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SU carbs flooding


Phil Siddall
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My Spit 1500 front carb often flooded on tick-over, in spite of replacing the needle/jet assembly and the float.

Just got it started after a lengthy lay off, and now both carbs are flooding.

Is the fuel pump delivering at too high a pressure. or is the latest petrol affecting the needle seating or something? Help, please!

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a lumpy idle can induce float overflowing 

so can rubber slivers in the supply line especially if you have recently pulled and refitted any  fuel hoses 

I ran into a strange problem of flooding which require new floats as the plastic pad that operates the float needle had very small ridges worn in

wich locked the float valve , some cleaning with fine sandpaper didnt work  but new floats did 

you need a  good magnifier to see the wear ridges in the float platform 

fuel pumps especially recent aftermarket have been producing up to 6 psi when the orig is max of 2.5psi

have you changed the pump ??? recently 

Pete

 

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Not changed the pump.

I'll take the tops of the float chambers tomorrow, and investigate- i have a hunch that the floats drop too far and stick.

They didn't when I first started the car after nearly a year out of action. A new float did not seem to cure it previously.

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  • 3 weeks later...

I have had this problem, a new pump had been fitted prior to me purchasing the car (Spitfire 1500). After changing needles to Viton tipped design, now fitted new filters before and after the pump. Keeping fingers crossed.

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Just a question that I think is relevant to this topic, is the unconnected stub pipe on my front carb (see pic) a vent/overflow and if the float doesn't shut the fuel supply off, should I see it emerging here?

I ask because I had a significant leak from the float chamber upper gasket which I have resolved but assumed it would have been coming out of this pipe instead?

IMG_20210518_085032_313.jpg

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yes its just a tubed vent , as for gasket . as it takes the easy route the gasket is lower than the top cover vent so 

thats the first escape route if the gasket is poor

fuel levels   worth checking the float heights there not much you can do with SU , and gasket seapage/leakage can just be down to the splish splash of fuel squirting out the needle valve  and doesnt mean the float or heights are playing up  hence the vent is higher up above the gasket 

Pete

 

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10 minutes ago, Pete Lewis said:

yes its just a tubed vent , as for gasket . as it takes the easy route the gasket is lower than the top cover vent so 

thats the first escape route if the gasket is poor

fuel levels   worth checking the float heights there not much you can do with SU , and gasket seapage/leakage can just be down to the splish splash of fuel squirting out the needle valve  and doesnt mean the float or heights are playing up  hence the vent is higher up above the gasket 

Pete

 

Ok, thanks for the confirmation. So if I have succeeded in now making a good gasket seal, any issues with the float needle valve not closing properly should result in excess fuel exiting via this pipe?

Was thinking of adding a pipe and possibly catch container to control petrol leakage if this should happen instead of petrol going wherever.

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Hmm, all looked good so took car out for a "shake out" run and smelt petrol again. Now peeing out the overflow. 

So took float bowl cover off again at side of road, float appears ok & valve appears to seal if I  blow down inlet pipe & raise float.

It is the type pictured, with just float, hinge pin & valve insert. I assume there is nothing missing?

 

IMG_20210518_104813_025.jpg

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2 hours ago, cliff.b said:

Was thinking of adding a pipe

good idea

 

24 minutes ago, cliff.b said:

with just float, hinge pin & valve insert

with the top cover inverted there should be a 3/16" gap top of float to top cover face 

the only adjustment is to add sealing washers under the valve

any small /fine wear groove in the float platform will jam the valve ,  which seems to pitch when these get worn ( needs spy glass to see them )

Pete

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19 minutes ago, Pete Lewis said:

good idea

 

with the top cover inverted there should be a 3/16" gap top of float to top cover face 

the only adjustment is to add sealing washers under the valve

any small /fine wear groove in the float platform will jam the valve ,  which seems to pitch when these get worn ( needs spy glass to see them )

Pete

When I disassembled roadside I thought the valve felt a bit "sticky". I cleaned it and it then seemed to move more freely, drove home about 25 miles & so far so good. If it leaks again I will look at the things that you suggested.

Many thanks 👍

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|I have a avid hate of SU  and then bought a Mk2 2000 with two of the blasted things 

she flooded and defied all normal solutions till i looked closely at the plastic float platform 

didnt buy a stay up float ( these tend to have a metal valve plate )  but new float sma as fitted and instant solution 

Pete

 

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2 hours ago, Pete Lewis said:

|I have a avid hate of SU  and then bought a Mk2 2000 with two of the blasted things 

she flooded and defied all normal solutions till i looked closely at the plastic float platform 

didnt buy a stay up float ( these tend to have a metal valve plate )  but new float sma as fitted and instant solution 

Pete

 

I must admit, I'm a bit surprised that a very minor fault can result in large amounts of petrol being let loose lol

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2 hours ago, Pete Lewis said:

|I have a avid hate of SU  and then bought a Mk2 2000 with two of the blasted things 

she flooded and defied all normal solutions till i looked closely at the plastic float platform 

didnt buy a stay up float ( these tend to have a metal valve plate )  but new float sma as fitted and instant solution 

Pete

 

I must admit, I'm a bit surprised that a very minor fault can result in large amounts of petrol being let loose.

However, yesterday I helped my stepson with a temporary fix for his Mondeo spaying high pressure petrol out of a hole in the pipe to the injectors.

So much for progress lol

 

 

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On 20/05/2021 at 12:50, Badwolf said:

I love a really technical mod but, you may need a bigger boat bottle. (apologies to Jaws) If you bottle is plastic make sure that it's petrol proof.

Lol, it's only there temporarily so that I will see if any further overflow occurs while driving. In which case I will have to try and fix it.

If I can't fix it maybe I can fit s longer pipe and tee it in to the inlet side of the pump 🤔

 

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The overflow/vent pipes were originally a long plastic pipe connected with a rubber hose to the float chamber top. The idea was to vent the petrol fumes to road level. 

I think as Pete says the top of the float is slightly worn, this is causing the problem. Mine were worn but the only way I could see it was to take a photo and enlarge it on the computer!! There was a noticeable ridge.

All the best

 

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So far I haven't seen a trace of fuel in my little capture bottle so I haven't investigated any further yet. So in this case, the venting may have been due to a sticky float needle/valve but I will continue to monitor & certainly look at the floats if the problem re-occurs. 

In fact, now that I have sorted this, replaced all the rotten fuel pipes and tightened everything, for the first time since I got the car there doesn't seem to be any petrol leaking from anywhere 🤞

 

 

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