Overflowing Fuel

[DevonS1]

Hi, I've recently re-commissioned a 3.8 complete with new needles and seats for all float bowls. The car ran fine for a few trips and was then laid up for a couple of months.
Now, as soon as the fuel pump is initiated fuel flow straight out of the overflow on the farthest forward float bowl.
All three floats are sound, floating fine and move freely. Needles and seats are correctly adjusted and newly replaced.
Any advice for the next step of diagnostics before I torch the thing for the insurance? Thanks

[cactusman]

Either the float has sunk or the float is stuck or most likely the float valve is stuck or a bit of detritus is stuck in the valve. Take the top off the housing and investigate? Modern fuels may damage the tip of the valve as they are usually rubbed tipped...mostly Delrin tipped...although in two months I'd be very surprised...
Only other reason would be excess fuel pressure...if you have a modern pump you need a pressure of no more than around 3 psi...any more will overcome the float valve....you might need to fit a pressure regulator.
The original submerged Lucas pumps have a pressure relief at the pump...seem to recall it is set to 2.5 psi.

[DevonS1]

Thanks Julian, appreciate the advice. The fuel pump is external rather than submerged, but is still a traditional low pressure SU unit. First job tomorrow will be to remove and inspect the valve as you suggest.

[abowie]

It's probably the needle stuck in the seat.

Before you pull it apart try tapping the top of the float bowl firmly. This may dislodge the needle.

[paydase]

In addition to tapping the top of the float bowl, another tip is to turn the engine sometime to allow fresh gas flooding the bowls and wait before firing it. I have noticed that it helps.
I think that after a (hot) run and non use of the car for more than a couple of weeks (in my case), heat soaking the engine and time passing may lead to gas evaporation, gum formation and needle sticking.
Letting fresh gas come in the bowl probably helps dissolving that gum and releasing the needle.

[phoenix]

Change metal floats for new plastic ones as the brass ones tend to leak.

[bitsobrits]

Hmm....in the last 50 years or so, I've owned 60 some automobiles and motorcycles that used carburetors. I currently have 6 older cars with 16 carbs between them. I've always checked the metal floats for fuel ingress as everything I read said to do so. And yet I've never experienced a defective/leaky float.

So I think "brass ones tend to leak" might be restated as "It is possible for fabricated brass floats to leak, but likely due to poor workmanship, not age, and any leaking ones were discovered and replaced ages ago when the cars were new. So check the floats, and if good, don't worry about them."

[DevonS1]

Thank you for all the advice.

Sadly this issue appears to be the straw that has finally broken this camel's back. After years of lavishing my Series I with parts, upgrades, blood, sweat and tears I have reached the sobering conclusion that I'm going to scrap the thing as I simply cannot get it to work.

It's a sad ending as I inherited the car from my late brother after 15 years laid up in a garage and vowed to recommission it back to the road in memory of him. Alas it has defeated me. I'm sure I'm not the first and won't be the last.

Good luck to everyone in the community and thank you for the advice and information over the years.

[Gfhug]

Ed, please don't do it!!
Why not say where you are? Maybe one of the knowledgeable of the forum lives close enough to drop by and give you a guiding hand.
Or are you a member of either the Jaguar Enthusiasts Club or Jaguar Drivers Club?
They will have local people who know and understand these engines.
Just make sure it is a genuinely knowledgeable person.
If you're not a member of one of those clubs just try giving them both a call and I'm sure they'll do their best to point you to a local person. Especially if it'll stop you going this next step.

Geoff

[DWW]

Not sure if this is relevant but could it be that on this carb the float needle is installed the wrong way round thus not doing its job, just a thought.

[nichmoss]

Hi Ed

I think we've all reached points in projects, cars or otherwise, where we despair of ever finishing. Spending a while away from it might help but the best would be to get some help as that can encourage you. The carbs are not the most complex parts to work on so, there is always hope.

I'm in Somerset, close to Ilminster if you are on this side of Devon. I've owned mine for 25 years and it can take some time to get these cars to just needing regular servicing and so you are not always working on the last issue that has made itself known. That does make for a very frustrating life.

I will have a spare float, needle valve etc for your carb - all taken from my car when I rebuilt the carbs some years ago. I could send one carbs worth to you if you decide to get back into it. We can meet if you're a good distance away and I'll help.

Best wishes, Chris