Some time ago I asked if anyone could help with an engine problem - no obvious solutions then, so I was wondering if anyone knew of other forums where I could ask the same question.

The problem:

My 1660cc x-flow engine runs well, pulls hard and doesn't overheat, or pink under acceleration, or any other vices. The trouble is, when I stop the engine after a run I usually get a very loud pop (or bang!) out of the exhaust, combined with a bit of blue flame. If I put it straight into the garage without giving it time to 'air' I get a powerful petrol stink that seems to be coming from the top of the carb.

The engine has been on a rolling road, and the carb and timing are spot-on. The only mods are a BCF2 cam, Bosch electronic dizzy, decent exhaust manifold and 32/36DGV Weber carb - in all other respects it's a standard engine. There are no fuel leaks anywhere - believe me, after the first stink of petrol I looked VERY hard!

For info - when I stop, I don't rev the engine or anything like that; I just trundle down the drive with the engine ticking over, then turn off the ignition. There doesn't seem to be a 'driver-technique' issue here (I don't think so, anyway).

So, I am again looking for suggestions - either something to check, or links to other forums.

cheers,
David

Perhaps the float needle valve needs checking? Maybe it's ok when you are running but when the engine is at idle it might not seal properly and allow the carb to flood extra fuel into the engine causing the exhaust pop.

What fuel pump are you using? electrical ones need the fuel pressure regulating.

HTH

Mark

It's the original mechanical pump...

I checked the float level a couple of times, and its settings, and it's been OK.

David

The stink would almost certainly be the fuel in the float chamber vapourising/boiling under the heat which accumulates when you stop. Not overly easy to fix, though lifting the bonnet off after you park in the the garage would certainly help dissipate the heat.

Not sure about the pop from exhaust. A wilder cam with more overlap than standard may allow some unburnt fuel/air to get into the exhaust when you switch it off, though whats igniting it is anyones guess. A lump of glowing carbon in the exhaust/cylinder head would do it though...

Have you looked down the carb when you stop?

On my DGV when I looked down the carb you could petrol seeping out roughly at the level of the gasket face and running into the engine until the fuel pressure had reduced, the cause was dodgy float valve and/or seat, and I reset the float hieght.

OK - there are a few ideas to investigate this weekend!

cheers (and other ideas gratefully received)

David

DJ

Do you have a pressure regulator and/or fuel return line?

I ask, because I have the same set-up on a Pinto engine without regulator or return. When the engine is switched off I don't get a pop, but certainly a petrol smell from the carb. The carb has been refurbed with new gaskets, valves etc.

Cheers
Nick

quote:

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Originally posted by nick205
Do you have a pressure regulator and/or fuel return line?

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Hi Mate,

i found the same thing with my 1640 twin webbers xflow and i had an electric fuel pump. I was going to fit a cut off switch and when i was going to park the car i was going to switch off the pump and leave the engine running to drain the carbs and rest of fuel system as i thought that might help????

Cheers

Brian

DJ

not sure if they're needed or not - I haven't fitted them. I just wonder if the carb is being overfilled with fuel, leaving a surplus when the engine is shut off.

Have you tried a good blip on the throttle just before you turn off? This may help.

Cheers
Nick

I'm afraid that I'll get an extra-loud pop!

Does the DGV carb have any sort of vent for the fuel reservoir? I would have thought that there would be some way to release any excess pressure other than through the jets!

cheers,

David

When you stop the engine you cut the ignition and as the engine runs down it still pulls fuel/air in. Some of this mixture is let out into the hot exhaust and ignites, some is left in the cylinder compressed and the rest is in the inlet manifold. You probably have a pancake filter so the smell is not hidden in the normal filter system and you notice it more. Every carb engine ever made does this to some extent, while fuel injection engines don't because when you turn the key the fuel delivery stops as well. Get used to it.

quote:

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Originally posted by bigbriglasgow
Hi Mate,

i found the same thing with my 1640 twin webbers xflow and i had an electric fuel pump. I was going to fit a cut off switch and when i was going to park the car i was going to switch off the pump and leave the engine running to drain the carbs and rest of fuel system as i thought that might help????

Cheers

Brian

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quote:

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Originally posted by gazza285
Get used to it.

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Hi

Its sounds like its a bit rich on idle, Have you had it mot'd recently? might be worth getting the emisions tested? Also is there any leaks in the exhaust?

Adrian

I'm afraid that with a carb there's no way to stop petrol being pulled into the inlet tract when you switch off the engine. I used to run my Escort with no filters (twin 45s) and that stank of juice all the time. All carb engines do it, its's just that, as you say, the foam filter does nothing to hide the smell. Likewise the pop in the exhaust, it's only because the pipe is so short, and with only one silencer, that you will notice it. Other than putting a larger airbox with a more restrictive filter and long intake pipe, it's not something that you will be able to cure. Until the vapour and condensed petrol has all evaporated, the car will smell.

how about an extractor in the garage, running off the light, with a 5 minute overrun. A 5" one should clear a fair bit of air