1986 VFR750F Restore--Eating Gas

Hey guys. I bought an old '86 earlier in the summer as a rebuild project. After working all summer, finally got it at least up and running enough to get back out on the road; and it was an awesome experience. But, through that process I've discovered that it's eating tons of gas...getting about 15 mpg to be exact. (Ouch!) At low rpms or when it's just idling, it sometimes drips gas or has some white smoke from the exhaust as well. I'm thinking this could most likely be an issue with seals in the carbs and that I should rebuild them. But before I got into spending a ton of money on a rebuild kit, I thought I'd ask what you guys thought. Thanks!

 

Carbs

Yes that is poor.Pull them off and clean them. Works most always.
http://vfrworld.com/forums/mechanics-garage/22449-cleaning-carbs.html#post170019

 

Yeah, it's worse than poor. But we cleaned the carbs earlier in the summer when we had them off the bike before it was running. So I think it must be seals and need a rebuild? Could anything else be wrong?

 

is the fuel pump stuck on? Could it be high fuel pressure?

 

no, the fuel pump is fine.

 

find out where it's dripping from.

there are 3 places where fuel might likely leak: from vent tube ( bad float needle or incorrect float height setting), or float bowl (bad gasket or loose screws), or fuel distribution lines ( bad O-ring or a crack).

nobody needs 90% of what's in the rebuild kits: they're a rip-off.

float bowl gaskets are available cheap from K&L Supply.

 

upon startup and idle in the driveway, gas drips from the exhaust right where the can starts, and sometimes from the lowest point of the pipe directly below the carbs. once ridden for a bit and warmed up, it doesn't drip, but there is white smoke out of the exhaust. all of this only happens on the left side exhaust. also, the air stream coming from the cans is much much stronger on the right side than said leaky left

 

ARE u certain that gas is dripping from exhaust and not water ??

 

I had this exact symptom and it led me to faulty float needles. I only needed 1 but Billy Carr's excellent deal (4 float assemblies for $28 shipped) I could not pass them up. I did all four today and have no more dripping and fuel usage is way down.

In the future I will change these out automatically anytime I do a cleaning.

 

Of course that could be twolf's problem too: leaky float valve needles or improperly set float height adjustment.

The best way to check is to remove airbox cover and air filter, then hook up fuel tank with a long hose, start the bike and watch for fuel bubbling up from mainjet tube just under the long slide needle.

 

Could be all kinds of things going on here. My concern is the white smoke out the exhaust. Make sure the ignition is actually firing on the cylinders that feed the left exhaust. You could have two cylinders not firing, this would explain the leaking gas and bad mileage. I would assume the power when the bike is running is not real good.

 

Check for gas in the oil. Does the oil seem overfull? Does the oil smell like gas? If a couple of cylinders are not firing raw gas will go through the cylinder and come out the exhaust unburned. Some of it will leak down past the rings into the oil. Check your plugs on these cylinders. Are they wet? Do they fire?

 

it's definitely gas dripping, not water. and many times at the first few stop lights within the first few miles of a ride, there's a ton of white smoke from the exhaust.

this morning there was a loud backfire while starting it up, so that's not good. but then the fuel light came on before i was leaving, so i ended up just leaving it at home since there's no use in my pouring gas $$ into it right now.

will check the needles, etc. later this week hopefully and get back to you