Yamaha RD400F refresh

[SoCal250]

I love it! As MTV used to say: Too much is never enough!

Looks like great minds think alike
And it was actually Billy Idol who said that on MTV!

[SoCal250]

Today I got the carbs pulled and installed new pilots along with a right side float valve. Idle was re-set and they were re-synced.
Also installed the new rear master banjo brake switch and got the brake system filled with DOT4 and bled.
And I put in a few more miles of shakedown, so just over 60 miles now since getting it running again. No major issues but I still need to tweak a few things, and find the source of a high speed vibration that comes in at about 55 or 60mph through 70+. I feel it through the seat and pegs but not really the bars, and it is not affected by pulling the clutch.

Tomorrow will be some more small follow-up items and additional road testing.

[SDDaytona]

Have your wheels been balanced?

[SoCal250]

Have your wheels been balanced?

Yes, of course. I even rode it over to the shop that mounted/balanced the rear tire a few years ago to discuss it with them and get input. We checked over the suspension, fastener torque, confirmed wheel weights were still in place, etc.,  and didn't come up with any smoking gun. He offered to put the rear wheel on the balance machine again if I wanted to bring it in, which I may do if I don't find anything.
In a conversation I had earlier in the week with John at Economy he suggested wheel bearings, which I have not done on this bike. So, when I have some time I'll be popping in a new set since I already have them on hand.

[SoCal250]

Since this bike has been sitting for about a month it's time to get back at it. I was trying to get it ready for an event in early July but it wasn't at the point that I thought it was reliable for 100+ mile rides. I worked on it right up until 8pm the night before leaving and couldn't get it sorted enough. I was chasing a mysterious jetting issue that requires further investigation because it ran great several years prior in the same configuration with the jets I started the project with, so they shouldn't have needed changing. (Especially having to increase pilots several sizes.)

So, now that I have more time and I'm not facing a deadline I can start plugging away at the remaining items. It needs the following:

1) Investigate and correct source of vibration at high speed.
     -Replace rear wheel bearings
     -Verify rear wheel balance
     -Check for runout on rear tire

2) Troubleshoot carb performance and jetting. Still doesn't run right below 1/4 throttle.
    -Leak down test
    -Re-jet

3) Repair transmission oil leaks. Some seals seem to have failed after getting it running again. Mostly on the left side, so I need to pull that engine cover to see exactly where it's coming from but I'm pretty certain the main culprit is the countershaft.
    Install new seals:
    -Countershaft and shift shaft
    -Neutral switch O-ring
    -Clutch pushrod?
    -Kick starter

4) Investigate reason for slight runout in pressure plate. Without the clutch window I would never have known this was an issue, but I discovered that when the engine is running the pressure plate has a small wobble to it. Not sure if it's a concern or not.

[SoCal250]

Realized I never posted the before/after shots of the right side of the engine since I was still working on that when I posted the left photos back in May.

BEFORE:


AFTER:


And how the bike looks now following all the recent updates during the refresh.

[Simmons1]

    

[SoCal250]

Here's the summary of all the work done so far on this refresh.

RD400F - 2025 REFRESH PROJECT, COMPLETED TASKS

CHASSIS & BRAKES
Front fender – installed new mounting hardware
Fork brace – installed new RSW Racing RD400F unit
Front brake – repainted and rebuilt OE front master and caliper. Then decided to install refurbished & rebuilt Zuma master, R6 caliper, & FJ1200 rotor with custom bracket and spacer, and all new hardware.
Brake switch, front – modified used OE Zuma switch to plug into RD400F harness
Switch assembly, right – repaired wire loom
Rearsets – replaced MotoCarrera set with 202 Racing set.
Rear brake – replaced OE brake master with CRF250/450 rear master that is integrated in 202 Racing rearsets. Deleted OE rear brake master, reservoir, pivot & push rod, return spring, & switch.
Brake switch, rear – installed Spiegler banjo bolt pressure switch, modified to plug into RD400F harness

ENGINE
Engine covers – replaced all 5 pieces with another refurbished set that was media blasted & repainted
Bolt kit – replaced all engine cover hardware with polished stainless Allen socket heads
Clutch window – installed Siberdyne kit in refurbished clutch cover
Oil pump – rebuilt OE pump. Then replaced with another rebuilt RD400 pump after finding issue with original.
Clutch – replaced frictions with new FZR1000 pieces
Carburetors – ultrasonic cleaned and rebuilt
Fuel hoses – replaced with new clear Tygon
Exhaust – repacked silencers 

[RDryan]

Looks great, well done   I gotta good question for you regarding your modified front brake. So that Angry Bees meet up that was already posted in the events section but I sorted double posted in the General Chatter section...well anyways there was a hopped up RD400 that had a similar front brake mod but it was cleverly switched over to the other side. Why is that? Is it too keep things better balanced I guess with the rear brake already fixed to the right side? As if to keep the forces of braking canceling each other out so to speak?...I dunno just find it interesting. 

[SoCal250]

Looks great, well done   I gotta good question for you regarding your modified front brake. So that Angry Bees meet up that was already posted in the events section but I sorted double posted in the General Chatter section...well anyways there was a hopped up RD400 that had a similar front brake mod but it was cleverly switched over to the other side. Why is that? Is it too keep things better balanced I guess with the rear brake already fixed to the right side? As if to keep the forces of braking canceling each other out so to speak?...I dunno just find it interesting. 

He used an RD350 front end which has the caliper mounted in front of the fork, so he swapped the fork legs in order to place the caliper on the rear for better handling (move weight lower and back) and for appearance.

[RDryan]

Ahh I see that makes perfect sense. Duh, I have my stock RD so I should know that about the caliper location.

[SoCal250]

Ahh I see that makes perfect sense. Duh, I have my stock RD so I should know that about the caliper location.

And just an FYI in case you're getting any wild ideas if you switch fork legs to move the caliper to the rear you'll end up with the speedo drive on the wrong side and spinning backwards, bringing all the issues that entails.

[SDDaytona]

Looks great. How did you attach the caliper bracket to the fork?  Nut on the backside of the fork tabs?

[Kawtriplefreak]

Beautiful work!!!  

[SoCal250]

Looks great. How did you attach the caliper bracket to the fork?  Nut on the backside of the fork tabs?

Thanks. Yes, M10 A2 stainless nylon lock nuts