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Converting a petrol tap to fast flow

Technical help for Series one, two and three Lambrettas. Models include the Li, Li Special, TV, SX, GP, Serveta and API/SIL models

Converting a petrol tap to fast flow

Postby Storkfoot » Thu Jul 07, 2022 8:38 pm

Is it a case of drilling out all three holes and scooping out the transfer very carefully with a dremel?

Image
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Re: Converting a petrol tap to fast flow

Postby Warkton Tornado No.1 » Thu Jul 07, 2022 10:36 pm

Prior to fast flow taps being available off the shelf, the conversion was the only option, although there was some very good 're-engineered' offerings in the 70's. Visibly different witch bigger bodies, but not as durable as brass or steel as they were zinc, they were made by OMG. Yes, decades ahead of 'Oh My God' & all that malarkey. I suppose they came too late to market, the boom having bust by then.

Primarily, for normal OEM type taps, the ports in the body need opening as much as you dare with drill bits. That is, all ports including outlet & inlet. So the first thing to do is procure some suitable bigger bore tube for the main position that will still enable a reserve. That way a suitable bit can be selected for a light transition fit.

This can be whatever you have to hand. Modelmakers alloy/brass/stainless tubing or even those broken bits of telescopic radio antenna - you didn't discard them, did you? :lol: They are ideal being so thin walled. Anyway, this is the opportunity to 'tune' the required amount of reserve :idea:

Finally, have a good look @ the rotating element, the 'valve' & get your head around it's function. That can be machined with something like a Dremel to increase flow but in addition, increased from nominally 90° to 180° as this will still function as an 'off' - 'main' - 'reserve' tap/valve but give the added benefit of allowing both 'main' & 'reserve' to be in function in the event of maximum flow such as racing. So, looking @ the kidney shape slot, it is opened up 90° ACW so that the bottom outlet port is still not connected.

BTW. The valve in the image has it's curvature the wrong way, but that was common enough. The modified slotting needs to be concentric.
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Re: Converting a petrol tap to fast flow

Postby Storkfoot » Fri Jul 08, 2022 7:07 am

Thanks for that. It’ll be going on a Stage 4 tuned 200, nothing fancy so I think I won’t need to open it up to 180. I am pretty sure I must have an old fast flow tap to take apart to check the internal measurements.

The brass tube covering the filter. I’ll need to take this off as the filter inside must be shot to pieces. I wasn’t planning to change the brass tube as I’d be quite happy with a standard reserve. Although, in reality, I always switch the tap straight to reserve anyway.

Any thoughts about the rubber gasket? It looks to have done very well to survive this long but really looks like it needs replacing.
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Re: Converting a petrol tap to fast flow

Postby coaster » Fri Jul 08, 2022 7:52 am

Storkfoot wrote:.....Any thoughts about the rubber gasket? It looks to have done very well to survive this long but really looks like it needs replacing.


If its a few years old its likely that it wont like ethanol very much so could cause grief (blockage) in the future :?
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Re: Converting a petrol tap to fast flow

Postby Storkfoot » Fri Jul 08, 2022 10:59 am

I suspect this the original gasket from 1960! You are right though. I’ll see if I have a gasket from a fast flow that is past its sell be date.

Some of you may be wondering why I am going to this bother. Well, this tap is very sturdy and well made. If you have ever had one of the plastic components break in a newer OMG tap, you’ll know why :)
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Re: Converting a petrol tap to fast flow

Postby Warkton Tornado No.1 » Fri Jul 08, 2022 3:39 pm

The latest type of filters with built in washer are quite good, but a quick scout around I made showed prices around a fiver. That's half the price of the brand new Scootopia complete tap, last time I bought one!

However, whether this will fit:

https://www.feked.com/fuel-tap-filter-r ... ilter.html

It's worth shopping around. Some MZ taps used to fit with the same thread....
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Re: Converting a petrol tap to fast flow

Postby Storkfoot » Sat Jul 09, 2022 11:30 am

Thanks for that. I had no idea you could buy such parts.

Annoyingly, I can see that the threads on this tap aren’t in the best condition now. I doubt that it had been apart before but about 2/3 circumference of one thread has come off just when I separated the two main parts. The thread isn’t deep so I am a bit hesitant to bother.

Is Loctite resistant to petrol?
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Re: Converting a petrol tap to fast flow

Postby Warkton Tornado No.1 » Sat Jul 09, 2022 11:32 pm

Dodgy threads can be cut back but the nut may then also need shortening to suit. The double threaded union nut has some work to do & the fine threads makes for a component not very durable when the things are made from zinc alloy. It's strange that such a soft material was used - costs I suppose - though some were brass or steel.
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Re: Converting a petrol tap to fast flow

Postby Storkfoot » Sun Jul 10, 2022 8:12 am

Warkton Tornado No.1 wrote:Dodgy threads can be cut back but the nut may then also need shortening to suit. The double threaded union nut has some work to do & the fine threads makes for a component not very durable when the things are made from zinc alloy. It's strange that such a soft material was used - costs I suppose - though some were brass or steel.


Your description is spot on. The internal spring is pretty fierce and there are only 3 or 4 fine threads stopping it forcing the mechanism apart and spewing petrol everywhere.
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Re: Converting a petrol tap to fast flow

Postby Warkton Tornado No.1 » Sun Jul 10, 2022 11:24 am

Although I tend to try & use as many OEM components as possible chassis wise, there are limits that we all must have little hesitation in utilising new. Tyres, for instance ;)

I rate the Scootopia tap in terms of build, quality & flow-rate but consider it essential to dismantle & reassemble prior to installation. The couple that I checked out had no issues but I took the opportunity to fit thinner walled tubing of a length to increase the reserve capacity.
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Re: Converting a petrol tap to fast flow

Postby MickYork » Sun Jul 10, 2022 3:38 pm

For about £15 (for a new fast flow tap ) is it worth all the hassle :mrgreen:
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Re: Converting a petrol tap to fast flow

Postby Norrie Bodge » Mon Jul 11, 2022 10:08 pm

Warkton Tornado No.1 wrote:Although I tend to try & use as many OEM components as possible chassis wise, there are limits that we all must have little hesitation in utilising new. Tyres, for instance ;)

I rate the Scootopia tap in terms of build, quality & flow-rate but consider it essential to dismantle & reassemble prior to installation. The couple that I checked out had no issues but I took the opportunity to fit thinner walled tubing of a length to increase the reserve capacity.


+1
& also a dab of loctite on the nut when reassembled
Had one come apart on me before :o
Use Chiggys rear exit ones now, they flow faster
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