Juat picked this bike up. Starts food but dosent sound right at all.
I havent ridden 2 strokes since i was like 8 so i dont remember how they are supposed to sound.
This thing has no power and when off throttle surges badly. If revved up at a stand still idle hags and surges so hard it starts to knock top end.
I cleaned the carb. It is running a 150 main and a 50 pilot u think. They are quite hard to read.
Ether says says no air leaks up top.
Also this thing wont smoke. I thought it should smoke some?
I put some premix in the tank. Pulled oil line off the carb and after a time it would push a drop out slowly.
Ive got tons of question for this thing, its not pretty but i really want it to run good. It was a gift from my amazing wife and when i test rode it i thought it was all good. But bext day it got nasty

Download a service manual from the tech section. Check your crank seals. Others will weigh in.

Where do i find this tech section haha sorry

top of the page look for the headers---on the left is "Home", then "Forums" etc. About the middle is "Tech Library". Hover over that heading and a drop down menu will appear. Slide down to "Service Manuals" and click. From there you can click on the appropriate manual for your bike.

Agree with Mako that your cranks seals might be causing your issue. Regardless its a good idea to replace them on any two stroke that hasn't been run much (stored) for a time. Hard to check without pressure testing which is not hard but if I were you I'd just replace them and know that is out of the way.

Relic

Congrats on the new bike. is it possible to see some pictures???

Are you able to post a video of the bike running? If so......put it near the cylinder to hear if the piston has rattle. The bike should smoke and blubber a little. I don't have a trained ear yet, but others on here can tell you if its running right just by the sound.

I agree with Makotosun, you may have bad crank seals. You said you sprayed ether around the top end "to see if it changed the engine RPM" . Did you check the compression release also? A really good way to check for a air tight engine is making a $20 leak tester. www.yamaha-enduros.com/index.php/kunena-...icle-about-air-leaks

Please describe: how did you clean the carb? This is what I ran on my 78 DT 400.....every bike is a little different. you have to give it what it wants.

From my log:

Colorado Elevation - 10,000 Feet + : 145 Main Jet. 65 Pilot Jet. Needle 2nd from top
South Dakota Elevation - 3650 Feet : 160 Main Jet. 75 Pilot Jet. Needle 2nd from top
California Elevation - 0 Sea level : 180 Main Jet, 80 Pilot Jet, Needle 3rd from top


How is the air filter condition? Does it have a new spark plug?
The exhaust could be clogged up with carbon/oil gunk. A torch and hair dryer works well in cleaning it all out. hopefully you don't have a mouse nest in yours.

Running pre-mix and autolube is ok if tuned correctly. Just be aware if you have to much oil to gas ratio it would lean out the mixture and you know what could happen after that .

You said it had no power. It should make lots of low end torque and drop off around 5,000 RPM. Looking forward to hearing what you find.

Your carb stock is a VM34SS- should have 1M200 stamp on it. The carb should have either a 180 or 190 main jet and an 80 pilot. I wonder if the previous owner switched carbs or just tinkered with the jets.

Ok ill try and get it all.

Carb says 1m2 on it
I pulled it all appart and sprayed it all down with carb clean. Really wasn't that dirty. Pilot was a little cruddy. Carb leaks like a mofo if petcock is left on. Out the drain. Floats all move good so float valve is leaking.

I didnt ether the decompression valve. Ill try that.

Pipe seems to flow good. Hand over tail pipe, but i guess it could be plugging.

Can crank seals be changed without splitting cases?

I will try and take a video soon to let yall in on it

Thanks for the advice!

yes,the crankshaft seals can be replaced without splitting the cases. to replace the Primary side,remove the kick start lever,side cover and the clutch with it's crankshaft drive gear. there is a little o ring that seals the gear and the seal itself in the case boss.

on the Magneto side,remove the cover then the flywheel then the stator and the seal is exposed.

this is a exploded diagram,you can order the parts needed at a local Yamaha dealer or through Partszilla and the others might have great suggestions too.
www.yamahapartsandaccessories.com/parts-..._%28DT400D_-_1977%29

on that diagram,you will need parts #14,18 and 19. you can also use a new clutch cover gasket which is part # 1M1-15461-00-00. this part too seems to be still available.

if you want to look up your own parts,this is the Yamaha Motor site.
www.yamahapartsandaccessories.com/parts-...road-mcy?ls=Off-Road

Do you know if the carb was empty when parked? If it was stored long term with fuel, spraying carb clean might not be enough. Lots of tiny ports that carb spray wont clean and requires removing all brass pieces. Some people dip the carbs in a carb dip and blow them out with air. I use an ultra-sonic cleaner with pinesol followed by compressed air.

Yes, you are right: the valve/needle seat could be worn out causing fuel to drain out the overflow. Another possibility is the float height level is not set to the proper height.

Another thing to check is the petcock. Verify it is free flowing. If you only get a trickle instead of a steady stream, the carb bowl wont be able to keep up and it will start to run lean when empty. The fuel tank cap should also have a clear vent.

If the pipe is really badly clogged it will be quieter, not as loud as a free flowing exhaust. Worth a try burning the crud out, it wont hurt anything only help

How do you set float height on theae with the floats mounted in the bowl?
And how do you do this hair dryer blow torch clean the pipe thing?