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Keep in mind the RD400 has that ballast resistor ahead of the coils so voltage right at the coils is not going to be 12 volts.

The ballast resistor has been bypassed. This was recommended by Economy when installing their replacement coils.

only time ive dont that mod revently was on my kz. only 75? somethings def amisd

Definitely. I do plan on tracing the voltage drop through the entire run. This was more or less a proof of concept to get to a real baseline. I was getting 9v at best at the coils prior to running through a relay from the battery.

There's a lot of great write-ups and tech data. Very interesting read.

Also picked up Haynes motorcycle fuel systems techbook, which isn't nearly as fun to read.

I ended up fitting it on one of the bolts of the rear brake piston mounting bracket I fabricated.

Voltage to the coils is good now and it runs much, much better. Still dialing the carbs and timing in as it runs great at 3/4 throttle, but not getting over about 75mph,stumbles a bit from a stop.

Many thanks to all who help out here!

Wiring the coils directly to the battery through a relay on an RD400, where did you place the relay? I have a 350 y-boot with a K&N filter. It's pretty tight back there.
Looking for advice before going forward.
Thanks!

I'm in Portland for the weekend and stopped in the other day. Super friendly folks. They have motorcycle maintenance classes, a garage for turning wrenches, and do motorcycle services. Highly recommend. I wish more places had spots like this

few qs.

what coils? are you sure they are getting over 11v when revved up?

To clarify-
At the coil?
Revved up how high? I measured at the coils and revved to about 5k and it never went above about 9v.

One other thing I experience is a right cylinder sputters/small backfires at idle. It's always done this. With a timing light, the right cyl bounces all over the place at idle. It cleans up fine with a little throttle.

I'm not sure it's related.

autocorrect.  one rich.

Ohhh I gotcha. I'll raise it to one notch above center. It may need to wait a few weeks after travels, so I'll order the recommended mains as well.

Thank you as always!

id get 170-180-190

also the needle is one right. usually w pipes they like the needle one lean or int he middle. start there. youre one rich. unusual w a P2.

I'm not clear on what you mean by "one right" here. Should I move the clip back to center or up one above? Buy another needle?

few qs.

what coils? are you sure they are getting over 11v when revved up?

the carbs, did you pull the jet tubes and verify they are clean?
can you try a 190 main jet?

It turns out I already had the 200 mains in. I'll have to order some more.
Any other recommendations on jets of any kind that I should throw in my basket while I'm at it and paying for shipping?

Coils are from Economy (with ballast resistor bypassed)
Jet tubes have been cleaned, recleaned, cleaned again.
I don't have any 190 mains.

The smallest mains I have are 200. I can try those and check the coil voltage when I have another opportunity. I've been test and tuning between rain storms.

I was wrong about the timing. The rh cylinder was off quite a bit. I must not have recheckdd after fixing some carb problems. It's set now and the problem remains.
 Actually, it seems sluggish all the way through, now, with a lot more sputtering.

After a few years of shelving my 76 RD project, I decided to dive back in. I posted here quite a bit back in 2020/2022 and got a lot of great advice. Unfortunately, life got in the way and I had to hit the pause button.

Bored one size over to 65.5mm
Aftermarket expansion chambers
New coils
Timing set 2.1mm btodc
RD350 y-boot with k&n filter
New points and condenser

Carbs:
Brass ball removed and air jet drilled 2mm
5DP7 needles one notch below center
169p2 needle jets
32.5 pilots
210 mains
Pilot air screw turned 1.25 turns from seated

I cannot get this thing to rev out. �It's decent on the low end, with some hesitation from a stop. The big problem is on the top end. From 3/4 to full throttle, it hesitates to accelerate. I can back off the throttle and feather it to increase the RPM, but it tops out well before it should. Probably 5000 in 6th gear. Lower gears are much better, but not nearly the power the bike should have.

Without a load, the motor revs up just fine to 9k.

I've tried 310, 220, 210, and 250 mains. Compression is good and leakdown test was good. No leaks in the intake. Floats are good and height is set correctly.

I'm not sure where to go from here. I can order some smaller mains or different needle jets. I'm just not sure which direction to go.

Thanks in advance!

You are very lucky to find it unscathed on the side of the road.

I was not looking forward to trying to source a new one for sure

Test run on the rd400 yesterday.

Today, notice the right side cover is gone.

Remembered I felt something touching my leg on the ride and thought it was the kick starter.

Panicked, I drove the short route and found it safe and sound on the side of the highway!

Turns out the rear master cylinder/bracket I fabricated was preventing the side cover from fully seating. Angle grinder and dremel to the rescue!