Popping exhaust noise and slight hesitation

[sking4]

Hi. Near the end of a long run today in my v12 E the exhaust started popping and we started to get a slight hesitation in third and fourth at around 2500rpm. If I planted my right foot it seemed to clear but if gently accelerating it juddered. I'm assuming dirty plugs, carburettor filter or fuel filter. It was serviced in February. Gets used all year round. Only recent change was adding fuel yesterday but same fuel as I always use with the addition of lead replacement.

Anyone had similar problems or know if I'm on track with my assumptions?

In advance thanks.

Simon

[J44EAG]

Running via Stromberg carbs?

Notorious in my experience for split rubber dash-pot diaphragms. Used to get lean mixtures on Triumph 2000/Vitesse when that occurred. Check also for split pipes and tightness of fit.

Just a couple of initial ideas that come to mind.

Mike K

[sking4]

Hi. Many thanks. I'll investigate. Wanted an excuse to dismantle the carbs to clean them up

A friend also thinks maybe fuel evaporation!?!

[oldtimer]

Not my experience, one split diaphragm in 40 years and rarely if changed when servicing.
When a diaphragm splits the effect is not proportional, it's like loss of 50 % plus power.
Certainly worth a look at though.

Just re - read again . Probably not possible to determine which bank whilst on the move I suppose !

Have never experienced popping down the exhaust pipe.

If there is a plug problem very unlikely to be more than one.

Just a thought, the plug lead connections can be a sod to get on, to ensure it is correctly and completely clipped in place -- has one come off ?

I think I would be looking at the Distributor cap and rotor arm for starters.

If you do take the dash pots off check that a carb is not flooding.

That's enough for tonight, let us know what you find.

Oldtimer

[sking4]

Thank you. Lots to check! Think that will keep me busy for the next few evenings. I will certainly keep you updated.

[oldtimer]

Have been "mulling over" your dilemma. For there to be a pop in the exhaust pipe there has to be some un-burnt fuel which I would suggest is being detonated by a working cylinder. What do you say to that ?

What I forgot to mention last night is:-
A lot can be analysed from the state of the plugs.
I would remove all the plugs and lay them out in exactly the order that they would have been fitted so that you know which plug came out of which cylinder.
Then make comparisons between the 12, hopefully one will stand out as having a different appearance from the others. There are a range of colours indicating various problems which I won't list at the moment. If one stands out as an odd ball at least the problem cylinder has been identified. At least this a simple straight forward job and you may learn a lot, however if all the plugs are about identical it will be back to the drawing board.

Keep us up to date with your progress

Oldtimer

[sking4]

Spoke to a friend today who works in the industry, he thought it could only be one of two things, cracked/ loose pipe between the carbs or maybe a split diaphragm in one of the carbs. I went round this evening all the pipes. There was one which was not tight but not off. Before I adjusted pushed it back I ran the engine for a while and got the popping noise, after pushing it tight no popping. I took it for a short drive and no hesitation. I am hoping that was it and the extra air was making it run lean but am finding it hard to believe a pipe which not off but also not tight could have such an impact. We will wait and see. Thank you for the feedback. If not successfully resolved then it will try looking at the plugs before dismantling the carbs to see if the diagrams are ok!

[sking4]

Oh, also gave her a stern talking to. I think that may have made the difference!

[sking4]

Quick update. I opened up the carbs, cleaned and topped up. Checked all pipes linking carbs and leading too. One was not off but not fully pushed on. Done two or three 20 miles journeys since and all seems ok. Can't believe that that slightly loose pipe was at fault as I can't see how it was drawing in air, not counting my chickens yet but all seems ok for now.

Thank you all for comments