Frequently Asked Questions
- History Behind the XS650
- Frequently Asked XS650 Tech Questions
- Ignition, Carburetor, & Clutch Tech Tips
- Model ID Chart (PDF)
- Step by Step Engine Overhaul Instructions
- Product Instructions
A Little History Behind the Yamaha XS650 Motorcycle
The Yamaha XS650 was built from 1970 to 1983. The first model was the XS1 (1970), followed by the XS1B (1971), XS2 (1972), TX650 (1973-74), and XS650 from 1973-83. It was a twin cylinder with the classic look of British twins, and a nice rumbling exhaust note. The engine has a reputation for being very reliable. It was also known for vibrating at highway speeds. It was very affordable, sold in huge numbers, and is popular today as a classic for those reasons and also its adaptability. The XS1 had drum brakes and no electric starter. Disc brakes and electric start were added in 1972. The Standard model was built until 1979, when it was replaced by the Special, Heritage Special and Special Ii from 1980 to ’83. The bike was rated at 53bhp @ 7,000 rpm with a top speed of 105mph. Base weight was 428 lb, with an MPG of 50. Due to its high production volume it has remained an affordable classic.
Frequently Asked XS650 Tech Questions
Q. If I change my exhaust or Air filters to a type different than original will I need to rejet my carburetors?
A. Absolutely! All aftermarket filters or exhaust flow more air & your system will require more fuel to go with that air. 1980-84 models with emissions type 34mm. CV carbs fitted in North America are a particular problem as they were jetted Very lean, these lack some of the tunable components found on the stock 1970-79 VM38 CV carbs.
Q. I am changing to aftermarket exhaust and/or air filters what jets do I need?
A. Every bike varies and a lot of factors effect this so a plug read & testing is the only real way to answer this (Altitude, ignition, engine compression & other factors effect tune). Spark plugs should show a light tan color on the insulator. Our Vague best guess is - 1980-84 models with stock 34mm CV carbs (North America) usually seem to require (about) a Main jet 142.5 - 147.5, Pilot Jet of #45, Air Jet of # 127.5 , Idle mixture screws set at 2.5- 3 turns out, carbs in sync, fuel level shut-off in float bowl set high. Check that fuel flow from petcock is good, No backup of sediment at float valve screen (stock). These carbs have a definite limit on fuel delivery and it seems that the more open the exhaust is the harder it gets to tune these carbs. Needle Jets need to be clean and there should be no air leaks or obstructions to flow of good clean, new fuel.
1970-79 Carbs usually need (about) a #140-145 main jet, up a size on the pilot jet,Carbs in Sync & pilot mixture screws adjusted. The 70-79 Stock CV carbs are very superior to the later types. Set idle to 1200 RPM. Make sure petcocks flow & that there is no air leaks.
Q. Why do my carbs flood when the bike is left standing?
A. Worn out, dirty or misadjusted float Valve (carb float needle & seat) OR defective or misadjusted carb floats OR bad fuel (dirty or gummy). Note: on 80-84 models the fuel may also leak past the O-ring on the outside of the push in type float valve seat. The Vacuum operated fuel taps often will not shut off properly (most 78-84's) and this contributes to the problem. Repair or replace these leaking petcocks.
Q. What causes my bike to backfire on deceleration?
A. An air leak in the exhaust system is the cause of backfires when you roll off the throttle. Air entering the exhaust hits the hot lean mixture in the muffler and ignites it. Check for loose clamps, holes or cracks in headpipes or mufflers or defective gaskets.
Q. Why does my Idle not come down quickly when I close the throttle?
A. If the idle is high or is slow to drop (hovers) then the system is receiving a lean fuel mixture. Check for carb holder air leaks or restrictions in the carb jets or fuel supply. Check cable condition and that they are properly routed.
Q. My electric start makes rattling noises & fails to start the engine. What is the problem?
A. The starter bendix gear that engages with the one on the crankshaft to is worn out & will have to be replaced. The gear is located behind the front edge of the clutch and a kit with the necessary parts needed is available.
Q. My Battery is not keeping a charge. How do I see if the battery is receiving a charge?
A. Use a volt meter and see what the battery charge is at 2000 RPM. System should read 14.5 to 14.8 volts @ 2,000 RPM. A fully charged battery will read about 13.5 Volts. Charge should be at least 12.5 volts.
Q. If charging system is not working what should I check?
A. Check connections & couplers for contact & corrosion, Check alternator brush length (should not be less than 1/4"). Alternator Rotor, Rectifier, Regulator and then the Stator are the next possibilities.
Q. Can I run the XS without a battery?
A. No, the XS has a non permanent magnet type alternator rotor which means the charging system requires a power supply to make power. The power supply to the charging system comes from the battery and the ignition system requires a power supply.
Q. My bike loses electrical power without notice, what's the cause?
A. Check the fuse panel used on 78-84 models as the fuse holders crack from old age.
Q. My 80-84 XS has weak spark on one side, why?
- Coil is failing from old age.
- Low voltage - System Not charging, Voltage drop in ignition switch or harness.
- Resistor Plug caps failing. (these start out at 5K Ohms & resistance rises with age).
Q. What can I do to improve handling?
- Replace the factory plastic swing arm Bushings with Bronze bushings.
- Replace the original Steering head bearings with Tapered Roller bearings.
- Change the fork oil. Many bikes are still running with the original oil (or none).
- Change the front fork springs. Originals sag up to 1.5" over time.
- Check to see if your rear shocks still dampen. You may have springs but no longer any dampening.
- Fit a front fork brace.
- Tighten up handlebar mounts and/or install new ones.
- Install modern tires. Newer types of tires are a dramatic improvement over 70's types available when the XS was new. Lower rounded profiles & sticky rubber are best.
- Have your wheels balanced on a high speed electronic wheel balancer. This makes a very noticeable improvement on All bikes.
Q. What is the length of the rear drive chain?
A. Chain size is 530 x 104 links with the stock sprockets (17 Tooth Front / 34 Tooth Rear)- for All models 1974-84. 1970-73 XS1/XS1B/XS2/TX650 require a 98 link 530 chain.
Q. Oil leaks from my engine. Where is it coming from?
A. Likely from the Clutch pushrod oil seal. This seal was never designed to be replaced without splitting the cases but can be if you are careful. The seal hole should be chamfered (razor knife will do it) and the new seal must be tapped in place very straight & square to the hole (coat the seal edge with gasket cement first). Repeat if it does not work first time.
Q. What Engine oil should I use?
A. We recommend a high grade 20W50 oil with a SAE rating of SJ or Higher.
Q. What valve tappet clearance do I use?
A. All Models 1974-84: Inlet: 0.003 inches (0.075mm.) Exhaust: 0.006 inches (0.15mm.)
A. All Models 1970-73: Inlet: 0.006 inches (0.15mm.) Exhaust: 0.012 inches (0.30mm.)
Note: Set valve clearance with cylinder being worked on at top dead center on compression stroke.
Q. I have bits of black plastic or aluminum dust in my oil. Where is it from?
A. Most likely the front cam chain guide bar. The guide has a plastic face that loosens & breaks up when its very old and eventually the cam chain starts to wear thru the exposed aluminum base.
Q. The long filter screen in the engine sump has a tear in it. What should I do.
A. The Sump screen filters the oil on its way to the oil pump and the original screen usually fails (poor design). An improved Sump filter is available, replace the original.
Q. The New cam chain I purchased is Too short & will not fit my engine, why?
A. The chain is Not short! New chains are pressure greased and will be bowstring tight when new. Often a small screwdriver will be needed to pry between a cam sprocket tooth and the link to get that last half a link in place before the joiner link can be inserted. The new uncompressed gaskets also add to the problem. Work carefully and once the engine runs the chain loosens up. Make sure you have ordered the correct chain as the early 1970-73 engine uses a chain with a larger pitch size.
Q. Why is it hard to get my bike in gear or to find neutral?
- Clutch Not adjusted properly at engine.
- Worn Clutch push screw parts.
- Needle bearing between clutch hubs is worn. (Very noticeable when engine is hot as neutral is difficult to find and clutch does not fully release).
- Cable worn, improperly routed or not lubricated.
Ignition System Tips
How to Test the Ignition Coil:
- Using the lowest scale on the meter, measure the resistance between the primary terminals with the wires removed. Should read from 2.5 to 4.5 Ohms.
- Using the highest scale on the meter, measure between one of the primary terminals and the center core of the coil. Should be infinite resistance. (open)
- Measure between one of the primary terminals and one of the plug wire terminals. Should be infinite resistance. (open circuit)
- Measure between one of the plug wire terminals and the core of the coil. Should be infinite resistance (open circuit)
- Measure from one plug terminal to the other. Should be 15,000 to 20,000 Ohms
Testing the Ignition System:
- Use a voltmeter and check for battery voltage on each of the red/white wires with the key and kill switch are turned on.
- The dual output coil has to have both spark plug wires connected to a spark plug at all times.
- To test for spark, connect one of the spark plug wires to a spark plug that is grounded to the engine.
To test for spark without having to turn the engine over, do this procedure:
- Remove the ignition rotor.
- Remove the locating pin in the advance rod.
- Reinstall the rotor, but without the pin.
- Replace the nut holding the rotor on loosely. This will allow you to spin the rotor to produce a spark without having to turn the engine over.
- Connect one of the spark plug wires to a spark plug that is grounded to the engine, but not installed in the engine.
- Make sure that the other spark plug wire is connected to a spark plug in the engine.
- Turn on the ignition switch and the kill switch.
- Spin the rotor while looking at the gap in the spark plug for a spark.
- Turn off the kill switch and the ignition switch.