YAMAHA YDS3 Technical Matters
YDS Differences: A question I am asked a lot is the difference between various years of YDS3 and YM1s.
The first of the YDS3s was introduced in June 1964, the YM1 came in February 1965. The model was offered in a purple blue colour to start, a black and silver version was quickly added. A greeny off white and black version was included as well, a few of the early YDS3Cs wore this colour (like Keith Battens old bike). The standard metallic blue and red was also added late 1964, these were to become the most common colours. Black and white on 1966 models is quite rare. Early black coloured bikes had silver side panel and oil tank and also the contrasting paint on the petrol tank was silver. This changed to the white contrasting paint on later models with the side panel and oil tank being black on these bikes.
Some of the main technical differences between years are:
Early bikes had no bolt at the back of the top yolk (triple tree)
The clutch changed from 4 to 5 friction plates after engine number 30412 on the DS3 models, all YM1s had the 5 plate clutch.
There were 3 main changes within the gearbox, up to engine number 18926, the gearbox was the small gear type which proved to be rather fragile. From between 18927 and 36320, there were several ratio changes within the box, the gears being replaced by much stronger gears with less teeth. The main and layshafts were also strengthened at this point. The third change came from YDS3 36320 and YM1 24145 where some ratios were changed again.
The kick start pinions were also strengthened from engines YDS3 35678 and YM1 24074. The number of teeth were reduced on each from 8 and 11 on earlier bikes to 6 and 9 teeth on later machines. It is a worthwhile modification if you have the engine apart to change these gears, the newer ones were considerably stronger. They are a drop in replacement for the early gears.
The top mount side panel (cover) changed after YDS3 25200 and YM1 12053 to mounting from the tab on the front of the air cleaner box.
Early YM1s (before YM1 12310) had no 305 emblem on the sidecover.
Inner fork tubes ( before YDS3 11026) had JIS thread top bolts on them.
After 11027, these changed to standard ISO thread.
Handlebar lever holders started off as YDS2 chromed MAZAC (no cable adjuster) versions up to YDS3 4736. After this, aluminum ones with cable adjusters were introduced.
Up to YDS3 34130, the standard YDS1 type 150 handlebar grip was used. After this number, new pattern 156 part number grips were introduced.
Up to YDS3 4761, a YDS2 style headlamp rim was used, this was changed after YDS3 4762 to a specific YDS3 one.
The front mudguard (fender) was the YDS2 style with 2 separate stays that bolted onto the bottom of the fork leg. After about YDS3 12000 or so, they changed to the new style one with bolt on stay.
An aluminium bodied cable splitter was used up to about engine YDS3 8000 or so where this changed to a plastic bodied part.
Round 148 part number YD3 tank badges were used on early bikes up to about YDS3 9704 (I have an original 1964 bike with all other early parts, this came with a rectangular badge tank and is engine and frame number YDS3 6564 so make your own minds up!) After YDS3 9705, this changed to the 156 type rectangular badge.
The rear tank mount rubbers and bolts also changed after YDS3 9705.
The front brake levers on the hub originally started out as YDS2 parts on the first models of the YDS3. These changed after 4737 to specific YDS3 parts. The front brake and clutch cable was also different on early bikes fitted with the YDS2 non adjustable lever holders.
Early bikes had a small YDS2 style tail lamp on them, these changed after about YDS3 9000 to the later, larger type. UK bikes also had a different lamp style for the newer bikes.
The early bikes also had a sprung seat, this had long springs between the front and the back similar to the YDS2. Later bikes had an all black foam padded saddle, 1966 YDS3s and YM1s had a black saddle with a whitewall all the way round it.
The rear wheel size also changed from early to late models. Early models started with a 1.6 inch wide rim with a 3.00 x 18 inch tyre. Later bikes had a 1.85 inch rim with a 3.25 x 18 tyre. The mainstand on the bike was also lengthened from 250 to 260mm to raise the bike further from the ground.
The cylinder head and shape of the combustion chamber was also different between 1965 and 1966 models. 1965 models had a square cut top to the top of the combustion chamber and were 14.3cc heads. The 1966 models had a 13.3cc volume with a rounded portion of the combustion chamber beside the spark plug hole. Make sure your bike has both the same heads!
The 1965 bikes also had different port timing in the cylinder barrels. The 1965 bikes had an exhaust port that started 31mm from the top of the barrel, 1966 bikes were 31mm from the top of the barrel. The bottom of the 1965 inlet ports were 82mm from the top of the barrel, 1966 ones were 87mm. Another worthwhile check on a bike!
The 1965 bikes also used a conventional rubber seal in the centre of the crankshaft. Yamaha changed to the newly designed labyrinth seal from 1966. It is possible to retrofit early bikes with the labyrinth seal by leaving out one of the circlips.
Early bikes also used a different kind of exhaust baffle in the exhaust silencer (muffler). This was changed to one that had a constricted end on it to quieten the bike down a bit. (Alasdair Cowan)
YM1 Starting problems:
Hi Damon, I had similar problems with my YM1. I stripped the carbs and fitted a pair of carb kits. This helped but it would still not fire correctly on one cylinder from idle to about 3000 rpm. I did the timing which helped a bit. I eventually swapped the carb body and this solved the problem.
For your problem, I would change the gearbox crankseal as this sounds your best bet. Also, it may be worth having a look at the centre crank seal (or labyrinth seal) depending on how old the bike is. It is also worth taking the top end off and cleaning out all the residue sitting in the bottom of the crankcase. This will also let you see what the pistons are like and if there is much blowby. Check your timing (1.9 - 2mm BTDC) with a DTI, they always go better after this. It is sometimes also worth steam cleaning the inside of the exhaust silencers (something I do as a matter of course now!) on the bike, this can also get rid of the sludge at the bottom of the pipe, makes it sound better too!!! Also check the carb to filter rubber if this is present for cracking, this can affect starting! You have to set the idle on these bikes first before balancing the carbs up!
I also meant to say that the revs on my YM1 hung up when I had just got it. After much head scratching, it turned out to be the rod that goes from the carb top idle adjuster to the carb slide was bent on both carbs. To check, remove the slide assembly and disconnect the cable from the side of the slide.
Take the slideassembly and remove the slides noting that they sit in a small hole top and bottom. After removing the spring, push the top down on top of the slide and rotate the small pin in your hand, this should show up any movement as it should turn with no sloppiness. If it does, remove the small split pin on the carb top and drop the rod out. Straighten as best as possible!
Alasdair
Tuning:
What you need to do is go thru the whole motorcycle and set everything to factory specs before you even attempt to try to diagnose anything. Anything short of this and you end up chasing your tail. As for getting the timing close, forget it, close doesn't cut it, it needs to be at 2 mm BTDC with the points set at 13 thou at TDC. You need a dial indicator to do this there is no other way to do the job.
So my advice is this, get a factory service manual, get all the stock jets in the carbs, set the float height to factory specs (15 mm) hook up the air box, throw away the starting fluid if you care at all about your motor, set the oil pump adjustments to specs and put in some high quality synthetic injector oil like Bel Ray SI 7 or Spectro , set the points and timing properly ,put the correct plug wires on the thing and the bike will run just fine. If it doesn't after everything is set CORRECTLY then it's time to start looking for the problem. Ed
Air filters:
Hi Alsdair, I have used air filters. They can be cleaned by soaking them in naptha. Which cover do you need? One has the mount for the side cover, one does not. The early one does not because the outer cover hangs from the top. The later outer cover hooks on in the front. Ed
Crankcase:
Ed, I'll look up the numbers and get back to you. question: if there is the "brown oily goo" in the crank area, must i split the cases? Is there an alternative?
Everything looks so good with this yds3... I just want to avoid mistakes.
thanks! Dan
Hey Dan, What I do lots of the time is to flush the bottom end out with kerosene . I fill it and dump it out in a clean white bucket (joint compound bucket), look at it, do it again and dump. Don't turn the crank yet, Just fill and dump. If there are no pieces of metal then its time to fill it with 2 stroke oil and work the rods up and down to revolve the crank. Dump out and repeat then you are done. I usually do this to all my motors. Ed
Paint: There are no codes. Its a 3 step candy .You need a good piece of
nos to match to.I have been painting these for about 15 years. I use House Of Color products. The pearl white is shot then the colored area is taped off and the white masked. Then the colored area is shot with a base coat(usually fine metallic silver) and oversprayed with the candy.Candy colors are clear. If you put them in a jar you can look right thru them. The color you end up with depends on how light or heavy you go with the candy.
It's not a simple spray job to do it right. After the candy is shot the piece is clear coated. This is how you get that paint that looks like you can dive into it and swim. There are some automotive finishes that mimic the candies but they are just not there. It's a hard job to do it right so shop around and ask lots of questions. The paint on these bikes is real important. They came from the factory with real nice paint work. My red YDS3 is original paint and so is the green DS6C. I shot the blue YM1. The color is much more vibrant in real life. The camera doesn't do it justice. Good luck, I hope this helps. Ed
Rust in tank: I use phosphoric acid . It takes it down to grey metal. It's good as long as the tank isn't rusty to the point that it's about to break thru.
I would do this even if I was going to coat it. I avoid coating because the fuel keeps on changing and there are no guarantees that the new "improved?" crap that they force on us isn't going to react with the coating and screw all sorts of things up. Eastwood's Oxysolve works good also as long as the rust isn't to bad. I use it straight out of the bottle and save it to use again. It takes a couple of hours at about 70 degrees to de-rust a tank. Then it has to be washed with soap & water ,rinsed , and dried.I use a hair drier to dry out the insides of tanks.. There can't be any moisture after this is done or the tank will rust within the hour. When it's dry I slosh some 2stroke oil& kero in the tank to prevent any moisture from getting at the metal. The products are somewhat dangerous and you must wear gloves, goggles, and a resperator.
Fork Oil: I make my own. I mix ATF with 10w 30 w motor oil in a 50-50
mix. It works fine for me. The service manual says 10w 30, but I found that too heavy for my needs. The so-called fork oils are way to light. They are formulated for modern bikes. An old timer told me he plays with the amount rather than the weight. I have tried this and it is a workable solution but you have to be careful not to put too much oil in or you will blow out the seals. What it really comes down to is your preference as to what you want your front end to feel like. Ed
YM1 carbs: A YM1 calls for a 130 main and if it just bogs look real close at the pilot jets. That is a sign of clogged pilots and weak mixture. The float level might also be to low. Set that to the factory spec. The float level adjustment is extremely important on these and all 2 strokes. It determines the air fuel ratio thru out the mid range.If it is too low the bike will run lean and exhibit symptoms like you are describing. It will also burn out your motor if it's too lean.
It sounds like all your carb settings need attention. Set everything to the factory settings and then see where you are at. A motor can't be diagnosed until all the tune up settings and carb settings are correct. 2 strokes aren't anything like 4 strokes when it comes to tuning so forget everything that you learned on 4 strokes.
You and everyone else that is just starting to fool with 2 strokes should get a copy of the 2 stroke tuners handbook. It is heavy on theory and explains all of these things in great detail. Another good place to start going is Macdizzys. There is a link in the 2stroke links file. It costs 11 bucks for a 1 year subscription and is well worth it. It is basically a racers site for 2 stroke ATV's but the stuff you can learn there can be applied to any 2 stroke I've been fooling with 2 strokes exclusively for 39 years and I still learn all sorts of things at this site. Ed
Carburetor adjustment: Hey Damon, As Neil points out the ex gaskets aren't sealing but the second part of his reply is what you should be looking at closely. We keep coming back to your carbs. The needle position that you said you have it set on (#2) it way to rich. The oily gooey mess is another symptom of this. Your bike isn't in proper tune yet. You need to go back and meticulously and methodically check and set all your tune up stuff. Everything needs to be exactly right for it to work right. Ed
Carburetor Adjustment: It sounds like you are talking about the pilot jet. The pilot is a small passage that passes from a small opening in the venturi area of the carb to the float chamber and has a small opening in the jet to control fuel-air mix at the lowest throttle openings. This jet primarily affects the operation of the motorcycle when idling and would cause the problem that you're experiencing. There is a small opening which passes through the pilot jet from top to bottom and it sounds like yours is clogged.
Get a rebuild kit from Alasdair (a member of this group)and replace the main jet, idle jet, starter plunger, the needle and the float valve assy. Before putting in the new parts, soak the carb in a good solvent (carb and parts cleaner) and blow out all the passages with compressed air. Reassemble the carb with the new parts and adjust the float to proper specifications. If you don't have a service manual, let me know and I'll look up the settings. If I remember correctly, it should be 23 mm.
While you are working on the carbs, it would be wise to flush the fuel tank and clean the petcock to insure good fuel delivery to the carbs. Make sure that the idle is set to about 1200 RPM and the idle should be even between the two cylinders. Check to make sure that the throttle cables are evenly adjusted for each carb so that the throttle slides begin to lift simultaneously when you begin to turn the throttle.
While you are at it, replace and adjust the points and condensers and adjust the timing. The points should be set to 14 mm and the timing should be 1.8 mm BTDC. Ralph Segal
What is the factory spec float level for the YM1? Hi Steve, it is 25.5 mm measured from the flat where the float bowl sits with the gasket removed. Pilot screw is 1. 5 turns from fully screwed in. Hope this is of help, Alasdair
Timing: YDS-3 timing was set with a dial indicator in the spark plug hole measuring 1.8mm BTDC. The standard main jet was #120 but of course it depends where you live. I recommend 2.0mm BTDC as 1.8 was never enough for the YDS-3. Point settings were .012"-.016" if I remember correctly. Air screw is 1 1/2 turns to 2 turns opened from the full closed position.
Never hold the kick started down after you kick it, as the older models (1965-66) broke kick starter gears.