Frequently Asked Questions

TX is the model designation prefix given by Yamaha for their four-stroke parallel twins for the USA model years 1973-1974. The three models were:

• 1. TX500 - This was a brand new model beginning with the 1973 model year which featured Yamaha's Omni-Phase balancing system and was the first streetbike to feature a four-valves-per-cylinder head. The engine also featured chain-driven dual overhead cams, a 180° crankshaft, and was of a wet sump design. In 1975, due to the bad reputation of the TX750, the model designation prefix was changed to XS. The XS500 continued to be produced through the 1978 model year.
• 2. TX650 - This model designation was given to the modified XS1, XS1B and XS2 models which were first introduced in 1970. This was a Japanese vertical twin which looked quite a bit like a British twin, but was totally different inside. It's engine had a chain-driven single overhead camshaft, a 360° crankshaft and was of the wet-sump design. It did not utilize a counter-balancing system unlike the other two TX models and is noted as a vibrator. The model designation was changed back to XS in 1975.
• 3. TX750 - This also was a brand new model beginning with the 1973 model year. It incorporated Yamaha's Omni-Phase balancing system but used two counterweights instead of the TX500's one. It's engine featured a chain-driven single overhead camshaft, a 360° crankshaft, and was of the dry-sump design. After many problems and factory fixes, the model was dropped partway through the 1974 model year.

WHAT IS THE HISTORY OF THIS WEB SITE?

Back in June of 1998 a fellow named Mike Robinson started the first web pages devoted solely to the Yamaha TX750. Some months later, after suggestions from several individuals, he also expanded the site to include the TX500 and even the TX650. TX owners were few and far between in the web site's early days. After I took over the site in February of 1999, I continued the site under the concept "TX Interest Site".

Recently, many more TX500 owners have come forth asking specific questions that I am unable to answer. My interest (and all my expertise) is in the TX750. A fairly new TX500 owner has come forth with lots of enthusiasm and with the ability to host a web page. His name is Karl Ivers and he has set up the TX mailing list. In thinking about the mission of this page, I believe it would benefit both TX750 and TX500 owners to have a page dedicated to their specific machines. Other than being 73-74 Yamahas and having counter-balancing systems, the two motorcycles are quite different. The TX650 is really an XS1/XS2/XS650 that just happened to gain the TX prefix during this time period and already has its own web page(s) (See Links).

So, in July of 2000 came the announcement of the creation of a TX/XS500 web site hosted by Karl Ivers and devoted to the DOHC 4-valve 500cc four-stroke twins which many of you own and love. The current TX Interest Site will refocus its content on the SOHC 2-valve 750cc four-stroke twins. This will enable each site to concentrate in more depth on one particular model. The link to the TX500 page is below:

TX500 Interest Site

and it also is found in the 'Links' page of this website. The mailing list will continue for the present to cover all TX models (although the majority of the messages seem to pertain to the TX500).

WHAT DIFFERENCES EXIST BETWEEN USA AND NON-USA TX750s?

• 1. FUEL TANK - USA models used a gold tank for 1973 and a burgundy tank for 1974, both holding 3.7 US gallons. Some non-USA markets could optionally choose a "racing green" tank. The Japanese domestic model had a 5.0 gallon tank and a shorter seat.
• 2. FRONT BRAKE - Non-European models appear to come standard with a single disc brake. European models came standard with dual front disc brakes.
• 3. TAILLIGHT - Non-European models had a round taillight. Some European versions had a taillight that resembled an upside-down Honda 750 taillight while others had a round taillight.

WHAT WERE THE PROBLEMS WITH THE TX750?

There were 3 main problems with the TX750. Each problem was addressed with factory modifications during the two-year model run.

• 1. LUBRICATION - The TX750 utilized two chain driven counterweights to tame the engine's vibration. The counterweights sit low in the engine case. Excessive revving, such as at a red light, could cause the oil in the engine sump to foam resulting in bearing failure. If the TX750 was treated as a touring machine and not a superbike, this problem didn't occur. The factory added an extension casting to the bottom sump plate effectively lowering the sump (and the oil level) to prevent the foaming problem. Modern oils also have less tendency to foam than the oils of the '70s. The head gasket and certain oil seals were modified to prevent leakage which was a problem in earlier engines.
• 2. HEAT - The TX750 engine is air-cooled and generates quite a bit of heat. The engine fins should have been larger. The crossover exhaust manifold on the front of the engine was added to balance the exhaust pulses, but it increases the heat load as well. The sump extension helped lower the oil temperature. An optional oil cooler was offered to help lower the temperature further for long trips on extremely hot days.
• 3. BALANCER CHAIN - The original TX750 engine did not have an adjuster for the counterbalancer chain. The sprockets were offset 1mm to account for the chain lash. Eventually, the chain will wear and if it is not replaced in a timely manner, the counterweights can begin to contact each other causing engine failure. An external adjuster was added for the 74 models, and a retrofit kit was made available for earlier model engines.

WHAT ARE TX750'S IDIOSYNCRASIES?

• 1. CLUTCH - The TX750 clutch lever is rather stiff. Additionally, when the engine is hot, it becomes more difficult to find neutral. Most riders shift into neutral before coming to a complete stop.
• 2. ELECTRIC STARTER - The starter sprocket where the rollers grip to turn the engine tends to wear quickly. After only a couple thousandths of an inch wear, the starter clutch will tend to slip. Also, if the battery is not at peak charge, it will also slip. The starter mechanism only uses 3 rollers where similar 750cc bikes utilize 4. Luckily, the TX750 has an auxiliary kick starter.
• 3. POINTS - The contact points are placed on the left side of the engine under a cover. Being down inside the engine rather than on top of the head means they run very hot. This heat will quickly evaporate the lubricant placed on the piece of felt that is supposed to lubricate the points cam. Consequently, the rubbing block on the points will wear down quickly and the points gap will shrink causing hard starting and in some cases the engine to stall when hot. A fix is to smear a LITTLE high-temperature grease (orange fibrous wheel-bearing grease) on the felt wiper rather than oil. The grease will last much longer under the extreme heat, but be careful not to use too much, since it could foul the points.
• 4. COILS - The coils are mounted under the fuel tank only a couple of inches above a very hot engine. After some time, the coils can experience intermittent failure causing stalling and uneven idling when hot. Replacement generic coils can be used of original Yamaha ones cannot be located.

WHAT ARE TX750'S GOOD FEATURES?

The early models had problems that were later solved. It also has it's quirks as all motorcycles have. There are many features that make this model desirable. These features are subjective and opinions can vary on them.

• 1. STYLING - The TX750 has typical early 70's Japanese styling. Lots of chrome, aesthetically pleasing looks with a slightly tilted engine that reminds me of the Honda 305 cc engine. It has the standard look before everything became plastic panels, but still has enough modern features such as disc brake and turn signals to make it useful for modern street riding.
• 2. TORQUE - The TX750 has good power for a 750cc bike of it's period. It's not a superbike, but a decent touring machine. The power comes on in the low rpm's and doesn't require constant shifting up and down to keep it in a narrow power band. From about 25mph on up, fifth gear works just fine.
• 3. SMOOTHNESS - It's a twin, but it's as smooth as a four. The omni-phase balancing system does it's job. You can ride for hours without the numb hands common with most large vertical twins.
• 4. VALUE - The price is still very reasonable for this model. When looking for a TX750, try to find as complete a model as possible as parts are becoming harder and harder to find, expecially the cosmetics.
• 5. COLLECTABILITY - The short model run combined with the bad reputation kept the number of machines produced low. It (along with the TX500) was the first model to offer a production twin with a counterbalancer. It also offered other firsts such as the fail-safe headlight circuit and a rear brake lining wear indicator. You also won't see dozens of them at vintage meets. If you like it when someone asks, "What is that?", then this bike is for you.

ARE PARTS STILL AVAILABLE?

The answer is a qualified "Yes". Cosmetics (tanks, side covers, mufflers) are the hardest items to find. A long-time Yamaha dealer named "Speed & Sport" in Bloomsburg, PA specializes in NOS parts for vintage Yamahas. They buy up stocks of obsolete parts from other Yamaha dealers. They claim to have close to 3 million dollars of parts on hand. Check my "Parts Suppliers" page for other sources.

Another good place to start is a local Yamaha dealer who has been in business since the early 70's. They often have old parts on their shelves that they would be glad to sell. I bought several items for my TX750 from my local dealer. There are several scrapyards that have or specialize in 70's Japanese motorcycles. I have noticed quite a few NOS TX750 parts showing up on Ebay recently. Because of the short time that they remain posted, a weekly scan of Ebay is recommended. There are other on-line motorcycle bulletin boards that have ads for bikes and parts.

Some parts, especially filters, can be adapted from other motorcycles. By having an oil filter adapter machined, you can use a standard easily-obtainable BMW filter instead of the expensive, hard-to-find Yamaha item. The air filters can also be replaced with standard Triumph items and a piece of hardboard.