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

I saw a recent thread and thought the issue was the same as mine and it was fuel. I was wrong, and they rider changed the coil packs and totally cured the prob. Im no mechanic, but I read a lot, read a little bout coil pack probs?
Good luck.

 

Thanks for the heads up Kundalini, i appreciate it. Im actually thinking more and more that its got to be ignition system somewhere. I just tried swapping out the spark plugs today (for fun, didn't really think it would cure anything) and of course it didnt fix anything. I also tried hooking a 2.5 psi fuel pump up to the bike just to see and it was still no different. Problem is that im 99 percent sure that its not a fuel issue as i say, ive had the carbs off the bike about 4 times now and they are spotless and diaphrams are perfect!? This is just soooo frustrating!! The coil packs seem to pass the resistance test but im wondering if they are breaking down under load somewhere. Hmm, thanks though, its something to consider next i think. If anyone knows how to maybe do a voltage test on the coil packs please let me know!

 

try this it helped me..........http://users.rcn.com/kochc/moto/spark/ig_repair.html

 

Thanks volks6000 for the link, i will check that out a little later!

 

Check this out, maybe it will help:

Daugherty Motorsports - Motorcycle Suspension Performance and Modification

 

Thanks Jamie, if i can narrow it down to being a fuel source problem for sure then i might just go ahead and do this modification. What kind of rpms should these bikes pull when they are running right, and do you think my problem could at all be a restricted exhaust? (even though i can't see what would be restricted, i just had it all apart)?? One more thing too, do you think that adjusting the needle on the slide up a little might help my problem or would that be of no help? Ive also been reading of other people that have had all the exact symptoms and they had their rocker covers off for replacement and apparently had leaks around them when they were reassembled causing this problem? This just doesn't sound right to me but what do you guys think? Would an air leak around the rocker cover really cause this?

 

Could you have a restricted exhaust??

Look what i found in a VFR muffler after 2 years storage:

 

They will run right into the rev limiter, no problem.

 

Jamie, are you being sarcastic or serious about the coils? I will be sure to check the timing with a timing light, what would i look for, just the timing jumping around? I just kinda ruled out the timing advance because when i read about it in the book, it said that the two modules under the seat control the timing advance on 2 cylinder banks each, so i just kinda figured it would be unlikely that both computer would go at once? But i guess its always possible that even if one module has died it could feel as though all cylinders were affected? Does this make any sense?

 

Whenever ignition problems exist folks always go straight to the coil - but they are almost never the problem.

Not so much jumping around, but irratic. You are looking for missed sparks mostly. It's acting like it's hitting the rev limiter, maybe the spark box/pulse generator(s)/etc is dropping out the ignition just like the rev limiter would do. You are correct, there is no worry about the advance, that's not at all what I'm talking about. The advance won't stop it in it's tracks like that - checking with the timing light will not tell you anything about the advance only the quality of the ignition pulses. Just point it at any surface, you are only looking at the strobe "beat". If you want to get real fancy and pull the timing plug and see what the advance is doing that's fine too.

 

Thanks for the tip on checking the ignition pulses with a timing light Jamie. Maybe i will give this a shot tomorrow evening. I guess its going to be a little difficult to do this though, as the problem only exists under load. Im guessing i will have to ride the bike and try to hold and watch the timing light all at the same time? or do you have a better way of doing this?

Secondly, are you sure that moving the slide needle up one notch wont help my problem? Im just curious as the problem seems to be in the main jet operating range?

 

Please don't try that. You should be able to notice the problem even if it's not under load - that is, if the ignition is the problem.

The slide needle does not affect the main jet at all. It only affects the part throttle midrange jetting.

 

So, these bikes DO have a rev-limiter? What RPM are they set to? I have yet to hit it!

I have to come back ot this thread later, there are some things mentioned here that is NOT your problem, that could be my problem!

 

its probly your cdi boxes and or harnes if it is not the coil

Rev limit on the vf500c magna is 10500 stock and the vf500f interceptor 11000 but it is a simple process to fix that. My bike did the same stuff before i replaced the cdi boxes and coils. Not a problem since.
And to mr doughtry i know you have been around and working on the bigger vf's for a long time, but alot of iginition issues can occur with older coils etc esp underlaod, or if there is internal corosion preventing grounding or voltage ramp up as alot of these bikes where not stored as properly carefully as they should have been. Most of the time they just sit outside or under a carport or tarp. This makes me sad for them but its the truth.

 

11,000rpm....really?

 

yes and the factory racers did 12500 why do rpms scare you people nothing like a v4 at 12-13k RPM just make sure you realy take care of your stuff if wanna try this to often cause it could get bad if you neglect your maintenance.

 

Yes, they certainly do have a limiter. Usually it doesn't hit until at least 12,000rom though. I suggest observing a rider-induced 9,000rpm maximum engine speed. Keeping the revs down is about the only thing you can do to <help> prevent dropped valves.

 

Aww... What's the fun in keeping the revs that low? lol

Thanks for the information though! It's looking like I've been a little bit harder on it than it should be, and I'll TRY to back off on it a bit! Actually, right now I'm dealing with cam chain noise, and probably valve noise. I need to pull the front cover to see what's going on in there, as the rear head seems fine in the valve adjustment area. It does seem to be the rear chain making the noise though. Good thing I've gotten to know the top end fairly well!

 

I think you were probably joking, but in fact it doesn't take away from any of the fun. The 500 doesn't produce any more power (read: it's still slow) at redline than at 9,000rpm. Plus, it's not very much fun digging valvetrain pieces out of pistons. Believe me, I've done it.

 

magnavmx5, thanks for the advice on checking into the cdi boxes and coils. Is there any way to test these items properly, ive done any and all resistance tests but i know they are not very accurate tests. I just dont really want to throw parts at the bike that it doesnt need, but i need to get to the bottom of this problem soon! Let me know what you think, thanks!