Not getting the full power out of my bike?

Hello, I just recently inherited a 1983 VFR750 from my dad who bought it brand new back in the day and I have been fixing a few things before it is ride able. So I did a complete carb rebuild because it wasn't idling and now it idles and I took it for a little test run because of the oil leak (another problem) and the bike ran good up until about 6000 rpms but at that point it would kind of bog out and not go any faster. Any ideas? Do I maybe have it adjusted wrong?

 

What happens with it 'unloaded' (sitting still, out of gear)? Does it still die at 6k? If it does, you have an electrical problem. But...

It is more likely something in those carbs you worked on - and it could be a variety of things frankly. Usually this kind of thing is related to the diaphragms and the main jet circuit.

 

+1 on the diaphrams.

 

The older the diaphrams, the harder to get them reseated proppaly in the groove.

In stubborn cases you can use some silicone sealer or Permatex "Super 300" Form-a-Gasket to stick the diaphram edge to the groove so it won't move when you replace the top.

 

Thanks guys, I did the trick on making sure the diaphragm seals are sealed and it didn't change much. I have also done some more diagnosis and it does rev all the way in neutral and it also seems to have more power with half throttle than full throttle so I am going to assume it is probably something with the main jet. I was talking to a guy about it and he said that they still are partially clogged after being dunked so I was going to talk to him about drilling them out. That's what he says he does.

 

Don't listen to THAT guy !!

Drilling jets is totally foolish unless you're tuning at the race track. Wires poked through the jets as well as the side holes in the jet holder tubes, however, is a recommended cleaning proceedure, and Motion-Pro sells a set of graduated wires for that purpose.

There are alot of small holes and passages in carbs that can clog up and cause your problem, and various air and fluid tests can be made on carbs off the bike to confirm or not that passages are clear. Basically, you need to put a thin wire through or into every brass jet or hole you see, followed by a spray of carb cleaner followed by compressed air.


BTW, is your bike an '83 or a VFR 750, cuz it caN'T BE BOTH ??

 

There is much power in the words of the squirrel...

So did you really rebuild the carbs or were they just dunked? Stay away from drill-bit man, here is how to actually clean your carbs:
http://vfrworld.com/forums/mechanics-garage/22449-cleaning-carbs.html

Here's some naked pictures:
http://vfrworld.com/forums/1st-2nd-...tor-fuel-air-circuit-identification-porn.html

Drill bits and carbs don't mix (carbs and alky-haul don't either):
http://vfrworld.com/forums/mechanic...-slides-avoid-buying-jet-kits-drill-bits.html

 

It's your main Jet. I bet you unscrewed the main jet orifice, but did you take out the jet out that's under it. The jets under the main jet orifice is what is plugged. A soak, or even a good spray will not clean those tiny holes. multi-strand copper wire is what to use to poke the holes clear, then wash all the crap out with a can of carb-cleaner. Yep, you've got to pull the carbs again!

If you don't do this you will have good power at low RPM, but when you open it up with any load, it will fall on it's face. It will not fix itself no matter how much Sea-Foam or carb-soaking you do. Been there - done that.

+1 on ignoring the guy who recommended the drill bits. You can pretty much just blow off any advise that guy has ever given you.

 

Emulsion tubes

 

Good call on the main jets. Don't make fun of me, this was my first one, haha. I pulled the carbs off today and when I opened the chamber with the main jet, three of the four screws that go into the main jets were just floating in the chambers... I swear I screwed them in. But with those correctly installed my god that bike picks up real quick. Thank you everyone

 

Seems like you might have done a less than thorough carb cleaning if you didn't remove the emulsion tubes the main jets screw into and ream out the side holes.

Use the 7mm nut machined into the tube, not a screwdriver into the main jet slot, to tighten the tube into the carb body.