RD400 first run after rebuild, very low power

[m in sc]

gotcha. you're getting it!.  HVAC guy by chance? ('wet bulb' comment).

[ElFuegoBlanco]

gotcha. you're getting it!.  HVAC guy by chance? ('wet bulb' comment).

Not by a longshot. Just really in tune to the weather saying it's 93 and walking outside and saying "well, that's bullshit"

*Oops, I realize I said wet bulb when I meant heat index. The damn heat is getting to my brain.

[ElFuegoBlanco]

I still can't get this bike moving.

After reversing the slides to the correct orientation and side, moving the needle to the middle notch, and swapping the 310 mains to 250, it still just won't move. It seems to run just fine when it first starts, but after a few feet, it won't go above ~3200rpm.

Fuel is flowing, oil is flowing. After a few minutes, it won't even idle.

If I let it rest, it starts and will go above 3200rpm in neutral, but bogs down as soon as I'm on the road. 

[msr]

It may seem like a simplistic question, but are you certain both cylinders are firing all the time?

[ElFuegoBlanco]

Going by the exhaust, yes. And I can pull up where the throttle cable attaches to the carbs and each causes the rpm to increase. But even then only to around 3200rpm

[BlueR32]

Possibly fuel starvation caused by fuel tank vent hole being blocked? Try taking fuel cap off and see if it makes any difference.

[m in sc]

id take carbs apart and verify the airjet in each carb is cleaned and the jet tube is clean (still).
just to eliminate it.

[2steve]

id take carbs apart and verify the airjet in each carb is cleaned and the jet tube is clean (still).
just to eliminate it.

Yessir, that needs to be done on a 400, regardless.

[m in sc]

well the brass balls were taken out prior, but since it sat a bit worth another look.   

[ElFuegoBlanco]

Possibly fuel starvation caused by fuel tank vent hole being blocked? Try taking fuel cap off and see if it makes any difference.

I replaced the fuel cap with a (new) spare I had from my xs750 thinking the same thing

well the brass balls were taken out prior, but since it sat a bit worth another look.   

Can't hurt, I suppose. But if the RS carb is blocked, I'm blaming you haha

I'll also take a closer look at the timing, since I've gone down the fuel path so far.

Thanks everyone for the help. I'm determined to get this thing over 30mph.

Also going to check the floats while I've got the carbs off. You never know.

[ElFuegoBlanco]

Unfortunately a more pressing issue has come up on this journey. I have no rear brake pressure. I rebuild the better of the two master cylinders that came with the bike (in a box like many things), and I should have known better.

Now I have to decide on custom fitting a cheap ebay special, getting one of these sleeves, or forking over the $$$ for the HVC Cycle replacement.

[Hawaii-Mike]

Going by the exhaust, yes. And I can pull up where the throttle cable attaches to the carbs and each causes the rpm to increase. But even then only to around 3200rpm

Feel the exhaust pipes or heads to make sure both sides are firing.  Don't burn your hand while testing.

BTW I just got an RD400 running.  It was only running on one cylinder.  I kept thinking, air, spark, gas.  Cleaned the carb, still not running.  Then I realized I had not torqued one intake sufficiently and the air was bypassing the carb, going around the reed gasket.  Torqued up the four bolts and now the bike runs great.

[ElFuegoBlanco]

Now that is interesting. I'm 95% sure they're both firing, but I'm definitely going to keep this in mind.

[pidjones]

I would have to go back and re-read the various write-ups on the "balls out" procedure, but remember that the balls got replaced with set screws on mine. Removal of the balls not being the object of this procedure but rather access to the orifice behind them. The only other thought would be to check that the exhaust is not obstructed. Was lucky with my '76 in that the basket case came together and runs beautifully. It has stock exhaust, though.

[m in sc]

heres the thing.. w out the stock airbox & the lines run back to it in theres no reason to close the holes back up.