I posted before about the troubles I've been having tuning a 1976 RD400.
Before I start up again, now that I have the case sealed up, I'd like to get some jetting advice. I've seen the Google doc on what others have done and I'm seeing conflicting information.
My setup:
1976 RD400
65.5mm pistons
Aftermarket pipes of unknown origin
RD350 y-boot with k&n filter
Brass balls removed from carbs, left open
220 main jets
35 pilot jets
2.5 slides
5i4 jet needles, clip on 4th notch (I believe, 2nd position from the bottom)
I just read the 5i4 on the needles a few minutes ago. It looks like maybe they're 350 needles? I'm not really sure, other than that I don't see 5i4 needles for the 400.
If there's anything relevant I've left out, please let me know. It's looking like rain for the next week, so it's a good time for me to get some parts together.
Thanks
Not just removing the balls, but cleaning the tiny air jet behind them?
Quote from: pidjones on August 01, 2022, 02:30:42 PM
Not just removing the balls, but cleaning the tiny air jet behind them?
Yep. I'm confident they're clean. Well, as confident as I could be. And I'll clean them again at least once before I put them back on the bike.
probably going to need a bigger main. but yeah.
should run. 5l4 needle is a stock 350 one.
Quote from: m in sc on August 01, 2022, 02:35:03 PM
probably going to need a bigger main. but yeah.
should run. 5l4 needle is a stock 350 one.
Interesting. I started at 310, went to 250, then to 220.
Should I stick with the 350 needle or buy standard 400 ones?
It "runs", but just runs like trash. I live on a hill in a 15mph zone, so I'm planning on heading to my father in law's garage on the other side of town to do a plug chop. Just trying to get some jet ideas beforehand so I'm prepared
I think 310 is definitely too big, and the 220 is probably too small. As I mentioned before, with a similar setup I'm running 250.
Quote from: SoCal250 on August 01, 2022, 02:57:07 PM
I think 310 is definitely too big, and the 220 is probably too small. As I mentioned before, with a similar setup I'm running 250.
I wrote your input from my last thread down. I'll go ahead and throw the 250s in to start and go from there.
Thanks for the advice. I'm really hoping to get it on the road this riding season. It makes me miss living in southern California, myself. I moved to WV about 8 years ago and riding weather is one of the few things I miss from home.
Rob
jet tube series is going to make a difference on main jet size as well. what jet tube is in there? :huh:
Quote from: m in sc on August 01, 2022, 03:06:09 PM
jet tube series is going to make a difference on main jet size as well. what jet tube is in there? :huh:
175p-2
so its a set of 400 carbs with 350 all brass? or 350 carbs? because 350 (US) carbs didnt have the brass ball in there at 6 o clock. :umm:
Quote from: m in sc on August 01, 2022, 03:23:06 PM
:umm:
Tell me about it.
400 carbs (stamped 1A1 00). One of them i bought from you back in 2020.
It looks like it's a hodgepodge of brass. Are the 175p-2 tube and 2.5 slides also 350 parts?
im pretty damn sure they are. I mean, it should work fine.
175 P-2 with 5L1 is RD400C/D/E; 175 O-8 with 5I4 is RD250/RD350
All those models ueed a 2.5 slide
(RD400F is 175 O-0 with 5FN39 and 4.0 cutaway)
And as Mark already said mixing the needles shouldn't be a big deal. They'll work.
I don't have the taper specs for the 5I4 but I think it may be just a tad leaner and longer than the 5L1? 5-series (B) vs. 5-series (A)
dont the 400's have a small air jet orifice as well? like .5 vs .8 (350) or something ? fuck i cant remember.
If the brass in the carbs is a mishmash of parts, you could get a Dave F kit from Economy cycle. That way you have all new brass and probably less headaches.
thats a solid plan for sure.
Quote from: m in sc on August 01, 2022, 10:15:19 PM
dont the 400's have a small air jet orifice as well? like .5 vs .8 (350) or something ? fuck i cant remember.
I checked and it appears the 350 and 400 both use a 0.5 AJ.
While we're on the subject does removing the brass cover and unshrouding the airjet change anything (performance/function/etc.)? Or does it not matter if the brass ball is there or not? I would think that Mikuni had to put it there for a reason.
it depends. on a dead stock bike, with the airbox connected, the idea was to equalize the air jet pressure to the airbox and not have it be in as much turbulent air. as soon as the stock airbox is gone, it serves zero purpose.
ive seen them run w a stock airbox with and without... i mean... the bell-mouth goes directly to the airbox so the pressure is the same. Ive never seen or heard of a performance loss.
Motor is back in the frame and only a few more things to button up before I try again.
Funny thing happened today. I realized I put the shifter pawl spring in backward when the shifter didn't spring back up. So I drained the oil and pulled the side cover.
And that's when I found my trusty penny I used to lock the drive pinion against the clutch :whistle:
When you first get it going, dont forget that what seems to be a jetting issue can be electrical or an airleak :cheers:
haha woah! Good thing you looked! lol
Quote from: Clem710 on August 02, 2022, 07:14:50 PM
When you first get it going, dont forget that what seems to be a jetting issue can be electrical or an airleak :cheers:
I fixed the air leaks around the reed cages and the left-side oil seal and I replaced the plug wires and caps. I SWEAR I have a set of coils around but have searched my entire house and can't find them. The coils are likely original and while they ohm out okay, I'm still wary. If nothing else, I'll pull the coils from my 750 and try them out.