Spitting webers

[LaikaTheDog]

After a rebuild I did about 6 trouble free miles to the MOT station
It sat idling for about 30mins
On the journey back it was spitting out the carbs and now I cannot get rid of the spitting out of all barrels after about 2000 rpm

I figured it is a lean condition so I cleaned out bowls, filters, checked timing etc

It idles like a watch and starts perfectly

So I check fuel pressure which I have never had to do before, and find it is about 1psi.

It should be 3 to 4 psi I guess, could this really be the cause of a lean condition ?

[nmauduit]

by "spitting" I understand you mean back firing ? a lean condition would rather make the exhaust popping...

Have you checked the fuel level in the carbs to be within specs ? 1psi running is fine (as long as it does not go down to 0 at high rpm), the purpose of the cuve is to have a constant supply of fuel at a preset level (which rests at atmospheric pressure)

[rgh0]

by "spitting" I understand you mean back firing ? a lean condition would rather make the exhaust popping...

Have you checked the fuel level in the carbs to be within specs ? 1psi running is fine (as long as it does not go down to 0 at high rpm), the purpose of the cuve is to have a constant supply of fuel at a preset level (which rests at atmospheric pressure)

I think lean running can cause the carbs to spit back. I saw this recently on my S1 Esprit that had not been run for 6 months due to Covid lockdowns and has an lean idle setting to begin with . Once I cleaned the idle jets to remove built up crud from evaporated fuel the spitting up to around 3000 rpm went away

1 PSI is a little low also. I would prefer to see 2 to 3 PSI with Webers. My Elan looses power on the dyno at full throttle if the fuel pressure drops below 2 to 3 PSI at the carbs. It took a new larger fuel line and better electric pump and regulator next to the carbs to solve that issue. but its trying to provide fuel for 180hp so you expect some changes would be needed .

cheers
Rohan

[ericbushby]

My Series 3 was spitting back. Liquid fuel was spraying out of the trumpets.
As they say `it was running like a pot pig`
It was a long time ago when I was slowly putting things right and I am sure it was caused by a weak mixture.

Since then the mixture is quite good as far as I know, not having any measuring equipment except Colortune. Timing is correct and airbox fitted and plugs are grey/brown.
Good luck and keep going
Eric in Burnley
1967 S3SE DHC

[elans3]

1 psi is too little for Webers 2 to 3 is correct. Spitting back through the carbs is normally a sign of idle jets
mal - adjusted, or air getting sucked in somewhere.. If the issue goes away just after 2000rpm, then it's certainly the progression circuit.
If you haven't run the car for a long time prior to this, take out the idle jets and clean them thoroughly.. See if that makes a difference. Check float height in the carbs too.
If you're still experiencing the issue, then you need to re-adjust your air volume screws. I can provide you with a step-by-step guide to setting up Weber DCOE's if you PM me.
Just one thing, you said it sat idling for 30 mins, could also be that you've fouled the plugs good & proper.

[LaikaTheDog]

I have cleaned all the jets and tubes and filters.
Replaced the plugs
Removed pertronix Ignition and installed new points(no change) returned to petronix.
Removed fuel filter completely, just in case it was restricting flow. (No change)

It was at that point that I started looking at fuel pressure

I have not checked the floats yet but the carbs were professionally rebuilt a year ago. Will check them tomorrow as they had not done a good job on aligning the butterflies.

[elans3]

Yes, check the float heights are correct for your Tipo of carb. If all looks good, then move to the progression circuit / idle jets.

[LaikaTheDog]

So I eventually got the floats out.

All emulsions, idles, jets match, floats are at the correct level.

I put in new plugs I got a replacement timing lamp and check timing

So in summary;
No air leaks
Good balance
Float level is ok
All internals match
Check fuel pressure, which is low, i fitted a new electric fuel pump which provided 6psi before regulating to 4psi and problem remains

Symptom;
Starts perfectly every time
Idles Perfectly, (like a watch really)

As soon as I have increased throttle it starts to run rough then at about 2000rpm it spits and coughs out the carbs hot or cold

But
If I use FULL choke it runs fine… this indicates to me a mixture problem rather than ignition, my logic being that it if it was ignition timing the error would present even with choke

Or
It is a faulty advance

Kind of don’t want to blow 300 quid on an electronic dizzy if it won’t fix the problem

[mbell]

Maybe get a color tune plug and see what the mixture looks like when it happens.

Have you checked the pump jets? My experience is they block the easiest.

[SENC]

I've been chasing something similar after my 7 engine rebuild - can't quite get the transition/progression circuit to my satisfaction. Mine are older Webers with the older style (blunter) idle mixture screws - which I have been told tend to leak air around them. EZ-turn fuelube (I'm sure there are similar products there) applied to the threads does, indeed, make a noticeable difference on mine.

[LaikaTheDog]

I have just been through the emulsions, jets and pumps, all working ok and clear.
No air leaks from gaskets, rings, mounts spindles etc.

Just run it up to temp and tested my own assertion that choke fixes the problem

I found that; yes, half choke makes a noticeable improvement BUT does not eliminate the problem when warm and full choke causes stall when hot or cold !

Listened carefully to the pops and bangs and think I am getting both a back fire and a spit… which made me look at timing chain and cam timing which proves to be fine.

Used timing light again and watched the timing mark move anti-clockwise as revs increased…. And retuned, so it “looks” like my advance is working

I have also loosened dizzy and rotated it by hand during running to see if I could manually find a better position and found no improvements so put it back to recommended advance.

Bit stuck as to what to look at next, but keep thinking I should just bite the bullet and fit a 123ignition dizzy to eliminate worn dizzy. But expect to be poorer and not closer to a resolution

[h20hamelan]

Vacuum leak, have you checked valve clearance.
Might have missed it, progression set correctly? You can see the butterflies are the same!
With the cart not running, looking through the carbs, opening the throttle you see a squirt of fuel?

Colour tune, or o2.

But to be sure your ignition hasn’t changed, might be worth new cap rotor

[SENC]

Laika - you might find this thread of interest as Keith Franck is helping me sort through my similar issue.

https://vintagetechnologygarage.groups. ... 80852#2427

[Billmack]

Just a thing to mention while everyone is preoccupied with carburetion... Retarded ignition timing can also cause spitting back in the carbs. Also although you probably dont want to go there cam timing deserves a quick look

[miked]

Probably wrong but I had something similar happen after refitting my exhaust manifold. Was chasing a stumble and had to remove the manifold to access the flywheel sensor. To examine it for damage/debris.
So nasty was the spitting that it et my air filter on fire. At the end of a cold air box trunking. Scary.
The design of the bespoke exhaust manifold had small hole near the clamp split area that I ommited to block. Probaby about 4mm diameter. Previously I had seen it and had a clip over it. I would not have believed it. Re fitted clip with sealant and it was fine. Fitted new cone filter at nose of cold air box and got shut of trunking to nose. Sorted.
I am on a Zetec with different carbs but was shocked by the disturbed running and then the smoke from under the bonnet when it torched my foam filter.