Petrol taps

[a101960]

I have been in the habit of using only one petrol tap  relegating the second tap for reserve use, so my question is this: In real terms do you get a better fuel flow by opening both taps. By that I mean, will using one tap only cause fuel starvation? My second question is this. Would the fitting of a float chamber extension to a 389 Monobloc help with fuel mixture by virtue of the increased fuel capacity of the float chamber, and also is there such a thing as high flow rate taps? The taps that I have currently fitted are the flat lever type which are beginning to show their age by being quite stiff to operate. This is the type that I have fitted at the moment. Perhaps I should also add that on the outlet side of the tap I have fitted right angled elbowed pipe connectors which allow the fuel line to be pushed on and then held in place with jubilee clips.

[A10Boy]

Have you had fuel starvation ? I would think if you had it was due to a partially blocked fuel filter or air vent not by the restriction in the tap.

Test it by pulling the pipe off the carb and seeing how fast it flows - it should pour out. If it does, can you imagine the engine actually using more than that? I might be wrong but I think the float extension was more to combat frothing than poor supply.

[Beezageezauk]

I have only ever used one tap for running any of my A10's.  Even subjecting them to motorway cruising and being fully laden with pannier boxes and camping gear I've never experienced any form of fuel starvation.

Apparently the Rocket 3 owners use both taps on their bikes to overcome this but on normal running they only get about 45mpg.

I would carry on using the bike as you have been doing.  I'm sure you won't have any problems.

Beezageezauk.

[a101960]

Have you had fuel starvation ?

I think that I might be experiencing fuel starvation. About 2 weeks ago the engine suddenly started do die the symptom being just as if I was running out of fuel or had forgotten to turn the fuel tap on. Anyway with visions of having to call out the breakdown service I backed off the throttle and the engine picked up and then continued to operate 100% normally and I continued on my way with no further problems. I was doing about 55 mph at the time.

[bsa- bill]

something to think about is the position of the bike when it cuts out.
I have had my bike engine stutter and die when heading down hill due to fuel ( low) flowing to the front of the tank away from the taps.
at the bottom of the hill it started second kick and I travelled on a further three miles to the petrol pumps without any problem.
Thinking out loud, would shaped sponge remain in place to act as a baffle - no wouldn't go through the filler, next thought, empty tank and some of that foam filler directed to the middle bottom of the tank, would it stick
Then there's the ship in a bottle thing - time for bed and medication

All the best - Bill

[Beezageezauk]

Ok, I think the first thing you need to do is to check your fuel filters.  One on the fuel tap you normally use and the other inside the banjo on the top of the carb.

If these are clear my next idea might sound a bit silly but I'm sure it will work. 

You say that you had the problem at 55mph.  How many mpg would you get at that speed?  Minimum of 55mpg?  That would equate to about 1 gallon every hour.

Put the bike on the centre stand and drain the fuel from the fuel tap you normally use.  Put a measured half gallon back into the tank and drain it off again using the same tap but this time see how long it takes to drain.  I reckon that if it takes less than a half hour to drain then there will be more than enough flow and the fuel tap is not the problem.  In fact you could do the same thing with the second tap and get a flow comparison between the two!!

I must admit that I've never done anything like this before and it's only an idea.  It certainly can't do any harm!!

If all appears to be ok with fuel flow then I would presume that you had a problem with the carb. 

Good luck,

Beezageezauk.     

[mike667]

can also be a plugged up gas cap vacuum hole -  if you experience it at 55 have you tried unscrewing the gas cap and seeing if this cures the problem??
 (sorry if someone suggested this already!)
m

[Triton Thrasher]

There are high capacity fuel taps. They're spherical valves sold for central heating systems.  

Something like this:



Hitchcocks the Enfield people sell ones with a filter.

[beezalex]

The picture you show of the fuel tap are ones that commonly have the rubber seals swell up and block the fuel flow.  They are crap and should be replaced with better or higher quality ones.  There are taps that look identical that cost $40 ea. and others that cost $10.  You get two guesses as to which are the ones that fail.

[groily]

My similar-looking B&Q/Bricomarché gas taps have now done thousands of miles and no swelling or blockage at all. Have 6 on various things, and a stand-by stock adequate to replace all other original ones as they fail. The seals in these £5/6Euro gas ones are a nylon-type substance. The bigger (£8) versions work as very effective anti-wetsumping devices in other machines, and can easily be modified to operate an ignition cut-out. They also haven't failed despite hot oil in their entrails.
Cork is for wine bottles. But even there, many fine beverages are now sealed with screw-tops and a host of vino is kept in check with, er, plastic/composite stoppers. If I were a Portuguese cork farm proprietor, I'd start thinking about diversifying - quickly.
Brass-to-brass cone and lever taps are a bit better until they go stiff and/or gradually start to weep. They usually do both. A light lapping can help, as can a new spring, but they're still not a patch on a humble gas tap in my view.
If one doesn't care unduly for the Playgroup-Pastel Shades in which the cheapo levers come, it's easy to make levers that look more in keeping, from brass or stainless.

So I'm with T-T - if you want taps that offer good flow and don't leak, can't beat the plumbers' merchant as a source.
Promise to report back - and eat large slice of Humble Pie - if anything changes.
Must go - got to get a composite stopper out of something  . . .

[a101960]

Thank you all for your advice and suggestions. Regarding the gas taps what thread size are they? would they screw directly into an A10 steel tank? I have to say I am pretty well convinced the rubber swelling proposition is a more than plausible source of trouble. I shall get a set of gas taps and see how they measure up.

[Triton Thrasher]

The picture you show of the fuel tap are ones that commonly have the rubber seals swell up and block the fuel flow.  They are crap and should be replaced with better or higher quality ones.  There are taps that look identical that cost $40 ea. and others that cost $10.  You get two guesses as to which are the ones that fail.

If you're talking about the tap A10 shows
, I've heard that too.

If you mean the nylon ones

I think they're pretty reliable and available in BSP thread.

[A10Boy]

I've had two brilliant ideas, 1, why not pull the pipe off the carb and see how fast the fuels comes out, 2 make sure the vent isn't blocked.

Genius....

[Triton Thrasher]

I've had two brilliant ideas, 1, why not pull the pipe off the carb and see how fast the fuels comes out, 2 make sure the vent isn't blocked.

Genius....

Are you losing patience with an owner determined to spend his way to biking happiness?

[a101960]

Are you losing patience with an owner determined to spend his way to biking happiness?

Now there is an interesting concept. With an old bike spending ones way to biking happiness is a way of life I would venture to suggest. The tank cap vent is not blocked on account of it being a Gold Star steel tank. The caps of which are well known for their incontinence, and secondly there is a breather on the tank itself. While I have not yet had the opportunity to remove the fuel pipe to observe the fuel flow, I will do it to see if this is indeed a problem area. What I am not sure about though is this. Is there a direct coloration between static flow and the demand from a running engine?

[A10Boy]

Are you losing patience with an owner determined to spend his way to biking happiness?

No not at all, we [I mean the responsible ones] are in a way like museum curators, we are taking the trouble to own and restore our lovely BSA's usually at great expense. we get HUGE enjoyment and its gets in your blood. Anyone involved should be helped as much as possible when needed, and I know I need help sometimes.

This forum is a very useful and enjoyable place to be.

[Triton Thrasher]

What I am not sure about though is this. Is there a direct coloration between static flow and the demand from a running engine?

I think so, but you should include the float valve area as a possible restrictive area too.

The old cork taps are marginal in flow capacity, on a big twin pulling hard and I do not care what counter arguments theorists come up with.  The lever taps seem to be prone to blockage by displaced sealing material.

The smallest cross sectional area in the fuel feed must be much bigger than the main jet, perhaps because fuel is sucked throught the jet while it only runs through the feed.  If you're unlucky and going fast, a single instance of fuel starvation can make your engine seize.

At 6000rpm, full throttle in 2nd gear, the miles per gallon would shock you.

[muskrat]

At 6000rpm, full throttle in 2nd gear, the miles per gallon would shock you.
Yep. On my A7SS racer running on methanol with 2 X 32mm concentrics it got about 12 MPG. But 2 of those lever taps fed it fine.
Cheers

[A10Boy]

A101960, If you are a normal guy running a normal bike at normal speeds you wont have any problem with one lever tap - provided that filters and vents are ok.

[Triton Thrasher]

A101960, If you are a normal guy running a normal bike at normal speeds you wont have any problem with one lever tap - provided that filters and vents are ok.

Yeah, until you have to leave town quick, overrevving mercilessly, pursued by zombies.

Actually, I think most people agree that the lever ones are good, except when faulty.