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I mean, ive had new carbs w sticky floats as well. you didnt put the floats  in upside down by accident did you? my tms had issues for the 1st few days.

I never opened them up before I put them on, im gonna have to take a look.

yeah dont sweat air pockets int he lines, thats normal. as scully said, and make sure petcock is flowing well.

I understand air pockets are normal, but the whole line is air right up to the carburetor, its running out of gas at high rpm. My old carbs, original vm28's didnt do this. They filled up almost to the petcock. The petcock flow just fine without the line attached. .

I just got these carburetors fitted to my bike, brand new genuine Mikuni VM28's. Im haveing an issue hopefully I can get some direction here. When I open the petcock the gas flows & fills the float bowls but the fuel line itself does not fill back to the petcock. When it is running as gas is consumed I can see more gas going thru the line. This seems ok at low rpm, cruising at 4k it runs fine. Above 5k I can feel it running out of gas, sputtering. .  Is there a reason why gas would only flow until the bowl is full & closes the needle?
Opening the gas cap does not help, it is not a vacuum above the carbs
There are no filters, the tank is pristine, gas flows freely from the petcock with  the lines removed.
I know it is running out of gas at higher rpms because, I removed the fuel lines at the petcock & prefilled them and did not have an issue at all until after 10 min or so when the line level dropped back down to the bowl.   
 

So I started the disassembly of my motor today & wanted to report a rather unusual finding. If you read my previous post the condition I described was rather extreme, today I found out why. See the pictures. When I pulled the gear that keys onto the crankshaft there was a piece of metal between the seal and the surface of the gear that the seal rides on. It seems like it may have been a thrust washer at one time, its definitely a hardened steel maybe .020 thick. What is this? how did it get there?

Swap coils around. If nothing changes swap condensers around.

agreed. if that doesnt do it, plug the choke crossover and swap carbs.

Thanks for the replies. As soon as I read this I thought It could not be this simple. I spent enough time on the points & timing to know the correct cylinders were sparking with the correct coil, but of course it is worth a shot. So with high expectations I swapped the coil leads & it would not fire at all, so I put them back & started it. Within 30 seconds the issue became all too apparent. Engine / transmission oil began spurting out of the right header flange. I shut it down & thought well thats what happens to a 50 year old rd engine that has never had the cases split. To be fair I was very far along with this engine before I even learned of the potential Crank seal problems with these engines, so I hoped for the best .  .   So we know what im doing or at least starting this week end.  .   Has any one seen one this bad that oil is preventing ignition? & spewing forth from the header connection? Or probably you guys know - Do not assemble the motor with out doing the seals.  .  I have a good out look here, chalk it up to experience & move on.   . 

An air leak would have the engine revving high.  What is your battery voltage while idling and at ~3500 rpms?

13 - 13.5 volts, admittedly I have a small battery 3AH , but in only running the motor right now. Seems the charging system is operating sufficiently. 

So I got my 400 running, half way, I only ran it for a few minutes. Ran very ruff & would not idle. It was apparent that it was only running on the left side as the left got warm & was smoking & the right stayed cool & only smoked very little. I am sure the spark, timing & points gap are all correct. I have not verified compression  but I am very confident it will be in spec. I would like any info that would help verifiy the carbs are working correctly & maybe an order in which I should check things. Seems to me that maybe the right carb is wonky, I suppose a leak down test is in order. Would an air leak around the intakes cause something like this?   

volt meter @ battery terminals. shouldn't really go over 14v , and should see over 12.5-13.00 at 1500-2000 rpm.

Thanks for the info, Even though this bike will have almost the bare minimum of wiring its still quite a challenge. Especially to make it look nice.   .   

so yes, it needs a switched 12v source to the brown wire

Thanks - just wanted conformation.   .   

On another note - Is there a simple way of determining that the charging system is operating correctly? after the motor is running of course.   .    Joe

I will be using the Rectifier/Regulator combo (see pic) from HVC on my RD400. All the old wiring is gone & I have most of the new in place. One question is about the Green & Brown wires on the combo unit that go to the generator brushes (I think ) . On the attached Rd400 wiring diagram it appears to show a connection to 12v on the Brown wire. I am assuming that if you plugged this unit into a stock harness that connection would be made somewhere. My harness is long gone - So is this correct? Run a fused 12v connection to that wire? I have ran into other diagrams that seem to confirm this but I want to be sure. Any help or info is appreciated.   .   Joe

K&N filters are junk , they pass as much dirt as the do air. Use Uni filters

Consider it done - Thank you

Thanks for the info, whats the issue with the filters with the capped ends? do they restrict air flow? Or do they not filter well?

I assume these are the stock carburetors,77 RD400, what are the inlets in the middle. Are they overflow for the float bowl? What are the other 2 smaller diameter inlets? Where should I run these lines to. Seems very difficult to find a diagram of all the lines that come off these carbs. 

Thanks for the reply, Im sure you have put together many of these motors so your method & opinion is great information for me. .   .   Joe

The next thing im going to do to my RD400 is install the top end. The cylinders have been bored & honed, the pistons are fitted to the rods. I am just wondering what the consensus is as far as the base gaskets, do you install them dry? Any type of sealer? For the head gaskets my gasket package came with the copper gasket with the raised rib. On the head bolts any assembly lube? In my experience with car head bolts Ive always used ARP Assembly lube.  .   .   Any info or guidance is appreciated.