help! electrical gremlin or something else

i had taken my bike in a month ago to have the carbs done and just over hauled. when the carbs were done i get a phone cal saying fuel system is great, but after running for a bout twelve minutes the front two cylinders lose spark. they swapped out cdi boxes checked connectors coils you name it and even tested all connection and everything passes within spec. they are at wits end and so am i i really want to get back on the road asap any advise would greatly help.

 

please post when you get it fixed..im having smae type problem

 

check the coil... it may be heatig up and shorting out

 

could be the pulse generator is shorting out when it gets heat soaked

 

thanks for the ideas, unfortunately we already checked those, arg what else could it be?at our wits end, but i refuse to give up on my 500 i like it too much !hopefully its something stupid and the mechanic has one of those a ha moment

 

will do dutch and let me know as well if you figure it out before i do. thanks again for everyone's response i really appreciate it !

 

will do...its absolutely driving me bonkers too lol

 

Hello Guys

Try this site out.It will help you.

http://users.rcn.com/kochc/moto/spark/ig_repair.html

Best regards

Gunnar

 

will do Gunnar thanks for the link! ill keep you guys posted with any changes

 

Gotta love them VF 500s, eh ??

Like hooba says above, i'd guess you have a bad pulse generator.

 

hopefully will have more insight tomorrow haven't heard any news from the mechanic. from what i've read squirrel you just tell it like it is,and i can really respect that, i'm gonna see if i have another one to swap out. the VF 500 obsession is more of a give and take relationship , they give us crap and we take it !

 

lol. just to let you know i have been scouring CL to see what newer vfr's are going for not saying im buying but keeping the options open for bike nimber two. like i said this little intercetor has a special place in my heart.

 

Btw would just the front two cylinders be loosing spark or all four>,stupid questions,i know, is there more than one pulse generator? electrical is not quite my thing, im more of a wrench turner.

 

I am a little rusty on my 500 skills, but each of the cdi's run half of the engine. I just replaced a CDI with the same problem and the front two cylinders is the clue I think.It was my clue.I would spoon into the pick up coil input at the CDI and if you still have the signal from the pick up coil after failure it must be the CDI or possibly a power supply problem to it as you said you have tried another. I have just had the worst ass kicking by an electrical system in twelve years just this week so I know your pain and anger.

 

like toecutter said, you have 2 cdi boxes that each run 2 cylinders. the pulse generators are an assembly located next to the starter clutch, there are 2 generators, 1 for each cdi box

 

thanks no new news today didn have a chance but hope fully more tomorrow i will check with the mechanic and see if he has any progress!

 

WRONG. There is a simple test to check the pulse generator in the shop manual.
VERY SIMPLE TEST and if the mechanic cannot do that test he or she should NOT be working on your bike.

 

When the bike is running clip a inductive timing light on the spark plug wires( ANY OF THEM) and it will show that cylinder firing.

I doubt that it would just stop after running for 12 minutes. Did they time it? Did they time it a second time and get the same result.?

Sometimes when you have that kind of problem I will tell you what it is.....OK ...A fuse - the glass cylinder type, can have a crack in the metal strip and when the fuse warms up the ends of the metal strip at the crack do not touch and so the circuit is open and the engine will quit. So check the ignition fuse.

 

When the bike is running clip a inductive timing light on the spark plug wires( ANY OF THEM) and it will show that cylinder firing.

I doubt that it would just stop after running for 12 minutes. Did they time it? Did they time it a second time and get the same result.?

Sometimes when you have that kind of problem I will tell you what it is.....OK ...A fuse - the glass cylinder type, can have a crack in the metal strip and when the fuse warms up the ends of the metal strip at the crack do not touch and so the circuit is open and the engine will quit. So check the ignition fuse. I have seen this problem twice in 40 years.

 

WRONG
the main fuse isnt glass its just a stip of metal, so you can rule that out. all of the fuses in the fuse block are blade style, so i guess you could spend the two bucks, replace them all then when it still dies after its good and warm you can have that ruled out too.Your right its not hard to use an ohm meter to test for 480 ohms or whatever it is on the 500 pulse generator, but if an electrical component is failing, only when its hot then wouldn't your fuse analogy be the exact same situation with a pulse generator/ign. coil/worn out plug wire/anything with current going through it.
you make some good points don, but i wouldn't rule the pulse gen out.
If it dies repeatably after 10-15mins, id have my mechanic check check resistance on the pulse gen./ ign. coils/ plug wires right after it dies so you can get an idea of what the electronics are doing at the time of death