The next problem...

After considerable effort, the carbs on my '86 VFR750 are re-gasketed, leak-free, clean, installed on new boots, and in perfect working order. However, seven miles into every trip, the bike dies. There is no warning -- no hesitation, roughness, surging, nothing. Just turns off. I have checked the floats, and, consistent with the sudden death, fuel seems fine. It is not charging/battery, since it cranks fine, just will not catch at all. Each time, rescued in a car, I have gone back later in the day, and it starts fine. The consistency of the seven miles is amazingly high -- it is plus or minus a few hundred feet each time -- I know since I have pushed the bike onto the same side street each time, and coming home it either makes it all the way, or dies a few hundred feet from making it the full seven miles back to my house. It would seem to be something electrical between the battery and the spark. The kill switch is fine, and my fear is that it is some peculiar heat problem with the CDI. I am not sure how to check just what it is, or why it should be so very consistent. The bike and I were happy together for 25 years, and now our relationship is in a rather rocky patch. Any counseling would be most welcome.

 

You need to trouble shoot it when failed, may have to pack the things you need to check what is wrong but my guess is that it is fuel pump related. Jump the pump to battery and check flow when failed would be a place to start. CDI's tend to fail only half the cylinders and the bike will most often run , just very poorly.

 

I wondered about a fuel issue, but I was able to check the floats just after it died, and would not restart, and they were full. When my fuel pump relay was erratic some years back, the bike would always hesitate before it died, as it does when one runs out of gas, and now it just turns off instantly. Those two things led me to discount the fuel pump/relay aspect. I wondered about some bad connection to the CDI, and cleaned every contact I could find, and it still died seven miles into the next trip.

 

Do lights quit when the engine stops ??

Could be bad ground somewhere, bad ignition switch or plug, loose battery terminal.

 

The electrical system seems to keep working. The starter motor cranks fine. There is no hint of the engine catching, though.

 

So you checked for fat, healthy sparks as soon as it quits ??

 

I have not been able to pull the plugs while it has been dead, since it dies out on the road away from tools, and generally when I need to be somewhere. I would bet heavily that there is no spark, since I have fuel and cranking, and no hint of catching. I will try and do a 3.5 mile trip and have it die close to home so I can test more.

 

I am thinking I should have a plan before the bike dies. Does anyone know what wires going to the CDI should be hot, and whether they are hot when the ignition is on, when the starter is engaged, or the bike running? Based on Toe Cutter's comment about CDI's, I am thinking that the problem is electrical between the battery and the CDI. I can easily have a volt meter with me, and test at the connectors anywhere it dies.

 

Keep a small screwdriver with you. When it quits crack open the drains on the carbs. If fuel comes out its electrical, no fuel - well u get the pic. This will eliminate half of the possible problems in an instant.

 

I've done that -- and fuel does come out. That is why I have settled on electrical.

 

It's easily possible to have some fuel in the bowls but not sufficient for the bike to run. For example, if the pump or pump relay quit, the bike would die slowly and still have enough fuel to drip from the bowls. If you remove the black plastic cap from the pump you can inspect the condition of the contact points for misalignment, pitting or burning, maybe clean them up a bit.

I never measured internal quantities, but i did time the drain period of a full float bowl to about 25-30 seconds with the screw opened 2 turns.

Always cary a spare sparkplug so you don't need to remove yours to test for spark, just remove a wire.

Usually CDIs are not prone to periodic, heat-related failures, but pulse generator coils are. However, since your bike has two independent coils, if one quit after heating up (7 miles would be about right), it should still run on 2 cylinders........

 

When I tested the floats it seemed like plenty of gas was in there. The extra spark plug is a good idea. Do you think there could be some heat-related loose connection of power to the CDI that would shut it off? Some time ago my kill switch failed, which also had rather a negative effect on the bike running. I have tested that switch this time and it is fine, but I wonder if there is some other erratic connection that does not like getting warm.

 

Further testing, with the bike failing on me three more times, reveals more hints. I checked the pulse generators, and one is within spec on resistance, but one reads infinite ohms. The cam pulse generator is also within spec. If there is a bad generator, though, I would have thought that just two of the cylinders would fail, and it is clearly running, when it runs, on all four, and when it dies, all four die at once. Is it possible that a bad pulse generator would read as an open circuit, and then work most of the time, except sometimes when the bike is warm, and also kill the entire bike when it fails? Then, if that is so, is replacing this within my mediocre mechanic powers? I can certainly pull the right-side cover, but not sure if I would need also to pull gears and the like to get at the generator. Any help would be most appreciated, as sitting by the side of the road for half an hour every trip waiting for the bike to cool is getting old.

 

I don't understand how your bike could run OK with one bad pulse generator.......but you need to replace the pair.

Not difficult mechanically, but study the FSM first.

 

That puzzles me, too. If one sensor is bad should all four cylinders fail? The OEM part seems to be discontinued. Should I aim for a salvage piece? And is a replacement gasket the only other part I will need?

 

I am having the same type of problem with my VF1000R......I idle it for 35 minutes then it runs ruff and turns off.....same time all the time.....I hardwired the fuel pump to a switch on the dash;eliminated a fuel pump issue. The rectifier is super hot upwards to 200F and am considering ordering a mosfet rectumfier.....My pulse generators are out of resistance when hot so I ordered a NEW pulse generator from powersportsplus.com.....$71 dollars plus gasket of 23....call first and they will give you a 5% discount code for online ordering.....expecting it this week....but not sure it is going to solve the problem. Keep posting and I will do the same

 

Our bikes do seem to share various failings. I had en erratic fuel pump relay, and a bad R/R in the past few years. And leaky carb seals, clogged jets, and various other signs of age. The pulse generators for my bike are discontinued, though. I am surprised you were able to find new ones for your bike. I have heard there is a chance that the lead wire is frayed under the cover, so there is perhaps some chance I will be able to splice it back. Though why the bike works at all with one generator not working -- or at least reading infinite ohms -- remains a mystery.

 

Hi

There could be a dry joint on the CDi circuit board, mabye just flow all wires into unit especially the supply and earth wires. I have never done it myself but had a similar problem some years ago with a BMW 318i car. Worth a look.

Goodluck
Wayne

 

Fuel cap vent or sticky tank diaphragm, blow out all tank vents and cap with compressed air.

 

Pretty sure it is electrical, rather than fuel, based on full floats, even when it will not run.