Air lock in new fuel system, or is it

[paulwaite]

As in a previous thread, this is the new Rally re-build with new SIP fast flow tap and new 24 inch long  thick rubber fuel pipe (6mm int dia). But on a couple of occasions fuel has stopped flowing and I've ground to a halt, which doesn't look cool as you are stood at the road side looking a dork and pretending that you are waiting for someone.  It will kick start and tickover, but not enough fuel to rev. But after a couple of minutes, with engine off, the carb must fill up and I'm off again. Sometimes for a couple of miles, sometimes longer.

FYI, fuel tank can be near reserve or full up and all filters on carb are clean.

Going onto the fuel line, its thick enough not to kink, but at 24 inch, it did look too long as I coiled it into the frame. But would this length of pipe cause an air lock and therefore, should I cut a length of the fuel pipe off. By the way, the 24 inch length came from a Vespa recommendation site.

Many Thanks

Paul

[vespasco]

My thoughts were that you have a bgm tap that has no breather pipe but we can rule that out.

Fuel pipe length. Make it as short and straight as possible. Like so short you have to disconnect it at the carb to lift the tank out. Mine is 540mm long on my rally. Traditionally, 2' / 610mm was always used.

Then my next thought was you simply have a blocked main jet, or main jet circuit. It idles, so fuel is getting through but not enough to supply the main cicuit, as in, when you rev it.

Check the breather hole in the cap too, or try it without the cap.

Ive experimented with fuel flow, taps, float bowl tops etc.
I found i got an air lock with the bgm tap if i interupted fuel supply from the tank and the only way i could get rid of it was by raising the carb inlet higher than the taps' outlet (by tilting scooter to the left for 10 seconds)....the bubble/air lock would flow upwards and out of the breather pipe and out of the tank cap hole.

Could it also be that your float is stuck closed/ partially closed, not allowing enough fuel through?

Give the entire fuel supply a good blast out, including the tap.
There have been a few issues with the sip tap rubber gasket. Is it possible this has torn/worn and is partially blocking the supply? Check the breather pipe has not become dislodged too.

If its a stock motor and after cleaning the fuel tap, jets and carb etc you still have the same issue, try the stock tap back on. It supplies more than enough fuel for a stock 200 and even mildly tuned 200s too.

Fyi, a stock tap and stock 24mm float bowl top with needle and float fitted, flowed 11.5litres per hour.
Sip fast flow and cosa top flowed 12.8litres/hr
Without the needle/float fitted, both tops flowed the same...13.8l/hr
And with just the banjo fitted, with the fuel pipe hanging straight down, flow rate increased to 19l/hr for the sip tap, with just 1litre of fuel in the tank.

When i had an air bubble (with the bgm) the flow rate slowed right down to 6.9l/hr. (I spent a day measuring all this). 6.9l/hr is enough to start, cruise around town, etc but give it some WOT and instant fuel starvation, over heating/pinking.

Has anyone ever used more than a tank full (8l) of fuel in an hour or less, on a well set up stock vespa while cruising at high rpm??? NO is the answer. (Unless you had a fuel leak somewhere)!

I only used, roughly, 5-6litres an hour on a stock 200, going pretty much constant WOT on motorways, (depending on exact conditions - hills/wind direction etc)


All that said, i still wouldnt rule out anything else although the entire fuel supply to the venturi would be the first thing to check.

[paulwaite]

Thanks for replies. On Saturday, chopped off 60mm from fuel pipe and checked out carb and jets, which were all clean. And today, I've come to work on it and so far its running OK. I suppose the test will come when it switches over to reserve, or if I run the carb dry and see what happens then. In fact, might do the latter within the safety of my drive so that I don't have to push it home.

As for other comment, which has disappeared from this thread, if the fuel side doesn't solve it, then I will look at the ignition system, but thanks for your comment. But its a re-wired stator, with new pickup and new Ducati CDI.

But what made me think fuel pipe is from when I re-built it. For instance, when I was ready to give it the first fire up, it didn't. Checked spark plug which was dry and had plenty of spark. Took fuel pipe off at carb and no petrol. So after taking ages to get the tank in place, or the fuel lever, I took the tank out, suspecting the new SIP tap. But once the tank was out, the fuel poured out of the rubber fuel pipe. Just saying all this in case anyone else has the same issue

And note Vespasco, that I've now fitted the ball end levers. One thing that I learn't from the pointed levers was arthritis in my clutch hand

[vespasco]

That looks better
And im sure they are easier and safer to use
If you wanted to go further with it looking 'just right' then dig through your boxes of spares and try and find the correct light switch. Its the same but different. Sorry, just practicing some Hindlish. I mean, its similar to what you have but with no kill button. Thats a lovely rally btw

I bought some side panel rubbers for mine recently, marked for a Rally but are actually the smaller ones for Super etc.... where did you get your Rally panel rubbers paul? Ive only seen the grey ones.

Anybody need some new black side panel rubbers?
Or swap for the larger Rally ones!? (black)

[henri]

good spot on the switch , thats a spanish super an other smallie one , vesp can ya not use vbb rubbers shortened for the rally ,buy em in one length/not pre cut to size an cut yaself.or are they a different profile . an are ya sure a quick detour to lucknows/SIL factory isnt do-able .
an those ball ends look better ,bet ya finding clutch control n take-offs a load easier now , i love the look of my ball,less ends (levers that is)but every year about now (cold/achy season) do consider going ball end .just for winter . H

[paulwaite]

Got the side panel rubbers from Beedspeed and from memory, they were over long and I cut them to suit. Ball end levers are far easier on the hand when it comes to the clutch bit. Must say, I'm getting to like Vespas, engine smooth and responsive, clutch and gear change like silk. And overall, the scooter is far lighter than my Lambrettas.

In the meantime, still not solved the fuel cutting out, it did it on the way home last night. But 30 seconds later it fired up and got me home. This morning did the same trip but I first of all loosened the fuel cap to eliminate any potential vacuum from a potential blocked vent hole, but the scooter blobbed on me twice within the first mile. But again, 30 seconds later, off I went for an interrupted 3 more miles to work.

Probably take out the fuel tank this weekend and check that the fuel pipe is not coiled awkwardly and make good. And check the internal of the fuel tap to make sure the rubber hasn't slipped. Plus strip a GP engine that I seized last week and get a series 2 fired up to sell. Well, probably not all in one weekend.

[vespasco]

The Rally rubbers are a lot thicker. The rubbers i have are for super,sprint etc. which are thinner, different profile.
Ill check beedies out.
A tip on rubbers, when ypunfit them, push them on a such a way ypu make the rubber as short as possible, opposite to stretching them, then cut them. They shrink.

Ah! Lucknow! Ive been there. Briefly, its not that pretty! Maybe H. Maybe
I could always start a little side line, sending goods from india!

Are you sure you've thoroughly blown out the jets and the rest of the fuel supply? Its quite common for people to say theyve blown out the carb and jets, they go through all kinds of other things trying to find out whats wrong, then they clean the jets properly and check them for debris etc and then suddenly, its all ok. Doh! (Have i done that? Yes)!

Do try one thing.....turn on the fuel, place a rag around the top of the float bowl (the round cover with single bolt) and slacken off the top, so fuel flows out. Its just possible it may bleed the system and get rid of any air trap. If there is a delay before fuel flows/no fuel you may just have found yoir problem
If no delay at leqst it proves the tank and tap and pipe are ok.