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

Mice are rodents just like some other animals I could mention........
:smile:

 

DKC - I must say that you write the longest responses on this forum. You should stop it, you are making the rest of us look bad!

 

You could have detected a clogged muffler with a simple vacuum gage check.

Sometimes mud stuck in a muffler will cause this same thing. No gases out of the engine=no air into the engine.

 

Donald, my vacuum guage readings were all over the board at idle, and im sure they are supposed to fluctuate a bit but they were bouncing all over the place? I just got the complete exhaust system off of the bike now. The mufflers look ok, i can't see light through them but i think thats due to the fiberglass and packing and the slight bend in the mufflers themselves, but i can however blow through them easily when i plug the drain hole so i think they are ok. The manifold collector assembly on the other hand looks pretty rusted apart inside. Before i got the bike running i had shaken a few rusted pieces out of the collector and welded up some pinholes in it. When i look inside of it now, it looks like its probably not plugged at all, but there are holes inside it cause all over the passage ways being able to bleed into one another due to large internal sections being rotten away and missing... how crucial do you guys think this is? Im thinking about cutting it right open at work and looking inside it to make sure its not plugged, but i can blow through each inlet to it with ease???? Opinions???

 

PS: What should a guy be looking for for a healthy vacuum reading, and should it be stable or bouncy on the vacuum guage needle? Thanks.

 

When you buy a vacuum guage there is a instruction sheet with it and it explains what the different types of readings mean. That is for ONE guage ONLY on a multi-cylinder engine.
On cars there is one carb or injection point and it goes to all cylinders. On motorcycles there is an intake manifold for each carb mostly.

If you have the guage hooked to all of the cylinders at once it will be confusing that is why there is usually a little thumb screw on each line or guage so you can turn all of them off so you can read one at a time.

A long time ago windshield wipers use to be operated with vacuum from the engine. So when the vehicle was idling the wipers would stop. and when you started accelerating the wipers would start going real fast.

So when you are looking at the vacuum guage it should be low and steady at idle and jump up on acceleration. BUT when the exhaust is clogged the guage might actually not go up, but go backwards. It will not be normal.

If the needle is bouncing all over it can mean the valve guides are worn, so the valves do not stay centered in the seat and there is compression leakage. That can of coarse be confirmed with a compression test. Usually you diagnose with a compression test FIRST.
So if you had bad compression and the engine is almost new you would start to think about a clogged exhaust.
Just like a modern car that has a broken CAT. You pound with your hand on the muffler and if you hear broken glass rattling around it means the exhaust is clogged with broken glass from the CAT. The CAT is like a thermos bottle it is glass lined with platinum sulfide on the surface.

Yes I would cut that thing apart and find out what is going on inside. Just cut a flap with a cut off wheel, and then you can easily weld it back together if it is worth while to do so. And a repair may be possible as well.

 

OK... I went back to the beginning of this thread. And I realize that if I was going to fix this bike I would start back at the beginning. I would do a compression check FIRST.

Also you said the the first thing you did was to take apart the carbs and you found clogged jets and a torn vacuum diaphram. You put it back together.
Yu got a better result

Now if you did not change the fuel filter or clean the gas tank and the bike had been sitting for a long time it could get clogged up AGAIN and no spray can is going to fix that . You have to take the float bowls off and make sure you can see daylight through the pilot jets.

You found debris inside the exhausts too.

BTW working on the carb settings is the LAST thing you do.
Vacuum readings is LAST. That is fine tuning stuff.

You need to get basic stuff fixed. Clean fuel. Clean fuel filter and a good solid battery.
Then see where that gets you.

So I would just back up a couple steps and drain the gas tank,and change the fuel filter, and clean the carbs again,(just the pilot jet and make sure the float needles are not stuck.) You HAVE TO KNOW you have a clean supply of fuel with no water if junk in it going to the carbs.

Forget all that electronic stuff for right now.
Also you can not diagnose problems if the battery is suspect. If you have to get a new battery. Otherwise you could be checking all kinds of stuff unnecessarily.

 

The vacuum gauge thumb screw (mentioned above) can be adjusted to reduce needle bounce, usually a couple turns in from wide open. Experiment.

Properly adjusted, the needle should hold nearly steady at any given rpm.....unless there's a valve problem.

 

Donald, first off thanks for the reply, you could probably be a huge help with this for me. I have done a compression test, all were ok. The fuel filter has been changed and the fuel tank has had a restoration kit run through it (3 part chemical cleaner, etcher, and sealer/recoat). All brand new sparkplugs, and a brand new interstate battery. Ive also had the carbs off multiple times and changed and cleaned what was necessary as you already know. The bike currently has brand new fresh 94 octane fuel in it as well, and even new fuel lines. All the basics are covered, and it revs up just fine in neutral, its only under load (riding the bike) that it acts up. It doesn't misfire or buck, it just simply stops reving any higher, almost like a slight bogging effect. I am a little concerned about the condition of the exhaust collector box though, and the wonky vacuum readings taken from the vacuum port on the cylinder head that feeds the fuel petcock. It fluctuates between vacuum and pressure at idle? If you go back a page or so i talked a bit more about what i saw on the vacuum guage. I can't remember what it was now though.

 

Given the length of this thread and all you've checked, i'd suggest finding another CDI box........it could be your problem.

Also consider the petcock mod by Jamie Daugherty. A frunky diaphram could restrict fuel flow enough to cause your problem.

Crack open your carb drain screws and catch the runoff to check for rust dust from tank which filters won't stop.

 

Im think another CDI Box is what is in store squirrely, once i prove this exhaust good or bad. Im going to try running the bike with only the exhaust pipes coming off the heads and see what happens. Other than that all i can think of is a coil, CDI Box, or Valve Springs?

 

You are on the wrong track if you think valve springs or CDI box's or coils are the cause. Coils almost NEVER go bad. Valve springs almost never, and CDI boxes almost never.

 

OK... Sounds like you are getting your ducks in a row. Good work.
How are the air filters? Make sure they are new as well If they have oil on them or were foam with oil the oil could have congealed and not allowing enough air into the engine. You are very close to a solution.
If it revs up in neutral you are not far from the answer. Check and make sure the choke (s) are operating correctly.

NOW I will throw this in. I ran into the same problem once and the problem was not what i thought. All the things I have talked about were fine but I forgot to check one of the most important things. The timing.

I found out the timing was off, and then I found out a woodruff key positioning the magneto had sheered in half! Allowing the mag to turn on the shaft and get the engine out of time ,so it revved in neutral- but when it was in gear would bog down and not rev up. So you might just want to check the timing to make sure and if it is off then you can suspect a component is bad or the alternator bolt is loose or somthing else is wrong.

With modern bikes we tend to forget timing because it is electronic. but there are timing marks.

 

The air filters are good, as a matter of fact ive run the bike without the air box on it just to make sure. The chokes are all working properly too, i made sure to check them while the carbs were off. Jamie actually mentioned the timing could be the culprit too. Im just not sure how it would have come out of whack when it only has 10,000km on it and my dad has had it since new and its been parked since 86. But i guess if something such as the woodruff key has broken then it could be a possibility. I have not yet checked the timing. I plan to run the bike without the collector and mufflers on it later today, and if that proves no different then i can put the exhaust all back on the bike and check the timing with a timing light. That sounds like my next plan of attack for sure. Where do you look for the timing marks with a timing light? Thanks for the ideas donald.

 

Actually, what I was mentioning was not the timing but rather the pulse generators. Those are the triggers for the ignition system. The check was to use a timing light to visually see what the spark plugs were getting from the coils. The pulse generators are a somewhat common failure. You are correct - the timing is non-adjustable and almost certainly NOT the problem.

 

If you have to ask where or how to check timing.....?

You don't have a manual. You are taking the exhaust apart and running the bike without mufflers for the fun of it. Some fun! Spin your wheels getting a manual and then read it. But just for the hell of it I just opened my Clymers to CHAPTER 2 and started reading on the first page'

" An Engine needs 3 basics to run properly: correct fuel-air mixture, compression, and a spark at the correct time. If one or more are missing, the engine just won't run. The electrical system is the weakest link of the 3 basics. More problems result from electrical breakdowns tha from any other source. Keep that in mind before you begin tampering with caruretor adjustments and the like." ​

The first thing I told you to check was the charging system. Even if you have a new battery you want to know if the charging system produces sufficent amperage and voltage to run the ignition system. Do you have a volt-ohm-meter (VOM)? You need one to work on the bike. They sell cheap ones at radio shack and Fry's. You need an ohmmeter to check the resistance of everything on the bike and you need a manual to tell you what the resistances are that you are checking for.

One of the first things you check is timing, even on a bike with electronic ignition. If you have not checked it yet, why? Don't have a timing light. They sell cheap ones, but I'd guess you will be happier with a decent light from Sears (expensive even on sale, great return policy, buy it, use it, put it in the box and take it back) or Harbor Freight (cheaper and often just as reliable if not as fancy, guaranteed to work) at $30 to $50. Unless you can get a good used one.

You need an ammeter and a volt meter to check the charging system. You need a manual to tell you how and what to check for. Read the manual. If you don't understand it hit the Forum with your questions. But you need to do some if not most of the foot work yourself. That means you have to get the right tools together, and that includes a manual. Someone on this forum can probably send you a copy of a factory manual over the net for free. Then you need the appropriate tools and the knowledge to use them properly. If you need that kind of knowledge you can find it around here by the barrel full. But you are going to have to put it together in your garage and figure the problem out ultimately with your own two hands and your own brain.

 

lol a damn mouse brilliant.

 

I might as well throw in my .02 worth of knowledge.....when you pulled the carbs off..did you put the boots back on right?.. you know the little black "rubbery things in between the carbs and the engine? not trying to sound like a smart ass. honest.. but if those arent on correctly you'll have problems..... and I didn't know that the went on any special way until I read it in my manual and they said specifically to put them on a certain way of the bike won't run...

anyway just "one more thing" for you to check...

good luck

 

IMHO, on the V4's you really don't need to check the operation of the ignition unless you have reason to suspect it as a problem. Even then, the first place to the start is the pulse generators. Those are inspected by measuring the resistance at the wire harness connector. My timing light suggestion was just to see what was happening at the rpm when the problems begin. It was an easy way to tell if it might be ignition related or if it was something in the carbs/fueling.

 

Sounds good jamie, I think i already checked the resistance on those when i did the resistance checks on everything else, but i will recheck them to be sure. Im going to bring a timing light home from work on monday and check the timing as well just for fun. The exhaust removal test really didnt seem to prove anything for me, as the bike runs like a complete pail with the exhaust off.