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Author Topic: What to keep stock on RD400?  (Read 889 times)

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Offline edglenn

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What to keep stock on RD400?
« on: October 03, 2013, 04:52:15 PM »
I'm on a roll with my questions today!
Another one: I want my '76 Rd400 to be for some in-town, and canyon-carving. Nothing too radical, I'm old!
What should I replace, and what should be kept stock?
I'm thinking:
Carbs, stock except for aircleaners and bigger jets.
Exhaust, I'm on the fence. The chrome baseball bat's are UGLY, but they are supposed to be pretty efficient. Should I go with aftermarkets? What kind?
Ignition. I know electronic ignition should be better, but I hear a lot of guys saying they don't have problems with them. Hotter coils?
Stock front forks, but adjustable rears?
And of course...stage II porting the heads, or just leave them alone.
Reeds? Stock? Add spacers? (If spacers, which side of the reeds?)

Man,....I know I just pulled the grenade pin!
:)

Ed Glenn

Offline jeffmn

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Re: What to keep stock on RD400?
« Reply #1 on: October 03, 2013, 04:59:03 PM »
Geez Ed,

You are asking all sorts of questions i have myself. I have been mainly focusing on one thing at a time and not so much the big picture but i think i need to get a better handle on my end game.

i will be keeping an eye on the replies you get.

Jeff

Offline iranana

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Re: What to keep stock on RD400?
« Reply #2 on: October 03, 2013, 05:52:40 PM »
Welcome to the forum! In my opinion, Yamaha's engineers really knew their stuff and I've kept my 250E entirely stock and it's a blast to ride. In saying that, however, I've never ridden a modified RD, so I can't speak for how they are with pipes/porting etc. I don't know how much of a difference changing the air filter alone is going to make, I've heard the stock air filter flows very well on its own and compliments the stock pipes very well. But, if you end up putting chambers on it you'll need to do the air filter and re-jet. I like the stock pipes as they keep some power down low, which is good when riding around town. As for the reeds... everyone seems to recommend the YZ125 Reeds, linked to below. I'm personally running Boyesen Dual Stage reeds, just because that's what came with the bike. Don't use the stock ones cause the steel will eat your engine if they happen to break...

http://www.economycycle.com/servlet/the-772/Yamaha-YZ125-Reeds-for/Detail

Offline SUPERTUNE1

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Re: What to keep stock on RD400?
« Reply #3 on: October 03, 2013, 06:06:46 PM »
I would say to start with the basics.
Inspect/Rebuild crank and lower end seals.
Bore job with fresh pistons and rings (pro-x, wiseco and wossners are great brands)
(Banshee pistons are a great replacement with a small modification to the intake skirt)
RD400's are fairly good with the head and porting from Yamaha (except the last year '79 us emission model)
Solid rebuild of stock carbs. (use viton & seats and new brass from Mikuni)
Lots of performance chambers on the market, depending on your budget and performance level you want to have. (I like Spec II's to start with)
Try and decide what you have is still good and reusable and a budget to spend on some things like an electronic ignition system. A nice add on would be a Vintage Smoke Dyna setup, (keeps the stock charging system) on the high end for a modern permanent magnet charging system go with the MZB. (replaces ignition and charging system)
Do the engine first, then you can do the upgrade later as points do work well, but need some finesse to setup and do need some mild maintenance intervals. (find them on ebay, new OEM Yamaha ones) 
The stock RD400 coils do work well most of the time. Ohm them out and see if they have the right spec's and use new wires and plug caps.

One trick I suggest to do on the RD400's is to use a relay system to power the coils, and use the stock 12v coil system to run the relay. Very simple to do and gives great performance for good voltage to the coils.
Stick with the oil pump for a mild street bike. You might need to rebuild the pump though.
The pumps are really reliable.  Premix is great too, but more prone to foul plugs if riding a lot city stop and go riding.
You really don't need reed spacers until you get more aggressive for more power.
Do use some '86 YZ125 reeds to replace the stock 40 year old metal reeds.
Intake manifold crossover and boost bottle system will help also, but can be a little work to get jetted just right.
Do lots of reading here will help a lot.

Chuck
Team Scream Racing

Racegas + Lots of oil = HORSEPOWER
2 time Daytona AHRMA Formula-500 winner '06
'78 RD400E
RD machine work, boring, porting, cranks and engine building.

Offline Yamaha179

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Re: What to keep stock on RD400?
« Reply #4 on: October 04, 2013, 05:37:12 AM »
I agree with almost everything Chuck said.  I have two street RDs, a 250 and a 400.  Both have stock exhaust and carbs/air boxes with K&N filters.  The 250 is not ported, the 400 is.  Both have stock ignition/charging systems except the 400 has a period (1980 something) points replacement
pick up device.  Both bikes are great!

My argument is with expansion chambers; they have "holes" in the performance curve.  They
will be strong from 3K RPM up to 5.5K then falter until they catch at 6.4K then run like a bat-out-
of-hell to 10K.  Yes, you can sometimes soften or eliminate that dip but not often.  Both Chuck and I used to race RDs when one class had to use stock pipes.  I won a national AMA race on my 400 with stock pipes and carbs and a ported engine.  They can be made to run fast; not as fast as bikes with chambers, but fast, and they are easier to ride on the street.  You can fit rearsets with your stock pipes so you have plenty of ground clearance and they will look good, so I say go that route.

All the other advice everyone has given is good.  The 400s are some of the best bikes on the road
and you can really enjoy them.
Lyn Garland


Offline Dart11

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Re: What to keep stock on RD400?
« Reply #5 on: October 04, 2013, 10:09:11 AM »
As for carbs and intake, I would recommend a y-boot with uni pod filter and proper jetting of course, which will depend on your specific engine mods, location, elevation and other factors.

Listen to Supertune and keep the oil pump, it's efficient and reliable. Make sure it is working properly and simply keep it full oil a good two stroke oil (I use Lucas Semi-Synthetic).

Stock exhaust isn't bad, but they are pretty heavy. They are smooth through the powerband, but there is plenty to gain in hp with chambers. Chambers are the biggest bang for your buck as far as power goes, but depending on your riding style and intended usage, they might not be for you. You will get more noise as well with chambers (sometimes this is an issue for some riders...and neighbors  :lol: If I were to recommend chambers I would have to go with Spec II, Motocarrera GP, or Moto GP Werks pipes. Stay away from DG's, yes they are cheap, but don't yield good performance. Yes you can mod DG's to improve them, but the three I mentioned above will still be leaps and bounds better. You get what you pay for when it comes to expansion chambers. There is a lot of R&D behind chamber design.

Vintage smoke makes a great electronic ignition for our 400's. No more feeler gauges and point adjustments. Price is right and Nick is a class act. Read this: http://www.2strokeworld.com/forum/index.php?topic=6800.0

Stock forks are pretty good, just rebuild them and you'll be smooth sailing. Rear shocks can be kind of in depth based on what you're looking for our of the bike. Werks shocks are top notch if you've got a deep pocketbook..someday I'll be able to afford them.

You can combat the flat spot caused by chambers in a couple of ways. One, drill out the air screw in each carb and replace needles and main jet seats. Two, go with reed spacers or a boost bottle....or both  :dance:

Glad to see that you're looking to make the bike your own. Best of luck and hopefully this helps you out!


Offline edglenn

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Re: What to keep stock on RD400?
« Reply #6 on: October 04, 2013, 01:19:50 PM »
Thank you, everyone, for the help & information!!!
I will keep you posted on the progress.
This is an awesome site!!

Online rdshaw400

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Re: What to keep stock on RD400?
« Reply #7 on: October 04, 2013, 03:59:19 PM »
stock pipes are better than DGs in my experience, performance and tuning wise.
 for street riding some of the old school .J R pipes if your keeping stock foot pegs.....but really changing out the wheels makes one of the largest positive changes..........you will be shocked at what a difference cutting that weight in half does!


Offline TerryD1111

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Re: What to keep stock on RD400?
« Reply #8 on: October 07, 2013, 05:56:02 AM »
Don't forget the brakes. Caliper re-build is easy and adds to safety.

Offline Dart11

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Re: What to keep stock on RD400?
« Reply #9 on: October 08, 2013, 09:00:45 AM »
Good point Terry. Anyone have a recommendation for a rear master cylinder rebuild kit? I've heard there are a couple of small passageways that NEED to be cleaned out too. Tips/tricks about the process would also be appreciated.

Offline TerryD1111

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Re: What to keep stock on RD400?
« Reply #10 on: October 08, 2013, 09:21:16 AM »
Compressed air and some solvent. The brake piston seal slots can be cleaned with a dremel and wire brass attachment.

Online rdshaw400

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Re: What to keep stock on RD400?
« Reply #11 on: October 10, 2013, 08:53:38 AM »
I usually bypass the whole wheel brake suspension dilemma. with 250 ninja mono suspension brakes rearsets 520 chain pirelli sport demons, clip-ons. takes about the same time as going through a stock set of yamaha brakes! :laugh:

Offline edglenn

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Re: What to keep stock on RD400?
« Reply #12 on: October 10, 2013, 12:10:18 PM »
RDSHAW:
I'm a ways off from that type of setup, but it looks awesome!
Could you post a thread (w/ pics) on how you mod'd the frame, the rearend, brakes, and how you built the seat? Looks fantastic!
Dumb question, where did you get the "Yamaha" graphics? Exact style I want for mine, after yellow paintjob.