Tacho tells fuel pump ?

Hi all, is it true, the fuel pump is regulated by the tacho ?. I ask 'cause my bike is being starved of fuel, and it seems to happen when the tacho stops working. ???

Thanks for any advise…

hi stratau, if you have a fe model you will have 2 cdi units located in the tail unit of the bike, as well as controlling your coils they also control the tacho and the fuel pump, (one does tacho, other does fuel pump,

if your saying that you have a loss of power at the same time as your tacho fails, i think it more likely that that you have a faulty cdi or possibly pulse generator, it could also be a broken wire in the curcuit, they are prone to this where the wire comes out of the cdi.

you can swap the cdi’s over, the only difference between them is the larger one has a rev limiter in…

if you have a later ff model you will only have one larger cdi unit, im not sure weather one wire feeds tacho and fuel pump, or weather they are on seperate wires.

hope this helps

As I have just about rebuilt every part that is electrical on my Vf1000fe I would have to say the spark boxes in the tail have nothing to do with the fuel pump at all.
The fuel pump is controlled by a solenoid which is connected to the ignition switch.
The fuel pump pressure in the line stops the piston in the pump from pumping fuel if its working correctly.so self regulating the fuel.
Either your fuel tank has rust in it and its clogging the fuel lines thus starving the carbs of fuel or your carbs need cleaning in a ultrasonic cleaning bay because they are full of crud from the petrol over years of use.
also fit a new air filter as this may help

these are old bikes and need servicing properly

best of luck

as i said windy

if your saying that you have a loss of power at the same time as your tacho fails, i think it more likely that that you have a faulty cdi or possibly pulse generator, it could also be a broken wire in the curcuit, they are prone to this where the wire comes out of the cdi.

on the fe model, the blue wire from 2-4 cdi unit tells the fuel pump relay valve to open, thus opperating the pump, this was done by mr honda as a saftey device so the petrol pump will not opperate if the engine is not running.

if memory serves me right i think its the yellow wire from the 1-3 cdi that controles the tacho… thats assuming its a fe… ff may be different.

Yes Pete, was’nt this feature with the fuel pump made because the V4 can be damaged by running on two cylinders???

might be on the later vfs but not on the old ones
it will still run without the solenoid connected(bypassed)
I think I said that the ignition switches off the power to the pump like every other vehicle on the road including my diesel transit van.

see thats what i get for trying to be helpfull, machine gunned down by windy [:D]

all i know is that on a fe the fuel pump relay is activated by the number 2-4 cdi unit, the fuel pump does not run untill the engine is turning, thats why you never hear the fuel pump run when you just turn the ignition on, unless you have used a jumper wire to bypass the relay switch.
the tacho is opperated by 1-3 cdi unit, In both cases the wire that feeds the tacho and/or the fuel pump relay is the same wire that feeds the coils… hence no tacho no spark to rear cylinders…

If it were my bike i would defo be looking along these lines, i have in the past had these kind of problems with the vf.

im not sure about why honda made the vf’s like this i had heard the same as you phil, about damage to the engine, i also heard it was something to do with the bike if it crashed, honda didnt want the fuel pump to empty the contents of the tank all over the hot exhausts causing a fire.

P.S windy… i have a old transit…my diesel pump is belt driven, one day i will be able to afford a newer one.

my mk 6 is a gem
75hp chain drive engine and solid as a rock
just fitted a new clutch kit,ford wanted £750 I got the clutch from Euro parts for £180 plus £150 to fit it
3rd one in 25 years
mk2 then mk3 now m6 drives better than my dads car

just a thought
When my bike been sitting for a while I bleed the system to prime the carbs and the needle jumps around on the tacho till it runs

most of these bikes have fuel issues because they are not serviced properly and rust in tank

yes windy, these bike do at times seem to suffer with fuel issues, through lack of servicing and sometimes being stood for long periods of time…

P.S my transits the one with the smiley front (happy van), it matches my out look on life and my generally happy disposition… unfortunatly being a builder in the worst resession since god was a lad makes me depressed, and occasionally a grumpy bugger lol.[:D][:D]
vans due its mot soon, so it will be back underneath with the mig and glue some more patches on, i swear its at least a 100lb’s heavier with all the mig wire and plate it had over the last couple of years.

Thanks Guys, for your advice. My VF is an F2F with a single CDI unit in the rear. Bike seems to stop running cause of empty carbie bowls, only when tacho plays up.
I bought another CDI unit from the wreckers. I asked the dude there,“How do I know this one works?” He said, “It was working when the previous owner crashed”.

Thanks again for your views, I’ll use the info to sort the old bitch out.

hi stratau,
good luck with the vf, could be worth a try bypassing the fuel pump relay, that would keep the pump running/ready to run while ever the ignition was on and should keep the carb bowls full, dont think it will do anything for the tacho though,
any way keep us informed, would be interesting to know the out come.


My only concern with that fix, Pete, is rate of fuel flow. Perhaps it’s constant, but I would assume differences between idle and full throttle. Your fix may work… I’d like to have the bike working as per factory specs.

Regards, Strat.

i know what you mean about having things working right, i ran my vf for ages with the fuel pump bypassed, the only difference you will notice is when the bike has been stood a while and you turn the ignition on you will hear the pump run for a second or two as it replaces fuel that has eveporated out of the carbs,

the pump is a low pressure pump, the amount of fuel it pumps is regulated by the float and float valve,all the pump does is fill up the carb bowls untill they are full, the float valve then closes, the pressure builds up so the pump stops, when you open the throtle and use some fuel out of the carbs pressure drops and the pump kicks in again…


Ok I’ll give it a go. Thanks…

on the FE model, the blue wire from 2-4 cdi unit tells the fuel pump relay to open, thus opperating the pump, this was done by Mr honda as a saftey device so the fuel pump will not operate if the engine is not running.

if memory serves me right i think its the yellow wire from the 1-3 cdi that controles the tacho… thats assuming its a fe… ff may be different.[/quote]

That’s my work from way, way back in time…

I think I posted up a modified circuit diagram too…
The fuel system on my FE was one of the worst I’ve ever seen for corrosion problems… The rust was everywhere!! I cleaned out and lined the tank, replaced the fuel filter and gutted/rebuilt the carbs…

The only thing I couldn’t get inside of and give a damn good clean to was the fuel pump…

I reckon that these suffer corrosion problems too and start to run sluggishly, drawing more current as they do so…

This increase in current draw seriously overloads the fuel pump control relay (not a relay at all) and it gives up the ghost…

I found that they’re NLA from Mr Honda, so I devised a new circuit, using a real relay. The revised circuit uses the original control unit wiring plus an additional earth for the relay coil. This means that the bike’s kill switch also kills the fuel pump and ensures that older pumps still get the current they need…

I may still have an e-copy of the revised circuit… I’ll ry to dig it out - as the fuel relay is NLA, someone will need it sooner or later…!


hi miti, have dug around on the forum and found your work, which explains why honda had the relay set up…hope you dont mind me adding it to this posting,…

This is a problem caused by Honda’s obsession with “safety” and an over-engineered solution that has come to it’s natural expiry date…

Honda knew that the VF range needed a fuel pump because of the layout of the bikes (tank not high enough above the carbs basically).

They got all paranoid about fuel spillages with a bike on it’s side, floats stuck open and the pump just pumping away… (what happens on a gravity feed bike…? It just leaks…!)

So they built a circuit into the pump relay that “rectifies” the power pulses from the ignition unit (1-4 on FE models). This means that the pump will only pump fuel with the ignition unit producing pulses (engine running).

You may have read up on how to prime the VF carbs by switching the kill switch off/on repeatedly…?? Works for the pump, but the ignition units are OLD and this kind of treatment is NOT what old electronics need (true about old capacitors & transistors, we need to be kind to these old circuits…)

So… What happens…? Well, the fuel pump gets old and sticky and draws more current than it really should… Not dangerous, just an old part showing it’s age…

However, the relay is old too and decides it’s going to give up the ghost… Result - no fuel… Gravity feed is a partial fix but often not good enough to sustain high speed riding…

Hot-wire link across fuel relay connector will revive the pump… but now it’s on ALL THE TIME… as long as the main switch is on, the fuel pump is on… Not necessarily a good thing…

What did I do…?

I fitted a “normal” £2.99 single pole relay into the wiring instead of Honda’s £60 item…

It’s mounted in the same place as the original fuel pump relay and uses some of the original wiring… It switches the pump on when the bike’s kill switch is in the “on” position and off, when it’s “off…”

Here’s what I did…

The harness wrapping on the rear of my FE was a bit tatty (to say the least). I unwrapped it up to where it joins the main harness under the seat…

I pulled the 3 pins out of the fuel pump relay connector. This gave me:

Blue Wire - Power pulses from 1-4 Ign Unit
White Wire - Power out to Fuel Pump
Black Wire - +12V from Fuse #5 (Ignition)

I reterminated the White and Black wires with 6.3 mm spade terminals (to suit the relay I was using). These connect to the relay switch - the black is the power in, the white is the power out.

Next; I exposed the splice where the blue wire joins the ignition wiring… I cut the blue wire off and re-insulated the splice…

Then; I dug into my box of wiring junk… found a nice green wire, terminated it with a 6.3 mm spade at the relay end (coil earth) and a 6 mm ring terminal at the other end… I slipped the ring terminal under the 6 mm bolt that holds the breather bottle clamp in place…

Finally; digging into the wiring to the ignition units (my FE has 2 remember) I found the splice where the black/white wire splits to provide +12V to both ignition units… I cut this out and replaced it with another splice, adding another black/white wire at the same time… This new black/white wire was fed across to the new fuel relay as the coil supply.

Taped the whole lot up, good as new and hardly a noticeable difference to the look of the bike… New fuel relay works a treat, took about 2 hours, tidied the whole rear end wiring up at the same time…

I’ve even modded my FE wiring diagram to include this change… I’ll try to get the file posted on a web-server somewhere and will add a link to it ASAP…



Thanks Guys for that invaluable info. Eons ago I put a new fuel pump & relay in, with a second hand CDI unit, still no luck at that point.

I’ll try the hot wire from ignition switch to the pump.

Would really like to see that circuit diagram.

Regards, Stratau.

the easiest way to bypass the fuel pump relay, and remove control of the relay/pump from the cdi unit is to use a jumper wire in the multi-plug for the relay, personally i would try running the bike like this before cutting into the wireing harness,


Thanks VF Pete, I’ll give it a go. First I have to clean out the carbies and de-rust the inside of the tank…Gotta love the internet.