Hi Folk, a quickie: I know the fuel pump keeps on pumping after priming on pre-1997 SS, but does the Mikuni carb set up with the SS tank draw fuel anyway? In short, would the bike run without a pump? Mine seems to start and run with pump disconnected, but didn't date txt it on a run? Sent from a mobile transmitter.
With full float bowls and the pump switched off, my 750 will do about 1.5 miles before it stops. It can't draw fuel if the pump isn't running.............the pump works 'uphill' inside the tank. (Yes, I can switch my pump off......done so I could test electrics etc without the damn thing running..........but as the switch is hidden, it may serve well if someone nicked it). What can happen if you brim the tank and the engine is hot and the weather is hot, if the breather valve doesn't let go straightaway, the pressure inside the tank can charge the fuel lines, overcome the float needles and dump a tankful by siphon, through the overflows.
I see now. It's down to the uphill travel in the tank then. Do any folk adapt the tank to run off gravity feed, without jeopardising performance? - given that it's so common to relocate the filter outside of tank - so the fuel filter needn't be a reason not to. Sent from a mobile transmitter.
Not enough head for gravity really, unless the tank is full to the brim, and then it will gradually decline. If you want to get away from the in-tank pump, fit a Facom Solid State for £35 approx...........but wire in an in-line electric shut-off valve in the fuel line just after it leaves the petock.....another £12 or so. You have to cut off the internal steel pipe that feeds the petcock, but leave a 25mm stub so you can revert to OEM if you wish. You can also do away with the silly fuel gauge sender and change the daft plastic nut for an ally or steel one; then fit a traditional Brit type petrol tap with On / Reserve.......feed the carbs via revised hose route........Remove the OEM petcock and bung up the hole.
Surprised, if drawing fuel directly from outlet at bottom of tank; is this an artifact of the Mikuni carb - are they not employed anywhere for pump-less feed? I'm thinking , given that any low fuel level has less pressure by gravity, it is carb suction that draws fuel. In your mod for fuel pump, do you suggest drawing fuel from petcock fitted to original electrical wire inlet ? Sent from a mobile transmitter.
There is plenty of info on Google about the SS fuel tank..........you need to see how it works. The supply is drawn from the bottom of the tank via a bag filter then pumped up to high level in the tank and back down to the petcock.
Cheers. I understand well how the standard original system is laid out. What I want to clarify is wether you imply a mod where a British type fuel tap is fitted to the bottom of the tank where originally, the fuel guage and electrical wires enter. I'll google to see what mods I come up with. Sent from a mobile transmitter.
Yes, that's exactly what I mean.......You can buy ally or steel nuts to replace the plastic one (which breaks easily)........you will find that one of the forum members actually sells ally ones..........but you will also need a blanking plug which fits inside the nut, which you can then drill and tap to suit a British type fuel tap.......make sure it's a large bore tap though. It will be easier to operate the British tap when it is mounted on the left side of the tank because there are no belt covers in the way.
Thanks for the detailed information - that is useful, even only to consider. I am thinking of making an alteration. My original pump has now fallen apart at the terminals, and my fix only lasted a few weeks. Some research on google got me interested in a vacuum fuel pump, for example MIKUNI DF44-18 Single Outlet 20 Litres per Hour. Its discussed in this post here: ducatipaso.org • View topic - Fuel Pump .. as well as few other places, and with good reviews.
I wouldn't get too confused by the detail contained in that forum topic........... All you need is a pump that delivers fuel at about 3.5psi and a return flow to the tank.........you don't need a pressure regulator if you have the return flow.........that is basically what you have at the moment. The OEM system effectively is based on how a gravity system works........ie, it just keeps the carb float bowls full as the engine is running, but because of the design of the tank and carb location, the gravity / head is insufficient to maintain that flow once the tank is about a 1/3rd empty; so a pump does it instead. The Facet pump that I suggested is this one...........Facet Posi-Flow Electric Fuel Pump 1.5-4.00psi 60104 - special offer with straight unions The place to mount it would be on the right or left side of the bike where the fairing lower fixing tube is bolted to the frame........it would then sit between the fairing and the frame. As yet I have only researched all this and collected a few components; because I'll be damned if I'm going to wrestle with the tank until the OEM pump packs up.....and then I'm doing it just once. However I know of three DD racers that are successfully using a similar set-up with the same pump.
Agreed about no need to use a pressure regulator if using a return flow. Good idea about the siting of a pump. The reason I gave that link above is because they speak of a Mikuni vacuum pump - no need for electrics - as fitted to Ducati Monsters. I am tempted to go for that set up. The pump diaphragm draws vacuum pulse from one carb inlet stub.
I'll give it a go then! (along with your suggestions as per stopcock and fuel line tank); its OK it'll easily swap over to electric.
I have seen somewhere an electrically operated petcock (with manual over-ride) but I can't find the damn thing now........ .........however you could always leave the existing petcock on and fit an electric cut-off valve for about £12. If you opt for removing the fuel level sender unit (which always seem to pack up within three days of getting it working again), the aluminium nut has a flange which retains the fuel level sensor flange with an O-ring against the tank. What you need to replace the sensor is an aluminium plug the same size as the base of the sensor so it has the flange for the o-ring......the plug needs to be about 12mm deep and then you drill and thread it to take the Brit type petcock.......but the petcock needs to be about 6mm to 8mm bore. You should find that either @final_edition or @Exige have the nuts..........the former could make the plug IIRC.
Your info the plug for the fuel level sensor makes complete sense. I shall be fitting a vacuum fuel pump (ordered) this week. I see by carful examination to access to a petcock - left and right side, that the left side is a must really, though a lever type petcock the r/s might just be accessible.... depending on the particular model, if you're lucky. In any case I suspect obtaining a swap over with accessible control mechanism, and with the matching thread would be difficult...? I must decide on the petcock. An electric or vacuum shut off valve seems easiest to fit and operate, but an accessible petcock is nice. Robust too. Interestingly, my fuel sensor is already fitted with an aluminium nut (1997 model SS)! A plug for the sensor is a fair bit of detailing... I have a lathe but not set up in workshop (to be built in next few months, as I gather materials and let ground soil settle). I think I must ask @final_edition, if necessary. Seems like I've talked myself into fitting an electric or vacuum shut off valve to begin with! Many thanks for information in pondering this one! Sure helps.
Although I no longer have a lathe; a plug for the ally nut wouldn't be that hard for me to make if I had a suitable piece of ally.........just 12mm off the end of suitable / near diameter ally bar would do. I would drill a 6mm hole in the centre, run a bolt through it an tighten a nut on the other side; clamp the bolt in an electric drill (bloody tight); clamp the drill in a vice (upside down) and set it on a slowish speed...........then get to work with a file as it is running, copying the end of the fuel sensor body. Sharp internal corners can be done once the basic shape is done (the files nearly always leave a slightly rounded internal corner) with something like a carbon steel Opinel knife.........(that's what I use anyway). It's slow careful work, but once done and polished, the centre hole can be opened up and tapped to the right thread for a petcock......just protect the plug with wood blocks on the vice while tapping etc.
Without a tank near me at the moment, I reckon it should be something like this................although the flange would be thinner.
