XS750
ManufacturerYamaha Motor Company
Also calledtriple
Parent companyYamaha
Production1976-1981
SuccessorXS850
Class750cc
Engine4 stroke 3 cylinder air cooled DOHC
Transmission5 speed
SuspensionFront: Telescopic fork (d:36mm)
Rear: Swing arm
BrakesFront: dual disc
Rear: disc
TiresFront: 3.25H-19-4PR/1.8 Kg/cm (26 psi)
Rear: 4.00H-18-4PR/2.0 Kg/cm (28 psi)
Rake, trail27 deg / 114 mm (4.49 in)
Wheelbase1,470 mm (57.9 in)
DimensionsL: 2,160 mm (85.0 in)
W: 965 mm (38.0 in)
H: 1,185 mm (46.7 in)
Fuel capacity17 liters (4.5 US gal)

The Yamaha XS 750 and Yamaha XS 850 was a line of inline three cylinder motorcycles produced by the Yamaha Motor Corporation from 1976 to 1981 for the worldwide motorcycle market. The last model year of manufacturing was 1981.Released in Japan in 1976 as the GX750 sporting wire wheels (as opposed to cast alloy in all other models) the XS750 became the name for the export model.

These motorcycles are usually referred to as 'Triples' because they have 3 cylinders.The first 4 model years the bike displaced 750cc. This was increased to 826cc for the final 2 model years but was referred to as an 850. There were various changes made to the model over the years.

1976 XS750 “C”[edit]

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Very few of these bikes seem to have been made and even fewer survived. The cast wheels were in an unpainted finish and the decals were in a distinctive stripe design on the tank and side panels. This bike had a 3-1 exhaust system, and Mikuni “Mark I” carburetors. The air box assembly was different from later years. The air filter could be changed by opening the seat. This model had triple contact breaker points making timing adjustment complex. Also featured was a separate regulator and rectifier. The seat has a short tail piece this year.

This bike received rave reviews in Cycle World, who called it a 'Bargain BMW' and rated it one of their top 10 bikes in the world in 1976.[1]

1977 XS750 “D” and “2D”[edit]

A number of these made it out to export markets in late 1976. This bike was pretty much the “C” with a paint job. The tank now sports the familiar piping around the contours picking out the detail. Problems with reliability led to a further release in 1977. A particular problem was with 2nd gear. This had a habit of dropping into neutral under load. Canny riders would short-shift from 1st to 3rd gear; the engine had enough torque to support this technique. The Yamaha fix tended to be temporary, so not worth doing. The 'D' had the same tail piece as the 'C' and early GX750.

Released to return confidence to the model the 2D with some modifications to the “D” model. The bike now had 3 into 2 exhaust system with silencers on both sides of the bike, and improvements made to the engine to improve reliability. Fitted with electronic regulator/rectifier unit. This bike has a different seat from the 'C' and 'D'. The tail piece is longer and doesn't fit the early seats.

1978

1978 XS750 “E” and “SE”[edit]

The now popular “2D” was upgraded to keep up with the market. Yamaha added electronic ignition this year but retained the mechanical timing advancing unit. They also replaced the carburetors for Mikuni “Mark II” CV models. These offered easier maintenance and a “two position enricher” (Choke) as opposed to the single position on the “Mark I” model. The engine again had some improvements including cam shafts to boost the power of the engine. The rev limit was raised to 9000 rpm this year from 7500 which the electronic ignition had allowed. Later “E” models also had a viewing window for the engine oil added in place of the dipstick.This year also saw the introduction of the XS750 “SE”, Special or US custom model. With longer front forks and a teardrop shaped tank with shorter exhausts and seat it had a “Chopper” appearance in contrast to the tourer or now referred to as “Standard” XS750 “E”. The change of carburetors also meant a change of air box design and the air filter was now changed without lifting the seat.The XS750 also came with a stock fairing with full storage and aerodynamic enclosure of the rider. The fairing also introduced additional stability to the motorcycle by creating additional rake to the frame. This was a first for bikes of this time, especially those in the 2400 to 2700 dollar price range.

1979 XS750 “F” and “SF”[edit]

As above but European models came with an optional 24 liter fuel tank and also a new paint scheme. The cast wheels from this year on were of the 'tubeless design'.

1980 XS850 “G” and “SG” “LG”[edit]

Yamaha XS 850

The 826cc replacement for the XS750 was a very similar beast. The engine received bigger barrels and pistons, a beefier crankshaft, a wider primary chain and better oil ways. The addition of an oil cooler helped keep things cool. The European 850 “G” came with the 24 liter tank as standard, plus a huge 8' diameter headlight. Also added were frame improvements including a new swing arm mounting and alloy footrest carriers.(Also to be seen in some 'F' models. In the United States, the 850 “G” had a more custom look with a seat with no tail piece like the “SG” and different side panels. The exhausts on the European models have an offset in them to improve ground clearance at the rear.The “LG” was the midnight special, sporting black and gold designs on the engine and other parts.The European models had a wider seat and tail piece than the 750’s, but looked much more like them than the American 850 “G”.

1981 XS850 “H” and “SH” “LH”[edit]

As previous year. Also the last production year although models continued to sell for a few years after this. One final change, the ignition system was updated to electronic advanced timing and the mechanical advance assembly was removed.The “LH” was the midnight special, sporting black and gold designs on the engine and other parts.

See also[edit]

References[edit]

  1. ^Ric Anderson. 'Yamaha XS750'. Motorcycle Classics. Retrieved 2009-08-24.
Retrieved from 'https://en.wikipedia.org/w/index.php?title=Yamaha_XS750&oldid=927549974'

How to convert your petcocks from vacuum-operated to manual (with Off / Reserve / On functions. See below for Later Type Taps Conversion

XS750-2D and XS750E models

1978 yamaha xs750 manual instructions

The vacuum-operated fuel tap (aka ‘petcocks’) on these bikes have two main failings.

The first type of failure is when the diaphragm on the back perishes, the fuel in the tank leaks into the vacuum lines, down into the cylinders and eventually into the oil.

The second type of failure happens when the vacuum plunger o-ring perishes or gets obstructed with debris from the tank, allowing fuel to pass. If the carburettor float valves don’t seal perfectly, the carburettors overfill with fuel, then the airbox fills with fuel, and it can also pour into the cylinders (and the oil). There’s a theme here!.

Both result in a dead engine from very rapid wear and tear.
Here’s my copy of the famous manual fix with Reserve / Off / On functions.

First remove the taps from the tank. Tip the tank forward on its nose to get any excess fuel out the way. Take the taps to the bench and label them left and right side.

Take the front plate off each tap and swap them over so the plate marked with an “R” is on the left side tap and vice versa. Take the opportunity to check the holey washers are perfect, as they will now be the only thing holding back the fuel from the carbs.

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Remove the vac outlet at the back, and the vac diaphragm spacer plate as shown. Set those aside.

Drill the centre orifice to 7mm in a vertical pillar drill or very carefully in the vice with a hand drill. The aluminium is very soft and the drill bit will draw through very quickly so drill at slow speed.

Use a standard 8mm plug tap through the hole in the centre.

Get an 8mm Allen headed bolt in the drill (hold the drill in a vice and use a file to machine it down) or lathe and turn the head down till it’s less than 10mm round. Make sure you put a taper on the inside edge as shown.

Cut the bolt to length and clean up the end of the thread. Make sure once fitted that it doesn’t protrude from the centre hole.

Using a fuel resistant gasket sealer or threadlock, coat the threads in the tapped hole and on the bolt and secure it from the read of the tap as shown with a 6mm Allen key.

Make a plate to fit the back by copying the sizes from the fibre spacer plate only drilling the 4 securing holes, and also make a gasket for it the same shape from a sheet of fuel-resistant gasket paper (the rubberised type is ideal). Fit the plate.

Take the tap handle and drill/mill the surface to look like the photo at the top. I used a drill with a 7mm bit.

Take the flat spring washer from the tap handle and using your thumbs, reshape it to be more wavy, effectively tightening the spring.

Grind or file off the “PRI” on the front plate and use metal teeps or a scriber to change this to “OFF”

Refit the handle, spring and front plate

Clean the gasket face on the tank and refit to tank.

Off will be the old “PRI” position on the plate (Reserve on this tap previously), “ON” will be on, and Reserve will be Reserve (Previously “PRI” on this tap prior to changing plates)

Done.

XS750F, XS850 and Later Models

Later taps will look like this photo below.

In order to convert this tap to fully operational manual with reserve there a few variations. The plate on the back and the removal of the vacuum diaphragm is still required as above. The modification to the tap handle is the same as shown above (even although the tap handles are at a slightly different angle, see below).

The bolt that is being fitted through the centre has less material to grip to because of an internal drilling in the body of the fuel tap. Great care must be taken when tapping this out. Also drilling it will not be necessary as the hole is already 7mm. Perfect.

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You will also need to drill an extra hole into the body of the tap. See photo below. Drill the top right blank with a 3-4mm drill bit. Drill gently till the hole is clear (Approx 5mm deep)

Make sure the drill bit is biased to the left, unlike mine! If you drill the hole too large, or too close to the right, it comes through the casing side. The material is very thin there.

Fit the centre Allen headed bolt from the rear as before with fuel tight sealant, fit the new back plate, seal it use a gasket, as in the write up above, and change the ID plates from right to left petcocks.

1978 Yamaha Xs750e

With the labels changed fromthe other petcock,all you need do is score off or re-label PRI as OFF. All the other labels needn’t change. Remember to change the ID plate from right petcock to left, not the handles. They remain with the original side.

Don’t forget also that the reserve filter tube should show the blocked part to the left on the right side petcock, and that it needs a blob of sealant to hold it in, and that the left petcock will be the opposite/ mirror image of this one.

1978 Yamaha Xs750 Manual User

This is the right side petcock prior to modification with the PRI shown on the left. Once the plates are changed over, it will be on the right side and will require scored off/ changed to OFF.

1978 Yamaha Xs750 Manuals

That’s it!