Honda VFR 750 RC36- High Fuel Consumption

Hello once again! I have a few questions..

The Bike is Honda VFR 750F RC 36 1990.. I dont think its related to "problem" but bike is "styled" a little.. Front fairing from VTR sp 2, rear fairing from something =D,190 rear tire..
I recently bought it so i don't know the complete setup of the engine.. The engine is stock (as far as I know) and only has a Wings slip on..But I dont think it's very open since the bike is not loud..
So when I bought it I rode it from previous owner to my home (about 70km). When I started the gauge was showing half a tank.. When I got home the gauge was on the red (empty) .. Opening and looking into the tank the upper part of the tank was dry and there where some gas in the bottom of the tank..The trip was mostly highway with about constant 5-6k rpm .So I poured in a 10 liters (the tank shows almost full,and for the next few days rode it for about 20 kilometers per day..So after barely 100km,s of riding like granny (about 60miles,no harsh acc,no high rpms) the same situation ,gauge on red (empty) and upper part of the tank is dry.. When I calculate that the consumption is about 9,68Liters on 100Kilometers..But with slow riding.. I thought, ok it's a V4 , they have a bad gas mileage (friend of mine has a Aprilia rsv4 and gas mileage is very very poor, but on the other side it is almost 200hp bike..).. After searching the net I see that people are getting about 100-140 miles on the full tank on vfrs which is far more that I got from mine.. The bike starts from the first touch of the start button and first stroke of the crank without choke,even after a month of standing still..Two things I noticed while riding.. 1st when closing the throttle and braking with the engine , there are no quiet detonations/backfires like on regular inline 4, but then after a while there pops a very very very very LOUD BOOOOMMMMMM.. If the acceleration was a little stronger before, the BOOOOMM would be brutal..It is so loud that I press immediately the clutch if there are some people walking on the side of the road..especially olders =).. Other thing , yesterday I decided to finnaly give this bike some rpms so I opened the full throttle , bike got to the 10k RPM, shifted to 2nd and full throttle again.. Bike got to the 10K rpm very quick again and then just stoped there, and won't go past 10 000rpm .. And it didn't sounded like limiter or something, just stoped there and like there was no more power to pass 10krpm.. So I was wondering is there some "classical" issue with the consumption on the VFR,s , something special to check, or just regular carb cleaning, new air and fuel filter, carb sync/adjust,spark plugs will do? Thank you for the answers and tips,and sorry for the long post.

Here is the potato xD : http://www.howbigismypotato.com/potato.jpg

 

Im sorry if I confused someone with liters and kilometers.. In short , the thing is : Bikes gas mileage is about 26MPG. That is the best i can get.. And with full tank to reserve the best I could get is + - 65Miles!!

 

For comparison I get 300km from 17 litres on my gen4.

 

I would check the jets in the carbs and see if someone has messed with them. If the bike won't pull in the upper gears it sounds rich and that would explain your poor mileage. Make sure the air cleaner is clean.

Jeff

 

On any bike new to you, check the color showing on the sparkplugs, then clean and re-gap, or replace. Next, check the air filter.

Signs that the bike's running rich are lowish power, blackish plugs, sooty exhaust pipe.

As mentioned, check that the carbs still have stock jetting or close to it. If you have a jetkit installed, adjustments may be necessary. Check and re-set float levels if they're not correct.

If the PO changed to lower sprocket gearing that could seriously reduce fuel mileage.

 

Another thing to consider would be a varmint nest in the exhaust, especially if it sat for awhile or not so long in the wrong area. If everything else checks out ok I would go there.

Jeff

 

Thank you so much people for the answers! Well since Im working on a bikes for a long time I know those diagnostic stuff.. Its just I had some bikes that had kinda their "own rules" , and this is my first vfr , thats why I asked if they have some sort of "classical issues" (besides R/R).. I will start with the spark plugs color and main jets condition..
@jethro : Im sorry, I dont understand what you mean by "varmint nest".. Did you mean on clogged exhaust?
Thanx!

 

Not clogged exhaust so much as some squirrels bedding down in your air-filter assembly (rodent nest.) Squirrel man leaves these in his bikes though, and just jets them accordingly :smile:

 

Varmint = red-neck tawk btw...example: Hey Jethro, you wanna go "varmint" hunting? That would mean in the queens language, Hey dude, you wana go out hunting and blast some squirrels?

No offense Squirrelman ok? Love them little Eichhornchens

 

I was thinking more along the lines of a mouse nest in there. I guess varmints tend to be bigger than vermin. Have I got that right?

Jeff

 

I'm guessin the main difference is that mice and things smaller may be vermin, while a few larger creatures could in limited situations in some states be considered varmits. (I'd be delighted to hear a bunch of coyotes or wolves howl around here occasionally.)

Determining which is a vermin, varmit, or merely a harmless pest is a matter of opinion until something's proved, either that or just one guy's prejudice.

Consult goverment rules; local fish and game laws; rare species determinations; the ecosystem; other animals; your pastor, rabbi, imam or shaman cuz hunting varmits is senseless KILLING, not Bible-approved imo. I guess i just like animals enough never to shoot one unless it were BIG and CHARGING.

Deer, i don't know !!!? Two or three almost hit my bikes a few times, and sadly, a deer killed a rider here yesterday in WNY.

Still, with that, why not hunt deer ?? But still you can't just shooting deer like you're in a movie theatre.

 

My appologies. The above is just alcohol-induced rambling and not intended to push a perfectly interesting thread off the tracks or onto another vector.

Where's my :embarased: smilie ?

By now hasn't almost everyone seen what i shook out of a VFR muffler that sat in a shed for 2 or 3 years ?? Just about anytime i've seen a really old bike started after long storage, acorns, seeds, and parts of acorns come shooting out the exhaust usually !

 

You still didnt address the fact that you accommodate vast squirrel condominiums in your air box and you modify your jetting for the fury little buggers...

Funny chit huh...whats wrong with some rants? Nothing....you left out Rastafarians...you know Snoop Dogg is now Snoop Lion.

 

Riding home from work I had a thought about this, could it be that the choke cable is sticking and the choke is not being fully released?
I don't know much about these things but if I forget to release the choke after she warms up, she gets hateful, and also this could be loading the cannon with fuel fumes for those mighty backfires. Bet there are no more acorns in there after that first blast!
What do you guys think?

 

^That was my 1st thought.

 

Oh I get it =D

Damn, this is just brutal :O xD

You are the 5th person who suggested that..

So today I finished the fairings, it is the beta beta version but will do for now, for registration and temporary riding.Then I got to the engine part ,since I didnt have the time, and lately I have problems with tools this is what I did..

First I checked choke since many people suggested it ,the cable is ok, I loosen it max, no problem on the choke lever, and on the carbs when i turn it off it goes all the way in.. So externally speaking the choke seems to be fine..

I lifted the tank and checked the 2 spark plugs on the rear cylinders ( Didnt have the time to play with the front ones), first the spark plugs where probably screwed in only by hand -.- , there where no force whatsoever,and the metal o rings on the spark plugs where not compressed at all (like on new plugs :S)..

plugs are obviously new, since the electrode looks like new, and the plastic around the electrode is white but not due to lean burning but white as from factory brand new white.. I guess that the situation with the other 2 plugs would be the same.. Picture of plug ( on the picture looks much worse and darked)
http://imageshack.us...0120802002.jpg/

The rear sprocket is stock (43T) ,but I didnt checked the front one.. I get about 100kmh (60mph) by clock in 6th at about 4000 + - rpm.

Next I checked the air filter.. And boy oh boy,it was full of everything, oil,dirt,and the up side was completely black. I cleaned it as much as I could and dryed it (temporary solution till I get the money to make full service). Removed the airbox snorkel, and went for a spin.. By opening full throttle bike was stalling and jerking alot. But strangely after a while it started to work better and better.. After a while I could open the full throttle whitout stalling but it was lacking some power. The backfireing was more occasional and quiter. But still would pop a loud booomm after some time.. And this is what doesnt make sense to me since I made it run lean without the snorkel.. Got back home, put back a snorkel and went for a little longer ride..By opening a full throttle there is alot of power and the bike is now hitting the limiter( at about 13000rpm).After 10T rpm there seems like there is some extra power, something like turbo spooling and hitting after 10 lol. But the consumption is the same, maybe got better but just by a bit. And I Iooked behing to the exhaust when I was expecting a boom and when it poped it was a huuuugeeee orange flame lol..So this is definitely a jetting, filter,syncing sort of thing and will keep you informed with everything I do on the bike ,and I will for sure post a solution when I find it..Need to earn some money to play with this things + priority now is to register the bike.

Sorry for the long post, here are 2 pics of the bike since you asked.. Front fairing is from VTR sp2 and the rear tail was already on the bike and I dont know from what bike it came. Maybe you do?