Yam RD "Blue Dream"- Ride,Maintain,Tune

Mobius is correct. Two strokes rely on sonic wave activity and those pressure waves travel at the speed of sound. Reed valves help by allowing the inlet to be open when it wants to be without the detrimental low speed impact of long duration ports. Exhaust valves are similar in that at lower engine speeds the valve is down (mild porting) and as revs rise, the valve lifts to more or less TZ race bike levels. That variability really helps to make more top end and not lose any mid range.

The other trick is to add capacity. A bigger motor at the same level of tune will make more power and torque than a small motor. With the 400, Yamaha went for a long stroke crank and that doesn't allow such high revs but on the street it loses nothing at the top and makes a lot more low down.

Getting more mid range is the sweet spot for the street and the usual solutions are an exhaust tuned for mid range - avoid race pipes, and more compression helps too, until it's too much. If you raise the exhaust ports you lose low speed compression so raising it helps on the street but at high revs it needs to be managed. That's where squish geometry can help too. Wide, thin squish bands raise MSV and that helps low to mid but at high revs it needs to be thicker and less wide to reduce MSV.

2 strokes can often use more ignition advance at low revs and low throttle settings so a fully programmable ignition is a useful tool.

Faster burning chemical soup type race gas can help too, but hard to get at a gas station off the Grossglockner pass I suspect.

Different reeds can also change the power band, but the effect is subtle. Try the YZ125 reed trick or even old school Boyesens to see what difference they make on your bike.

You could also try reed spacers https://www.economycycle.com/product-category/yamaha-rd250350400r5ds6ds7-parts/fuel-and-airintake/reeds-spacers/
 
DG's aren't doing much to help low end. The stock pipes hit the power band earlier than most pipes. So for a relatively stock engine and wanting drivability stocks pipes are great. I put DG's on a bone stock RD400 engine but then put the stocks pipes on and haven't looked back. A much better riding bike.

I would suggest putting the stock pipes on (I understand aesthetically if you don't). I would definitely get YZ125 reeds. Then try changing your sprocket gearing. I know I changed mine for more low end. I just have to check to see what they are.
 
Mr. Carlos, it's a shame I don't have my little piston-port MZ* anymore. I would have loved to give you a ride on that one, instantly killing your complains. Unfortunately the guys are right, regarding the DGs shifting the powerband upwards. We could alter the rear cone and install a longer stinger, which in theory would give you a bit more midrange, but it would also make the spannies look different.

That said, you could also go out and do some research on other expansion chambers that offer a broader powerband - as I told you back then: DGs are the cheapest and by far not the best. Some Jim Lomas, Spec II or HiggSpeed will definitely deliver both more power and a wider powerband, but they'll all end up costing a lot more (as in close to what you paid for the RD)!

Oh and don't even think of tempting me into going back to building expansion chambers... I haven't got a sheetmetal roller and unless you find one very cheap on Willhaben... A well, there you got me thinking. Feeling bad now? ;D

On a serious note, you may simply want to reconsider your riding mode - one of the things I had to work very, very hard on on the racetrack: On a two-stroke you have to step the gears down until you hit the power-band. Dare to hazard a guess, why I ride a big, tuned V-twin as my daily? ;)

*It was tuned for high-rpm, following the MZRC-tuning guide
 
Re: Yam RD "Blue Dream"- Ride,Maintain,Tune

Hey guys!

Long time no hear.
I've been busy on my XS750 project,and now I'm pretty much back on track on the RD 350.
I'm getting the Bike ready for MOT.Since my MOT engineer is a bit butthurt I will change back to stock exhaust especially not to draw any attention to any more details which have been changed since the bike was 250 :)
Rejetted (130mains 25 idles) and cleaned the carbs,lets see how she will run.
This summer I want to tackle a fresh combustion chamber design (Mobius style with O ring and squished step in the head), since I still have a pair of stock 350 heads on my desk.
And I need to investigate on the rear suspension of my RD....she is hard as a rock,so I guess I will need to change the swingarm bearings and see if my stock suspension is maybe the problem...winter is coming to an end finally :)
71dd77e51e895df72f8467fade3eb1ad.jpg


Gesendet von meinem SM-A310F mit Tapatalk
 
der_nanno said:
Mr. Carlos, it's a shame I don't have my little piston-port MZ* anymore. I would have loved to give you a ride on that one, instantly killing your complains. Unfortunately the guys are right, regarding the DGs shifting the powerband upwards. We could alter the rear cone and install a longer stinger, which in theory would give you a bit more midrange, but it would also make the spannies look different.

That said, you could also go out and do some research on other expansion chambers that offer a broader powerband - as I told you back then: DGs are the cheapest and by far not the best. (I agree 100% - PJ)Some Jim Lomas, Spec II or HiggSpeed will definitely deliver both more power and a wider powerband, but they'll all end up costing a lot more (as in close to what you paid for the RD)!

Oh and don't even think of tempting me into going back to building expansion chambers... I haven't got a sheetmetal roller and unless you find one very cheap on Willhaben... A well, there you got me thinking. Feeling bad now? ;D



*It was tuned for high-rpm, following the MZRC-tuning guide

As you probably know, the MZ250/300 was basically the 1965 'race' (ISDT) motor. It got quite a lot of development over the years and really surprised a lot of people with 100mph top speed and relatively good handling (as long as the fuel tank wasn't full)
In the early 80's it had 7" travel front forks which got fitted to a number of Japanese 'trail' bikes as they generally only had 5" travel (at least around the area I lived/worked)

Ryan Stecken said:
Hey guys!

Long time no hear.
I've been busy on my XS750 project,and now I'm pretty much back on track on the RD 350.
I'm getting the Bike ready for MOT.Since my MOT engineer is a bit butthurt I will change back to stock exhaust especially not to draw any attention to any more details which have been changed since the bike was 250 :)
Rejetted (130mains 25 idles) and cleaned the carbs,lets see how she will run.
This summer I want to tackle a fresh combustion chamber design (Mobius style with O ring and squished step in the head), since I still have a pair of stock 350 heads on my desk.
And I need to investigate on the rear suspension of my RD....she is hard as a rock,so I guess I will need to change the swingarm bearings and see if my stock suspension is maybe the problem...winter is coming to an end finally :)
71dd77e51e895df72f8467fade3eb1ad.jpg


Gesendet von meinem SM-A310F mit Tapatalk

I was an MOT tester (nback in the day) it isn't a personal thing, you can lose your inspection licence if bike isn't at least close to street legal. (and generally lose your job if you can't do MOT tests) I know the exhaust laws have changed at least 3~4 times since I moved to USA, they never get any easier to pass. One other issue, was test center in town or out in the wilds? We were about 2 miles from police headquarters (horses, helicopters, and all the traffic police you don't want ;D ) and 1/4 mile from main station so got very frequent visits (just dropping in for a chat or coffee) One thing good though, we did get warnings of who was on duty and hated bikes plus times of shift changes, otherwise 130+mph road tests wouldn't have been any fun 8)
 
Thing is, Mr. Stecken and me, we both live in Austria and strictly speaking any modification is forbidden, which means, police can't pursue them all and in turn means, that minor offenses are being overlooked. Unfortunately it is very much left to the inspector's discretion, what's minor and what's not.
 
Oop's I forgot that your 'foreigners' ;D
I was tester in Britain, German test is supposed to be most difficult one to pass (outside of Japan where it's cheaper to buy a new bike every few years when test is due)
It should be possible to just fit stock pipes for test then swap back to 'spannies'.
The test only states things are legal on the day, I had the same bits 3 times one day, guys were swapping wheels and lights for test then swapping things back after testing. I knew what was happening but couldn't do anything about it as bike was 100% legal when I tested it
 
Re: Yam RD "Blue Dream"- Ride,Maintain,Tune

Just for your amusement.
The last time i did MOT (and I found a testing officer who is actually quite nice and easy) the tester told me that my front brake line was too long....
So I went to a brake shop and shortened the brake line went back and got MOT.
What the tester did not see was that this was a brake line with a screw joint (old one) which is illegal in austria,so now i'm running half screwed half press fit in front looks stupid but this is how things go here.a major PIA :).


Sent from my SM-A310F using DO THE TON mobile app
 
Hey guys!

Long time no hear.Just MOT´d the bike....found a super relaxed workshop in Vienna, they found no problems with my bike.
It was however quite some work to fit the "stock" exhaust on my modified Frankenstein motor with its early 350 cylinders (late 250 gearbox).

I was able to get 350 downpipes (smaller diameter than the 250 ones) and flanges....I fitted these together with a few seals (which take up the missing diameter) from England and some Dirko and the bike STORMS!
Its amazing how torque the motor gets and it still sounds really nice (maybe because of the KN filter).
The bike wheels in 1st and 2 nd gear as soon as the powerband hits.
One thing I also changed was the front sprocked from 2 down from stock to 1 down from stock....way nicer to ride!
After trying out 135mains I ordered bigger ones cuz I think the bike still runs a bit lean (K+N,carb mod, stock exhaust and modified squish).I will have some rejetting runs to see whats ideal for the bike.
Guess it will end up 140 ish...

the bike ran 165´s on the DG chambers...


Here´s a little video of the bike how it sits now:

https://www.youtube.com/watch?v=s6jgZ-wuRzA
 
Hey guys!

So I´ve been busy the last weeks/months with marrying and other unimportant stuff ;D

I´m currently switching between riding my XS750 and my RD and its a blast to see the difference betwenn these bikes.
There is however one BIG problem I encounter on the RD...the bike is nicely tuned has good performance and stopping power but its HARD AS A ROCK.

I already switched out the stock rear shocks for period correct KONI shocks (which I´m pretty sure need rework)...could it be that the swingarm bearing is shot?
If yes, is this something I can switch on my own with my knowledge and tools?
There are different possibilities...bronze bushings to needle bearings what would you guys suggest?

Its really no fun to ride a bike that hard, so I hope theres a solution for this.

Thanks in advance!
 
Re: Yam RD "Blue Dream"- Ride,Maintain,Tune

I may be very unqualified to give advice, but wouldn't a loose bearing/bushing make it feel really sloppy?


Sent from my iPhone using Tapatalk
 
farmer92 said:
I may be very unqualified to give advice, but wouldn't a loose bearing/bushing make it feel really sloppy?


Sent from my iPhone using Tapatalk

yes but a seized bushing will make the swinger hard to move. Pull the shocks and try and move the swinger up and down, It should move with very little resistance, it will tell you if its the bushings./
 
Pretty unlikely the swing arm bushings are a factor - usually they are too sloppy. Probably your springs are too stiff or there is some issue with the shocks. Adding a bunch of weight (like a passenger) should give you an idea about the spring stiffness.

A lot of people seem to not understand the swing arm assembly. The arm has two plastic bushings pressed into each side. The outside faces of the bushings have shims and dust covers which control the axial play. The plastic bushings ride on steel bushings that do not rotate and are clamped very tightly between the frame sides and a center spacer by a through bolt. The inner steel bushings are very hard and don't wear very much but can be damaged by corrosion. The outer bushings are soft and often are worn.

The swing arm pivot should be tight but not stiff. Take off the shocks and rear wheel so you can move the arm easily by hand. It should move freely with zero play. Axial play is adjusted by shims that go between the outboard flanges of the outer bushings and the dust covers. Radial play is adjusted by the fit between the inner steel bushings and outer plastic bushings, so if there is radial play you need to change the outer bushings which are a press fit into the arm. You can check the radial play by pulling the arm tight to the frame with one hand while pushing and pulling the end of the arm at the axle mount. There should be zero motion. Check axial play by pushing and pulling at the pivot. It is best to check after disassembling the whole works, cleaning, and reassembling dry. Bronze bushings are the generally used upgrade but needle bearing components are available. Personally I don't think needle bearings are worth the investment. New bronze bushings and correct shimming result in a very good assembly. It is a somewhat tedious procedure, but worth the effort. I put everything together with something really light like WD40 and check the play. Add or subtract shims until the arm moves freely with zero play. Then assemble with grease. The arm should be very tight, but still be able to fall from its own weight. It will very soon free up with use.
 
I agree with Mobius: Bronze-bushings ARE the better solution, but require a proper engineer to ream them to size, whereas needle bearings are a simple press in and forget fitment and don't require someone with reamers to make them fit properly.

@Ryan: As much as I agree with the above, have you tried adjusting the pre-load on your Konis? And if I remember you told me that they were Konis with the right length, but not the standard code for RDs. Maybe they simply are too hard? I have a set of Konis here, which are softer (too soft on the SR500), so depending on the model we could perhaps do a swap.
 
NK type needle bearings with an inner ring are pretty damn precise, but they cost a bunch too. I totally agree on using bronze bushings, but I also think it's important to note that you can find extreme precision with a needle bearing. I would expect most precision needle bearings need to be pressed on for proper fit. Also, a needle bearing is for high radial load and high rotational speed. They're not really necessary for this application.

Koni is now Icon, you may want to run some numbers through them and see if you have the right spring.
 
Thanks guys for your advice!
I will get back to you when I checked everything, really not nice when a bike is no fun to ride because of its ergonomics...
 
Hey guys!
Long time no hear!

I´m mainly working on my XS 750 cafe racer project but the RD is ridden regularly...still struggle with the hard suspension, I will pull off all the stuff of the swing arm when the season is over and check the swingarm for mobility.

My forks started to leak so I will need to reaseal them...
I have a question right here: Would you guys advise running progressive fork springs (the PO installed PTFE plastic shims in the forks to make them stiffer) or should I run stock, is it worth the $$$?
Could these plastic shims in the forks be also a reason why the bike is so god**** hard :)?
Thanks in advance!
 
Ryan
If the the plastic shims are increasing your spring pre-load then the forks will be stiffer. Suggest you first remove the shims and see how much improvement you get. Do you know the thickness of the shims? 5 or 10mm does makes a difference.
 
Back
Top Bottom