I,m having trouble with my twin 1 1/2" SU's overflowing fuel out the breather holes under the fuel inlets. The carby's are only about 18 months old with around 6000 miles done, I thought it would be the needle and seats so I removed and checked them and cleaned them out and they seemed fine. Also the floats (plastic type non adjustable) seem to be Ok aswell. The biggest problem is it doesn't happen all the time just enough to be annoying and dangerous, petrol drips straight onto the exhaust pipe. It can happen to either carby or both at any time.
Could it be to much fuel pressure ? It's only just started happening in last few months. Nothing was changed or modified.
Any advise or help would be good.

Thanks
Phillip.

_________________
https://t.me/pump_upp

Too much fuel pressure could be the cause , what is your pump ?

EDIT , what type of float's are in the carb's ? If they are plastic take them out and have a look to see if they are half full of fuel ..

_________________

Electric ,brand unnone,I will go look .

_________________
https://t.me/pump_upp

It's probably the fuel pump over pressure. When does it happen??

3 PSI is all you really want with SUs More and it will just hold the float needle and set open and flood the carbies

Minimad

_________________
You can take the boy out of the racer.........but not the racer out of the boy!

fuel pump is facet type,
It mainly leaks after I've warmed it up turned it off and let it sit for 10mins or so .

_________________
https://t.me/pump_upp

As stated floats are plastic type but are Ok. Thanks for your thoughts anyway but I did check them.

_________________
https://t.me/pump_upp

I have exactly the same problem with my 1 1/2"s, done the needles and seats, not a float problem, not a fuel pressure problem - makes no sense whatsoever

happens at all different times - on the track at Wakefield, driving on a freezing cold night in the rain going to Shepparton - the only constant, though hard to prove was that it'd do it when shutting the throttle after a lot of revs. It'd also sometimes just do it at idle, but never on first start up, only when it was hot

it seemed exactly like the needle and seat was leaking and the bowl overflowing... but I reckon it's the heat that's the real culprit

So what I did was get a couple of float bowl lids that have a vent tube, rather than the little hole, I've put a piece of tubing on those, into a T piece and into a little container to catch the overflow - though I discovered the importance of having adequate ventilation in that overflow container. It was just a bit of hose shoved into a hole in a plastic peanut butter jar, not especially sealed on purpose, but it turned out to be a real pain when driving in a hot headwind to Adelaide in November last year. The fuel was vapourising in the bowls whenever we stopped, bubbling it all out, pressurising the catch container, and not allowing any fuel into the bowls - was a real pain to start the car. I poked a few holes in the top of the plastic lid to correct that one...

however, the proper way to keep the heat away from the carbs is with heat shields, I discovered that the bases of the bowls were getting seriously hot (too hot to touch) and boiling the fuel, especially after turning the engine off, where the flow of fuel wasn't cooling them. Discovered this while we had it on a dyno, and it wouldn't start between fiddles.

I have now made some 2mm alloy heat shields, and it's perfect

so Phill, do you have heat shields?

_________________
did I tell you that I won a trophy?

Simon ,yes I do have heat shields but only the thin steel standard type. I might try some alloy thicker ones to see what happens.
Thanks for that.
Phillip.

_________________
https://t.me/pump_upp

get it to overflow and feel around under the float bowl, you'll soon know if it's a heat problem. Mine were too hot to touch, and now with my heat shields I can hold my finger on them.

You could try some of that heatproof weave stuff too

_________________
did I tell you that I won a trophy?

Simon, I just sat it ther for about 2 mins with the key on but motor not running, just the fuel pump ticking away and no overflowing. I then ran the motor to warm it up to operating temp no overflow yet, turned it off waited about five mins turned the key on without starting again and within 1 min it was overflowing, first one then the other. The bowls were still cool to touch , the heatshield was hot to touch but didn't burn.(if I was quick)
Phillip.

_________________
https://t.me/pump_upp

Ok ,I tried a few things if anyone is interested, 1st, new needle and seats in both carbies; no good didn't fix it. 2nd, I got a Speco fuel pressure regulator ,set it to 3lbs no good. 3rd , replaced one of the carby tops ( the bit that the fuel line goes onto) that seems to be the main leaking one and set the regulator to 2 1/2 lbs so far so good , time will tell.

This is the regulator.

_________________
https://t.me/pump_upp

how is the gasket on the floats?

I don't quite know what you mean, The floats are sealed unadjustable plastic type, they seem fine and are still sealed.

_________________
https://t.me/pump_upp

Umm, you can adjust the unadjustable type. You change the thickness of the washer under the needle and seat.

I think the problem is too much fuel pressure and possibly a slightly high float level.
How much fuel pressure does it run when running? (to test this you need a gauge fitted to a T-piece)

Theroetically (spelling) the pressure gauge is at 2 1/2 psi ,it's adjustable from 1 to 6 psi, but I havn't put a gauge on it. I get what you say about the washers under the seat but how do you tell what height to set it at ?

_________________
https://t.me/pump_upp