1977 RD400 carb question

[kgbhans]

I am new to 2 strokes and picked up a 1977 RD400 last year so apologize.  I got it running yesterday but I have some questions about the carb settings.  Can anyone tell me what the starting point is for the air and idle screws (how many turns out).  I have no idea what size the jets are but it has DG pipes if it makes a difference.  I appreciate any help.  I checked some manuals but  I couldn't find any settings.  I just got it running and don't want to blow it up.  Thanks.

[SUPERTUNE]

Welcome my RD friend!
Don't stress...
Tell me a little more about your RD400.
Are you still running the stock airbox? Do you know what filter you have? Uni replacement or still the stock paper unit?
Are you still on stock oil injection pump?
Have you done any ignition upgrades?
Stock timing for 76-78 RD400 is 2.3mm BTDC and needs to be retarded to 2.0 for today's 91*-93* fuels, (use pump gas no older than 8 weeks)
When using aftermarket chambers, due to making more power farther up the powerband, I would recommend to drop 1 tooth off the front sprocket to a 16T and not a stock 17t for the stock log pipes.
RD400 used 17/38 and the Daytona model used a 17/37 for the emission cylinders they had in the last year we got them in
'79.
Reply back here and I'll get you on the right track!
Chuck

[kgbhans]

I have the original air box but it has a newer filter (not paper).  I have not done any upgrades, to be honest, I don't know much on the bikes history.  I have not set the timing and my head hurt from you just talking about it!  I can't find any good videos or a manual with good pictures to properly understand it.  Thanks for the reply!

[Seizer]

http://www.aircooledrdclub.com/manuals/400C.pdf

You'll need this. And don't worry, these old bikes are fairly easy to work on. The carb settings are important as are the crank seals. Take it slow and methodical and you'll be fine. There are a lot of friendly people on here with decades of experience who will advise you should you need help. Good luck, you've got this!

[SoCal250]

This may help explain the timing procedure.
An old video from our own m in sc: https://www.youtube.com/watch?v=Iqardto3Kbs

It is similar for an RD400, just use the timing numbers that Supertune supplied above (2.0mm Before Top Dead Center)
It's fairly simple and can be done with minimal tools. You will need a small-faced dial gauge with a 14mm threaded base that will screw into the spark plug hole. It helps if the gauge is metric but you can use an SAE one and just convert the desired value. You will also need feeler gauges for checking point gap and spark plug gap.

Here you can find the point gap, spark plug type and gap, and other specs. (The jetting requirements will vary from factor specs depending on air filter, exhaust, engine mods, and altitude.)
1977 RD400D factory specs: http://www.2strokeworld.net/forum/index.php?topic=40.msg662#msg662

Tip: If you need to adjust point gap it should be done before setting/adjusting timing.

[kgbhans]

Thanks for all the help!  I did not have that manual so hopefully it will have the air and idle screw settings.  Thanks for the information and encouragement.

[SUPERTUNE]

Start with a 27.5 pilot jet, 135-140 main jet, leave the stock needle position in the middle for now.
Set the aircrew at 1 1/4
There is a set of hoses that come off the bottom inside of the float bowls on the carbs and connect to the bottom of the airbox plenum. (right under where the air filter is)
Just disconnect them from the airbox and just leave them open and not connected to the stock box, you can zip tie them together to keep them from flopping around if you like.
Chuck

[SoCal250]

And to add to the advice above from Chuck, make sure you use authentic Mikuni jets, not copies or 'equivalents'. Also, stay away from carb rebuild kits such as Keyster brand. 

[SUPERTUNE]

John at economycycles.com has bowl gaskets and Viton needle and seat valves, (get new red fiber sealing washers too) think he has OEM mikuni jets, don't remember. I have them if not.
When I rebuild carbs I always use new needle jets too. After all these carbs are 40 years old and you have no idea who's been there before and poked and reamed at them, The needle jets do wear out the hole over many years of running and vibration, the anodized needle is harder than the brass.
C