Running rich - I am going mad

[Per]

Marginally better? But still lean popping and crackling.

Absolutely the whole carb has been apart and cleaned in ultrasound bath, then blown through with compressed air. Inspected.

I am honestly running out of ideas. I cannot see anywhere there should be airleaks either. I have used permaseal between the thick heatblocking gasket and a new paper gasket between carb and thick heatblock. Cannot see that there should be any airleak between heatblock and papergasket. Shaft for throttle is reasonably tight in housing so no major air leaks there either.

[Per]

How sensitive is the carb to float setting? It may be that the required 7mm is closer to 8mm in practice so outside tolerances. Btw 7mm is the original spec for the leaded fuel. So if modern fuel is a bit denser maybe 6mm would be more correct.

[millieman]

Have you checked gasket between head and inlet manifold. Had one years ago that ran lumpy until i pulled manual choke out then ran perfect.

[WestonE]

Please check through the High Tension Ignition components before going further. You are looking for corroded connectors on HT leads (check all the ends) plus burnt or corroded contacts in the distributor cap and rotor arm. Also check plug gaps and lead condition i.e. dirty burnt completely rigid.

Then consider low tension connections i.e. are they clean terminals on clean connections.

That should remove most normal ignition issues.
 

You can also spray WD40 or if you are braver easy start to the carb to manifold and manifold to head joint engine running. A change in running will show you have found an air leak.
Are there any open air ports on the carb that should be plugged? 

Float level is important. Use the factory spec.

Use a Colour tune plug to set the idle mixture with the engine HOT unless you own a good gas checker. For FI you would use a wide band Lambder sensor and gauge but Carbs are always a compromise or fuel air mix.   

I hope this helps.

[Neil-yaj396]

Are your slow running jets clear and in good condition? I had terrible fuelling issues with my Coupe that only really cleared up after driving the car to Italy. They returned last summer, popping, banging and I could only drive at high revs. The slow running jets went in some paint solvent for a couple of days and smooth running returned.

[Per]

Good strong spark with Pertronix ignition. All the jets look clean with no buildup of old fuel residue. Could you actually see anything on the jets Neil? Will check for leaks at the head to manifold gasket. Did not find any old easystart when looking a few days ago but CRC or WD40 should give an indication at least.

I will just for the sake of experimenting put the float at 6mm. Modern fuels are slightly denser than the old leaded 98 so float will ride higher today.

[Per]

Aaaaarrrggghhhhhh, I feel like an idiot  

Turning the idle bypass screw fully in and both low speed jets fully down it runs sort of ok'ish. So still overfuelling then. Needle valve is new, float closing a wee bit earlier than spec for the same fuel density. Pump stops when priming carb is done so no major leak-by. Jets do not look particularly worn but will they overfuel before one can actually see significant wear?

Edit: What made me realise it was still overfuelling was that I found an old can of easystart and spraying directly into the carb immediately killed the engine.

[Per]

Went for a drive and worked ok'ish once warm. Time for new jets maybe?

[Neil-yaj396]

Nothing was  visible in the jets and they had been blown through with an air line, but after 2 days in solvent some noticeable residue had been removed.

[mangocrazy]

If the carb is running rich/overfuelling, wouldn't it be case of the jets being worn and allowing too much fuel through? I'd be tempted to change out the old jets for new (assuming they are still available at sensible prices, of course).

[Per]

I agree, and today I tried a pair of smaller new primary jets I had laying idle, yes bad pun  , and the engine struggled badly to provide any real power. One thing I do know is that the surface smoothness of the jets is critical for proper running. So I have dropped the original jets into solvent. I will leave them for a couple of days and then try again. If still too rich then an order for new jets will be made. Yes they are available fortunately.

[Per]

Jets in paint thinner for 48 hours. Now it runs quite well. So I will order new jets but happy enogh for now 😊