RD400 first run after rebuild, very low power

[ElFuegoBlanco]

I restored a '76 RD400 (US) back in 2020 and never got around to running it when I was done (I ran into winter and 2021 was a mess).

Some info:
oversized pistons 1 size over
unknown aftermarket exhaust (someone said Coffmans, but I couldn't confirm it)
RD350 y-boot
K&N filter
brass balls removed from carbs
35 pilot jet
310 main
new points

The motor started after the third kick or so. It wouldn't stay idling without keeping on the throttle a little bit. When I put it into gear, I really had to keep on the throttle to keep it running. Away I went. Very little power through full throttle. Into second gear, the engine died. Started again, same thing, very little power throughout the turn of the throttle. I managed to get all of three houses down before riding back with a sad face.

Also, there's oil leaking from the exhaust in cyl 2 (between the pipe and the part that bolts to the engine, connected with springs). I'm really hoping it's just part of the break-in process, but I thought it was important to mention.

Any advice on where to start?

thanks,
Rob

[pidjones]

Did you replace the ball with a set screw? Oil from the pipes is kinda common, I think.

[ElFuegoBlanco]

I did not. They're left open. I replaced one carb with one from a forum member that had the ball already removed. So I removed the other ball and left it on recommendation from him.

[rodneya]

Did you set your timing with a dial gauge?
I would start with double checking it is correct.

[ElFuegoBlanco]

I'm still new to mechanical timing. By dial gauge, you mean a micrometer threaded into the spark plug hole, right? I did.
I talked to an old 2 stroker and he immediately said check the timing. Once it cools off a few degrees in the garage, I'll run out to verify.

[2steve]

Is your 310 main really a 210?
310 seems too much.
My good running setup with FPP's, UNI's, boost bottle and update porting:

[ElFuegoBlanco]

Is your 310 main really a 210?
310 seems too much.
My good running setup with FPP's, UNI's, boost bottle and update porting:

Interesting. They're definitely 310. I bought 220, 250, and 310 and the 310 are the ones not accounted for, so they're on the bike.

I can definitely drop down to either of those mains. Based on the setup, Lyn suggested 250-310, so I started at 310. 220 is what was on there when I got it (complete basket case, so no telling if the po ran it with 220s.

Thanks for the advice.

Thanks!

[2steve]

Mine is stock bore and what you could call "below stage 1" porting. So, do be careful.

[m in sc]

dumb question. did you make sure the slides are in the carbs the right way. easy to mix up, the cutout needs to face the air filter. IF they dont, swap the left and right slides.

310 seems really steep on the main but verify the slides, then timing then test ride.

reason i say slides is the idling bit. .02

[ElFuegoBlanco]

Whoa whoa whoa. The cutout on the slides? Are you saying the groove alone the side of the slide faces the right (brake) side of the bike?

There's a tiny nub in the carb body that I figured (apparently incorrectly) corresponded to the groove along the side of the slide.

If the cutout means the sloped part of the bottom of the carb, they are indeed in backward.

Edit: or the slides are swapped between carbs 

[AAAltered]

I believe that 99% of 'us' have done that at one time or another...

[m in sc]

swapped between carbs. like said, it happens.

in this pic of the carb cutaway, the air filter would be towards the right.   

[ElFuegoBlanco]

swapped between carbs. like said, it happens.

in this pic of the carb cutaway, the air filter would be towards the right.   

That's exactly what happened. Thank you so much for that.

Now I'm getting a flat spot around 1/4 throttle, so I'm looking at the needle position.

Right now it's the second slot from the top.

[m in sc]

good, glad it was simple.
run it to the second from the bottom. (4th position). always better to err rich when testing. if its blubbery, then it has to be the middle  .

[ElFuegoBlanco]

good, glad it was simple.
run it to the second from the bottom. (4th position). always better to err rich when testing. if its blubbery, then it has to be the middle  .

2nd from the bottom was too rich. Moved to the middle and swapped the 310 mains for 250 while I was in the garage.

It pulled much, much better... Until I ran out of gas as soon as I left my neighborhood. I fueled it up a bit and had a somewhat difficult time starting it. When it started, it was even more sluggish than before. Came home and found the plugs are oily. So I swapped them out for fresh ones to be sure they're not the problem.

It's still over 100 here on the wet bulb, so I think I'm done for the day