Engine question…

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AGPlant

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Hard to describe, but what could be causing a jerking sensation when driving, eg every second? Not so noticeable when accelerating, but say if cruising with slight accelerator it’s a general jerking in time to the engine? All clearances set, new points and condenser and plugs and all tuned.
 

Coda

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Sounds like you're describing a misfire. All your HT cables OK and firmly connected?
 

AGPlant

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HT cables are fine. Has had new points and condenser and setup ok. I got an old Bosch one from Stanford Hall that needs a general clean up. Only difference is hole in side for the connector is square rather than semi circular.

It’s weird as doesn’t feel like a misfire, just gently nods your heads backwards and forwards like a chicken! 😂
 

JohnVW

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My mate had a similar issue in his 2cv and he fixed it by putting in a slightly larger main jet in the carb.
 

purpledog07

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Hi plant, some more info would help.
What vehicle and what engine is fitted?
Was it all good before you changed these parts and tuned up?
Did you time the spark dynamically or static?
What carb are you running?
Which bosch dizzy is fitted? there are numbers stamped on the side.
Is the dizzy a like for like swap?
Did you swap the rotor arm?
Is the dizzy vacuum pipe connected?
 

NigelDenham

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If it was ok before the replacement parts were fitted I’d check for any obvious fitting errors then try backtracking, putting the old parts back on one thing at a time. Just because it’s new doesn’t always mean it works.
 

AGPlant

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Hi. Firstly it’s a bay crossover 1600 stock. I’ve done all the checks I can think of. So am putting it down to either distributer or carb. It’s a fully standard setup. Timing with a strobe is spot on. Not much adjustment on the carb as screws are poo. It’s a Bocar solex 34 pict-3. Rotor arm and cap are both very clean. New plugs gapped right, even replaced the coil. Vacuum connected properly and working. It’s always been juddery just seems worse than usual.
 

Richy1

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Have you checked the inlet manifold boots, if the ignition system is new and set properly and it fires up easily I would move to the fuel system, is the fuel filter clean? Is the inlet manifold air tight (boots and gaskets on the head, bocar carb could be the issue you mention there’s hardly any adjustment due to the screws being poo, a rebuild kit is cheap they include new seals for the screws, finally air filter, if oil bath is the oil clean? If paper or foam is it blocked?
 

Richy1

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Sorry forgot to mention the float in the carb and the float valve, these can also cause the problem you’re describing
 

Richy1

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Finally the other thing that will cause a misfire/ rough running is the generator or alternator starting to fail, often overlooked but if not producing enough charge will cause hiccups, backfires etc easy to check with a voltage meter to eliminate
 

Richy1

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Finally, finally, are your valves set correctly, need to be done stone cold preferably after sitting all night and before you start the engine, How to keep your Volkswagen alive by Jon Muir gives the best explanation of why and how to do this properly.
 

ozziedog

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Just had an alternative thought, possibly have a look at your brakes and wheel bearings or even your drive shafts. :unsure:

Ozziedog,,,,,,,,,, a thought just outside the standard envelope :);):)
 

Mechanoid

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Just had an alternative thought, possibly have a look at your brakes and wheel bearings or even your drive shafts. :unsure:

Ozziedog,,,,,,,,,, a thought just outside the standard envelope :);):)
I was also thinking about driveshafts! A friend of mine had a T25 with symptoms like you described and spent ages playing with distributors and carbs only to find that it was a CV joint siezing up!
 

AGPlant

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Thank you for everyone’s suggestions, has given me loads to go away and look at.
 

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