Fuel pouring out of Twin SUs on MkIV Spitfire

[David Taylor]

Hi there, my Spitfire MKIV is running fine but there is fuel pouring out of the top of the twin SUs. Given that I've replaced both the pipes and the clips that retain them, can I assume that the gaskets have both gone on the top of the SUs and just need replacing?

Thanks in advance

David

[Pete Lewis]

as you have been twiddling its a good chance you have bred some rubber slivers  made by pushing hose over metal tubes 

these float about and jam the back of the float needle valves 

the fuel does not in normal running get to the top of the float chamber and its gasket face that is only done with splash and slosh 

so something is fouling the valves and the chambers are overfilling 

pete

[Clive]

Nope, there are needle valves and floats inside. 

Either they need replacing, or you have recently? fitted a new fuel pump that is giving too much fuel pressure and overcoming the valves

[David Taylor]

10 minutes ago, clive said:

Nope, there are needle valves and floats inside. 

Either they need replacing, or you have recently? fitted a new fuel pump that is giving too much fuel pressure and overcoming the valves

I did actually fit a new fuel pump last year Clive. So what do you advise I do? 

[Pete Lewis]

if you have the old one see if you can swap the main spring over

or add a couple of card gaskets to space the pump away from the block 

but  was it ok  before you changed the needles or were they changed due to a problem youve not mentioned  ???

rubber slivers are crafty but cheap to fix  

Pete

[David Taylor]

15 minutes ago, Pete Lewis said:

if you have the old one see if you can swap the main spring over

or add a couple of card gaskets to space the pump away from the block 

but  was it ok  before you changed the needles or were they changed due to a problem youve not mentioned  ???

rubber slivers are crafty but cheap to fix  

Pete

I noticed the new pump was quite different to the old ones (got it from Rimmers). TBH nothing on the carbs has been touched since I bought the car in 1988. They've always just worked fine. Sounds like I may need to overall the carbs/look at putting in some spacers behind the fuel pump.

This may be a job for my very lovely local garage!

[Pete Lewis]

but when did the flooding start ????  before the float needle change or after it ????

pete

[Clive]

14 hours ago, David Taylor said:

I noticed the new pump was quite different to the old ones (got it from Rimmers). TBH nothing on the carbs has been touched since I bought the car in 1988. They've always just worked fine. Sounds like I may need to overall the carbs/look at putting in some spacers behind the fuel pump.

This may be a job for my very lovely local garage!

Sadly most garages will not "understand" that a new fuel pump doesn't work, so fit another new one with the same result. They simply don't get a new part may not actually be any good. And won't do the necessary legwork (or google searches) to find the real cause and solutions.

Much of this sort info is restricted to either very specialist garages or more usually enthusiasts. Apart from a stack of gaskets (easy enough to do at home) the other alternative though less tidy is a fuel pressure regulator. 

[dougbgt6]

David,

Another vote for slivers! Before you start messing with the pump, take the reservoirs off the carbs, remove the valves and clean them. Flush through some fuel and replace. This can be done without taking the carbs off the manifold. I've had to do it twice in quick succession, on one occasion. The gaskets can be reused if not badly damaged. There are 5 screws holding each reservoir in place, 2 at the front 3 at the back. A friend once removed the 4 in the corners, thought the thing stuck and levered with a screw driver! Oh dear.

Doug

[Pete Lewis]

doug  this is SU only 3 screws      

agree the fact that there has been some work in the fuel hose zones makes them little sods a prime contender 

always do the simple first  before you dive into redesigning the fuel system 

Pete

[Fraser64]

Can these rubber slivers affect the running of the engine?

After I replaced the clutch on my 1500 and refitted the carbs petrol leaked from the fuel bowl on the first run. I took this as something sticking and gave the bowl a tap which stopped the leak but since then the engine runs incredibly 'lumpy' as if its struggling for fuel.

[Pete Lewis]

they certainly can if they stay put and partilly block the float needle so running becomes erratic due to being unable to 

maintain a fuel level in the float chamber 

Pete

[cliff.b]

I had exactly this problem last year when I first got my Spitfire. I had replaced bad fuel lines and the car had been standing for a year, so it could well be the dreaded rubber slivers or sticking for some other reason.

Took top off float chambers at side of road, removed floats, cleaned float pivots, valves & valve seats with petrol, reassembled and tested by blowing gently into fuel inlet pipe while moving float. When float down, I couldn't blow through so reasoned it was now working which proved to be the case. I have covered 4000 miles since then and it has been ok ever since 🤞