Mike asked me to update his info for porting on RD/RZ series engines so here goes...

First of all, I am very sorry, but because of the number of people calling and saying things like "Well, I have only followed one of your tips and my bike isn't much faster, can you help?", I have decided to take my contact info off this page. There are just too many lazy people out there. So, the following is offered "as-is". If you follow the advice your bike will be fast. If you don't, it will be slow.

A lot of what I have to say involves info that needs a fairly good grounding in engine performance theory. I found the following books to be very helpful in gaining that knowledge.

1). The Chevrolet Racing Engine by Bill Jenkins
2). Smokey Yunick's Power Secrets by Smokey Yunick
3). Race Engine Prep by Wadell Wilson
4). Performance Tuning in Theory and Practice: Two Strokes by a A. Graham Bell

There are many others out there, but these are written by people that have actually built engines that win. As far as four stroke vs. two stroke, there is cross-over technology that applies to both and reading the books will only help you in the long run.

As well, I have written some recent articles on heat related power loss in two strokes and carb modifications that are very relevant to this info. Mike Hammer has turned these into HTML and they are available here. For more info on RDs I recommend that you contact:

Doug Johnson
Assoc. Of Classic Two Stroke Owners
1-509-453-1976

Request volume 3 #3, volume 4 #1 and 2. These relate to heat and power loss.

Request volume 4 #3. This outlines modifications to 28mm Mikuni's for additional power and driveability.

I do all my port timing with a degree wheel as who knows what the last crazy person did to your barrels, I'm only concerned with what the current crazy person is doing! When it all comes together, the only thing that matters is where the piston is when it is time for a very specifically timed event to occur. The only way to ensure this is to work with a degree wheel. Get a good quality one and learn how to find TDC with the positive stop method.

Squish clearance is very important to get correct and every effort should be made to get the right values. When this is done correctly, the engine will develop more power and be more resistant to over-heating and detonation. The value that I like to use on the RD/RZ series engines are .030" to .035". The info in Doug Johnson's ACTSO articles listed above will describe what the desired end result is and how to get there. The angle of the squish area of the head is best set to 14 degrees.

Because I set the squish band much closer than what comes out of the box, I always ran pretty high compression for air cooled engines, on the order of 175 psi. I would check this when the porting was done and the final adjustments were being made to the head. The squish clearance will have been set and confirmed by this point. I would assemble the engine and place a good quality compression gauge (with a weak schraeder valve) in the spark plug hole and boot the kick-starter over (no carbs attached) until the highest value was reached. If the value was lower than what I wanted, then the head would have to be surfaced again, the squish band redefined and tried over. The idea was to reduce the volume of the head to bring the pressure up to what was wanted. If the compression value was too high then the head would need material removed from the hemi-shaped portion nearest the spark plug. DON'T remove material from the squish angle area. This will reduce the compression but will also increase the clearance that you tried so hard to set to .030".

We have used these specs with Toomey pipes for top-end (11,500 red line) and Lassek pipes for more mid-range(10,500 red line). They are a very forgiving set of ports. We have also used 29mm carbs to 36mm carbs with great results. I personally like the 29mm carbs (bored set of stock R5/RD) as they have a very wide power band with only a minimal loss of top end. I would stay away from the TMX style Mikuni's as the needle jet is not a tunable item i.e. not replaceable.

Unless you want the engine to run worse, do not run open carbs or individual filters. We ran the stock rubber air boot with a tall K&N filter. This alone was good for a .2 second decrease in 1/4 mile times along with a 2 mph increase in speed over open carbs. This is nearly free horsepower. Your out of luck here if you run anything other than stock carbs though. (Mike's note: As Bell's book points out, tuned intake length is the important thing here. You might try long, narrow taper intake horns if you are running non-stock carbs to get the same tuned length as a stock RD. This helps things considerably though you still lose some bottom end.)

Carb parts are:

Air jet: 2.0mm

Needle jet: 169 series P2

Pilot jet: 30-35

Jet needle: 5J9

Main jet range: 180 to 230

Slide cut-away: 2.5(stock)

Air screw: 1/4 to 3/4 out

The carb parts are available from Sudco Mikuni 1-213-728-5407

Although Lassek pipes are no longer available from Lassek directly, I have seen posts that list a source as:

Tommy Crawford

1-909-658-4205

Part of tuning is knowing how to determine what changes to make and the best way to do this is to learn the art of plug reading. This took years of observation to figure out a discipline to reduce this process to a quick and accurate race day drill. I include the following to help. Forgive the fact that it reads a bit out of context: I copied it from a post I made to a two stroke list

Been reading the string about plug chops and I thought that I would add my advice as well.

The first thing that must be understood about 2-strokes (Yam RD's anyway) is that they are horrible at pumping out the bottom end. Has anyone noticed that when the barrels are removed the crank is swimming in old oil? This is what was left on the cylinder walls and everything else when the engine was shut down last and all that oil has to get out of the engine as it will color the plugs and make things look richer than they really are.

Best thing to do is to go down to a local auto parts store and pick up a box of plugs. Now the RD's use ND W27xx and NGK B-9xx for racing and these plugs can be had for about .75 cents each. Those of you with the high zoot rides with the primo-expenso plugs are gonna have to bite the bullet on this one.

At the races, I would fully warm up the engine for 10 minutes blipping the throttle. Nothing serious-maybe 6-7 grand. I would do this to get the old oil of the crank. I would also be using the old plugs that I had run in the previous race meet main event. After the bike was fully hot and the exhaust smoke was running clean, I would put in a fresh set of plugs-cost of $1.50.

Now comes the next most important part. Just before practice starts, warm the bike up again. When you are released to the track, DO NOT give full throttle to the engine for at LEAST 2 minutes. Dumping a main jet load of pre-mix or straight fuel on a cold plug will color it rich and quite possibly begin the fouling process that so many are aware of. I start out giving the engine maybe 1/3 throttle for about 4 corners (at Sears Point) with no more than 6,000. Then I steadily move up the throttle and rpm until the first straight (about 1 minute into practice). When the first straight comes up, I roll the throttle on VERY slowly, 6500 shift to 4th, 7500 shift to 5th, 8500 shift to 6th and then bring the throttle up to full slowly. By now the plugs have been fully warmed up, what residual oil was left in the lower end has been slung off the crank long ago and what the plugs will see from then on will be much more representative of how the engine is jetted.

I used to take plugs out of the long-rod motor that were bone white all the way down to a very faint tan ring at the very bottom of the porcelain which is the ring your looking for. You will NEVER see that in a plug that is one race week-end old, so get used to throwing away the plugs often.

I used to have people run over to me and put plugs under my nose with the accompanying question " How is my jetting" . And looking down at a set of coal black plugs I would reply "Which race?". If I knew that this person had another set of plugs, I would throw them away and force him to put a set of new plugs in. A bit extreme maybe but after the bike started to respond to proper tuning changes a lot of racers learned the value of this philosophy.

So clear out the engine, warm the new plugs up slowly, learn what the plugs are telling you and change the plugs often.

Although there are very expensive oils out on the market, I have found that either Oilzall or Golden Spectro Synthetic mixed at a ratio of 32:1 (4oz./gal) worked very well for me under extreme racing conditions. By extreme I mean full throttle applications for 1/2 to 5/8 mile long straight-aways common to California race tracks. Piston wear and crank life were always good. If I had to choose between the two I would use Oilzall because being a castor based oil, it smells cool!

I have found these specs to work for just about every required purpose. Get yourself a porting tool, port everything to this stuff and start your own business. I'm not kidding. I used to get $150-$500 for the info I'm putting out here. So knock yourself out!

Exhaust Opens: 82 degrees after TDC Duration 196 degrees

Exhaust Width: 70-75% of bore (46-48mm). The top edge of the port looks like an oval. This is not the place for a sharp edge as that will make the power band too sharp. The sides of the port actually extend over the top of the transfers but sides of the port go from the stock location on the bottom of the port in a straight line to the side of the port. The best way to describe the shape of a finished port is to visualize a trapezoid with a curved top edge.

Transfers Open: 64 degrees before BDC Duration 128 degrees

The rear edge of the main transfer is brought back to eliminate the mismatch between the liner and the barrel. I have used epoxy to remove this in extreme cases. This leaves about 1mm of cylinder between the main and auxiliary transfer but who cares, it only acts to support the ring.

Rear Boost Port Width : 20mm This is angled up to make the new height and cleans up really well in the RZ's. The RD's will need the help of epoxy and then angle back to make the lower edge of the port at the intake about 50% deeper.

Intake Height: Raise to 1mm below bottom ring with piston at TDC. Can raise to 1mm below top

ring if top ring is a Keystone type ring and you discard the second ring.

Bottom of Intake: Can go as low as desired, just don't go through to base gasket surface!

Intake Width and Bridge: I believe that it is much more important to provide for piston support so I don't make the port any wider or the bridge any narrower. There is plenty of hole when you get done with raising the port.

Lower edge of liner: ONLY in the area of the main transfer lower edge of the liner, remove 10mm worth of material bringing the edge up closer to the top of the barrel. We want to increase the area that will allow the scavenge gases to into the main transfer port. DO NOT do this all the way across. The motor doesn't like it.

The best combo to use for a standard 400 would be to use the Daytona pistons as they do not have the cut-away in the bottom of the exhaust side skirt. Plug the hole above the exhaust port with a set screw after tapping the hole to accept the screw. Loose the exhaust butterfly valve on the Daytona (duh!). If you are having the crank serviced, use the Daytona rods as they are have slotted lower ends and this allows oil to reach the bearings easier. Use early model TZ (from the B,C,D,E in the 70's) lower end rod bearings. They have silvered cages and free rollers that reduce friction and heat. By far the weakest link in the 400 is the crank. It is very heavy and prone to spreading the mag side so welding is a must. The center axle between the two halves is also very prone to snapping in a high power application. Anything that you can do with the Daytona to get rid of the flywheel ignition and replace it with a Krober or Motoplat or anything lighter will help greatly. We used TZ 750 reed assemblies at first and then went to RZ reeds when they became available. A lot of metal has to come out of the intake port to do this a quite possibly you will grind through to daylight, but a through application of epoxy will save the day here.

Many of these were built with TZ 750 pistons but the supply dried up and just as well as the last models had a very short skirt which was bad from a wear point of view. I did make one of these (66mm bore) with a DT 175G enduro set of pistons. The pin height difference in the pistons made it necessary to cut 5mm off the bottom of the barrel and re-locate the headers to prevent dragging them on the ground. What we wound up with was a very potent air cooled bike that could consistently beat my long rod RD 375 for the win. Of course I had built it for a very close friend. The only recommendation that I can make is don't give your friends bikes better than yours.

Pretty much everything said about the RD 400 holds true for the older brother, except that we had head gasket problems. We used a 400 head gasket and finally a TZ 750 cylinder head O-ring that stopped all the gasket weeping. This is outlined in the articles that Doug has at ACTSO. Copper Coat on the copper gaskets works real well for stopping seepage.

With this motor we used DT 175G pistons from Yamaha to bring to bore to 66mm and displacement to 375cc. The pin height allowed almost a bolt up assembly when we used the Daytona rods with TZ bearings. With the change in rod/stroke ratios, the stock cylinders will only need minor port work to make the figures listed above. If I remember correctly, .070" needs to come off the top of the barrel to get the squish band right This is the combination that I used for years to gather tons of trophies. It never blew up. Couldn't kill it. I tried!

I only built one of these for my girlfriend (at the time) that was racing in the AFM. In 1988, she got second in class in Calif. In the 450 Prod. Class. This works. I could never catch her after I built this one! It is also a little more difficult to pull off. Side thrust washers have to be made out of Ampco 45 for the lower end of the rod as the Daytona rod is narrower than the RZ rod. The porting is somewhat tricky too as the ports don't quite line up as they should, so maybe do some other port work before you tackle this one. With chambers...well it's too scary to think about. Should be illegal.

Good hunting...

Dale Alexander

San Bruno, CA