1991 3rd gen Lack in power between 8k-10k

Hey guys so after being in an accident on my first VFR then going to a GSXR and ZX7R, I am now back at another VFR (Spur of the moment, good deal) now here might be why... The bike starts up and runs just fine. first or second turn of the crank and she fires right up... When I am accelerating in first and second gear she does fine. When I hit 3rd and 4th and try and get on the throttle the power goes FLAT right around 8k-10k. I mean I got beat by my friends Mazdaspeed 3! (cobb tuned and I had a passenger who weighs 100lbs soaking wet) ... Long story short, especially up top it is noticeable the bike goes Flat, it struggles to hit 115mph... anyone ever heard of these problems? I was thinking spark plugs or maybe a carb balance?

 

Sounds like your slides are not functioning properly. Are you planning on removing them and trouble shooting? This bike should hit 150 mph, some take longer than others.

 

Carb problem? I had another 91 vfr and that thing had to be about twice as fast (also had jets, foxx racing suspension, ect) but this thing struggles once it gets to 100... I was thinking about doing a carb rebuild but want to make sure that is the problem first, thinking about using my key chain cam to make a video... let me know if that would help?
I think I might just pull the carbs off as this bike is new to me. Anything anyone would add would be much appreciated!

 

Trust me, your slides are not opening fully, all or one, two, or three. You get the picture. You have to pull the gas tank and blow air into the black t-fitting at the base of where the carb-hats are. This T goes into a seconday air filter that is on the side of the air box which most people ditch. Blow some compressed air in there with the top of the air box off, so you can substantiate that the slides are in fact lifting. If they are not, which dollars to donuts they are'nt, your gona have to remove the assembly and do the same drill with compressed air while fideling with each carb hat unitil you get all four moving simultanuously. The carb hats with the diaphrams can be fiddely, the hat has to seat well and kind of float before you tighten down all four screws. When you have everything good, they will sound like skeletons ratttling around (thats just my take, and I am :loco Good luck.

 

do you think their is any chance that air filter has anything to do with it and secondly is this the T-connector you are referring too?
Or is this the T-Connector you are referring too?

 

Well man I wish I could buy you some doughnuts because sure as shit you were right! now I know my problem, just need to fix it! Video coming in a minute!

 

Okay so I just did it a couple more times and got kind of mixed results, I think it is the angle at which I am blasting the air too cause some of the slides not to open because the further back I put the compressed air the more they all seem to open up... :confused-new:
Video one: https://www.youtube.com/watch?v=okreZeFck_I
Video two: https://www.youtube.com/watch?v=tFdzotUPDLY

Let me know what you guys think

 

So, before, they did not rise like in your videos? Now, they look to be ok to my eye. A new air filter could'nt hurt btw. :thumbsup: I don't eat donuts but would and have worked for beer/gin tonics :lol: It looks like there are no rips or anything in those diaphrams by the way they were taking air, you kinda wana be careful as you could blow something oot.

Keep us posted oh-tay.

 

actually, air filter looks pretty clean. Anyway. :vtr2:

 

I was thinking it looks like an aftermarket airfilter and maybe the jets are off because I know (and by that I mean I think) with no air filter it runs like crap when you get on it?

 

I'll take the donuts if he doesn't want them.

 

You have to run this bike with the air box lid on, air filter installed, etc-etc. You 'know wut I am saying?' You have a stock exhaust? Snorkel still in place on air box, Did someone try to de-rack these carburetors? You should never take the top plate off these carburetors, even when you buy a new oem gasket re-build kit, they give you large round o-rings with some do-hickees on the inside, these are meant for the and if you remove the velocity stacks. Do not, I repeat, Do Not, use these, remove the velocity stacks no matter what.

If you don't have the factory repair manual, get one. Stock jets are 130. Air filter looks like the stocker to me. That air box lid provides restriction, I had a bike years ago and used to run it withoot the air box lid, it was a loud obnoxious pig of a bike. Anyway, stay at it and you willl succeed.

 

So here is where I am, I have also realized there is a sweet spot, if I don't give the bike it's all on the throttle, it seems to pull MUCH better than if I floor it. The bike hasn't left me stranded in over 1 nearly 2k miles so I know it is running fine, my question at this point. Is what can I do to make it run better?!

 

Glad to see other members getting in on the action! But thank you ridervfr for your guidance!

 

No problem, I got a soft spot in my heart for these bikes, but would try to help someone oot regardless. Like I said, these bikes should run up to red line into the rev limiter and do a top speed of aboot 150 mph or so. I shift my bikes into sixth gear at aboot 8000-9000 grand which may equal 90-100 mph. Both bikes have new clutches etc, (side-bar) my older bike has 80,000 miles or so and I did a clutch replacement, I really did not noitce a difference except at speeds over 120 mph, then it seemed like it had a little more there. The old plates and frictions looked good without any blueing or cracks etc. If you do a clutch, replace the springs always. Anyway, good luck.

BTW wish I could hook up another Fox Shock for my latest bike. I got one that I bought new in 1995 and it cost me $650 and its been rebuilt 2 or three times.

 

So I finally got some time to take out the front two spark plugs, which wasn't as bad as I had expected considering. Just loosened the radiator and the fan with a 5/16 and with a little trickery, Wah La!... Now for the bad part, I was hoping that these would be the original spark plugs (which they might be, only has 20k miles) but they look pretty new (see attached pic) so all I am left with has to be a carb balance, which I feared to begin with! If anyone has any suggestions to save me $100 I would really appreciate it!

 

If you lived near by, I would trouble shoot it for you. I don't think carburetor synchronization is gona cure your problem. It helps for rideability at lower speeds, once your on your main jets like the highway, it is'nt in the equation. Thats my two cents. Keep us in the loop.