I have a 75 RD250, stock and mint. 1300 miles. given to me by
my broker when his wife told him it wasn't moving with them. He bought
it as spares for his race effort and for his wife to ride about 18
So what doesn't run right on your 250? Fouls plugs right? There are
a couple of solutions. The easiest is to ride it harder. Keep the revs over
5000 at all times. Don't sit idling for more than about 10 seconds. Next
easiest but most dangerous is to put in pilot jets and main jets about
2 sizes leaner, spark plug one range hotter. If you're *really* dogging
it, this will work. If you get on the freeway and cruise along at 70 after
doing this, it'll seize first time you back off the throttle. Best but
most complicated fix is better coils. I put Kmart ones for a Chrysler on
one years ago, worked great. You need to use the ballast resistor too.
Accel might make coils for this application which put out more VA than
You could also carry a few brand new spark plugs and change them
Go fast. Take chances.
Thanks for the info mike S.
My plugs do foul but it doesn't seem to affect the running much.I was
thinking that it might be the oil ingector.the engine will ocasionaly
rev on its own, but when put under a pull it will slow down to normal.
It seems to have very low power acording to what I have heard it should
have. I would like to know exacly what coils and resistors you suggest.
[tale of deflicted RD250 and possible solutions deleted]
>Thanks for the info mike S.
>My plugs do foul but it doesn't seem to affect the running much.I was
>thinking that it might be the oil ingector.the engine will ocasionaly
>rev on its own, but when put under a pull it will slow down to normal.
Sounds like an air leak. Especially considering the age of the
bike. There are two places that are primary leak spots. First and
easiest to check is the boot between the carb and the cylinder. Get
some ether, sold for starting hard to start cars. Carefully spray a
bit of it on the boot while the bike is idling. If it revs up every time you
do this, the boot leaks, replace it (assuming the clamps are tight).
Second place to look is crank seals. If the right side crank
seal leaks, the right pipe will smoke more than the left from sucking
oil/air mix in from the clutch cavity. If the right side leaks, you
can try the ether trick but the points might ignite the ether, giving
you a face full of fire. Easiest to just replace this one if you've checked
>It seems to have very low power acording to what I have heard it should
>have. I would like to know exacly what coils and resistors you suggest.
Cheapest ones you can get for an older (non-electronic ignition)
car. Go to Walmart. Even the el-cheapo's have 10 times the power of the
stockers. There was an article in Cycle mag about 20 years ago about
this cure. After you check for air leaks, lemme know and I'll dig it
out if you want.
(much excited banter about RDs deleted)
I've got an RD400 racer as a backup for my singles bike. Back east, I
built an RD400 sidecar. Fun bikes.
You need to join the two strokes list - 2str...@microunity.com. Lots of
idiots like you and me there gabbing about RD's and other 2 strokes....
I've got a '76 that I've been building for a year and a half. It's nearing
completion. Jeff Bratton-built crank, extensive porting, 34 mm carbs, TZ
cages, Spec II chambers, electronic ignition, Spec II racing clutch,
Novella rearsets, bitchin' custom Corbin solo seat, Koni shocks, clip-ons,
etc... It should be a pretty angry bike. Actually, I know it is - it was
all put together last summer, then I decided to make it look as good as it
ran. Since then, almost everything has been powder coated, frame, wheels,
engine, bits and pieces.
There are lots of 2-stroke-specific resources available. Here are some:
The 2-stroke mailing list. Well worth joining. Send e-mail to
2strokes...@microunity.com asking to be added to the list. After
you've been added to the list, send postings to
2str...@gaea.microunity.com. There's plenty of RD-lovers there, lots of
discussion of 2-stroke tuning, repair, and maintenance.
Send e-mail to Ric Naylor at cz...@cityscape.co.uk, ask him about the Well
'ARD Air-cooled RD club that he runs. He's a good guy, he's on the
2-stroke mailing list. He helped me to track down a nice electronic
ignition for my RD. These aren't available in the States any more, or so
it would seem. But there's lots of cool stuff still available in the UK
for RDs, and he can help you find it.
Call Doug Johnson at (509) 453-1976 and ask for information on The
Association of Classic Two-Stroke Owners (ACT-SO). He also sells lots of
vintage and performance parts.
Let me know if you get some sort of a RD-specific mailing list going. I'd
be interested in joining, and I know a lot of other people who would be,
The following is Ric Naylor's RD FAQ, reprinted without permission:
The info in this FAQ is what I've acquired from working on my
personal bike (RD350 with 400 brakes and wheels) and what I've picked up
off the 2-strokes mailing list. A lot of it is sort of general but I try
to be as specific as possible. As is true for most things, YMMV, and I
certainly don't know everything there is to know about these bikes. If
there is something blatantly wrong in here tell me and I'll change it and
similarly if you've got more info please tell me. Info on European models
would be helpful, as I don't have much specifically about them. E-mail to
dil...@minerva.cis.yale.edu until 5/95 at least. Share and Enjoy.
What sort of bike is it?
Between 1972 and 1975 Yamaha produced the RD350 and the RD250,
which are basically the same except for displacement and the 7-port
induction (Torque Induction) of the 350. These were a development of the
piston ported (as opposed to reed valved) R5 model and were themselves
transformed into the RD400 models, with had a longer stroke (same bore),
rear disc brake, mag wheels, different styling and a few other minor
refinements. The Daytona edition (RD400F) was the last pre-RZ(YPVS) two
stroke street bike marketed in the US. It had a few refinements over the
garden variety RD400, discussed later, but for the most part it is very
similar. The RD250 continued to be produced during this period with many
of the improved features of the 400, but it wasn't imported to the US, so
I'm not familiar with it.
After this, the RD350LC was developed with dual disc front brake,
water cooling, monoshock rear and redesigned frame. This in turn became
the RZ350 in the US and the RD350LC YPVS in the rest of the world.
There is also a model known as the RD200 or 200 Electric. This
was an RD with electric starting and was produced for a very short time
in the 70's and which I've only heard of once. I assume it's pretty
similar to a 250.
How much should I pay for one?
RD's can be found cheap because there are a lot of them out there
but clean examples can be mildly collectible. Pristine Daytonas can fetch
$1700 to the right buyer in the right market (San Francisco, for
example), but a decent RD400 runner is worth about $500 or so depending
on state of wear, after market parts, whatever. RD350's are worth a
little less. When looking at a bike and assessing how much your going to
be spending fixing it think about this:
Top end rebuild (rebore, new pistons) $200
Lower end (new bearings, seals) ~$300
Case rebuild (new seals, DIY) $40
Steering bearings (tapered roller) $50
(new balls) $5
Exhaust (chambers, new) ~$175
Gas tank (good used) $50
Most non-critical parts can be found used for cheap and there are
always great bargains to be found from someone cleaning out their garage
or whatever. I've never had trouble getting parts from Yamaha and there
is a good basis of knowledge and suppliers for after market hop up parts.
In England especially the RDs are alive and well, and it seems every
motorcyclist in the US has a story of either themselves or a friend
owning, modifying, or crashing an RD.
Where should I start?
The RD is a simple, easy to work on bike. Get a Yamaha service
manual (many of the others just aren靖 worth getting, like the Haynes
one) and don't be afraid to do the work yourself. This bike is very light
and can be tuned to produce enough power for kicks while still staying
reliable and streetable. Keep it simple and it can be a cheap source of
kicks and a great intro to working on bikes. It isn't really worth
putting too much into an RD because if you want all out performance you
might as well start with an RZ350 (RD350 YPVS) or even a grey market, RG,
RZ, NS, TZ or whatever.
A nice basic set up engine-wise would be something like good
expansion chambers, pod-type air filters, mild porting (just smoothing
the ports, not changing timing), and of course re-jetting. Beyond this
you could go with things like changing port timing, milling the heads (or
after market if you can find them), larger reeds, and bigger carbs.
Weak points in the engine are the crank (especially the
long-stroke RD400) and the alternator rotor. The latter is what keeps the
redline at 9500 (they start to disintegrate beyond that, apparently), so
you can lighten it or remove it all together for a racebike to get some
safer revs. Welding the crank is advisable for engines which are run hard
and can extend the time between retruing, but it also limits the number
of times it can be rebuilt. Again, the long stroke of the 400 makes
welding a very good option.
Replacing the stock exhaust is a given unless you are restoring
it for a total stock look. They are heavy and very detrimental to
performance. Expansion chambers vary in design and performance but most
will give you 8-12 hp right off the bat. Spec II pipes are reported to be
good while Factory Pipe Products have never been particularly popular.
Toomey makes good pipes but they have a rather narrow power band and are
Replacing the airbox is also a cheap and easy way to get power.
For replacement filters, K&N (folded paper type) look good and last a
long time, but oiled foam filters will protect your engine better and
probably flow better. Some people have had problems getting their bikes
to run right with filters with metal or plastic caps on the end, so your
best bet would be to go for all foam sock-type filters. Otherwise you
might need things like spacers between the carb mouth and the filter to
get it to run right. Note that intake noise on an RD is not
insignificant, and removing the stock box can make your bike noticeably
louder. Also note that later airbox designs (like the RZ YPVS) are much
better, and you can actually decrease performance by removing it.
Larger carbs will give you more top end but can be harder to jet
and can over carb your engine at lower revs. To fully appreciate the
power potential of the larger carbs you will have to do extensive
porting, so it is not a trivial swap. Some people say that after market
reeds (Specifically Boyseen 605) can increase lower end performance but
replacing reeds is more of a maintenance thing than a serious performance
booster. Other people report good things about cutting their own reeds
out of thin fibreglass. YMMV. Note that removing the reed stops on the
blocks can increase top end flow some but can also lead to early failure
of the reeds which could end up as a fried crank. Check to see if your
reeds are designed to be run with the stops or not, as it varies with
design. RZ 4 petal reeds are an easy conversion, as there is plenty of
material around the intake of the RD to allow the grinding necessary to
make room. The bolt pattern between the two should be the same. 6 petal
cages are pushing the limit, though, and you'll have to be careful when
you're opening up the ports not to grind the metal too thin. One note on
porting: don't spend a lot of time trying to get very smooth passages. A
rougher finish will help mix the fuel/air mixture and give you a faster flow.
Milling the heads is a good way to get more power, though
you'll probably want to get someone that knows what they're doing to to
it. Basically you want to get the piston to come very close to the
flatter part of the heads to push the mixture to the center for a more
centralized burn. I suppose reading some of the books on two stroke
tuning would cover this stuff, and I really don't know much about it.
New ignition parts are a common improvement for RDs. There are
some after market coils available, but the lowbuck trick in the 70's was
to swap them for K-mart automotive coils. People have been happy with the
Spec II coils but actual performance gain is minimal (though a good set
of coils can lead to a better running, easier starting bike) and they
aren't exactly cheap. Your RD will run good on whatever will give you a
good spark and not drain your battery. When swapping coils, check if the
new coils are internally ballasted or if they need external ballast
resistors. These help prolong the spark and prevent excessive current
draw at low RPM. Also make sure the coils are wired correctly, as wiring
them backwards can often cause a much weaker spark.
In the past, electronic ignition kits have been available for
RDs, though I don't think any of these are still in production (in the US
at least). The RD400E model (available in Europe) and the Daytona
(RD400F) had electronic ignition, but I know the RD400E at least also has
a completely different flywheel generator and you would have to swap the
whole thing. People have used Chrysler and GM HEI units on RDs, and a
wiring diagram can be found for this in the apr-jun.93 file in the
archives. Things have also been done like swapping Kawasaki 4 lost-spark
units on and building their own, but none of these have met with raging
success. You could also try a European supplier such as Boyer Bransden
for an electronic ignition unit.
The RD series is equipped with the Yamaha Autolube system which
meters out oil according to throttle position and RPM. Some people like
to remove this and go to straight premix. The advantages of premix are
lighter weight and less worry of total lubrication failure from a failed
pump. But it also means you have to mix in your oil whenever you get gas
and any gas:oil ratio will always be a compromise optimized for one set
of driving condition. Pre-mix would be good for someone who uses their
bike for competition, when the bike is mostly going to be in one RPM and
throttle range and light weight is important, but the Autolube pump is
a very good system for a bike that sees a wide range of conditions. Just
make sure your pump is in good condition, your hoses aren't kinked and
there is oil in your tank.
The RD350 and 400 share a number of parts, including clutch,
heads, and many of the internal engine parts. The only major difference
is the longer stroke of the 400, and so cranks and barrels are not
swappable. The Daytona is almost the exact same as the regular 400, but
the tachometer drive is different, and will cause a non-Daytona tach to
read low. Some non-Daytona 400s are equipped with an extra exhaust port
designed to improve low RPM running. It's effect on performance is
negligible, and many people just tap and plug them. The Daytona 400s are
equipped with throttle operated butterfly valves designed to reduce
emissions. They are not the same as YPVS and they do not improve
performance and are best tossed to save weight.
The RD motor is very similar to the TZ racing motors of the same
vintage. Swaps can be made to give your RD water cooling and other
performance advantages such as larger reed valves. But as old TZs get
rarer and RDs get older these sort of swaps are becoming a bit of
overkill, as your RD will never match a newer two stroke's performance no
matter what you swap on and you will end up spending a lot of time and/or
With your increased power, you might want to beef up your clutch
to handle the extra torque. The RD350 and 400 share identical friction
plates, and RZ plates will work too. Spec II has high performance clutch
kits for these bikes as do many other after market clutch suppliers.
Similarly stronger springs will reduce clutch slip, though they will
cause increased lever stiffness. To take full advantage of any extra top
end power you can also go down one tooth on the front sprocket, though
this will cause your bike to rev higher on the freeway.
Remember that whenever you change part of your engine you will
probably have to rejet. Stock mains are about 120. With a K&N in the
airbox and pipes you would probably want to start about 150. For
individual air filters, pipes and a mild port this would probably be
around 230. To check this you can use the plug inspection (read that FAQ)
while other people use oxygen sensors (not very accurate for precision
jetting, but look for the article in Roadracing World and Motorcycle
Technology for more info) and exhaust temp sensors (ideal exhaust temp is
between 1100-1300 degrees F, and you can get dual gauges for $145 from
AAEN). Remember that hex-shaped jets are numbered by flow rate, while the
round ones are by physical hole size. One option which is good for people
who run their bikes in varying altitudes or temperatures are the
Dial-a-jet additions, which allow you to change effective jet size
without taking apart your cards. These are available from most bike or
snowmobile shops and are a pretty simple installation, though they do
need regular adjustment to stay in tune.
When rebuilding, try to avoid using Weisco pistons, or if you do
make sure the person doing the rebore knows what they are doing. Due to a
different mode of manufacturing than most other pistons (OEM or Pro-X),
Weisco's will expand more when heated, and so need extra clearance. They
are also made with softer aluminum than the other pistons available, so
will go sooner than the others if something is out of whack. If you're
using Weisco's, it might be advisable to look into the various piston
coating out there to give then a little extra durability (Kalgaurd Piston
Kote for one, but look in bike or hot rod magazines for more info.
Specifically, Hot Rod had a survey about engine coatings some time
between may-july '94)
Brakes and Suspension
The RD will never be a world class handler by virtue of it's old
age and basic design, but it certainly is much better handling than many
of the other two strokes of it's era (like Kawa triples). There is not
much you can do to improve it short of a good set of rear shocks
(Progressives are highly recommended) and keeping the rear swing arm
bushings in good shape or swapping them for needle bearings (Spec II or
your local bearing supply store). Similarly, the front end can benefit
from new springs and tapered roller bearings in the steering head, but
short of a fork swap there is not much else within reason worth doing.
Aftermarket air fittings have been available for RD forks (mine has a set
of unknown origin) but I have no idea if they actually do much for
helping handling. I know one of the hard-core drag setups was to run with
air shocks only, no springs. The weakest point of the RD frame is the
swingarm, and Spec II and probably others make high performance
replacements, though they aren't cheap. Bracing around the steering head
and swingarm pivot also helps improve the frame somewhat but is not
essential. Monoshock conversions have been done without too much trouble,
using early dirt bike parts like from XTs, YZs or later RDLCs. You will
have to relocate the battery and do some minor fabrication (weld on a new
shock mount, for example), and I suppose handling depends on what sort of
shock and swingarm you use. (Look at the article in the 1st Well 'A.R.D.
newsletter of the Aircooled RD Club for a little more info.)
Swapping in the mag wheels from the 400 to a 350 is a straightforward
procedure, though you need to swap the rear swingarm too. With this you
also get a (absurdly powerful) rear disc brake, for which you will have
to mount a master cylinder and swap some brake lever parts from a 400.
Later RDs had the front brake caliper relocated from the front of the
fork leg to the rear for better handling, but this is a minor refinement.
The Daytona forks are the best of the RD forks (short of swapping LC or
YPVS forks in) and might be a little larger.
The disc brakes for the RD series are very good and should give you
all the stopping power you need. The earlier two piston types are a copy of
a Brembo design of similar vintage and are generally considered superior
to the later swinging caliper type. Getting some good pads (EBC or SBS)
and putting on stainless steel lines should give you all the power you
need. If your brakes drag excessively or lock up it's time to rebuild
them (the rear is especially prone to this), a cheap and easy procedure
which takes about a day. Just follow your manual and keep everything
clean. Of the RD series, the front and rear discs of the early 400s with
the two piston opposing calipers and the front caliper behind the fork
leg is the best set up and is just a matter of swapping it on. Drilling
the discs can reduce heat build up and improve performance in the rain as
well as reduce weight, but the difference is subtle.
Tire wise the word from England is Metzeler ME33零 on the front,
and don't try to stick big fat tires on a bike that wasn靖 designed for
it because it will probably just end up hurting your performance. You
could potentially fit a 110 on the front, but it isn靖 pretty and it will
handle like crap (don靖 ask how I know). Most people run a 90/90 or
100/90. For the rear, the Brigestone BT37R (with dual tread compound) is
supposed to handle better and wear longer than the matching Metzeler (the
ME99). The swingarm won't permit fitting of a tire larger than 110/90,
though swapping swingarms (I'm not sue what with) can give you more room.
Cosmetics, Electronics, Miscellaneous
Though a wide variety of dress up parts were made for the RD at
one time or another these have mostly gone out of production. Many people
swap on a set of drop bars or clip-ons for a sportier riding position and
rearsets are available from at least Spec II and possible Novela.
Fairings and solo seats are now only found second hand though TZ parts
can be made to work. Try places like Spec II, Airtech, or other fairing
suppliers. I'm also told that Doug Johnson has a good selection of
vintage seats and fairings for RDs and other older bikes.
The antiquated electronics for the 350s are swapable with the
400s and the later's solid state regulator and rectifier should plug
right in to replace the 350s old electromechanical dinosaurs. Halogen
bulb swaps are also an easy way to increase night ridability.
There aren't any big design flaws in the RD, but of course some
things will go before others. Rough running and oil burning in the right
cylinder can mean your crank seals are gone, the same with running lean
on the left. Timing is very important on all two strokes, so it is best
to set it with a dial indicator wherever possible. Pipes can get clogged
by carbon buildup, so make sure those are clear if your bike feels weak
or underpowered. Correct fuel/air mixture is also critical to getting
your bike running right, so make sure there aren't any air leaks in the
intake system, and make sure there aren't leaks in the cases or around
the cylinder gaskets.
Sloppy handling can be causes by worn out steering head bearings
or swingarm bushings, as well as worn out shocks. Replacing the fork oil
is also a good idea if the front end is giving you trouble.
Brake lockup means a slave cylinder rebuild, and you might as
well do the master, too. Mushy brakes means bleeding them or if that
doesn靖 help, replacing the lines (preferrably with stainless steel
When pulling the rotor, you can use the rear engine mount bolt to
screw into the threaded hole in the rotor, pushing against the crank.
You'll have to hold the crank in place, best done by putting the bike in
the highest gear and using the clutch-hub/sprocket holder on the
sprocket (A highly recommended tool, mine has two small cylinders on the
back to hold the sprockets. It looks like a pair of mutant locking
pliers.) You might want to file or grind down the first thread or two on
that bolt, since the pushing can cause mushrooming and make it hard to
get the bolt from the rotor. When putting the rotor back on, avoid using
locktite at all costs, especially the really strong stuff (I think it's
the red stuff). There should be a good enough fit as is to prevent
slipping and the keyway should prevent rotation. Using locktite means
that the next poor sould who tries to remove the thing might have to
resort to a hack-saw, blowtorch, and probably dynamite to get it off.
When removing fork internals, sometimes you'll need something to
prevent the inner workings from rotating when you remove the allen bolt
on the end of the fork. I used an aluminum dowel (3/8" diameter) and
flattened one end to fit between the inner tube wall and the flat on the
side of the damper rod. Other tips include using a broomstick or leaving
the springs in to put force on the internals and hold them in place.
And when disassembling the brakes, the manuals always call for
using compressed air to remove the pistons, but if you haven't got that
you can pump the brakes to pop them out. Sometimes one will stick in
which case you have to use another method. Rebuild the side you can, then
reassemble the brake. Take two metal strips, put one in between the two
cylinders like where the disc normally goes. Put the second one on the
outside of the rebuilt piston, and use it to clamp the first one tight
against the face of the rebuilt piston (use two C-clamps or locking
pliers). Pump the brake lever until the other pops out. This method is a
bit messy and requires disassembling and reassembling the calipers twice
but it's something you can do at home without compressed air. Also be
careful what you use to clean the insides of your brakes, as most
solvents will cause the seals to swell and your brakes will be screwed up
again. Best just to use brake fluid, but watch out with it because that
stuff must be the most effective paint stripper known to man (and it
doesn't do anything good for your skin, either).
When looking for basic mechanical parts like bearings, don't
immediately go to the OEM supplier. Most of these are just standard parts
which can be gotten through an industrial supply place for a lot cheaper.
Get a catalog from the supply place (usually they'll give you them free) and
get out a micrometer or some calipers and start measuring. The only
exceptions are bearings which have been specially machined for keyways
or whatever, which you'll have to get from Yamaha (Spec II also has a
wide range of RD/RZ parts for a lot less than most dealers).
* Peter Crandall *
* Adobe Systems, Inc. *
* 1585 Charleston Road, P.O. Box 7900 *
* Mountain View, CA 94039-7900 *
* e-mail: pcra...@adobe.com *
* tel: (415) 962-3789 *
: (much excited banter about RDs deleted)
: I've got an RD400 racer as a backup for my singles bike. Back east, I
: built an RD400 sidecar. Fun bikes.
Its a rd350-powered sidecar and YES ITS FUN!
-PeterC ... The fortunate SAMCO-sponsored vintage sidecar racer
Boy, you can't get a much better description of a problem than that! ;-)
Jim Moore (j#d#.mo...@canrem.com)
* Q-Blue 1.0 *