Help Please! '84 VF500F won't rev up while riding

Did you check the resistance with the engine hot? The pulse generators are often ok at room temperature but fail the test when the engine is warmed up.

 

I havent actually tested the pulse generators with the engine hot, but i know for sure that the problem with the revving is still there when the engine is cold or hot so im not so sure. Anyways, i will do this test to be sure. I have a timing light here now too, and i will check the timing as well over the weekend if i get a chance.

 

Electrical checks?

Sounds like you own an Ohmmeter. That usually means you have a volt meter too (i.e. you have a VOM). Now all you need is a cheap Ammeter and you can check your VF500's charging system. You can often pick up a used one for a couple bucks at a swap meet. Actually, cheap ammeters that they used to sell in Auto parts stores only cost around 2 to 5 dollars back in my day ( the 60's). Ammeters are very simple parallel circuits that you put in to the main charging line so as to force all the current going to and from the battery through it. Cheap ammeters are not terribly specific about exactly measuring the current through them. But they are sufficiently accurate to determine that the charging system is able to keep the battery fully charged while making sufficient over current/voltage to drive the 'load' required to keep the bike running. If you can afford a good ammeter you will have to do less guessing about the actual amps being drawn by the operating load. Regardless, you need an Ammeter that has some amperage rating on its face. Don't be satisfied buying an Ammeter that only specifies 'pos +' or 'neg -'. Cheap or fancy, make sure it has some amperage value (+/- 30andor +/-60amp positions are common on cheap ammeters) on the face. If you have a good quality VOM it might have an ammeter capable of measuring to 10 amps built into it. You can use it too. You will have to switch between voltage and amperage when taking measurements for the test. Once you are satisfied that you have a solid reliable charging system its time to go on to the Ignition system.

You will need some wire, say 10 or 8 guage for the Ammeter and 16 -14 guage for the VOM, and some crimpon fittings: Eyelets/ alligator clips/spade type connectors/ micro clip ons/ that allow you to install the volt meter and ammeter into the lines. You will also need a manual in order to find a schematic that shows how to connect the various meters and what values you should see when the bike is operating.

You say you have already checked all the resistances. Did you check them when they were isolated from the rest of their respective circuits? Resistance checks need to be made with the devices being tested removed from their circuits. If you wish to test them warm or hot you still need to unplug them from the rest of their circuit before you take the reading.

So you have checked the primary windings of all coils, the secondary windings of all coils with and without their HT leads attached? And you should check for any sort of short to ground in the coils as well.

You should check the voltage (use the volt meter) going to the coil primaries with the ignition on while the motor is off. With the ignition on, the coils should get at least 9 or 10 volts to the primary coils without the motor operating.

And you have checked the pick up coils for resistance with the leads removed from their connection sockets.

If you have done all these tests then you are capable of doing the charging system test if you get an ammeter. You might also do a fuel volume delivery test while you are at it. If you have to get into fuel problems you will need to know that the pump is delivering sufficient fuel. The test for fuel delivery volume is an electrical test.

If the Bike passes all these tests then its time for you to find good replacement CDI units. You need to find ones that came from a good running 500 V4 motor. You simply swap out the old CDI units for the 'known good controller" and try out the bike with the alternates in place. If there is no change then you are ready to go on to the Fuel system.

You may think doing all these electrical/ignition checks is rediculous. No it ain't. Its just that most people find electricity sort of mysterious and try to avoid it like the plague. If you are intending on riding/keeping an old 'classic' like the vf500f then you need to be able to do the electrical tests.

 

Since many of you have grown up with electronic ignition.... You CAN do an ohms check on the plug wires. If the readings are very different from each other on each wire, it means the spark plug wires may need changing, but you can just take your timing light and clip it onto ANY spark plug wire and watch for a steady pulse. Very good diagnostic tool.

 

Ok so first thing, i have a question. Will a CDI box from a '85 vf500f work on my '84 vf500f? They seem to have different part numbers??

Other than that, i did a couple checks today on the bike. I did a resistance test on the magnetic pulse generators both hot and cold, when they are cold they are within specs and when they are hot, they are still ok, they are just about 100 ohms higher than the spec (specs say when tested cold) so i figure this is ok. One thing i did notice was when i have the engine idling, the rearmost two cylinders do not get nearly as hot as the other two until i rev it up and actually run it off idle for awhile. When i put the timing light on and went to check the timing through the timing hole in the side cover, it seems to be all over the place jumping around instead of being steady. At one point it looked ok, then it was all over the place. I also noticed that the strobes from the timing light are not uniform, and misses some pulses?? One more thing to add too, is that the tachometer is VERY slow to respond when the bike is cold, and gets a little better as it warms up but never seems to be quick enough to show accurately. Does this ring forth with any more ideas? Im thinking either the pulse generators (even though the resistance test is ok) or the cdi boxes? Thanks guys...

 

It would probably work. I don't remember if I've ever done it, but normally the different part numbers just reflect slight changes in the advance curve or something like that.

I would say that it's NOT ok! I think that the pulse generator is a likely culprit based on your measurements. That's why I had you check it hot, if it goes over spec that means it's not within mornal operating range. It runs ok when cold but gets worse when hot, right? That's exactly what the resistance measurement tells you.

You may have some other stuff going on with your carb sync or your tach causing these problems. I'd sort out the pulse generators first. Do not jump right to the CDI, there are many people out there with a spare CDI box because they replaced it and it wasn't the problem. In my experience they rarely fail intermittently, they are either good or bad.

 

Doing Good.

There are actually 2 CDI units with your bike design. There is a controller for the 1-3 ignition and another for the 2-4 ignition. Make sure you are looking at the same units when you make your 84 vs 85 comparison. If you are having problems with the rear cyclinders at idle (i.e. cold pipes, back cylinders don't warm up) then you might have that rare item, a bad 1-3 CDI unit. But lets not jump to conclusions yet.

First, did you get someone to send you a manual yet? I went searching for one myself. I found lots of cheap Clymer manuals on line ($5 to $15). A Clymers manual is better than no manual at all, Bobabreno. Get one.

First lets get to the timing light pulse jumping around. :nono: The flash from your timing light should be dead steady at idle and the timing mark should sit there like a rock, steady as grass, on the timing mark. The only thing you might see when reving the engine is the idle mark moving away from the mark on the access hole in the cover in a 'stately manner' (not jumping) as the CDI unit 'advance' marches the fire point relative to the speed of rotation. You can really only tell if the timing is being advanced as the RPM increase and little else while looking through the view hole. But, like was said above, the strobe is supposed to be composed and deliberate at idle and as you increase the RPM as well. No jumping or hopping or intermittently dropping out.

There are ways of hooking up timing lights that causes them to jump around. So take the light over to your car or your other motorcycle and hook it up on some other ignition system you know operates correctly. Without even pointing the light at the timing marks it should create a nice, constant and bright spotlight effect wherever you point it. Here I need to warn you that prolonged operation of the light will cause it to burn out. So if you don't want to be purchasing a new strobe bulb and possibly waiting for it to arrive by mail, don't play around with the light.

If it does not produce a bright constant pulse focused spot of light then the problem is in the timing lights bulb or the inductive pickup (the big clamp you put on the plug wire) or the way its hooked up. The light hook up should be 3 wires. The two 12V power leads to operate the strobe light (Red and Black to their respective battery terminals or some equivalent 12 volt tap) , and an inductive pick up that is usually a clumsy big clamp that is hooked up by inserting the desired plug wire to check timing (usually cylinder 1) into a slot in the clamp and making sure that the clamp is securely closed so that the plug wire is encircled by the clamp of the timing light.

In the case of the Vf you have, you could hook it to the #2 plug wire and check the operation of that ignition controller using the marks for the 2-4 cylinder bank as your reference relative to the mark on the cover access hole. Then change the inductive pick up to the #1 plug wire and check its ignition controllers operation. In fact, this might be the check for a bad CDI unit. If hooking the clamp on the #2 plug wire results in a nice steady light pulse but clamping on the #1 plug wire produces a lot of misfire and dance stepping by the light then you are looking your problem in the face.

As for the Tacho read out being slow or strange, well, you need a wiring diagram. That wiring diagram is in the service manual you still don't own. I don't have the time to open mine up and run through it in an attempt to determine if its related to your timing light jumping or to the fact that your 1-3 bank won't heat up at idle. Try to get a manual. If you don't get one get access to one online if you can.

DKC
Thats all i have time for now.

 

If you are ready?

I hope by now that you have tested your timing light, found out that it is OK, and that you have found that there is actually something wrong with one or both ignition circuits.

The follow on question is: could the tach be the cause of the timing light jumping? Probably not. The tachometer is basically a glorified volt meter. I am not going to tell you how to trouble shoot your tachometer. I don't want to be liable for you destroying it yourself while poking around.

What I can tell you is that your tachometer is getting its signal from the same wire lead that your coil gets the signal to fire plugs 1-3. The source is the CDI unit for the 1-3 cylinder bank, and the lead color is yellow. It can be distinguished from the unit that controls the 2-4 cylinder bank by the color of the spark regulation lead going to the 2-4 coils, which is blue. The power feeder lines to all coils is black with a white stripe (or the reverse). Please be aware of the fact that both the 1&3 plugs fire whether they are on the compression storke or 180 degrees away from compression. In other words the plugs fire twice for each complete 4 cycles. When Cylinder 1 is firing compressed gasses, Cylinder 3's plug is firing into a dead cylinder.

The yellow wire is doing double duty as the tach drive signal. The tach is driven off a parallel circuit with the 1-3 coil unit. So if you have a bum tach its very possible that it will cause problems for the parallel yellow line going to the 1-3 coil. To test the tach as the source of the problems with the spark jumping around take the tach out of the circuit. You can take it out of the ignition circuit by simply unhooking the yellow wire that goes to the tach (make sure to insulate it from ground). Make sure you do not inadvertently remove the connection of the yellow wire between the 1-3 CDI unit and the 1-3 coil set. Wih the tach removed retest the 1-3 cylinders with the timing light. If the jumping has stopped you have eliminated the problem. A competent instrument repair person can trouble shoot your tachometer and probably fix it with a simple component replacement.

While we are involved with the wiring at this level you should know that the 2-4 CDI unit has the equivalent spark control line (Blue) doing double duty as a lead that goes to the relay that controls the shutoff of the fuel pump. So if you have a problem with the 2-4 CDI unit you may experience fuel starvation because the pump is shutting off and on. The FUEL CUT RELAY is essentially a safety feature. If the motorcycle goes down and the engine stops the 2-4 CDI unit stops pulsing to its Blue spark control line that runs in parallel with the FUEL CUT RELAY and the power to the pump is shut down.

If you had a manual you could be tracing all this out for yourself and not taking my word for it. Please get a manual.

DKC

 

The tach is driven off one of the spark boxes. The signal for the tach comes from this unit, which gets it's input from the pulse generator for that bank. A tach that freaks out or dies can be an indication of spark box failure only if it's accompanied by running difficulties that mimmick the tach operation. In this case the tach needle will jump around randomly or just die altogether.

I really don't think that's the problem here. My suspicion would be that moisture or something has gotten into the tach and is making it operate sluggishly.

 

This thread is like reading "War & Peace"

Just one thing I don't think I've seen reference too.

Electrical components can go stupid when hot and recover when cold. So, does this "rev limiting" thing only manifest itself when the bike is hot?

If this is the case then you could eliminate all the air/exhaust/valve clearance questions in one hit as the probabilty is that you have an electrical fault somewhere.

Also can you use a Megga (sp) to check if the insulation (preferably hot and cold) between the coil wiring is failing?

Good Luck

Tris

 

Been there, done that. If taking the tach out of the circuit fixes the problem then you have a bum tach. The place to unhook the tach would be at the connectors for the instruments around the head tube. The wire color for the tach signal is Blue/Green. This is actually the "ground" wire. It switches the ground to the tach off and on, this same signal wire switches the coil ground off and on as well. Somewhere on the wiring loom there will be a BLUE/GREEN wire that connects to a Yellow wire. That connection needs to be disconnected to take the tach out of the CDI cuircuit to test the ignition to see if the tach is the cause of the problem.

 

Don't be afraid to take the Tach out of the circuit.

If you had a wiring diagram I would tell you to trace the yellow line coming out of the 1-3 CDI unit. You would find that it went to the 1-3 coil unit. However, the yellow wire does not power the coil, the black/white wire is the power source for the coil. The yellow wire is the signal wire that makes and breaks the ground of the "primary" circuit of Coil. It does the same thing for the Tach. The tach is powered by a black/brown wire whose ground is switched off and on by the same 1-3 CDI controller. Its the opening and closing of the tach voltage source that results in the tach dial (a volt meter mechanism) rising and falling as the currrent is switched off and on by the CDI unit. You can take the Tach out of the circuit without damaging the circuit or the CDI unit. just make sure that you don't ground the power in to the tach (the Black/brown wire) or the Blue/Green or yellow wires that go to the CDI unit.
Back to the wiring diagram. In tracing the yellow wire you should see that there is a point where the L/G (Blue/green) wire goes to a connector and on the opposite side of the connector it comes out as a yellow wire. Thats where its convienient to remove one of the spade connectors to disconnect the Tach. Use a jewelers screwdriver to depress the locking tab on the female connector and push it out of the connector. Make sure you tape it to insulate it from ground before you start up in order to test if the timing light has steadied.

If this does not result in a steady timing light flash then the CDI unit is suspect.
DKC

 

DKC, thanks for all the help so far, and everyone else as well!! I actually managed to get a proper factory repair manual in my hands now. I have had company over so i havent had much time to do any further checks. I will be back at it soon. I can tell you that the timing light is good though, as its the one we use at work almost daily. I will try taking the tach out of the circuit next and see if it steadies the timing light pulses. A few of you guys also asked me if this problem is only when the bike is hot, and NO, it is ALL THE TIME. I can start the bike and hop on it and it will rev to 5 or 6k and just stop revving anymore, hot OR cold. I want to recheck the magnetic pickups again cold as well to be sure but they were definately about 100 ohms higher that spec when the engine was hot. I will recheck the timing with the bike cold too, just to see if it jumps around like it was when it was hot. I will report back as soon as i can. Thanks again guys... talk about frustrating!

 

Cold Check is best.

Don't sweat it, take your time. I am glad you have a manual and I hope it includes a wiring diagram. If you have a few minutes take a look at it and trace down the wiring that comes and goes to the "Spark" (CDI) units/boxes. It will make it easier to understand what is going on.

As for the worry over the resistance of the pickup coils check hot and cold, don't sweat that either. If you know anything about Physics you might remeber that cold wires conduct electricity better than warm or hot wires. The pickups are nothing more than coils of fine copper wire wound around a metal core. The reason you check them "cold" is because thereis going to be less variation in the resistance if teh coils are checked at "ambient temp". If Ambien temp will only vary a few degrees in the comfort zone (60 to 90 F). This is the temp where Honda expects you make the resistance test. So the stated variation is what might be expected in that 30 degree F interval, plus or minus acceptable error. When the wire is hot the increase in the intermolecular motion in the wire acts to impede the flow of electrons caused by hooking up the ohmmeter. This results in higher resistance measurements hot. Its normal for the resistance to increase. If you could remove the pick up coils and place then in Dry Ice (Solid CO2) the resistance would be reduced. If you are getting normal readings at ambient temp then your pickups are OK. What you are checking for is a shorted pickup coil (very low or no resistance) or an open pickup coil (infiinite resistance). Its improbable that a pickup coil would be good when at ambient temp and then short circuit when it gets hot. Its improbable that a pickup coil would be good at ambient temp and then go open when it gets hot. But go ahead and check it again just to be sure.
DKC

 

Thanks again DKC, i actually checked out the pickup coils at ambient temperature and both were right within specifications, so that rules that out. Thanks to you too tinkerinWstuff, i would like to hear more of what you have to say. I do have to finish checking into the CDI Boxes by probably getting a couple spares and plugging them in to the bike to see as i dont believe there is a way to test them? The fuel delivery is more than efficient and the exhaust ive verified is NOT plugged. As i mentioned before, there is something funny going on with the firing of the cylinders because when i start the bike up from cold, only the front two cylinder heads and exhaust pipes seem to get hot to the touch, the rear two get luke warm, but definately not hot like they would be if they were actually firing. I think this is also related to my timing light pulses being very out of pattern.