1985 vf500f wont rev past 5k under load

I couldn't find any factory or aftermarket plug wires sadly, but I was able to get spark plug terminal adapters that make them compatible with automotive plug wires, so it has a set of new custom kit plug wires from orielys. Looking at the different between the spark strength of the new and old coils, there really isn't much difference, so I think your right about the coils not being bad.

 

Gremlins abound...
Took the carbs off again and went through the jets, and emulsion tubes.
Found that the emulsion tubes were dirty still, I just didn't clean them well enough I guess .

But now after being put together again, it idles at 3k to 4k rpm... Hopefully it's just a bad bench sync but I don't know yet.

With the cut out around 5k rpm still happening and the plugs still reading rich, I'm thinking maybe I have a bad pulse generator or maybe even bad cam timing? All the compression readings seemed low to me, but not low enough to make it hard to start... that to me says that it should still be able to rev all the way out while maybe lacking in top end power.

 

Sorry, but the fact the carbs went back together with dirty emulsion tubes leaves me with little confidence regarding the rest of the job. Those are the second easiest thing behind the main jets to clean / verify.

Pulse generators also seem extremely unlikely given what you describe. Maybe, just maybe, the spark unit. But I still highly doubt it.

Why would the cam timing be out? Did you have the cams out? Do you think it was parked with the cams out of time?

It's almost always STILL THE CARBS with first timers.

Also, what condition were the carb insulators in? Still supple? Inspected for cracks? Are you sure you have the carbs fully seated properly?

 

they always claim they cleaned the carbs first time, second and third time, sometimes still not right.

hard to clean properly unless one knows how carbs work and what each part does

 

side holes need to be probed with wire

 

Yes I know... I'm very new to anything carburetored. The intake boots are still mostly soft, they don't have any cracks that I can see.

I did prob all of the small holes in the emulsion tubes with a wire and did the same for the vacuum passages to the diaphragm. The only reason I though the cams could possibly be out of timing, is that the first owner of this bike (the guy my buddy bought it off of) said he did engine work if I remember right.

I did a good amount of research on the spark generators, and it doesn't seem there is anyway to test them.

This weekend I'm going to take out the carbs again, and do another cleaning round. If there's any pointers you can give @Captain 80s I'd really appreciate it!

I'm young and dumb, but I really want to get this old girl going!

 

My 1986 VFR700F2 wouldn't rev up beyond a certain point. The problem ended up being the top rubber vacuum diaphragms. My fault, as I didn't get it to seal correctly. I also learned to follow the service manual exactly, as it took me three tries to finally clean the carbs properly.

 

---"My 1986 VFR700F2 wouldn't rev up beyond a certain point. The problem ended up being the top rubber vacuum diaphragms. My fault, as I didn't get it to seal correctly. "---

the diaphragms may shrink or expand over the years making it difficult to get them seated properly in their grooves, a common problem. imo, its usually unnecessary to remove the slide caps for cleaning if the needle looks good.

 

Thank you guys @squirrelman @Glenngt750
I'll definitely take a look at the manual to get a better sense of what im missing with the cleaning, and the slide diaphragms again. As far as I know they're the originals. When I first cleaned the carbs one diaphragm was pinched but I was able to get it to seal (I think lol) I have a new set of diaphragms, but I couldn't figure out how to replace them and didn't want to tear the originals incase I couldn't put the new ones on.

Also, when I work on the bike again, ill take a video of the slides in action so everyone can hear the engine running, hear the weird cut off, and see how far up the slides move.

 

---"My 1986 VFR700F2 wouldn't rev up beyond a certain point. The problem ended up being the top rubber vacuum diaphragms. My fault, as I didn't get it to seal correctly. "---

the diaphragms may shrink or expand over the years making it difficult to get them seated properly in their grooves, a common problem.

 

I'm going to figure out a way to replace, the diaphragms for sure. I was reading on another thread about pin holes and micro tears, so I'm thinking that's probably part of my issue.

 

if your diaphragm is in good condition youll hear an air puff as you lift the slide with a finger. leave originals in place if they work.

 

@squirrelman
I do get an air puff, and the slides slide a little slower down like they're sucking air as well. I'll leave them if place like you said

 

test for proper action of the slides [before mounting carbs] by blasting low pressure compressed air into the oval-shaped section on intake side of carb.

 

yes sir, ill be able to test it tomorrow

 

Great news!!
I bought a carb cleaning kit with all the small wires and cleaning rods/brushs. Went over the carb again, bought some #95 jets from young powersports. Put the girl back together and BOOM, she runs like a dream!
Seems to run lean in the top end so maybe the jets are a little small. But I'm going to concentrate on getting it road worthy so I can test everything thing out and eventually tune the carbs so she'll really run her best. Thank you all for the help! I really appreciate it