Author Topic: Mk 5 carbs  (Read 2032 times)

0 Members and 1 Guest are viewing this topic.

Offline eden1941

  • Member
  • *
  • Join Date: Jan 2009
  • Posts: 14
  • Location: Leicester.UK
Mk 5 carbs
« on: 28 Feb 2014 at 14:29 »
My Mk 5 has never ticked over reliably.The other day I left it ticking over with the petrol switched off and as the carbs emptied the engine went faster and faster and then stopped.This made me wonder if the float level is too high.Does anyoneknow what the petrol level should be and how to check it?Grateful for any help,Mick.

Offline tck

  • Senior Member
  • ***
  • Join Date: Jul 2004
  • Posts: 279
    • old racer
Re: Mk 5 carbs
« Reply #1 on: 28 Feb 2014 at 16:38 »

with the petrol supply cut off as the mixture got weaker and weaker it went faster.
turn in your pilot jet and the same effect occurs
Not a lot to do with float levels most ICE engines will do it.

Offline eddie

  • Master Member
  • ****
  • Join Date: Mar 2006
  • Posts: 1575
  • Location: Hampshire, UK
Re: Mk 5 carbs
« Reply #2 on: 28 Feb 2014 at 17:38 »
         If our engines were only required to run at a constant speed and with a constant load, the carburettors could be set up to provide the best running conditions for that task. Unfortunately, we expect our engines to run at any speed from tickover to flat out, carry any load we might put on the bike, and then go uphill or down. To achieve this we may have to compromise on some of the settings, and the idling mixture is often set on the rich side to prevent flat spots as the throttle is opened. Providing you are happy with your bike's performance, I would leave well enough alone. Having said that, I have found that modern unleaded fuel can cause the engine to run weak on full throttle - to this end, I have increased my main jets by 10, reduced the slide cutaway by 1, and then compensated by lowering the needle. With the reduced slide cutaway the idling mixture can be weakened slightly without the risk of a flat spot.