After seeing a 1969 DT1 advertised on Craigslist for the past month or so I decided today to go and see what nobody apparently was interested in. It was the second owner, been in storage for the past 26 years, "ran when parked".

The good:
matching numbers
clear title
current non-op registration
original black & gold Calif plate
minimal rust
complete extra DT1 engine assembly
2 original aluminum front fender assemblies
a couple boxes of extra parts and a service manual

The bad:
picture speaks for itself - rough and needs complete restoration



Upon arrival I discovered that the bike had a 2" frame lowering kit installed, an aftermarket extended swing arm, Webco skid plate, Webco dual spare spark plug carrier, and a steel brace welded onto the rear frame loop section



I've never seen the rear brace before, does anyone recognize whether this was part of a kit, or custom made, and what the purpose was? Perhaps to stiffen the frame between rear shock mounts? I had thought to grind it off and return the frame to stock during restoration process, but perhaps it has a legitimate purpose and should be kept.

Anyway, I offered the guy $600 for everything and he happily accepted. All of the stock pieces that had been removed came with it in one of the boxes. Due to the lowered frame, I no longer think I'll try to return the bike to a stock restoration. Perhaps a period correct desert racer type build? An MX/Enduro crossover with aluminum wheels, high front fender, 21" front wheel, yet leave the street legal equipment on it so it can be licensed?

Ideas welcome!

First step will be checking both engines for functionality, both have compression but I looked no further yet. Degrease and disassembly of the entire bike coming soon. More will be revealed...

Welcome & Wow--lucky you & good score. some close ups of the frame mod sometime would be great. I'm in NZ & do remember seeing the mod in magazines but never saw one done. Rear wheel looks the first type from the square arm which is correct of course but the round arm fitted you say is aftermarket?. Will follow this with interest thanks. Got my DT1 going today after a long hibernation. Throttle was stuck shut with old fuel residue & the same wit h my AT1, Bugger to get the carbs off-- lazy me-- & down at my shed with no tools so found something to screw the idle speed screw in & it lifted the slide a fraction enough to broke the bond. Mine is as rough as a bears bum but a good runner. Look forward to hearing yours runs, & the spare motor too. You did well.

She is alive! A quick flush of the tank and cleaning of the carb is all it took after 26 years of sleep.


Still hoping somebody knows about the rear brace welded on the frame, I've never seen one before and it looks like some sort of aftermarket production item as opposed to a custom fabricated addition. Anybody??

Good one. Would the rail be to lift it out of the mud in enduros. Or for putting one foot on when riding verticaly down the highway scaring the hell out of motorist lol, maybe not.

Tore the engine down for rebuilding and discovered that the previous owner had cut and shortened the bottom of the piston skirts by about 7.5mm - I assume this was done for some sort of performance enhancement? The cylinder bore is the standard version (not MX or GYT) and there has been no obvious porting done, the piston was the standard Yamaha 2 ring for this early DT1 non reed valve motor. Is there any actual improvement to be gained by doing this? It seems to me that it might only change the intake timing some and I don't see the point on an otherwise stock motor. Or perhaps it was done to lighten the rotating mass? Anybody have experience with this modification? My plan at the moment is to rebuild it to original configuration.

Is it possible that nobody here has any knowledge or experience regarding the usage of this shortened piston? That is unusual, I was hoping to learn.

I did that to mine when it was new. I really don't know if it helped, but it was a trick from one of the magazines back in the day. I am sure it effects port timing, but whether the effect is positive or negative will require Enduronut or one of the other real mechanics on this site. I am a hack.

Mike

It's funny how on these forum sites some threads catch fire and there's a ton of input, and other threads sit quiet after multiple posts from the OP. I have no knowledge of what you're asking, but just wanted to say don't get discouraged by slow replies at this time. I have experienced this on several different sites as well, then all of a sudden the thread catches fire. Great guys on this site of course.

I can tell you what I do know, that's a nice find! Numbers matching AND a title is a big deal. My next project is a 69 DT1 that is about the same condition as your bike, less the title. Keep on posting and putting up pics!!

It seems to be quite a cut from the piston. You can do a little but once you start any performance mod the rest of the parts to actually make it work get real pricey. I think you would find more usable power with just a stock piston.

Yamaha and Suzuki Enduro piston ports of that era are especially weak on the intake timing in terms of "high rpm performance". This is not bad as it reduces the blowback through the carb at lower rpm (no reed valve... piston skirt is the only thing stopping the blowback)

7.5mm cut seems like a lot of added timing on an otherwise stock engine! I'd go with stock piston.