

> ysr50 and dt50 share the same connecting rod. Wiesco stocks them got a

> 1.0 over bore. sent cylinder for bore and hone. going to plug oil

> injection, most likely carb swap. another interesting thing the coolent

> sensor is the same as a vino 2012 and up i believe.

I wound up buying another stock carb off eBay. My plan is to get it running as close to stock as possible, then start modding to document the actual performance gains. I think I'm gonna buy an HPI ignition before I buy a kit for the top end or anything.

It's my understanding that the YSR50 engine is almost identical to the DT50LC. Dos cycles also carries pistons/rings for these bikes

Re: 1989 Yamaha DT50 build thread

the ysr50 is also air cooled but pistons are close enough to work. couple of small differences but over all dimensions work.

Re: 1989 Yamaha DT50 build thread

So, I bought a 41mm ball hone to actually hone the cylinder right. I bought Hobbit rings from Dos (they said they fit DT50's) but it turns out they don't actually fit the stock piston. They updated the description to reflect this now but it was too late for me. So I wound up putting the stock rings back in after my very light hone. The rings were seized pretty good on the piston so I had to boil the piston/rings and free them up using a paperclip. Ring gap was within spec so I've been running them.

The first time I really rode it was at the Dcons rally, where it became apparent that the rear wheel was way out of true and the flasher relay was shot. I still need to get the wheel trued but I used a 6v flasher relay off of a KE100 I had laying around and it works fine. The bike rips, pretty easy to wheelie in first and second gear. Can't really ride wheelies for a good distance, but after I true the wheel and replace the chain/sprockets I'm going to start modding the bike. My roommate has a rm65 or rm80 reedblock so I'm going to try to make that work.

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Re: 1989 Yamaha DT50 build thread

1st and 2nd gear are fun. 3rd is a big let down and when you dump it into 4th the party is over. If you do decide to go hpi it’s gonna lose all that wheelie power, the stock flywheel weights like 8 lbs vs 280g. I noticed a very large difference in the power delivery on mine, it kinda made 6th useless too. My ns50 with a ninja pipe, 19 carb and an hpi blows the doors off of my dt that I spent so many months trying to eek any power out of it. It is best stock, I would pick up an 1mm over bore piston and don’t fuck with it too much.

Re: 1989 Yamaha DT50 build thread

I can confirm that a ysr piston fits with a bore and hone. Just finished it up and have been doing tuning with a phbg 15 which fits perfrcto in stock intake and airbox.

Re: 1989 Yamaha DT50 build thread

^ I was running a 19 phbg too, But I deleted the air box and battery spot on mine because it was all cracked to hell and there was an acid explosion at some point on it. Pretty big improvement over stock, mine always had a little dead spot I couldn’t tune out. Other crossover parts; Intake from a rt bolts right on, but you lose the boost box. It has a 26mm spigot diameter so you can run a tm24 or pwk, the reed block can also work, but requires a spacer.

Re: 1989 Yamaha DT50 build thread

Dang, that is a nice looking bike with a bad engine, exactly the opposite of mine. Following along as I struggle with the carb on mine. Do you need to rebuild the carb you just bought? Where are you finding parts?

Re: 1989 Yamaha DT50 build thread

> Mr Chubbins Wrote:

> -------------------------------------------------------

> Dang, that is a nice looking bike with a bad engine, exactly the

> opposite of mine. Following along as I struggle with the carb on mine.

> Do you need to rebuild the carb you just bought? Where are you finding

> parts?

I bought the carb off eBay and just cleaned the jets. I accidentally left the original in a bucket of carb cleaner and now it's basically disintegrated into a pile of dust (it was pretty far gone anyways). If you need a carb a 19 PHBG fits perfectly into the stock intake, wish I would have known that before I bought another stock carb but whatever.

The only parts I've bought so far have been the carb, chain, sprockets, tires, battery, and passenger pegs. The first 3 were from eBay and the last 3 were from Treats(edited)

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