free hit
counters
Carb leak - Fuel System/Carbs - The Lotus Forums #ForTheOwners Jump to content


Carb leak


Big Vern

Recommended Posts

Hi folks,

I seem to have a leak via the top of the newly (ish) refurbed carbs. Have a look at the pic below it seems to be from the black cover. Forgive my ignorance but is it a faulty gasket, or is it overflowing slightly with fuel?

Any help would be appreciated.

Thanks

Brett 

IMG_2235.jpg

Link to comment
Share on other sites


Upgrade today to remove Google ads and support TLF.

That's the vent to atmosphere, so suspect a stuck needle valve in float chamber. Does your fuel pump stop ticking after turning on ignition? It should after a few seconds, if not fuel is flowing somewhere, likely into barrel and airbox, so be careful.

Link to comment
Share on other sites

Definitely a leak, probably needle valve stuck. Ticking should stop completely once pressurised. DO NOT crank engine till leak found. Whip off carb top and see if anything obviously wrong. trouble is, just doing that will almost certainly 'fix'it, and it may never happen again. Or it could be a bit of dirt that got through the filters. There should be a filter where fuel enters carb. These are small plastic gauze types. Check if actually there first. I did have a stuck needle valve once, and never happened again, but did leak fuel into the barrel and airbox.

Link to comment
Share on other sites

I will check, so many thanks for the reply. the only thing i would say though is that the pump has always done the same thing for years even before the carbs were refurbed. Do you think the pump could be faulty too?

Link to comment
Share on other sites

30 minutes ago, Big Vern said:

Do you think the pump could be faulty too?

That much fuel passing a stuck needle valve would be pouring out onto the floor, sounds more like a leaking pump diaphragm, which for a 36 year old pump isn't surprising. If the fuel staining on the carb top is what you were initially worried about, don't be they all do that. clean it off with acetone or cellulose paint thinners. :thumbup:

Cheers,

John W

http://jonwatkins.co.uk

Link to comment
Share on other sites

If you have fuel dripping from the carb, your float needle is stuck open. There is a piece of trash between the needle and seat that needs to be blown out. You can try an old trick by tapping on the carb housing with a hard plastic hammer to shake the object out of the needle and into the bowl. Another trick is to crimp the inlet ho to stop fuel flow and let the engine stall, tap the carb housing and then un-crimp the line. Turn ignition on and allow the float bowls to fill. The rush of fresh fuel and the needle at the bottom of the house can flush the junk out and past the needle. Otherwise you need to pull the top off of the carb and blow the needle out.

Tap lightly at the arrow.

 

1346588220_InkedLotusfloatneedle_LI.jpg.9c7525c96383852b8a5920dfd3deb11f.jpg

 

 

Edited by jcslocum

Jon - 1984 Esprit Turbo

Link to comment
Share on other sites

  • 4 weeks later...

Thought id pop out today and have a go at the above suggestions. I have however noticed that both carbs are leaking at the top in the same manner. Would that therefore mean that it is more likely to be a faulty pump? Im still going to have a look at the carbs today and try the above anyway, but was just wondering if that may be the case.

Link to comment
Share on other sites

On 12/03/2020 at 13:47, jcslocum said:

 

If you have fuel dripping from the carb, your float needle is stuck open

 

IMO its not likely to be the pump, as Jon said, it is most likely to be the float needle valves. Even if Jon's suggestion works I suggest you'd best fit a new pair of  Vitron tipped needle valves, they are around £15 each from Eurocarbs assuming they are still operating at the moment. Don't go for the cheaper brass ones, and when you remove the old ones I'd bet you'll see a very small groove worn  around the needle tips of the ones you are replacing and that will be the cause of your leak

Normally Aspirated - and lovin' it!

Link to comment
Share on other sites

5 hours ago, Big Vern said:

 I have however noticed that both carbs are leaking at the top in the same manner. 

As I'm you're aware the distibutor sits directly beneath the carbs & starting up an engine with a petrol soaked distributor really isn't a good idea unless you enjoy watching firemen work. Just thought I'd mention it. 😲

Edited by jonwat

Cheers,

John W

http://jonwatkins.co.uk

Link to comment
Share on other sites

  • 2 weeks later...

So the carbs are now fitted with Viton tipped needle valves. On removing the old ones they were in fact fine with no wear, so i guess that now leaves the fuel pump as its still ticking away relentlessly....

Link to comment
Share on other sites

Perhaps take a thorough look around within those recently refurbished carbs. Could there be a fault with the floats? An Esprit which catches fire goes up spectacularly quickly and is easily a total loss.

Link to comment
Share on other sites

I did check the floats while they were off, and they are gapped correctly and they do float so im not sure what else to check. At the moment there are no leaks around the carbs and no leak in the airbox either so i can only assume that the pump is the only thing left. In fairness its one of the only things to not have been replaced on the car since ive owned it!

Link to comment
Share on other sites

Just a quick thought. There was someone on another forum (possibly vintage Alfa Romeo) with the same issue that you have..........newly rebuilt carburettors with a leaky top cover.

He didn't assemble the float-needle valve correctly. The notch on the float arm is supposed to hook into the slot on the needle-valve and he didn't do that resulting in a poor running idle and perpetual leaks from the top cover.

dellorto.jpg.e1265766c515a5fd5105dbbcf8260ce9.jpg

  • Like 1
Link to comment
Share on other sites

On 17/04/2020 at 02:07, Big Vern said:

I did check the floats while they were off, and they are gapped correctly and they do float so im not sure what else to check. At the moment there are no leaks around the carbs and no leak in the airbox either so i can only assume that the pump is the only thing left. In fairness its one of the only things to not have been replaced on the car since ive owned it!

You can easily check that with a fuel pressure gauge and this should run around 1.0 - 3.0 psi. Mine were running around 1.2 - 1.8psi at idle.

Link to comment
Share on other sites

Thanks folks, thats correct there is no regulator on a N/A but good suggestion anyway. Also Eric i did double check it was in the float arm before i put it back together but again thanks for the tip.

Link to comment
Share on other sites

Brett, can you not check the pump functionality by clamping the fuel hose before the carbs?

I think it should shut off once it gets to a certain pressure? (Mine slowed as the floats got to the top before stopping).

Could the shut off solenoid be causing any issues?

Link to comment
Share on other sites

9 hours ago, DaveyT said:

Brett, can you not check the pump functionality by clamping the fuel hose before the carbs?

I think it should shut off once it gets to a certain pressure? (Mine slowed as the floats got to the top before stopping).

Could the shut off solenoid be causing any issues?

Fuel pressure gauge takes away any guesswork and I would consider that an indispensable tool.

https://www.dellorto.co.uk/shop/car-accessories/fuel-pumps-regulators-accessories/pressure-gauges-carburettor/wfr150kit-webcon-fuel-pressure-gauge-0-15-psi-line-adaptor/

 

Link to comment
Share on other sites

I've been thinking about this, and despite all the things that can go wrong, could a faulty pump really cause this? 

For example, a leaky diaphragm could cause the pump to continue running (ticking) but surely that would be fuel leaking from pressurised side of the rubber to supply side, and not cause more fuel to be supplied to the carbs. The pressure of the supply is dependent on the strength of the force of  the pump plunger (given the fixed nature of the area etc), so for the pump to start to supply excess pressure (as in it didn't used to do this), it must be that there's now additional force on that plunger, well it's still getting 12v (ish, perhaps 14v when engine running) and magnets don't suddenly get a stronger field, resistance would surely decrease force finally some sort of sprung force, well if that's so great it would most likely stop the plunger moving the other direction and so the pump points would never energise.

 

 

I think the pump ticking may be a red herring and it's still carb as the cause.

  • Like 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...