I'd like to do what I can to get more low end grunt on this RD400c. I had a 1980 RD400G for a few years and it was so torquey in the low/mid I loved it so much for driving around town.
The only thing I can think of is correct the squish. If I'm correct that will add power mostly to low mid ? I have all stock intake track and stock exhausts.
Any other tricks?
is the carb tuning dead stock? have the carbs been taken apart and the brass ball drilled out and cleaned behind(air jet)? if not, start there. :twocents:
I havent actually built the motor yet. I bought the bike couple weeks ago and it was running like crap. Once I had a look at the hack job on the cylinder ports and one of the carbs was missing the main jet washer I knew it made no sense to try and tune it until I replaced the cylinders and reworked the carbs.
I have ordered stock 175-P2's and 115 mains and 25 pilots all mikuni stuff. The 5L1 needles look fine. That's what's in the carbs now but I wanted everything new and clean.
I'm praying and hoping that if I put everything to stock... I wont run into jetting nightmare. The only thing that wont be stock will be the cyclinders at 1mm over. All porting will be stock and untouched as well.
yeah should be good to go.
I was under the impression that the later 400s had less exhaust port duration than the earlier models. And were torquier/less revvy. Or was that just the US Daytona?
looks like it was just the Daytona to me
http://erlenbachracing.co/portmaps.htm
So it seems the porting I had on my 400G is very close the the RD400c I have now.. If they run similar and have to same low / mid power I will be happy. The Daytona must be awesome in the city with that porting. These bikes arent any fun, for me, when they are so tuned and piped that they literally make almost no power until 6000 rpm then it pulled hard. Almost a literal light switch power band.
The RD400G had DG's on it and a 2 into 1 filter set up. I HATED that bike... had to rev the freaking snot out of it just to take off from a light, was ridiculous. Went apeshit after 7000 rpm but so what? The bike would only be good on a track like that.
The intake drone was killig me so I went a found stock airbox setup and after tuning carbs I could not believe how much better the bike was. i was really shocked because I had spent years with this bike and couldnt stand the power. After that I scored some stock pipes and rejetted... again I was shocked what a wonderful torquey bike this turned into. I learned my lesson after that with these old two strokes to keep them stock for the kind of relaxed riding I do. Plus I adore the stock pipe's sound. Just so much more of a pleasure to ride.
Dropping a tooth on the front sprocket would help. Could do a 520 chain conversion while you're at it.
I'm very happy with the Stg 1+ job that Supertune Chuck did for me. That plus the pipes and the down geared final drive along with the modded carbs and Vforce reeds really improved low/mids. The bike pulls very hard off the line and just keeps going.... all depends on how far you want to go.
Here's the bike I just bought in Toronto. Going to spend the winter rebuilding it.
Quote from: Organicjedi on October 29, 2019, 04:21:45 PM
Dropping a tooth on the front sprocket would help. Could do a 520 chain conversion while you're at it.
I'm very happy with the Stg 1+ job that Supertune Chuck did for me. That plus the pipes and the down geared final drive along with the modded carbs and Vforce reeds really improved low/mids. The bike pulls very hard off the line and just keeps going.... all depends on how far you want to go.
I am going to keep it as stock as I possibly can. I'm so afraid to go down that rabbit hole after the 2 RZ350's and the RD400G I had. My tuning days are over!
The only thing I would change is to an electronic ignition and maybe get the squish corrected to 1mm. That's about as far as I'm willing to go. I think with how short the gears are already going down a tooth in the front isnt in the plans. I'll stick to stock. I guess my aim is to make the bike comfortable for bombing around town without too much effort.
Higher compression heads seems like a good move.
I'm so very pleased with the added grunt of having found some cheap heads that had been doctored and Chuck's update porting job - which is also great for stock pipes. He doesn't change port timing, just makes your engine a more efficient "pump."
Might need some tuning tweaks though.
I'm curious now.... Does Chuck have a website?
The Kawasaki Triples guys claim that adding +/- 4" intake runners between the pods and carbs (basically like a y-boot in theory) helps bring back some of the low-midrage that is lost when ditching the stock airbox.
It did seem to help with rideability on my KH400, but not sure how much this translates to a reed valve motor, as the KH is piston port.
I guess I could try a reed spacer but there isnt much room there with the stock airbox which I definitely want to keep. I'm not a fan of intake noise... plus after installing the airbox into my RD400G and seeing how it transformed that bike I've come to realize those Yamaha engineers knew what they were doing.
I think it looks like my only real choice for improved bottom/mid is to get that head shaved. I think economycycle pins the heads for that. After I get the bike running perfectly I'll see about getting the squish corrected.
Is the 520 chain conversion so that they can run o-ring chains?
Quote from: rd400canuck on October 29, 2019, 06:14:22 PM
Is the 520 chain conversion so that they can run o-ring chains?
520 chain is lighter than the stock 530. In theory, the heavy overkill 530 stock chain robs some power.
change your gearing and chain (520). Thats a simple easy change that you can do to give your bike more torque
OP is right, tho.
Yamaha R&D knew what they were doing. For an around town grocery getter, there's no beating the stock setup.
They didn't call it TORQUE INDUCTION for nothin' :dawg:
Too bad I've been 100% unsuccessful at keeping my bikes stock.
Quote from: pdxjim on October 29, 2019, 06:21:29 PM
Quote from: rd400canuck on October 29, 2019, 06:14:22 PM
Is the 520 chain conversion so that they can run o-ring chains?
520 chain is lighter than the stock 530. In theory, the heavy overkill 530 stock chain robs some power.
More hp to the wheel has been proven with a 520 chain vs 530. Simple mod for more power.
Quote from: rd400canuck on October 29, 2019, 06:14:22 PM
Is the 520 chain conversion so that they can run o-ring chains?
Do not run o-ring or x-ring chains. Run the simple DID Roller chain.
Quote from: quocle603 on October 29, 2019, 07:51:26 PM
Quote from: rd400canuck on October 29, 2019, 06:14:22 PM
Is the 520 chain conversion so that they can run o-ring chains?
Do not run o-ring or x-ring chains. Run the simple DID Roller chain.
Yes, it's assumed the o/x-ring seals rob some power too, but for a streetbike ridden in all weather IMHO it's totally worth the .5hp loss for the ease of maintenance, etc.
I like the DID 520VT2. Lighter than the rest and the size of a standard 520 with the ease of use of an o/x ring.
https://www.powersportsuperstore.com/products/d-i-d-520vt2-112-520-vt2-enduro-racing-t-ring-chain-112-links-gold?CAWELAID=120009580000067813&gclid=CjwKCAjwxt_tBRAXEiwAENY8hdNMowK0Lo1vl07APt4_Z8evPnm7loyB3tKoVmP85X2IsxG6dYjeohoCkgwQAvD_BwE
On a racebike or landspeed bike, absolutely run the lightest/strongest plain roller chain you can afford.
Put an ignition with timing curve in and have better low AND top end.
Stock is a compromise.
ok... I didnt know about the 520 conversion thing... thanks guys. I'll prolly run whats on it... I suspect it's a 530 because I remember thinking that is a chunky looking chain. When it's time I'll do the conversion and prolly do the x-ring chain just for the ease of use and longevity.
Funny you mention ignition, Brad-man. It occurred to me today that since it's a points ignition there is no ignition curve. From what I've learned over the years about engines is there is a lot to be gained from a good curve. So much power must be left behind with no curve.
I like the Vape because it has a 150 watt accessory coil plus it will add a little flywheel effect which I dont mind at all. I dont like that they arent keyed to the crank... I'm hoping they never slip. The other thing I dont like about the Vape is you dont get an ignition module for that money... if you want a curve and control over it you need to drop hundreds more on the module and its handheld programmer. That's a lot of damn money.. by the time it gets to me in canuckistan it'll be $1000.
However, I do relish the opportunity to tune in a curve to get all the power I can so.... maybe it'll be a treat to myself and something I can do over the summer after I got everything running good.
If you get your Vape system from HVC they offer a key service for $75, it'll never slip but you can't adjust your timing without a ZEEL box and programmer. I have the keyed Vape on my 400 and it's awesome. There's a few spots on the case and cover that need to be "massaged" but it's really easy to install.
I used the same VT2 chain, it's a thinner, lighter, stronger chain for moto cross, aluminum rear sprocket and 16/39 gearing and it's great!
Pull out the stock pipe baffles and burn them clean.
Rebuild engine with a fresh crank and a proper bore and hone.
Rebuild the stock reed cages so the reeds seal 100%
Stay with stock airbox, uni filter is fine just jet up for today's modern fuels.
30 pilot 1 3/4 out, 120-125 main jet, 120 for summer and 125 for winter.
Remove the ball in the carbs to clean the .5mm air jet, then tap hole with 5 x .8 tap, do only 2 threads!
Then replug with 5mm x 10mm length set screw.
Make sure you keep the airjet hoses connected from the floatbowls to the plenum of the airbox.
Set timing to 2.00mm
I would even add 1 tooth to the rear only.
17/39
If you use aftermarket .020 base gaskets and bore to 65.00 mm you don't need to
'SET THE SQUISH'. 400's are fine in that area. The aftermarket basegaskets are .004 thinner than OEM Yamaha gaskets. Torque heads to 24 ft lbs also.
Chuck
Chuck is absolutely correct. The changes you need to make to a RD 400 to make it an ideal street bike are minimal. You know from experience what you get when you "tune" an RD engine, they are great on a twisty road but a bear in town. My last 400 was stock except for the filter in the air box, the carb changes Chuck mentioned, and the handle bars. I left the ignition stock and it was no problem at all (but I've been messing with RDs since 1974). You will probably want to spend some time rebuilding the brakes also. BTW
I sell base gaskets in varying sizes if you decide you need different thicknesses.
Lyn Garland
this is what i was driving at w the carb comments. set the stock base tune with everything serviced correctly, 400's are tractors stock. (and i mean that in a good way).
Do what Chuck said, I did it to mine and I love it. Basically I was never happy with how my RD400 ran, because about all I do is tool around town in traffic.
I sent him my carbs and heads, he did his magic, I followed his instructions on the pipes and coil wiring relay, when I installed the carbs it fired on the second kick, and idled perfectly. The bike starts and idles clean and 'drives' like a modern(er) bike, lots more torque, or at least it pulls clean from low rpms.
:twocents:
wow, thanks everyone for all the great info :)
I went and pulled a baffle out... omfg it's like someone dipped it into thick grease. Ive ordered some baffle packing and I will take a torch to them. I ordered some different sizes of pilot jets, too. I didnt know I could clean the air jet either... thanks for that tip!
There seems to be a middle piece in this baffle and it can slide up and down about 1/4 inch. Is that normal?
Thanks Lyn.. I will most probably come looking for thinner base gaskets once I get everything back and see what kind of clearance I have.
Btw here is what I am planning on having the bike look like. Not what the bike looked like originally but I love this look. It's not the stock blue either, it's the same blue on the R1 and R6's.
I guess I'll start build thread
Quote from: hayduke on October 30, 2019, 10:00:18 AM
Do what Chuck said, I did it to mine and I love it. Basically I was never happy with how my RD400 ran, because about all I do is tool around town in traffic.
I sent him my carbs and heads, he did his magic, I followed his instructions on the pipes and coil wiring relay, when I installed the carbs it fired on the second kick, and idled perfectly. The bike starts and idles clean and 'drives' like a modern(er) bike, lots more torque, or at least it pulls clean from low rpms.
:twocents:
Wow,
Time flies!
It will be 3 years ago in 2 weeks that I did your carb rebuild and rejet! :cheerleader:
I looked at your notes and I did have you drill your baffles and run no packing on them.
I did re-drill to tap for removable air jets and used a .7 air jet with a 135 main jet
I set the air screw at 1 3/8 at the time for 1st fireup.
Chuck