Author Topic: Mark 4 carby questions  (Read 1724 times)

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Offline Ian

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Mark 4 carby questions
« on: 28 Aug 2014 at 00:44 »
Well, we have gone to the dark side and now have a MK4 for Paula to ride. I have had to recommission it as it had never been ridden on the road after restoration ages ago.

It had two RHS carbs - but I have managed to source a correct LHS one which I fitted last night. It has the correct choke as well which is missing from the ones which were on the bike

The questions I have are :

1. I have put the standard size 80 main jets - but am wondering if with modern fuels I should go up a size - doesn't quite pull as well as I would expect on full throttle but mid range is fine
2. Re the choke assembly. What actually holds the slide on to the rod ? Mine fell off and there doesn't seem to be a positive locator.

Offline eddie

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Re: Mark 4 carby questions
« Reply #1 on: 28 Aug 2014 at 06:23 »
Hi Ian,
           Here in the UK, I have found that the postwar machines run better with a slightly larger main jet - say 5 or 10 larger. With these fitted, the engine tends to run a little cooler - in fact, I am running my Dragonfly with the original valves and seats without any of the seat erosion problems that were predicted.
    With regard to the choke assemblies: the bottom of the main choke plunger should have about a 4m wide groove around it, into which the back of the choke slide is punched in order to retain it. Once the slide is fitted, it is almost impossible to remove it again!! I have long since discarded the chokes and just resort to tickling the carbs for a cold start. In any case they only have the 2 positions - on or off, so give little control of the mixture when starting from cold.

  Regards,
                Eddie.

Offline Ian

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Re: Mark 4 carby questions
« Reply #2 on: 28 Aug 2014 at 07:06 »
Thanks Eddie