Lotus Elan

Flooding Stromberg Carb

PostPost by: david.g.chapman » Sun Sep 27, 2009 6:52 pm

This has happened to my +2 twice in the last year - the first time I did now recognise it for what it was.

The symptom was a reluctance for the engine to idle, and the engine then dies and is difficult to start. The spark plugs were dry. As I have a standard air box and trunking, I did not see any fuel leakage. The first time it happened the fault cleared when I removed the air box, so I was left in the dark.
The latest time it happened, the fault persisted with the air box off, so I could see what was going on. After much churning with the starter, the engine ran (roughly) and would pump fuel out of an air hole next to the carb inlet. Revving the engine would stop the pumping.

It then seemed pretty obvious that the carb was flooding - the needle valve was probably jammed open by dirt.

With a stubby driver, it was possible to remove the float chamber with the carb still connected to the engine. I then unscrewed the valve with a half inch open ended spanner and blew it clear, and re-assembled the valve and chamber. The engine then ran OK.

This is worth noting if you have Stromberg carbs and the engine dies like this. After half an hour you can be on your way again - if you are careful and don't drop anything!

Incidently, I have a fuel filter fitted, and I cleaned and coated the tank not so long ago - but there was still a fair amount of red sediment in the float bowl! It must have got past the filter, so I am replacing that.

I also wonder how clean our fuel is from the petrol pump ? :shock:

Dave Chapman
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PostPost by: Carlos A » Mon Sep 28, 2009 12:04 am

Check the needles? They may be the cause but... After I tried everything (including needles) I found out that the cause of flooding on my Stromberg carbs was the fuel pump (it was putting 6 psi). I replaced it and found out that the new aftermarket put too much pressure (4.5). So I got myself an electric one with 3psi and this problem is solved.
Last edited by Carlos A on Mon Sep 28, 2009 5:20 am, edited 1 time in total.
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PostPost by: Dennis 45/9760 » Mon Sep 28, 2009 2:31 am

I'll second the too much fuel pressure possibility.

I too replaced the fuel pump with a modern one . . . tried everything to get a decent idle after that with no spitting back thru carbs to no avail.

We finally put a pressure gauge on the line from pump to carbs. As I recall, about 5.5 to 6 PSI.

Got an adjustable Holley LOW PRESSURE regulator (about $30) and installed it. I think it is factory adjusted to about 2 PSI (I did not mess with it).

Solved all. Carbs are now working almost flawlessly. Just need a little tweaking yet.
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PostPost by: david.g.chapman » Mon Sep 28, 2009 11:15 am

Sorry - forgot to mention that I also have a pressure regulator set to 1.5 psi, and a mechanical aftermarket pump. However, regulators have been known to fail....

The replies are right though - fuel pressure is probably the number one cause of carb flooding - both Weber and Stromberg types. Number two, though, could be dirt in the fuel.

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PostPost by: HardTop » Thu Oct 01, 2009 5:03 pm

Although this is not the cause of the current problem
It is important to note that fuel density has changed since 1970 so float levels must set carefully
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