Carbs leaking ~1GPM!

[lammbn]

Please bear with me on this. i just got done with putting my bike togather after working on it since 7am this morning, or i guess its yesterday moring now ( currently 1:30am my time). this was the third day straight of working on my bike like this. after everything i did i expected at least one thing to go wrong but i'm a little confused with this one. long story short i was installing a self made sandwich type oil mod and figured if i had the bike torn down that far i might as well do everything else why i was at it. but as far as the carbs go i was planning on tearing the bowls and the top diaphram/plunger apart and cleaning everything up even though i've had no problems in that department with this bike. after i tore the first diaphram/plunger apart, #4 carb i believe, i saw that it looked spotless. and since i had never had any problems and didn't believe that it was really needed i just put it back togather and decided to just concentrate on everything else and get this all done.

now looking back i realize that i did do a big no-no according to the clymers manual. in order to be able to take the dome/cap off easier i took the bottom half of the air box plenum off the carbs allowing them to flex and twist a little while i was messing with them.

but now that i have everything done and back togather i have a big problem on my hands. the carbs are leaking tremendous amounts of fuel when the bike is running and only when its running. i kill it, they stop leaking. i would say that it is at least half a gallon per minute if not more. when i noticed it i quickly got my compressor and blew everything off so that it would evaporate and cleared the air out of my garage quickly. it just looks like it is coming from everywhere when you look up into the carbs while its doing it though.

I've given up for the night and am trying to figure out what i need to look into first when i get them back out but i don't know these quad carbs very well. my first thoughts are that since it is not doing it when its not running but still has full fuel pressure from the pump it cannot be the floats, the fuel connecting pipe, or any of the starter jets. i could see it being the diaphram i took apart if it was getting too much vaccum. but if anything when i put it together i didn't get it sealed right and it would be losing vaccum.

please, all of you who know these carbs. is there anything i could have done by either taking that apart or any twisting/flexing while the air box was off that i need to look at that would cause these symptoms?

[GreyVF750F]

You didn't say where the fuel was coming from exactly. So I'm going to assume here. If thats all you did was twist the carbs around and they started leaking it's most likely the inter connecting fuel tubes. There are three tubes that run between the carbs for fuel supply. These tubes have O-rings on each end to seal. Most likely one or several seals are not sealing now. Just follow your fuel line from the tank and you'll see them. You MIGHT be able to spray a lubricant like WD40 in to the carb holes where the tubes go and then take needle nose pliers and try to rotate them back and forth a little. This MAY get them to seal. If they do, go out a buy a lottery ticket. It's your lucky day! Other wise you will have to remove them and put new O-rings on. You should be able to match the O-rings from an auto parts store or hardware store. Put a little,very little, grease on the new ones to aid in sliding the tubes back in. Good luck and no smoking while doing this!!

[slippy]

Yea, some of the guys know much more about this than I do, but there's these little plastic 90 (maybe T connectors too or instead? i forget) degree fuel lines that apparently break or come off everything single time you take that airbox plate off. So I would guess you have a nice hole in the fuel line somewhere for gas to just pour out of it. Hopefully someone can back me up/correct me on this. Good luck.

[lammbn]

thanks for the response guys. but wouldn't those points leak from fuel pump pressure alone? it doesn't leak when the key is turned on and the bike is not running. only when the bike is actually running does it leak. i heard the pump turn on for a few seconds when i turned on the key and i checked for leaks before i started the bike. it has to be something tha would only work with vaccum pressure from the running engine or maybe with turning throttle while its runnning.

and as far as where its coming from it seems to be coming from everywere under the carbs right in the middle. thats why i couldn't see the actual soruce of the leak.

[GreyVF750F]

Take your air box and plate off then start it up and see. The pump I believe only applies pressure when the bowls need it. It can not come out of the slides. It could push up thru the vent if you have a sunken/stuck float possibly or dirt holding the needle open. It's all a guess until you can look down on them from the top.

[lammbn]

well i just got them out of the bike. i held them over a catch pan and started up the pump. it looks like you guys where right about the fuel link tube between the carbs. it doens't leak very much but when you touch it with a screw driver or shake the carbs a little it turns into a gyser. so that would explain why it seemed like it was doing it only when the bike was running. i know what joint it is so i will be tearing them apart to take a look at that seal. but just from the looks of it i think that it might just be in a little crooked. it looks like it is angled down a little at that joint so it might not be seated all the way. the seals are hopefully good. the carbs were supposedly totally rebuilt about a year ago and my small amount of tinkering with them seems to confirm that.

from what i've heard and read its a big pain to get these back togather right when you seperate them. anything i need to watch out for or do to make it all easier?

thanks again for all your help guys.

[DANIMAL]

lammbn,
Fuel pump runs for a few seconds when you turn on the Key then it stops.
when engine is running fuel pump runs all the time. this is due to the fuel pump cutoff relay. A safety feature to keep from flaming your ass if you go down in a crash. hopefully preventing you from going out in a blaze of glory. depending on what year there is also a bank angle relay that works in conjunction with this. You are gonna need to lube or replaced the old o-rings

[Bernieswanson]

My 86 VFR700f was leaking fuel and I thought from the bottom. So I remove the carbs and work my way up with bowl gaskets, float valves and each time I remounted them the leak was worse that before. It did turn out to be the o-rings on the plastic T fittings that feed the carbs. Go to home depot and buy a package of 10 1/2 OD black rubber o-rings. Fit them on the tubes and reassemble and I bet you leak disappears like mine did. And you will have 6 o-rings left over from your $1.79 purchase.

[lammbn]

my bike doesn't have the fuel cutoff relay or the stock pump for that matter. this was an old race bike. they put on an aftermarket exhaust with almost no back pressure and jetted the bike real high, i also suspect aftermarket or custom ground cams. it has almost no balls below 5.5k but from there clear to 9k it screams. the pump in my bike is just like a pump for an old carburated car. it is made to be able to pump up to a certain pressure and then stop till the pressure drops. basically it doesn't have the power to pump over PSI that so it stalls out, so the last owner bypassed the realy so that the pump is always powered up. i realized it was not the stock pump when i did a quick free flow test for 6 seconds. i think it came out to 11gph. well over that of the stock specs but apperently someone thought it nessesary to run the bike.

thanks for the size of the o-rings. i will pick some up before i start in on it. new is always better, especially when it doens't cost that much to begin with.

[lammbn]

Um..... it looks like i'm screwed. o-rings are all still good and pliable but this doesn't look so good.



any suggestions for a "sooner rather than later" kinda fix? preferably something semi-permanent.

[masonv45]

They sell replacement sets on e-bay. Get the ones from "fngster" or sumpin'