85 VF500F float bowels & vaccum lines ?

[rainee_fly]

Hey Viffers! New guy here, got a 85 VF500F minicepter that I picked up 3 years ago from a guy that had no clue how cool the bike really is. It was in great condition due to a 15 year stint in storage. Only 16k on it & I have put an additional 5k since with a daily commute. But early this year the fuel pump went out so while I was repairing it I figured there was no better time to do some long over due maintenance. So I did what I could & had a wrench work on the more complex stuff, the long and the short of it is now it fires up runs about 8 to 10 minutes or about a mile down the road with easy throttle & then putters out like it is out of petro, if you give it gas it just boggs faster. I have put a lot of nights into it thinking it s something simple, but then the wrench pointed out the possibility that maybe now that it idles correctly & is clean that the float bowel is suffering because it seams to be missing some vaccum lines. so I have been poking around in shops & talking with mechs but nobody can tell me where these lines might be running to or from. it looks like there are 2 larger lines that possible drop out of the bottom of the airbox & then connect to the #1 & #3 near the float bowel, but then there seams to be smaller lines that also look clipped & capped that run into each cylinder just below the carbs... there is only one line still attached & it comes from 1 of 2 ports from the petcock below the tank & to the #1 carburator bowl near the main fuel pumps in.

If anyone has advice or some high res pics of that area of your V4 that would be awesome!

[reg71]

Hey, welcome to the club. I bought one of these babyVs for my wife. Unfortunately I can't help you much on narrowing down the problem other than to say it sounds like you are on the right track. I had a similar problem on a Kawasaki I had back in the 80s.

[rainee_fly]

Thanks Reg, & it is good to know I am not off track.

[jchag1718]

Thanks Reg, & it is good to know I am not off track.

I have an '84 VF750F. Looked at the bike and the Clymer manual and didn't see any mention of vacuum lines. Each cylinder has a vacuum port with a screw in it on the intake and its used for synchronizing. (no lines hooked to it)

The only hoses I see connected to the carbs are vent hoses (overflow) coming from the bowls.

It my understanding that the fuel pump is gravity fed by the tank and the carburetors are electronically fed by the fuel pump.

I would start with the only changed part in the system (ie; new fuel pump).
You are either getting too much fuel or not enough. I do not believe there is any adjustment on the fuel pump.

Being that it is new, maybe its overloading the carb bowl and the float needs to be adjusted. (this could be cause of too much fuel; flooding)

--- OR ---

Maybe the fuel pump needs to be purged. Might have an airlock in it. (this could be cause of not enough fuel)

See if this helps.

[rainee_fly]

Thank you for the reply. I do also have the Clymer service manuel & you are right it doesnt mention vaccum lines except from the fuel shut off valve from the bottom of the tank, on this bike the tank seals shut & creats a vaccum on the line so when the ignition key is turned on or when there is power to the fuel pump the electro magnetic pump starts pumping & the vaccum should keep the line full (according the manual). On California models there is a PCV valve that connects vaccum lines from all carbs to an ACVThe vent hoses may be what I am seeing, but if they are "vents" then why would they be capped? I have some pics on the site below if that helps illustrate what my delima is.



The pump is the stock pump specific to 84 -85 VF500 as 86 it was removed. Before I hooked the pump in I tested it by timing fuel flow into a metric jar for a 10 second average (10x6=1min) of 700cc/minute which is within the factory specs, I will have to check to make sure there is no bubbles in the lines or pockets in the pump, that is a good possiblity that I will check out.

I guess I am just hung up on why there would be these hoses coming out of the three carbs that were sniped & capped with silicone & the #1 carb has the line that runs to the vaccum diaphram on the fuel shutoff.

needless to say I am still scratchin - but all the help is great, at least I'm not watchin the clueless expressions come from my wife! :D

[jchag1718]

Thank you for the reply. I do also have the Clymer service manuel & you are right it doesnt mention vaccum lines except from the fuel shut off valve from the bottom of the tank, on this bike the tank seals shut & creats a vaccum on the line so when the ignition key is turned on or when there is power to the fuel pump the electro magnetic pump starts pumping & the vaccum should keep the line full (according the manual). On California models there is a PCV valve that connects vaccum lines from all carbs to an ACVThe vent hoses may be what I am seeing, but if they are "vents" then why would they be capped? I have some pics on the site below if that helps illustrate what my delima is.

Your right. I forgot about the extra emissions stuff on the Cali model. Your flow rate according to the manual is well above the 660cc/min minimum. As for why the line is capped, i'm scratchin too