My fuel tap on my 1994 Daytona refused to turn off - petrol poured out regardless of tap position. The tap has three positions - on, off and prime. On and off are supposed to be controlled by a vacuum operated diaphragm that pulls a valve open when the engine is running. Prime holds the valve open via a cam in the tap so is the only position that should let fuel out of the tap with the engine off.
I managed to break the plastic knob when I was removing it. I had the 1991 Trophy one so could use it for the time being. The plastic knob engages with the aluminium fuel selector casting through a flat cast into its circular recess. This flat was the part that broke on the 1994 plastic knob. The 1991 one has the flat 90 degrees from the 1994 version, meaning the visible pointer on the outside of the plastic knob does not point down for reserve, back for on and up for prime. Instead, it points forward for reserve, down for on and back for prime.
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| Rebuild kit from Sprint Manufacturing |
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| Extracting tap from tank |
The body of the tap is held on to the tank with two long M6 screws that pass through the selector housing and fuel filter housing to engage with captive nuts.
Fuel systems don't like grit so it's important to have somewhere clean to do the job. I have an old set of stainless steel camping pans for jobs like this.
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| Vent hole (indicated byscrewdriver tip) to allow diaphragm to pull valve out when the engine is running. |
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| Removing diaphragm housing, diaphragm valve closing spring visible in the centre of the picture |
The diaphragm is housed in a chamber at the rear of the tap. The cover is retained by four M4 Philips screws. It is likely to pop off under the pressure of the larger of the two springs in the tap body - get ready to catch it when it goes.
There is a vent hole at the bottom of the diaphragm chamber, behind the fuel selector mechanism. I think my problem was probably dirt ingress through this vent hole interferring with seating of the diaphragm valve.
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| Aluminium plunger with o-ring under diaphragm |
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| Diaphragm valve seat location |
The diaphragm is actually two diaphragm components that attach to an aluminium plunger with an O-ring at one end. The two diaphragms fit either side of a plastic collar. There is a hole in the diaphragm that locates over the vent hole - a raised bump in the plastic collar helps to make sure it is round the right way on reassembly.
After pulling the diaphragm housing apart, it was very clear that dirt certainly could have been responsible for the problem. So a thorough clean was required. There were traces of corrosion in evidence too so it carefully (there's a word) rubbed the sealing surfaces back with wet and dry on a foam sanding block.
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| Cleaned and ready for reassembly |
I used silicon grease sparingly on the sealing surfaces, eased the new diaphragm into its plastic collar then, checking that the vent holes were aligned, installed the new spring and tightened down the M4 screws.
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| New (left) and old (right) diaphragms |
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| Installing new diaphragm, making sure the vent hole is aligned to the matching hole in the new diaphragm |
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| With retaining screws released, the fuel selector is pushed up by the small screw on the prime operating rod and can be lifted out. |
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| Fuel selector pushed into place and retained by screws. The fuel selector positions are cast into tap body - these make sense with the 1991 tap but don't match up for the 1994 tap |
8 comments:
Nicely done!
Hello from Australia,
The fuel tap on my Daytona broke in a similar way, and it was barely a one year old replacement part, I'm going to buy another replacement and fill in the voids on the rear side of the tap with a plastic epoxy or abs plastic filler to strengthen up the inner part from breaking again when too much torque is applied and the plastic center flexes.
Also, do you know if you can buy that plastic fuel pickup anywhere? I was told by a local dealership that you have to buy the whole fuel tap assembly at $170 AUD (£110 GBP), which seems like extortion.
I only just noticed your question - sorry for being slow.
It's a good idea to support the internal part of the plastic knob with some epoxy filler to make it more robust.
By plastic fuel pickup, I'm guessing you mean the filter that protrudes into the fuel tank when the tap is in place. The only other plastic part I can think of is the internals of the selector. Neither are available as spares though so it makes no odds which. I'd say your best bet is to take a chance on a second hand tap and a get a repair kit. I guess you'll have fixed it by now anyway.
You mentioned you got a rotary oil seal in the kit as did I, but you didn't mention replacing it. I can't work out how to get the old one out. Did you manage it, and if so how?
Hello Andrew
I decided to leave my original one in place because it looked fine. I did prod, poke and pull at it a bit to see how happy it might be to leave its housing. It was very snug. If yours really needs replacing, I'm guessing you'll have to lever it out carefully so you don't damage the ally body of the fuel tap. Pouring a kettle of boiling water over it first should help by expanding the body. That's how I get wheel bearings our of ally wheels.
good luck!
This is a really clear and useful guide. I have just replaced the fuel tap parts on my 1993 Trident 750 using the Sprint Manufacturing kit. I had to replace the rotary seal because fuel was leaking past it and through the selector. I used lots of WD40 and a pair of bent-nosed pliers and after a good deal of twisting and pulling the thing came out OK. I wanted to avoid levering it out (using a screwdriver against the body of the tap) as I had no way of knowing how strong it was and didn't want to break a piece off. Good tips LeT. Andrew C
Thanks for the great post. If my fuel tap's diaphram is shot, would it leak fuel into the airbox via the vacuum line??
I had a backfire though my carb (a very loud one) and then fuel began to lead out of the airbox.... any help would be appreciated.
It is possible but unlikely. The vacuum line connects to the front of the second carburettor, near the cylinder head. In other words, on the side of the carb opposite the air box and with the carb butterfly valve in between. Fuel would more likely run into cylinder two than back to the airbox.
I think it is more likely that you have a problem with your floats. It's probably dirt trapped on one or more of the float valve seats and so preventing the valve from closing properly. That would cause overflow and dripping from the airbox. It's also fairly common for older bikes in general.
You may also have perished intake rubbers, causing an air leak that would explain the back fire. Air leaks on the induction side can create the conditions for combustion on the wrong side of the inlet valves. Check them over whilst you have your carbs off. Hope that helps.
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