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Discussion Starter #1
My Sud 1.5 Ti Green Cloverleaf is driving me mad :mad:

I cannot eliminate an intermittent misfire which occurs at about 2500- 3000 revs on light throttle. If I use full throttle or a heavier throttle it disappears.

Listed below is what I have done to try to cure it but I can't eradicate it.

Please help! :)
Ignition System
Bosch Distributor

Distributor Cap Replaced
HT Leads Replaced
Coil Lead Replaced
Rotor Arm Replaced
Spark Plugs Replaced Lodge 25HL
Replaced Bosch Super4 507
Replaced NGK B7ES
Distributor Advance Mechanism Stripped, cleaned, re greased & working
Distributor Advance Pipe Intact, the correct way round and connected to correct point on carburettor.
Mechanism is advancing.
Ignition Timing Adjusted & Correct
Ignition Coil Replaced

Fuel System
Fuel Pipes flexible & rigid Replaced
Fuel Pump Replaced
Breather Pipes & manifold Cleaned
Air Filter Replaced K & N panel filter
In line filter pre fuel pump Fitted (had been sucking up dirt)
In line filter post fuel pump Fitted (had been sucking up dirt)

Carburettors
Weber 36 IDF
New Carburettor Kits Fitted
Gaskets Replaced
Needle Valves Replaced
Floats Checked
Float Levels Checked
Idle Jets Blown clear & carburettor cleaner used
Main Jets & Emulsion Tubes Blown clear & carburettor cleaner used
Pump Diaphragms Replaced
Carburettor filters Replaced
Idle Mixtures Adjusted professionally
Synchronisation & balance Adjusted professionally
Warm & Cold Air Intake Pipes Replaced

Other
Exhaust Replaced

Compression Test Not carried out but engine idles smoothly & evenly

Tappets Checked (but maybe a bit tight)

Fuel Super Unleaded 97 Octane
 

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I have a similar problem with my 33. I have a small stutter/misfire just off idle, and I'm certain it is a carburettor thing. I have tried countless times to synchronise the carbs, the linkage is perfectly aligned, and rotating the mixture screws identically always yields the same stutter.
I have only ever been able to move the stutter up or down the rev range, to the point where the stutter is at idle or around 2000rpm and when I rebuilt my distributor it improved significantly but is still noticeable.
Only things I have not tried are rebuilding my carbs and renewing my advance diaphragm which is seized, but seeing you have tried all these things I'm beginning to think its a trait of the carburettored twin carb engines.
 

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What plug gaps have you got? I had a similar problem cured by reducing the plug gap to .5mm. Strangely enough, problem solved.

Just noticed this: Distributor Advance Pipe Intact, the correct way round and connected to correct point on carburettor. How can this be if you have twin carbs??
 

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Discussion Starter #5
I have set the gap at 0.6mm.

The carb on the left bank of cylinders has a brass connector to connect the advance pipe to.

cheers

dave
 

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Well there you go - never heard of vacuum advance on a twin carb before Dave. :D . I need to get out more.

Have you isolated which cylinder is misfiring or are all cylinders affected?

One cylinder suggests a localised problem (plug/lead/air leak), all cylinders suggests a global issue and you've covered pretty much everything off.

Do you have the 2 oil breather lines at the base of each carb? I would check these for cracks and leaks and replace if necessary.

Drop the plug gaps anyway and see if that helps. Mine were at .6 also and as crazy as it sounds, it made a big difference (light throttle) even though the car would rev cleanly all the way to the redline once past the miss.
 
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