Calling all carb conversions

[adam quantrill]

Sorry - this is a bit off-topic.

A friend of mine has just converted his RV8 P6 3500S from twin SU's to a big old Holley.

It runs OK but after leaving it overnight he thought there was a fuel leak. However he couldn't find where it was coming from. I did though - it was leaking out of the sump - siphoning in through the carb, down via a cylinder!

I've had him move the fuel line down to below the level of the carb but it's still happening - any ideas as to how to stop it? The fuel pump (electric) is about 2 foot of line away from the carb, and about the same height in the engine bay.

[NTEL]

Not really familiar with holly carbs but first thing that springs to mind would be a worn needle valve and float levels set too high. Is it dribbling out of the accelerator pump jets? Have you checked that the cam that operates the accelerator pump is in the correct position at idle?

I would have thought the fuel pump should be fitted next to and below the level of the fuel tank?

Edited by NTEL on Thursday 6th May 07:28

[ferlin]

a non return valve should fix that! available in different sizes to suit fuel pipe diameter but heres one:
http://www.thornycroftparts.co.uk/product207754_42...

[Barkychoc]

I am no expert on carbs but I've looked through them in the past - I seem to remember that some of them with certain manifolds need an adaptor plate as otherwise the carb doesn't sit level as the RV8 is fitted slanted back I think.
Just regard this as a wild guess.

Chris

[rev-erend]

ferlin said:

a non return valve should fix that! available in different sizes to suit fuel pipe diameter but heres one:
http://www.thornycroftparts.co.uk/product207754_42...

What he said..

[adam quantrill]

I'm not sure how a non-return valve will stop the siphoning, after all the flow is in the same direction as the normal flow of fuel. However this is assuming that it's coming along the fuel line - maybe it isn't, maybe it's the return line? There's a thought. A non-return valve would help here. [edit - Actually it isn't the return line - the "leak" stopped when he plugged the main fuel line].

There are no needles in this carb, it's a big Holley.

Yes, angle might be a factor, but if you got it level, what if you park on a slope - would you get the same problem? Which reminds me that he must test this parked on a downhill slope....

Edited by adam quantrill on Thursday 6th May 12:24