VF fuel system issues

So, I’ve now done a few thousand clicks aboard the VF, and it is endearing itself to me.

However, even the most carefully stored 30 year old bike can develop a fault or two and thus I have discovered with the battle cruiser.

Heading into work last week, it started getting sluggish, like it wasn’t running on all four, and so I started to pull in off the motorway.

I managed to get it off onto a slip road and into a populated area before it stopped.

It would appear as if the positive battery connector had worked loose and there may have been a bit of arcing. Bugger!

Anyway, I managed to get it started with a new battery and thought I had a lucky escape. Halfway home, it did the same again and this time it was terminal. Home it came in the back of a truck.

When I managed to strip it down, it turned out the fuel pump was knackered.

I got a new pattern one, but one without the inbuilt elbows on the pipes, so I had to resort to a little creative plumbing. I also took the liberty of changing the fuel filter.

I put it all back together and it fired up after a few stabs of the button.

Away I went to work the next day, happy with my handy work. I got about a mile and half home before it stopped again, fuel starvation!

At home once more, I went through everything thoroughly and the fuel cut off relay was dead.

Down to the local breakers it was, and no joy on getting a CF304, but they did have a CF318, from the early CBR600 and VFR750 models. As the fuel pump I got was supposed to work for any of these anyway, I figured it couldn’t be that far out, and the connector is the same.

I tried it and away she went.

This is a good thing as the CF318 relay is far more available than the CF304, which is getting pretty rare these days, at least this side of the pond.

PS: Apparently there are Yamahas that use the same kind of fuel pump with the elbows, so must look further into that.

I’m still struggling with fuel starvation issues and I have a lead.

The bike starts and runs fine until I head out onto the motorway. After about 30 minutes or so at 120kph cruising, the float bowls seem to be empty and it will start to struggle, dropping on to three, and then two and then dying altogether.

This is with a full tank. Sitting by the side of the raod for a while will eventually get it back to running but never quite the same until its sat maybe over night.

It’s not a vacuum lock, AFAIK, as there’s no air rush on opening the tank.

On testing, the flow from the new fuel pump is not great at all and a quick voltage test shows that the pump is only getting about 7volts, when it should be getting 12v.

Anyone familiar with the wiring on this? Is there a splice or junction/connector that I should be looking at or is it likely to be just a short or chaffing etc.?

Hi ascalan
If I was you I would try running the bike without the fuel pump relay… just bypass it by bridging the black and white wire in the fuel pump relay conector with a short piece of wire…
Another thing to concider is the output of the aftermarket fuel pump… most of the ones I have seen pump far less than the original vf ones…

That’s a good idea Pete, thanks for that.

I spoke to the previous owner and he said he had not done any modifications in this area, and frankly was a bit baffled by the issue. He had done an extensive rebuild on the bike having used it for several years first.

I’ll try that and see what the result is.




I did a voltage test and the fuel pump connector is only seeing a maximum of 8v or so, with the engine running, but more like 6 or less with the engine cranking on the starter.

I traced the wiring back and the fuel cut off relay receives 12v on the supply side and on the signal side. However, the output that goes to the fuel pump connector only sees the same voltage as the pump, obviously.

Why is there a voltage drop across the relay?

I got another compatible relay, from a later CBR600, and it does the same. Even with the engine running, it never gets up to 9v to feed the pump.

Why is that?

surely the relays must be faulty if the voltage coming out is not the same as whats going in, is there any chance the cbr600 relays you are using have the in and out wire crosed over ?
May be the voltage through the relay is less at lower revs as the signal wire activates the relay everytime it sends an pulse to the coils…

:frowning: fuel pump relays are like mosquetos, they have no real purpose, just intented to iritate >:(

OK, have verified that the signal from the CDI to the relay is 12v, in fact with the engine running, it is more like 14, which is fine.

So the relay is getting the full signal voltage to activate.

It is also getting the same level of voltage for the fuel pump supply.

So, I’m baffled. Unless both relays are borked in the same way, I don’t know what is the issue.

For now, I’ve just put in a shunt across the relay to deliver 12v to the pump whenever the ignition is on.

I know there’s a risk, but fuck it, a reliable bike is more important right now.

Hi ascalan. .
I haven’t had a relay on any of my vf’s for years now and not had any problems… I think the risk thing that people get on about is a bit tedious… if I crash the vf I’m imagining there will be fuel everywhere and a large fireball.wether I have a relay fitted or not… ;D ;D

Well, fuck it.

No joy.
Ran fine for about 15 minutes, running on country roads in 100kph + range and then she started running on two and fucking about again.

Arse biscuits.

I think there’s nothing for it now but to pull the carbs and see if there’s something going on with the float bowls.


could be the spark coils ? already had that problem
thought it was fuel but it was not 8)

That has occurred to me.
A coil pack packing up with heat would feel like the same sort of thing wouldn’t it?


hi ascalan,
it could well be a coil pack that is failing like windy says…

Question, when the bike started to lose power this time was it the same kind of feeling as previousley ?. did you manage to keep it running on 2 cylinders both times?

Thing is, if you previously lost all power as if you had run out of fuel, but this time, assuming you were running with the bypas fitted on the fuel pump relay you only lost the front 2 cylinders, and were able to keep it going (in a fassion), this may point to the 2-4 pulse generator which normally would control the fuel pump relay ,
from my own experience they tend to start with an intermittent fault, failing when the heat builds up in the crankcase, loose all there risistance, then when they cool back down they come back to life…
may be worth testing when you test the coil pack.

Yeah, that does sound more like it all right.

This time, it did definitely stay running on 2 cylinders and was much more willing to restart than before when it felt like there was no fuel at all.

It’s the fact that it runs bloody fine for about 15-20 minutes before the issue arises that suggest something heat related.

And if the failing item is the one responsible for sending the signal to keep the fuel pump energised, that would explain why there were dry float bowls and general fuel starvation symptoms.

Right, the pulse generators live inside the gene cover, do they not?

There might be a set in my spare engine. :slight_smile:

I’ll have to have a look and see.

abut 480 ohms each
just pop a multimeter on each pair of wires in the connector
my ones died on me and came back to life but they then died compleatly
had to make a new loom from good parts :slight_smile:

@windysolar1: Thanks for that.

So, is it possible to get new pick-ups?

I’d rather solder in new pickups if they are prone to failure, than put in another set of 30+ year old ones.

Has Electrex World in the UK got 480 ohm pick ups?

UPDATE: There is a set of pick-ups in my spares box :slight_smile:

I found some Ducati coils from a saved webpage
and am going to contact them to see if his suppliers
will let me contact them
£25.00 each
tricky but not impossible I want a spare set of new ones

will update as i go 8)

as they get older they break down

Last time I looked CMS still had the pulse generators in stock. They are listed for the 1984 fe/intersepter… I’m pretty sure they will be the same as what’s in your ff… They come as pairs with the wiring attached so “plug and play” no soldering…

Can I just clarify, this is the actual pick-up coils we are talking about, not the CDIs themselves?

The CDIs don’t suffer the same heat breakdown as the pulse coils, do they?

Sorry, just a comment from someone else got me doubting myself.

BTW, you are correct @vfpete: CMSNL.com lists this:

An assembly part to supersede the original.

Just a further add, if you want to completely eliminate the fuel pump as the cause of the issues, run a fuel line directly from the tank to the carbs, brim the tank and take it for a run. If the issue continues, its not the fuel pump and you can look elsewhere.

Ran my Bol like this for a while, due to not being able to source a relay.

WHEN time permits, and i can open a knackered pulse coil to get a look inside, i’m going to see if i can wind my own bobbins, and 3d print them into a similar housing. You’ll then just need to solder the new ones in. However, this is going to come after the universal V4 Collector box i’m working on gets finalised.


@atassiedevil: Yeah, thanks for that.
I did that by the side of the road during the early part of this particular issue and it got me home before.

I’m fairly confident, having bypassed the relay on the last outing, that the issue is not now fuel pump-related, though the voltage drop across the relay is still puzzling.

Anyway, as I mentioned, I have the spare set arriving Saturday and I went ahead and ordered the new pattern assembly from CMSNL too, so that should give me plenty to play with and trouble shoot.

I just hope it isn’t the CDI :slight_smile: