Repair and Restoration

MANUALS

General Information on Yamaha Manuals and Parts Books

In order to keep your TX750 running, a service manual is a necessity. This is a book that shows how to accomplish various repairs from adjusting the clutch to a complete engine rebuild. Another useful publication is a parts (spares in some countries) book. This publication shows exploded diagrams of every component of the motorcycle along with the Yamaha Part number. This is very handy when trying to order parts and can also be a help when servicing your motorcycle as well. The third publication is known as an owners manual. An owners manuals is a small book that came with the motorcycle when it was new. Often, they were kept in the pocket located under the seat. While not as helpful as the service manuals, they are useful for routine maintenance chores. The 73 (TX750) and 74 (TX750A) models each had one or more versions of each publication. Several versions of the U.S.A. manuals are shown below, but there may be other variations of which I am unaware.

There are several places where manuals can be obtained. The first place is your local Yamaha dealer. The service manual and parts book are available on microfiche. Some dealers may be reluctant to order them or plead ignorance, but keep trying until you find a cooperative dealer. Of course, you will need a viewer to make use of them. Many public libraries have viewers, some with printers. Microfiche readers are regularly sold on EBay at very reasonable prices.

Speed and Sport (see Parts Suppliers) has permission from Yamaha to print out manuals from the microfiche. They have bound versions of the manuals at reasonable prices. The reprints from microfiche aren't quite as sharp as having an original manual, but they are better than nothing.

For those of you familiar with EBay, service manuals and parts books are regularly auctioned there. Prices there can vary greatly depending upon condition and how much someone is willing to pay at that particular time.

I have excerpts from the service manual on my web site showing some routine servicing, such as carb adjustment, points adjustment and timing. Most of the service bulletins issued for the TX750 have also been included.

To the best of my knowledge, there has never been a Clymer or Haynes manual produced for the TX750. There was one third-party manual for Yamaha four-stroke twins produced by Chilton in the mid 70's which covered the TX500, XS/TX650 and the TX750. Yamaha produced at least 4 versions of their official service manual and at least 2 versions of their parts book and two versions of their owners manual.

Service Manuals

Parts Books

Owners Manuals

AIR CLEANER

Replacement Air Filters

The standard air filter element for the TX750 consists of a metal frame and foam side panels which is supposed to be cleaned and oiled every month. According to my 4th edition TX750A Service Manual, a paper element was introduced late in the model run. I've never been able to find a NOS paper air filter element from any of my usual sources. An oil/foam filter works OK as long as you clean and oil it regularly, which very few owners likely do. After 26 years or so, the foam is probably deteriorated as well.

I don't have to clean and oil any of the air filters in my 4-wheel vehicles, so my mind went into gear trying to find a replacement for my TX750 oil/foam cartridge. I went through most of the auto filters in Pep Boys trying to find one the right size. Most auto filters pass air through the element down top to bottom, not through the sides. I checked out the small 4" round dry filters used for street rods, but they were too high to fit in the airbox. I remembered that my only non-Japanese bike of many years ago, a Triumph, used small round paper filters. Triumph used the filters in both 650 and 750cc twins, so they should have enough breathing capacity. There's quite a cottage industry of new replacement parts for old Triumphs, so future availability of filters should be good. I obtained a set of Triumph paper air filters from British Parts Chicago and set out to try to make them work.

The Triumph filter is round, 5" in diameter and 1.5 " tall. The airbox is only 8" wide inside, so the filter has to be squeezed to make it into an oval, 4" wide. Two squeezed filters will then just fit inside the airbox. Next, a backing plate of smooth 1/4 hardboard needs to be cut to seal the back of the filters so that the air gets sucked through the sides. This plate is placed against the back of the filters. There may still be a little slack between the hardboard and the back of the airbox. If this is the case, a small shim of 1/8 hardboard then should be inserted between the 1/4 hardboard and the airbox to tightly seal the rubber gaskets of the filter to the airbox front and 1/4 hardboard back so there are no leaks. Be aware--this modification will void your factory warranty.

At the time I bought my filters, they were $5.00 apiece. British Parts Chicago charges an order processing fee of $10 so you may want to order several filters at the same time. I tried my local Triumph dealer, but the new Triumph company doesn't carry parts for the old Triumph company bikes.

Triumph Filter Solution

Air Filter Installation

ELECTRICAL

Replacing Stock Coils with Universal Replacement Coils

If your TX750 starts normally cold but when hot runs erratically or refuses to start, your ignition coils may be bad. Yamaha coils have a reputation as weak units when new. I replaced my poorly performing stock coils with replacements from J.C. Whitney for only $15 apiece(see coil package and ad Emgo Packaging and J.C. Whitney ad). Stock items were No Longer Available from Yamaha; Speed and Sport didn't have any currently in stock and if they were in would have been about $70 apiece. I ordered a pair from J.C. Whitney hoping they would fit in the small space allowed for the stock units. They fit (barely) and are working better than I could have hoped. Even in stop and go traffic when hot, the engine idles smoothly without having to rev it to keep it from dying. Kick starting a hot engine usually takes only one or two stabs.

Step 1. Remove the fuel tank.
Step 2. Remove the old coils.
Step 3. Cut the leads off the old coils. Solder or crimp terminal ends on the cut end of the leads. Place brown lead on plus (+) coil terminal, orange lead on minus (-) terminal. Make sure you don't reverse coil leads. Bike will run, though badly if reversed. I found out the hard way. Does anyone know why it even runs when reversed?
Step 4. Drill two new holes in mounting bracket to match new coils.
Step 5. Mount new coils, reattach bullet connectors, replace spark plug wires.
Step 6. Replace tank.
Step 7. Start engine and marvel at smoothness at all engine temperature ranges.

Replacing Contact Breaker Points with Newtronic Electronic Ignition

One of the shortcomings of the TX750 is it's stock breaker point ignition. The placement of the points inside the engine cover causes them to run hot and causes the rubbing block on the points to wear down quickly. Before you know it, the points are too close together and difficult starting occurs. Difficult starting can quickly wear out the electric starter clutch mechanism, which is barely adequate on this model.

I know there are aftermarket electronic ignition systems out there, but I have never found one specifically for the TX750. I emailed Newtronic in the summer of 2002 the possibility of their producing an electronic ignition system for this bike. They mentioned that the Yamaha XS650 kit they sold could be adapted to the TX750 with some minor modifications. After several emails back and forth, I ordered the kit.

The Newtronic uses light sensors unlike other kits that utilize magnetic waves to fire the plugs. The Newtronic kit merely replaces the points and utilizes the stock advance mechanism and coils requiring a minimum of replacement. Click on the following Australian link for more information on and a review of the Newtronic Ignition kit.

My brother and father were both mechanics--I'm a mainframe computer programmer. Tearing out the old points ignition and cutting and fitting the new parts was just too much for my ability. My brother was in the process of moving and the kit just sat until the spring of 2004 when the time finally came to move forward.

My TX750 is much easier to start now. Stay tuned -- I'll be posting my impressions of the Newtronic as the weather warms and I roll up miles on my bike.

Click on the link below to see the installation process on my 1974 TX750.

Newtronic Ignition Installation

Replacing Contact Breaker Points with a Homemade Electronic Ignition System

Hi Roger,

A few weeks ago I informed you about myself building an electronic
ignition
for the TX750.
You mailed me about the newtronic ignition and I must say, it is
almost the same.
I will try to explain the differences with the one I made.

1. Newtronic has a rotor which replaces the contactbreaker axe.
   I made a rotor which I can put on the contactbreaker axe.

2. I think ( looking at you pictures ) that the newtronic rotor has
   only one gap with two optocouplers , for each cylinder one optocoupler,  
   am I right ?
   My rotor has two gaps instead of one, because I will fire both
   sparkplug at the same time, this way it is easier to get the sparks on 
   time for both cylinders.
   (maybe I will need colder sparkplugs, but that we will see) 

3. The electronic of Newtronic is a black box, because I don't think
   you have a schema.  I took the schema from the German site (the same 
   as on your site) which works with contactbreaker point and I change 
   the schema a little so I can always make a new one when it brokes.

4. The Newtronic ignition system costs about 150 $ (aus), isn't it ?
   Because I made all parts myself, the schema now costs about $20
   (USA) inclusive the optocoupler. 

If you wish I can give you more details.
So, the electronic fires both sparks at the same time with the original
coils. I only have to make the spark for one cylinder to fires on time, the
other one will be alright automaticaly.

I already took a short ride and it feels good.

Best Regards, Leen  
The Netherlands

p.s. 

You can look at  Electronic Ignition
and  look for the restauration part  of the TX750, there you will find a description
in Dutch ( so that's not nice ), but also some pictures.
And with that what I told you already, you maybe will have an idea how
things work.
If you have any questions, I will try to answer them all.

Wiring Chart and Wiring Diagram

TX750 Wiring Diagram - Color Pictoral Wiring Diagram (554K JPG)

TX750 Electrical Circuit Diagram - Black & White Schematic Wiring Diagram (176K JPG)

OIL FILTER

Oil Filter Modifications

The standard TX750 Oil Filter looks as though it was designed as an afterthought. It is now very difficult to find and expensive when you are fortunate enough to find one. The German TX club has come up with solutions that use standard easily-available filters. Many thanks to Peter Weidenhammer for sending the information below.

Solution #1

This solution consists of two machined aluminum pieces that sandwich a Honda FT500 Oil filter. These two pieces plus the filter replace part #6 shown in the parts manual image. Bolt #7 is used with a copper washer to secure the new filter mechanism in place. Seal #12 is used along with o-ring #11.

Adapter - Drawings for 2 Machined Parts (25K)

Drawing - Page from my TX750A Parts Manual (111K). Note the deep sump standard on 1974 models

Solution #2

This solution consists of one machined aluminum piece that allows use of a standard BMW R65/R80 oil filter. Since the BMW filter is longer than the Honda FT500 filter, only the outer machined piece is needed. Bolt #7 is used with a copper washer and only o-ring #11 is needed. A rubber seal on the BMW filter takes the place of seal #12.

Adapter - Drawing for 1 Machined Part (25K)

Adapter Installation

PAINT

1973 Paint and Decals

1973 TX750 Paint

This message from Bill Johnsen describes the process for painting a 1973 Yamaha TX750. (Step 13 is optional).

1974 Paint and Decals

1974 TX750 Paint

1974 TX750A Decals - 1974 TX750A Tank and Side Cover Decals - Computer Design (94K)

This file came from Mike Robinson's Original Web Page. I don't know who posted it, but it contains the 1974 model decals in several image formats.

SUSPENSION

Replacement Rear Shocks

Red Wing Chrome shocks are available from Allyn Air Cycle Products. These were popular non-OEM replacements in the 70's. They have a similar look, but are not exactly the same as stock units. I replaced my leaking original shocks with the Red Wings and have been satisfied with their performance.

Allyn Air WWW Page