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Model introduction...

RD350 was built from '73-'75. The RD350, like the R5 has a spirited, quick revving motor based on the factory TZ roadracers that dominated world competition for years. The major upgrades to the new RD were a six-speed transmission, reed valve intake, cleverly marketed as 'torque induction', and a hydraulic disc brake up front. Wheels are light-weight spokes. Front disc brake is very powerful, rear drum is adequate. Shorter wheelbase than the RD400 for quicker turning.	The frame of the RD is dimensionally the same as the TZ350, with an even stronger, thicker tube frame, making it virtually a de-tuned gp bike with lights! By '73 the 350 race bikes had already clocked 164mph & dominated the big bikes at Daytona for several years. Consequently, the RD350 was known as the giant killer, with a power-to-weight ratio higher than most super bikes of the day. The little bike gets more respect than possibly any other bike of the decade. With it's performance reputation being what it is, how could any enthusiast not own one? The motor, although smaller, is just as potent, if not more so, than the later, longer-stroke RD400. The wire wheels and racy motor make the 350 my choice, but it's easy to put 350 wheels on a 400. As for collectability, it's a toss-up & I highly recommend owning one of each.
RD400 has torquey power due to it's longer stroke, and a rubber mounted motor. It featured a longer wheelbase than the 350's and had cast wheels with disc brakes front & rear. Yamaha produced 35,000 per year for the U.S., for the '76, '77, & '78 model years.	Many parts are interchangeable between the 350 and 400 including the engines, they share the same motor mounts. A popular swap is the wheels. While many 350 owners like the modern look of the cast RD400 wheels, serious 400 owners will switch to RD350 wheels to save lots of weight, most of which is rotating mass. When it comes to lightening a machine to improve it's power to weight ratio and improve handling, bear in mind that one lb of rotating mass (wheels, brake rotors, chain, etc.) is roughly equivalent to seven lbs of static weight. The heavy cast wheels of the U.S. RD400C-E were upgraded to a slightly lighter rim & rotor combo in Europe with the RD400E model and in the U.S. with the RD400F.  They are still quite heavy.
RD400F Daytona Special. Limited production, less than 5,000 built for the U.S, for the '79 model year. Featured upgraded chassis with better footpeg mounts yeilding better cornering clearance, lighter, wider wheels, lighter brake rotors and 35mm fork tubes. Motor featured updated porting & produced more low end torque. Not all the changes were beneficial.	Unfortunately for the U.S. market, the motor had to meet the first emissions standards ever imposed on motorcycles, and featured a crude butterfly exhaust valve system that actually closed to prevent exhaust from escaping the combustion chamber. It passed emissions but it's performance suffered. The crankshafts were upgraded to a newer design that proved to be faulty. The new process eliminated heat treating and consequently, most Daytona cranks will snap in the center under heavy load. The brakes were changed to a newer, weaker design. All U.S. spec Daytonas had point ignitions but Canadian and UK models featured electronic CDI ignitions and had no emissions equipment.
Priorities - Where to begin:
First things first, the chassis...
Bronze swingarm bushings are probably the first thing I would change on any old sportbike. Stock bushings were made from flexible phenolic material & allowed flex and play at the swingarm pivot. Bronze bushings virtually eliminate that wallowing & wiggling you feel when leaned over. Easy to install, just remove swingarm, knock out your old bushings with a drift or large screw driver & press or tap in new bushings with wood or other soft material, grease & re-install with inner collars able to turn free & re-install. It's a 2-3 hr ordeal for most, but truly worth their weight in gold! For pricing info. go to our handling page.	Replace your stock steering head bearings with the real deal - tapered roller steering head bearings. The problem with the stock ball bearings the bikes came with is they have very little surface area.  In order to move smoothly they have to be slightly loose. This slight play translates to head shake & shimmy, especially at speed. The stock bearings also tend to get a notchy feeling as the balls will eventually leave indentations in the race.  Easy to replace. Just remove your old races from the steering head and lower triple clamp. Install new races in your steering head, pack bearings with wheel bearing grease & install - they'll only go one way, top or bottom. The smooth feeling will spoil you for good, I guarantee it! For pricing info. go to our handling page.
Steering dampers are easy to install and make any motorcycle feel more stable at high speeds. They are so important that they are required by many racing clubs. With 7 levels of damping, you can set it low for easy steering at lower speeds and reach down and give it a few more clicks for more damping before you approach higher speeds. Like the chassis mods mentioned above, the stable feeling will truly spoil you!	Braking power is maximized with a steel-braided brake line. Stock rubber lines expand under high pressure, thereby absorbing some of the hydraulic pressure that would otherwise be going to the brake caliper. When it comes to brakes, although good in their day, most older Japanese sportbikes need all the help they can get. Never compromise with your brakes. Remember, if you've got the go, you better have the whoa!
Brake pads need to be checked regularly. Most pads nowadays are kevlar based and work pretty well. Replace pads as necessary, especially if they have gotten dirty with brake fluid or any oil.	Brake shoes like brake pads should be inspected regularly. If brake drum is rusty, clean thoroughly & lightly sand the shoes to remove any glaze.
Tires are the most important part of any bike. Don't try to save any money in this area by installing anything but the very best. Most tires on the market are not soft enough for a high performance, light weight two-stroke. We currently recommend Avon or Bridgestone, but 95% of our sales are the Avon Road Runner or Super Venoms. They are the softest, stickiest tires that we know of, followed by the Bridgestone Battleaxe, and a new vintage race tire by Dunlop. It seems like almost everybody winning on 18" tires lately is running the Avons. For the street and most road racing applications, there is no need for anything wider than a 90/90 front or a 110/90 rear on an RD350 or 400. For an RZ350, a 100/90 front  and 110/90 or 120/90, in either H or V rating. I like the lower speed rated tires because they have fewer belts in their construction, translating into a softer, more pliable sidewall, allowing the tire to warm up quicker. For racing, slightly wider tire sizes may be best, depending on your skill level & lap times but usually require a wider swingarm or wheels. Call us for specifics. Unless your rim is stamped tubeless, you must use a tube, even with a tubeless tire. Always have them spin-balanced and check your air pressure often.  For info. on pricing go to our tires page.	Your drive chain is probably in need of replacement unless it's fresh. We don't like o-ring chains because of the extra drag. We like using RK standard quality chain & replacing it every 3-5,000 miles, or every 10 races, or so. For high output custom applications we like the DID X-ring gold chain, but it's triple the price of a standard chain. Use a quality synthetic chain lube & apply it after every ride. Make sure your battery vent tube is long enough & routed away from your chain. Many vent tubes I've seen were routed to drip battery acid directly onto the chain, crystalizing the steel & destroying it.  Sprockets should be changed with your chain unless they are not visibly worn. A worn sprocket will ruin a new chain instantly. We like the light weight and beautiful Sprocket Specialists brand sprockets. If you want to try different gearing to enhance acceleration, or to run lower rpms in top gear, just divide the number of rear teeth by the number of front teeth to determine your desired final gear ratio options.
cables	Stock fork springs on all bikes of the era are in need of lots of improvement. Modern aftermarket springs not only have a stiffer spring rate, but they are progressively wound with the ability to react to even the smallest ripples in the pavement for a vastly better feeling front end. Although no springs are available specifically for some models such as the RD350 & Kawasaki triples, we have found springs available that will work if cut to the proper length. Always cut the widely wound end. Install with the closely wound coils, the heavier end, on the bottom to keep the weight down low.
battery	A good performance upgrade is a set of composite reed valves. The dual-stage Boyesen reeds enhance throttle response, stiffer TDR single petal reeds enhance top-end power. Although rare, if a stock stainless steel reed petal breaks, it could cause lots of damage. Composite reeds wear out more quickly but they are ingestable if they break.
Tuned exhaust pipes, or expansion chambers have always been a popular modification for more horsepower on a 2-stroke since their invention in the late '50's. The basic idea  behind their function is to reflect the exhaust sound wave, at the proper speed & frequency, back toward the motor, thereby stuffing additional air-fuel mixture that has escaped out the exhaust port, back into the combustion chamber. This produces more power. The better they are, the wider their rpm range, or the more efficiently they perform. Old school pipes usually perform within a very narrow range or powerband. The power was usually very peaky & not very streetable, unlike most modern designs. Computer technology has improved the expansion chamber by leaps and bounds (which is why 30 yr-old pipes cost a lot less money!). Our most recent designs not only produce more power than ever, but the power comes on sooner and more smoothly, delivering much more useable torque. As the saying goes, "horsepower sells engines, torque wins races." We've demonstrated this to our competition for years. Peak horsepower is meaningless if the motor doesn't accelerate strongly at all rpms.	carbs & filters
Engine Basics	Crankshaft
If you're new to these bikes, you will find that proper tuning is critical. Even if your bike was tuned by a good mechanic, the specs he or she used could be dangerously obsolete because of today's gasoline. On a Yamaha RD350 or RD400, timing should be set at 1.8mm btdc, instead of the printed specs of the day. Don't find out the hard way with a melt-down. On any old motor that's been sitting for a long time, the crank seal & intake manifold integrity is suspect. If it leaks, it'll burn right down. Check with a leak-down test. For a diagram of how to build your own go here. Assume that tuning is wrong, check timing & jetting specs before you run it. To check for top end wear, test the compression. Each cylinder should run 125-130psi, if less, a fresh bore is necessary. A tight, straight bore, yielding strong compression, is critical for a good running engine.	The crankshaft is the heart of the motor. They not only go bad from wear, but most damage we find on motors that have been sitting, is rust on the big-end rod bearings. As a rule of thumb, 12-20,000 easy, well-lubricated street miles, or 20-30 hours on the race track is all you can expect to get out of them. Rebuilding the crank consists of pressing the crank apart, replacing the main bearings, crank pins, thrust washers, big-end bearings, and rods. It is then pressed back together and carefully trued. This is difficult to do and should be done by only the most experienced mechanics. Always insist on genuine main bearings. Identical size ball bearings without the locating pin or circlip grooves are sometimes used to save money. How are you to know. Don't cut corners when it comes to your crankshaft, it doesn't make sense. For info. on our crank  services go to our engine building page.
Carburetor Jetting
Correct carburetor jetting is important for proper combustion. If the carb is jetted too lean the combustion temperature could get too hot resulting in either a seized piston, or a hole melted right through the top. Just one size too lean is all it takes for possible disaster, therefore we offer you some guidelines that you want to consider as you refer to them. We at Moto Carrera are in no way responsible for any damage to your motor as a result of applying any of our advice or tuning specs. If you need to do it yourself to save the money, just be willing to be learn and accept the consequences of a piston failure. Remember, you seize or burn-down, it's your fault! Our recomended method is play it safe; get several main jet sizes in the range you're working in, and just start a little rich & work down. While not everyone that owns these things will want to learn this stuff, the other 99% of us realize that tuning is the essence of the 2-stroke performance culture. It is what separates us from our 4-stroke loving counterparts. I'm no musician but the tuning of all motors is closely akin to tuning of a musical instrument in that the end result is very audible. This is especially the case with the two-stroke. From the intake's howl, to the scream of the expansion chambers, you need to know when it's right. You either have the instincts, (you know who you are) or, as a result of practicle experience, will develop an ear for tuning a 2-stroke.  It's not just the love of the sound, it's the ability to play the music in tune, at the right pitch & tempo. You need to know when it's just right and what adjustments have to be made to get there. What is jetting? Carburetor adjustments, usually involving changing of quickly-removeable metering orifices called jets. Besides the jets, needle position adjustment, or changing, as well as changing slides are all part of the adjustments available. Why the need for jetting in the first place? Any time a modification is made to the motor, such as install a different exhaust system, or air filter, you need to rejet the carbs to compensate for the difference in airflow. If air flow is enhanced, fuel flow must be adjusted accordingly. The optimum air fuel ratio is 15:1 for gasoline. It has to be just right. When exhaust gas temperature is optimum, 1250-1275 degrees F, the spark plug insulator will be a light tan color. Too hot & it'll burn light gray or white, too cool & it'll burn dark brown or black. Get familiar with exhaust note changes when jetting and get used to checking your plugs often. They are windows into your engine's soul. Other factors requiring jetting adjustments are changes in air density, altitude as well as types of fuel. Get a Sudco Mikuni tuning manual if you don't feel real comfortable with carbs. It's worth it's weight in gold.	The indispensable Sudco Mikuni manual. Carb Jetting Guidelines - Just a ballpark range based on years of customer feedback and personal experience. Read your sparkplugs at different throttle settings, aim for a mocha, light brown color  Application Stock Porting main jet pilot jet needle pos RD350 y-boot stock pipes RD350 y-boot  DG pipes  RD350 y-boot MC GP pipes 150-160 210-220 230-250 25 25-27.5 25-27.5 3  4 4 RD400 y-boot stock pipes RD400 y-boot  DG pipes  RD400 y-boot MC GP pipes 125-135 220-240 230-270 25 25-27.5 25-27.5 3  4 4 Remember, use these specs at your own risk! Play it safe - start rich & work down. The specs above are a general range for U.S. spec RD's at sea level. Higher altitudes or humid conditions will require proportionally leaner settings. If you're new to this, it helps to practice removing your carbs and replacing your main and/or pilot jets as well as adjusting the needle clip position. It doesn't take long before you're as quick as a pro & really inspires your tuning confidence. For a great carburetor website with lots of diagrams and charts go to www.sudco.com, For information on our tuning services go to our
Ignition Timing
Timing is simply adjusting the point in the stroke of the engine at which spark takes place, starting the process of combustion. This must happen just before top dead center to get the fuel to ignite completely and to generate as much heat as possible. All fuels have different burn or flash rates which is referred to as octane rating. The higher the octane, the slower it will burn. Two-strokes are very sensitive to proper timing. If your timing is set just slightly too advanced for the fuel you are using, you will experience detonation, or knock. It is  destructive for a two-stroke to detonate or ping for more than a few seconds before the piston overheats and starts to melt. Since today's fuel is lower octane than the good stuff available back when these bikes were new, timing must be set slightly less advanced than the manual recommends. For Yamaha RD's we recommend 1.8mm btdc instead  of the '70's spec. 2.0-2.1 btdc that the manuals have printed. To properly set the spark advance you will need a dial gauge indicator, or have a good 2-stroke mechanic do it for you. This is the most critical setting there is and there is absolutely zero margin for error.	Below: Central timing kit with dial gauge indicator.
Don't let this happen to you! During knock, or detonation, the piston overheats quickly. In fact it only takes a few seconds until it finally melts or scuffs up tight, also referred to as a seizure.
It starts like this. Exploding fuel at the front edge of the piston is caused by either too lean carburetion, or timing that's too advanced for it's fuel. It may have started from an air leak from a worn crank seal or a something as simple as a tank of low octane gas. Piston starts to melt & starts to scuff from over-expansion, sometimes locking up the engine.	As a rule of thumb for any engine- don't overheat it & don't over-rev it, if you want it to live. Above is an example of what can happen when a piston lets go. A few seconds earlier the piston might have looked like the photo on the left. In the next instant, the rod bends or snaps, sometimes putting a hole through the cases, destroying the motor as in the photo below.
The 2-stroke piston engine is a beautifully simple machine. It wants to be tuned to run happy, and doesn't tolerate much abuse with regard to over heating. With conservative timing and jetting however, they are very reliable and potent powerplants. Always play it safe & use the finest lubricants you can buy. It makes zero sense to try to save $30. a year by running average oil. We use Motul synthetic oils & we recommend any of the top synthetics. We have had great results with premixing Motul 800 at 40:1, or 3ozs per gallon. For injection systems we recommend Motul 600. We use only Motul Transoil for all 2-stroke transmissions.
Spark Plug Reading Reading plugs should only be done by doing a "Throttle Chop" - a hard wide open throttle run followed immediately and simultaneously by killing the ignition, pulling in the clutch, and closing the throttle, coasting to a stop and pulling the plugs out for inspection. Great links for learning about reading spark plugs: NGK Tech Page How to read spark plugs How you can read spark plugs and select them
Ignitions
	When diagnosing misfiring take nothing for granted, test everything, especially new components. Convince yourself that all components from carbs to spark plug caps are sound & functioning correctly. Assume nothing & troubleshooting will go much more quickly.

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