Author Topic: Carb icing on 1924 2 3/4hp?  (Read 3504 times)

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Offline spency777

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Carb icing on 1924 2 3/4hp?
« on: 17 Aug 2013 at 11:49 »
Hi All,
Went for a quick run out on Dougie yesterday, dry roads temp 19-20C (had rained earlier in the day) and suffered what I think might be carb icing.
The bike ran fine for a couple of miles then progressively began to stutter as if fuel starved until it stopped by the side of the road. After being stationary for only about 2 minutes it started up and ran OK again for another mile or so before doing the same again.
I tried reaching down and pressing the carb tickler to flood the carb but that made no difference likewise adjusting the air lever made little difference either.
However after 8 miles and about 5 stops later I arrived home and noticed that the top of the inlet pipe directly above the carb (see the pink arrow in the photo) had condensation on it and was very cold.
I hope you can see that the carb does have it's inlet pipe drawing air from near the exhaust can but I'm wondering if I can do something else to warm the incoming air?
Any ideas or similar experiences from anyone would be appreciated, my worry is if it ices up when it's 20C in the UK it will be useless for the rest of the year when it's 8C and raining!
Thanks
Richard

Offline eddie

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Re: Carb icing on 1924 2 3/4hp?
« Reply #1 on: 17 Aug 2013 at 13:52 »
Richard,
              The carb icing you experienced, whilst affected by the ambient temperature, is mainly caused by the level of humidity in the air. Lower temperatures along with less humidity may well result in no icing. Icing is also more prevalent with engines that are running well - the more efficient the engine is, the greater the vacuum in the manifold (the main cause of the icing). Presumably, you are riding carefully whilst familiarising yourself with the bike - this can also contribute to the icing. As you become more at ease with the bike, you will probably get to be more adventurous in your riding style, and with the use of more throttle, the problem of icing will reduce considerably. As you work the engine harder, the vacuum in the manifold will be less, and the exhaust will be hotter (giving more preheat to the incoming air) - in both cases, reducing the risk of icing up. My 1913 TT 2¾HP suffers just the same - I have found that it pays to warm it up on the stand, then set off fairly briskly, on the basis that larger throttle openings don't generate the ideal conditions for icing.
    Don't let the icing put you off riding the bike - the more familiar you become with it's characteristics, the less of a problem it will become, eventually you will be able to predict it occurring, and ride accordingly. 2¾'s are great fun to ride, and can give a good account of themselves in the right hands.

      Regards,
                      Eddie.
       

Offline spency777

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Re: Carb icing on 1924 2 3/4hp?
« Reply #2 on: 17 Aug 2013 at 16:01 »
Thanks for the advice Eddie,
You've hit the nail on the head, I was riding fairly gingerly. I'll try warming it up before I set off and then be a bit more "spirited" in my riding style.
Cheers for now
Richard

Offline Black Sheep

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Re: Carb icing on 1924 2 3/4hp?
« Reply #3 on: 17 Aug 2013 at 22:18 »
It does seem unusual to get carb icing at such a high temperature and dry conditions. I certainly have never experienced it on my 1913 2 3/4hp. My Norton is very prone to it in wet conditions when the temperature is close to zero. If it is carb icing, a check is to lean the mixture when it occurs. This should counter, at least temporarily, the increasing richening of the mixture caused by the icing. Stopping the engine and letting the bike stand will of course melt any ice and hopefully evaporate any water present in the carb. And of course as Eddie mentioned, riding with the throttle wider open will reduce any likelihood of icing occurring. As an aside, whim I was flying for a living, the temperature range of +3 to -5 was where we expected icing to occur.   

Offline spency777

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Re: Carb icing on 1924 2 3/4hp?
« Reply #4 on: 18 Aug 2013 at 19:16 »
What a difference a day makes, just thought I'd check if the carb tickler was actually doing anything and sure enough it wasn't.
It turns out that I had a partial fuel line blockage and pressing the tickler was re-filling the float chamber so slowly that it was no wonder it made no difference to my breakdowns!
Subsequently blockage was cleared and the same test route ran without a single hitch. :D

Cheers for the advice anyway, how daft do I feel?!