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jonny.k

32/36 Flat spot

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I recently got my mk3 back on the road after a 5yr hiatus and have found that even after a rebuild kit being fitted to the carb it still has a flat spot when accelerating. It was there before the kit and i hoped a kit would sort it, but it hasn't, Could it be the Power valve diaphragm needs replacing because that wasn't in the service kit, but i have noticed it's included in the full rebuild kit.

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Assuming as part of your rebuild you cleaned out the jets and the filter on the fuel intake?

 

Also did you check/set the float level?

 

Outside of fuel is the timing set OK and have you checked for air leaks on the intake side/through any of the pipes connected to the manifold including the vacuum advance one?

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All the intake has been checked, it's a new manifold gasket, and the timing is spot on. The carb is off my 2.0L mk5 and when i ran it on that it had the same fault but worse. My mk3 has now got a 1.8L pinto and had no flat spot with the twin choke Pierburg, but it had no acceleration either. Now it's got loads of acceleration but a small flat spot if you floor it, so it's definitely a fuel delivery problem, because the 1.8 would need less fuel than the 2.0 hence it has less of a flat spot.

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Is the accelerator pump squirting when pressed (look down the throat & see if cracking throttle dos it) if not try a new diaphragm. 

Think I've got one if needed.

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Assuming you are getting vac advance. I had a bit of a flat spot and noticed the vac tube to dizzy was cracked, probably stopping it from advancing right if i gave it a bootful or on a hill. Just chopped half an inch off and reconnected that sorted it out.  

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I just rebuilt one of these. My power valve diaphragm was leaking you can test it by placing a finger over the port. It should hold some vacuum. Don't think the PV would cause a flat spot - just make the engine a bit gutless. 

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