My CX / GL Won't Start or Runs Poorly

The CX500 family of engines are particularly prone to starting problems if the bike is left idle for several weeks or months. This doesn't usually signify a serious problem, but coaxing a CX mill into life after some time of inactivity can cause you some stress. Here's how to persuade / coax / force that V-Twin alive again.

Firstly, if you plan to lay up your bike for winter hibermation, as I do, then make a point of starting the engine once a week and letting it idle for 20 minutes. This keeps things in order and keeps the battery charged.

If for some reason you can't do this, remove the battery and top it up if necessary before laying up the bike. You can leave the battery on a trickle charger if you want.

There is additional information about reluctant and non-starters in the Fountain Of Wisdom page.

OK - so the engine won't run at all. What should you check first?

Two daft ideas first...

Is there petrol in the tank? It's not unknown for petrol to be stolen, so if you are doubt, switch to reserve and have a look inside the tank. No, NOT with that naked flame ...

Is the kill switch on the right hand side handlebar cluster set to "Off" ?

Is the battery dry, partly dry, or more than a couple of years old? Many starting and running faults are caused by a bad battery, and this isn't always obvious at a visual inspection. Try jump leads (see further down the page) or fit another battery, which is known to be good.

Ok, now for some more detailed faultfinding.

Do the neutral and oil pressure lights come on when you turn on the ignition? If NO, the battery is flat or there is a bad contact. Charge or replace the battery, you can use jump leads from a car, but don't use them with the car engine running. Disconnect and clean the battery's contacts with a stiff wire brush, and afterwards smear them with Vaseline (not grease).

You fuses may be faulty. To the side of the battery is an opaque bullet-shaped fuse holder which splits longways. Check that this fuse has not blown, as it's the main power line. Other fuses are in the handlebar section, under the flat plate which lies directly behind the ignition key hole.

Does the starter motor whir when you press the button? If NO, despite having charged it, the battery is probably knackered. If there is an audible click when you press the starter button, but no starter action, locate the starter solenoid to the side of the battery and clean its connections with a stiff wire brush, then Vaseline them. If this has no effect, disconnect the thick wire strap from the starter motor where it joins the solenoid, and using a pair of insulated pliers to hold the strap, momentarily touch the disconnected end to the battery's positive (+) terminal. This bypasses the solenoid. If the starter kicks off, the solenoid is knackered, replace it. You may still be able to bump-start the engine, especially if it's warm.

If your starter motor starts to smoke, stop at once. The starter motor has either developed a major fault, the starter clutch has failed, or the engine has seized. All these are serious or even terminal faults, and outside the scope of this page.

As the bike ages, you tend to get corrosion in the handlebar switchgear. Split the right hand handlebar switch cluster by removing the two long screws from underneath, and thoroughly clean the contacts for the starter motor button and the lights. Then either spray them with WD40 or rub with Vaseline (not grease). If the switchgear is very corroded you will have to replace the bad parts, or even the entire switchgear assembly.

Sidecar Bob comments "WD-40 is primarily a Water Displacer, and also works poorly as a cleaner and not very well at all as a lubricant. Wrapping the connectors with plastic isn't the greatest idea either - if the bike is out in the rain, water WILL eventually find it's way inside the plastic, and will probably stay there long enough (it can't easily evaporate) to do some damage. And WD-40 only displaces water when it is liquid - after it dries, it is only residue that dirt can stick to. Cleaning the contacts with contact cleaner and then applying dielectric grease will work much better."

If the starter motor whirs very quickly but the engine doesn't turn, then the starter motor clutch is faulty. This unfortunately means removing the engine and alternator rotor, but corrective work is not difficult. In such a case, there is sometimes a pronounced thunk as the starter motor is just about to stop turning. This is the one-way drive disengaging. The bike may still bump start, especially if warm, if the sparks and fuel are good.

Okay, the battery is fine, the starter whirs, but still the engine won't run.

Remove one sparking plug and reconnect it to the plug lead. Rest the plug's metal body on the engine casing (not the cylinder head covers - use the actual cylinder head, or the exhaust pipe) and briefly spin the engine on the starter motor.

Is there a spark at the plug? If NO, try a new plug. If this has no effect, check the thin wire from the black barrel-shaped ignition coil under the fuel tank is connected to the wiring harness. Trace the wire back, and it's worth cleaning its contacts. Still no joy? Do the same with the other sparking plug and coil. Then, replace the long spark plug caps with either new ones or ones known to be good. Try yours on another engine.

So - now you know that you have no spark at either plug, but the engine turns over strongly on the starter motor and the connections to the harness are good and have been cleaned up. Remove the tank and saddle and trace the thin black wire with a white streak. This is the low-tension ignition circuit and it runs to the ignition switch and the kill switch. Normally, this circuit is "open", i.e. not connected to earth, and the engine should run. However, a fault on this wire, such as where it has chafed on the frame and is rubbing on something metal, can short the circuit to earth, causing loss of ignition. This is how the kill switch works - when you flip the kill switch, or switch off the ignition, the low tension ignition circuit is earthed, and the engine stops. A short circuit here will do the same as using the kill switch. Disconnect this wire and try again for a spark

You can test this circuit with a multimeter, or a simple 12v bulb and some wire. When the engine is supposed to be running, this circuit has no earth connection, it's "open". If you connect a 12v supply to a short length of cable, with the other end of the wire on the bulb and the bulb touching the low tension ignition wire, the bulb should not light up. If it does, or the multimeter shows a connection to earth, the wiring is faulty. Somewhere in its run, it is making an unwanted earth connection. This is usually either a failed kill switch or a chafed wire somewhere.

Try disconnecting the wire inside the headlight shell, to eliminate the kill switch. If the circuit then behaves properly, the kill switch is defective. Otherwise you will have to examine the main wiring harness carefully in the undertank and headlight area, to find the damaged part. Favourite places to chafe are (a) at the edge of the tank (b) against the engine holding nuts and (c) on entering the headlamp shell. If you find the chafe, reinsulate the wire and the harness immediately around it, and reroute the harness if possible to avoid further damage.

You can safely leave the low tension wire disconnected ... but then the only way to stop the engine is to stall it or turn off the fuel tap!

If you have CDI ignition, the next step is to test for a failed CDI unit. The only proper way to test this without specialised electronic equipment is to swap it for one that is known to be good, and to test yours in the other bike. However, you can make sure that the CDI unit is producing the correct current to the coils. You'll need a multimeter; set it to AC. Trace the left hand coil (with the yellow wire) back to its connector with the CDI under the saddle, and disconnect it. Poke the positive lead of the multimeter into the lead from the CDI and the negative lead to a convenient earth, perhaps the battery's negative terminal. Spin the engine and you should get about 180 volts DC or 50-60 volts AC.

Gary Lowell adds: "I was recently having problems starting my 1979 CX500. After living inside your website for a week and trying everything possible. I've come to realize that I probably have a bad CDI. The last diagnostic came down to 2 things. Stator or CDI. Based on advice from a local motorcycle mechanic I tried this test:-

Set multimeter to DC. Clip leads to battery (Black -, Red +); should register close to 12v. Start engine; should be at around 14V at a high idle. If this is your situation then apparently your stator is charging your battery.

I hope this is helpful. It was a simple test that wasn't anywhere in the manual or on your website (my new bible)."

Reggie-CX (an electrical wizard) adds : "I was doing some electrical testing on the bike today and thought you may find this useful.

Coil testing: a coil can appear fine but break down under pressure. You can only prove this by substitution. This basic test will give a general indication of its health.

(1) Primary side test. Disconnect the yellow and peach wires under the seat. Zero the leads on your meter by clamping them together and noting the value displayed; typically around 1 Ohm possibly less. (NB as its normally such a low resistance we want to be able to discount the resistance in the leads). Clamp the negative lead to the battery earth terminal and the positive lead to the yellow or peach wire going to the coil. I get about .7 Ohms (zero point 7) on a good coil.

When you consider where the current goes, from the meter, through the coil then through the frame to the earth terminal, this also tells me that the coils are well earthed to the frame. So a high reading here may indicate bad earthing rather than faulty coils.

(2) Secondary side test: Leave the test lead clamped to the battery earth. Remove the plug cap and measure the resistance between the wire
in the centre of the HT lead and earth. This should usually read around 8,000 Ohms ( 8 K)

Why remove plug caps? Some plug caps have resistors inside which act as suppressors. My original ones were troublesome so I changed these for straight through types."

Reggie has made up an excellent page on starting problems.

If you have transistorised ignition (500 Eurosports, GL500s and all 650s) I can't advise a test as I've never worked with one, perhaps a reader can comment?

If you have no luck by now, you are most likely to have a failed alternator stator. This can be diagnosed here.

Now let's assume that you have a good fat spark but the engine still won't run at all.

To bump-start your bike, turn on the ignition, fuel, pull out the choke, make sure the kill switch is set to "run" and the gearbox is in neutral. If you have a couple of strong chums to push you, this can be done on the straight and level, but be warned, it's no mean feat to push start a heavy CX on the flat. If at all possible, get your bike up to the top of a hill or slope. An icy, slippery, or wet surface is not recommended.

Either way, get the bike up to the fastest speed you can. Being pushed is unlikely to get you over 10 mph, but coasting downhill, you can get up to 20+ mph. Whilst still in neutral, pull in the clutch and as quickly as you can, toe the gearbox into 3rd gear. You have to be quick with this, as the cold engine and clutch will drag quite a lot. Then, let the clutch out sharply, with as much throttle as your engine normally needs when it starts.

Be ready for the back wheel to lock up briefly. If it stays locked up, declutch, stop, and try again in 4th or 5th gear. But hopefully the engine will stagger into life, even on one cylinder. Declutch, tease the engine up to 3,000 rpm and select neutral. Allow the engine to warm up before you do anything major with it, and then ride to the top of a slope, switch off, and try a normal start. If the engine won't go on the starter motor, you can always bump-start it again.

Being towed by a car is a dangerous way of bump-starting as it tends to induce a lot of wobble to the bike under tow, and you can easily get pulled over sideways. You can do it if you are extremely careful.

Jump or Booster Cables

If you use jump or booster cables from another vehicle to help your bike battery, don't run the other engine. Attach the black (negative) jump lead from the negative post on your bike's battery to the same post on the other vehicle's battery. Then attach your red (positive) lead from your bike's positive post to the same one on the other vehicle. Once one end of the red lead is connected, take great care not to touch the other end to any metal parts of either vehicle, or a powerful short circuit will result, damaging components and possibly starting a fire. Always connect the leads first to the flat battery and then to the good battery.

Remove each spark plug in turn. Is it damp or wet, can you smell petrol on it? If NO, then the petrol feed to that particular carburettor is faulty. Remove the carburettors and give them a good clean, under surgical conditions if possible. If both plugs are dry, it is more likely to be a problem with the fuel supply as a whole. Try changing the fuel - swill out the tank and use fresh petrol, or rig up a temporary feed (beware of fire). Use a new length of fuel pipe between the tank and the carburettors; I like to use clear plastic piping so I can see that fuel is actually flowing. Some owners fit an in-line fuel filter to trap any foreign matter.

Variants with an automatic (vacuum operated) fuel tap are distinguished by having two or sometimes three pipes connected to the fuel tap. One is the petrol feed to the carburettors, and the other pipes are connected to the inlet tract between one carburettor and the cylinder head. As the engine turns over, a vacuum is created in the inlet tract and up the pipe. The fuel tap has a valve which is spring loaded closed, but opened by a vacuum. Thus whenever the engine stops, the vacuum decays and the valve closes itself. If this vacuum pipe is blocked or obstructed, no fuel can get to the carbs. To test this, disconnect the fuel feed pipe at the tap end and hold a small jar under the tap. Turn on the tap, no fuel should come out. Now disconnect the other pipe(s) at the carburettor end, and suck firmly to simulate engine vacuum. As you suck, the valve should open and fuel should spill out and into the jar. If it doesn't, then either the pipe is blocked - easily checked with a rod or pipe cleaner - or the tap is faulty.

Also it's not unknown for the pipes to be cross connected at the tap end, i.e. the vacuum pipe to the fuel feed and the fuel feed pipe to the vacuum left. The vacuum pipe(s) face inwards towards the main spar, the fuel feed pipe faces backwards.

Drain the tank and remove the tap from the underside. Pull off the tall gauze filter. This can disintegrate from old age or get blocked with dirt, so clean everything thoroughly and also fit an inline filter - these are only a pound or so from your local marina and they fit along the run of the petrol pipe. Make sure you fit them as indicated by the directional arrow!

So now you have : good sparks, good fuel, but still the blasted thing won't run at all.

Having reached this point we are running out of options. My own experience of the CX engine is that it can be very perverse, and that the solution is gentle coaxing. Here are some hints:-

> A good condition battery is essential. CX engines have a massive compression ratio and a battery which appears to be 100% in terms of spinning the engine and working the lights etc can in fact be weaker than it looks. Try jump leads, from a car or a spare battery. In fact I'd recommend using a secondary battery when you first start your CX after it comes out of hibernation. If you use your car as a booster, don't run the car engine.

> Don't run the starter motor for more than 20 turns at at time, and if it gets too hot to touch, let it cool down.

> CX engines seem to like being tried and then left for 10 minutes. I dunno why, but if the engine starts to show signs of life, whilst it's so very tempting to continue trying, walk away and have a coffee break for 10 minutes, then try again. I know this technique does work.

> Push the choke lever in and apply 1/2 inch of throttle instead as you spin the engine. This seems to clear the combustion chambers. Experiment with variations of choke and throttle.

> Squirt WD40 or suchlike directly into the air intake box. This gives an artificially rich mixture and has been known to start the most reluctant engine. The Australians apparently have an aerosol called "Start You Bastard" which neatly illustrates the point!

> Peer at the carbs whilst operating the choke lever. Does the linkage work BOTH left and right carbs? The linkage might be broken, obstructed or misaligned, leaving only the left carburettor choked when you pull up the lever. Also, I've seen cases where the soft rubber boot from the airbox to the left carburettor has gone a fraction too far over the aluminium body of the carb. This leaves the inside edge of the rubber boot fouling the choke mechanism to the right carb. Slacken the circlip and slide the boot 1/4" backwards, then retighten the circlip and check the choke action again.

Sidecar Bob adds that on his CX650 the carbs "... are mounted splayed ... the chokes are connected by a pair of metal strips (like leaf springs) connected to the chokes, pointing towards the air box, with a pin on one and a hole in the other. This allows for the angle between the shafts and permits easy separation of the carbs. The leaf on one carb had somehow become bent (if it wasn't so hard to get at, I might suspect vandalism) and disengaged from the other, hence the hard starting and one side starting after the other and the popping from the exhaust ."

The engine runs on only one cylinder

CX engines are well known for the peculiarity of starting on one cylinder (usually the left one) and then the other one chips in suddenly as the engine warms. I'm blowed if I know why this happens, but it's fairly normal and unless you have serious starting problems, I wouldn't worry about it, if the engine runs ok when it's warmed up.

If you're not sure which cylinder is firing, cautiously feel the cylinder head or the exhaust manifold, be careful as these parts, especially the manifold and downpipe, get very hot very quickly. After even a few seconds, the cylinder which is firing is definitely warm, and the bad one will still be stone cold.

However, if you have an engine which simply will not run on both cylinders, try these tips. I'l assume that you have the normal situation of the left cylinder firing and the right one not being interested.

I'll assume that you checked the fuel, and that the choke mechanism is operating on both carbs.

On the cylinder which won't go:-

> Check the spark (as per the above section) and replace any doubtful parts such as plug cap etc.

> Test the coils. Try the left spark plug in the right plug cap, to diagnose the plug. If the left plug (which is known to be ok) does not work in the right plug lead, then:-

- either the thick black HT lead is faulty. These come as part of the coil, but you can try unscrewing the plug cap and trimming off 1/2" of the end of he thick lead. You do sometimes get corrosion or wear here. Remember though that if you trim off too much, the lead won't reach the plug, once the plug cap is back on. Also try wrapping insulating tape all along the lead, in case it is "leaking".

Sidecar Bob comments "While I have no reason to doubt that you are right concerning early models, the coils from both my '81 GL500 and the CX650E I took apart last summer are the type that allow replacement of the wires. In fact, I would recommend that anyone with an older model replace their coils with the newer type and put on new HT wires before they get stranded somewhere in the rain with no spark because their HT wires are leaky."

- the plug cap is faulty; replace it.

- or the HT coil has failed. To test this, remove both plugs from the cylinder heads and trace the two thin wires (yellow for left and pink for right) back from the rear of the HT coils to the undersaddle area. Disconnect them both, and put the pink lead into the yellow circuit. Now try the left plug again, using a plug known to be good. If this produces a spark, then the right HT coil is faulty. Before replacing it, remember that the HT coils need a good earth connection with the frame, for them to work. Dismantle them from the frame and use a wire brush to clean up the bolt and locating areas. If the suspect coil works afterwards, it was just a bad earth connection; reassemble the HT coils, I recommend wrapping a shopping bag or cling film over them to keep out muck and dust.

> If the suspect coil still does not produce a spark, it should be replaced.

> If the right plug is firing but weakly (compare with the ok plug) you probably have an electrical leak somewhere between the CDI unit / transistorised ignition boxes, and the plugs. Trace the wiring carefully, looking for chafing or corrosion, and clean up / reinsulate where necessary.

The engine starts ok and runs on both cylinders, but there is misfiring or power loss ("engine bogging")

There are several common faults:-

> Poor fuel, fuel contamination with rust or water, accumulated dirt in the tank etc. Swill out or replace the tank; fit an inline fuel filter, which is a small plastic case inserted in the run of the fuel pipe between the tank and the carburettors. This only costs a pound or so, and is dead easy to fit. It's a good idea to swill out your tank once or twice a year, using a 50/50 mixture of petrol and engine oil, which will pick up dirt or rust flakes, and general debris.

> Stator failure is diagnosed here. Low circuit failure results in very poor performance below about 5,500 rpm. The more common high (blue wire) circuit failure results in very poor performance above 5,500 rpm. The stator page gives several places which rewind stators; I can personally recommend West Country Windings.

> Faulty ignition coil. Having had the dreaded 5,500 - 6,000 rpm misfire, where the engine bogs down, I checked the stator voltages and found they were at the minimum. So I had a spare stator professionally rewound, and fitted it. The engine performance was very much improved, until the misfiring returned a few days later and I had to replace both coils in the space of a few days. I think that the old coils were simply at the end of their lives, and gave up when the new stator threw full voltage at them!

> Bad contacts. Remove the saddle and disconnect all the multi way connectors, also those inside the headlamp area. Use a fine wire brush to reach into both the male and female halves, to remove dust, dirt, any corrosion, etc. Afterwards spray with WD40 and wrap the connections in cling film or a shopping bag. Pictures of these components are on the stator page.

> Decoking may be necessary at around the 40,000 mile mark.

> Dirty sparking plugs. Cean them with a wire brush, and set the gaps as per this page. I've found performance diferences between the NGK D8EAs and the DR8ESLs. It's a marginal difference, but it did help a misfire at about the 5,500 rpm band.

Edvard Korsbæk adds:-

"My bike ran extremly poorly from 4500 RPM, and was next to impossible to get over 4500 RPM. If it ran over 6000, it begins again, and ends at about 8000 RPM. It started immediately, and ran well until the 4500 RPM limit. Check with a stroboscobe showed missing sparks under load - without load it spins freely. The reason was that shortly after Spring, I had an accident, and was down. The air filter was clogged with engine oil - which was impossible to see, and the filter was less than 1,500 km old."

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