HELP! I hate carbs - weird SU leakage problem

Major Ledfoot · 2017-10-02T06:54:35+00:00

It's a long time since I played with SUs (my 140s have webers or strombergs) but that looks like an overflow hole. If it's overflowing, by guess your float...

jrhendo

If the float is metal, and they usually are, shake it. If it's leaked, you'll hear fuel sloshing inside. If in doubt, take it with you to the MG centre.

tbro

Put the old pump back on?????
That will tell you straight away IF you have run this old pump.

egads (she/her)

Old pump it down to Yass if that works enough and we can fit the reg I have on the shelf along with refitting the new pump.

Major Ledfoot

tbro;120228 wrotePut the old pump back on?????
That will tell you straight away IF you have run this old pump.

Old pump delivers ZERO fuel. It's totally cactus. It gave up the ghost completely after struggling to get to the Bilpin Pie Day.

egads;120244 wroteOld pump it down to Yass if that works enough and we can fit the reg I have on the shelf along with refitting the new pump.

It doesn't seem to be the pump - it seems to be an extremely worn needle and seat.

Have just replaced the float, plus the needle and seat in the front SU, and IT doesn't leak any more.

But.... BUT... now the back one is leaking. Matriarchal Fornicator!

Did I say this before? Oh. Well, I'll say it again : I HATE CARBS.

Major Ledfoot

PS:

This is the replacement fuel pump, it's a FPP4400 pump, I don''t know if it's adjustable for pressure, one would think the relief valve ought to limit the thing to a handful of PSI.

tbro

3.8 lbs MAX, ran a cooper s with 2lb pressure and it was wunderbar.
You do know that if your stuck that you can lap the needle and seat in with brasso or metal polish but be gentle.
If you have the black tipped ones your stuffed.

Major Ledfoot

tbro;120264 wroteYou do know that if your stuck that you can lap the needle and seat in with brasso or metal polish but be gentle.

No, I didn't know that... but do now! Many thanks!

I'll give it a shot tonight, and if it's still cactus, it means a trip to Burwood via Banksia tomorrow.

1971_144GL

If you can find them I recommend the substitute system sold by ipd. No more needle, seat or float. I have found them to be great. Not sure where to buy them at short notice however.

tbro

Isn't there a joint at Riverstone that does minis

Mulgrave, https://minikingdomonline.com.au/contact-us/

Major Ledfoot

1971_144GL;120269 wroteIf you can find them I recommend the substitute system sold by ipd.

Thanks, but I must have something within 20 hours, or it's no Nats. Regardless, I plan to drop kick these antiques into high orbit upon return from the Nats, and go MS and EFI. Did I mention that I hate carbs? :)

tbro;120270 wroteIsn't there a joint at Riverstone that does minis

Ah, yes; so there is. But unfortunately the Hawksbury isn't on the way to Banksia, which is where the group buy sway bars must be collected from, tomorrow... and Burwood is. Sorta.

egads (she/her)

This where you are heading? http://www.carburettorservice.com.au
Got an SU kit off them many moons ago.

Vee_Que

The su carbs are amazing, very simple adjustment. And they provide as much fuel as the engine asks.

Major Ledfoot

Moonlight update:

After a late-night dash from mountain hideaway to the north west, Torben has lent me the float covers, needles and seats from his immaculate 1800S, which sadly is having some overdrive issues at present.

I'll fit them in the morning which may save me a trip to Burwood (to the place @egads (she/her) mentioned) before the Nats. But it means I'll have to go there sometime after.

Vee_Que;120285 wroteThe su carbs are amazing, very simple adjustment. And they provide as much fuel as the engine asks.

Uhhhh, well, my trouble is they're providing rather a lot more fuel that the engine isn't asking for....

Vee_Que

When in good condition they don't...

Max

I had an old BM Bike. Left carby did as you describe. Leaked onto my foot.
The nylon float did indeed gain weight over years and ie: not seal the seat.
As suggested above, brass floats can get a bit of fuel in 'em over the years.
Also, for tunign the SU's - check the spindle on the butterfly as they wear and permit ingress of Air.

Major Ledfoot

Max - with the Volvo B20 setup, they're not a cross flow head, so leaking carbs put the fuel straight on the exhaust manifold. It's a recipe for disaster if left like that.

Today's adventures:

Okay, so... fitted Torben top cover and flat assembly - it STILL leaked!

Took up Torben's suggestion to add an inline aftermarket fuel filter to maybe drop the pressure a wee bit. Result: same.

Then I had a brain flash.

(Server isn't letting me upload pics today, so I'll use the maker's pic)

This is the replacement fuel pump.

See the big nut on the top?

Well, apparently, it's a pressure adjustment...

I got a socket, thinking 'what harm can it do to turn this thing and see what happens, that car is already cactus if it's leaking fuel so what have I got to lose?' ... and lo and behold, no more leaks!

Lessons learned from this exercise?

1. Torben is a legend, and the Oz Volvo brains trust is awesome.

2. PTZ FPP4400 replacement fuel pumps for B18 / B20 / B30 engines have an adjustable regulator, by means of a nut on top of the pump, unlike the stock pump.

3. Worn parts - i.e. needle and seats - in the float bowls of HS6 carbs will cause fuel to spew out of the breather.

4. Floats are prone to failure, and the float level is ideally set to one-eighth of an inch.

5. Finding SU parts at your local Repco, etc, isn't usually possible; they have to order them in.

6. I have found more reasons to hate carbs.

All I have to do now is collect sway bars from Woop-Woop and get to Yass! Easy!

familyman

Isn't it... kind of odd that a carb can't contain the max pressure it can deliver, without leaking?

jrhendo

Pretty standard stuff with SUs I'm afraid. I've had the same with webers. Same sort of system: a float holds a needle valve closed. Too much pressure overcomes the force the float can exert on the needle valve.

Or, of course, the needle valve is worn - as maybe the case with bgpetc above - and forces fuel past anyway.

Having said that, I LOVE carbs, especially SUs - there's a beautiful simplicity about them.

Vee_Que

I only used su's for a short while she the only leak I had was hoses. Webers. I'm becoming an expert!

Major Ledfoot

Webers actually created my hatred and contempt for carbs. These SUs have reinforced that POV.

Strombergs have that stupid plastic plug which likes to break / leak and pour raw fuel over the B20's exhaust, so they're not in my good books either.

Nope; not persisting with these PITA antiques. Larry's getting either MS, or a B230FT.

But to add even more joy, seems like there's a tank problem - I m getting random fuel surge now, even when the tank is full. Which made yesterday's trip... character building.

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