73 Dt3

[LoserShoes]

Picked up a Yamaha 73 DT3 enduro about a month ago, has 10k on it and not running of course.
Cleaned the carb and a new set of points and its ok, except that at wide open throttle it falls on its face near top end. Feels like restricted gas flow. No tach on it so I don't really know what the rpm's are when it falters.

Don't have a manual right now, but what is the float height supposed to be and where to measure from? This carb has the independent floats.

What else could be causing this? Case seals? Bad reed valve?

Hoping some has had one of these and knows what the problem is.

[audijunky]

Hey there shoes,
How did you come across this bike. My boss asked me awhile ago to keep an eye out for one. i have been looking all over and cant find anything one them. Would you be willing to sell it. He might pay a pretty penny for it. Bikes kinda nostalgic for him. I see you just got and are probably not willing to part with it but if you got a figure in mind let me know and I'll pass it on.
Thanks

[LoserShoes]

Know the feeling, been looking for a long time myself, and found it setting beside the road with a for sale sign it just a mile down the road from my house.


Steve

[webbcraft2150]

Having desert raced the DT/AT/RT/YZ series for years when my personal healing powers were much faster, I offer the following.
As with any Yamaha, make sure the carb is well cleaned, ditto for the air filter. You can pull the reed plate off, make sure the reeds are sitting flat on the plate, if not, flip em over so they are or replace them. Try a high speed plug read. Put in a new plug, run it up to where it starts to bog, hold it for a few seconds them shut the engine off, coast to a stop and pull the plug. That will tell you if you are running rich or lean on the top end. Are you running the oil injection system? If the bike has sat for a while, the oil in the tank will go bad just like gas. Drain it, flush and fill with a GOOD grade of two-stroke. I ran Yamalube for years. If you are running the stock muffler, it well may be plugged with two stroke ca-ca after all these years. Pull the cap off the end of the muffler a look down in there, could be really yucky. I actually took the muffler off my DT400, cut the seam, pried it open, cleaned and gutted the baffles out of it and welded it back together. Midrange suffered alittle, but I usually ran these bikes at full throttle. I cant help ya with the float heights as my manuals are at home in the garage, collecting dust. Ah, the memories.

[LoserShoes]

Yep, cleaned carb, replaced enricher plunger which wasn't closeing, did clean pipe some, was really gucky from the rich running cause of the choke valve. I do really suspect the reeds, will pull them next chance I get. The falter always happens the same way every time, like reed flutter. Thanks for the feedback.

Steve

[webbcraft2150]

Originally posted by LoserShoes
[ like reed flutter

Steve [/B]

Forgot to add, if you can find em still, go with the Boyensen Reeds, TREMENDOUS difference from OEM. I was given a set from a Boyensen rep at a race, installed em on the 400. Bike would top out in the mid 90's on the OEM's, observed 103mph with the Boyensen with no other mods. I ended up buying them for all my 2-stroke rigs.