Hi I’ve had my series 3 for many years and it’s always been fine. However recently it runs really badly when cold, it always starts ok and seems to be ok until I hit a hill when it starts missing and spluttering. However if I let it really warm up (I mean a good 15 minutes or more) it seems ok. However even when it’s running ok it seems very slightly low on power. All ignition components are new and the timing is set at 3 degrees btdc. The carb is only a year old. I did wonder about mixture but I believe the mixture screw only sets mixture at idle ? It idles fine. Any ideas ???
Not running right when cold
- Thread starter Chrisball
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Colthebrummie
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Did these problems start soon after the new carb was fitted?
Col
Col
Turboman
Mab An Gov
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What sort of carb? And what sort of ambient temperature when this is going on?
Yes they did
It’s a Zenith carb. I guess mostly ambient has been below 10c although last weekend it was a bit warmer and it still played up
Colthebrummie
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Most of the new Zenith carbs are actually copies of the original and they seem to be less reliable. The main problem is that the the two halves are not flat enough to to be airtight. They surfaces need to be lapped to get them flatter, I've not done it myself but there is advice on here somewhere. Basically it involves getting a piece of glass to use as a flat surface, attach some very fine emery paper to it and gently rub the flat surfaces of the carb on it. Use a steel rule to check for flatness. Some of the carbs have been bad enough to let air in between the mated surfaces and this causes running problems.
Col
Col
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Mab An Gov
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They are usually better than a Weber in cold weather. But the old ones are often worn, and the new ones often aren't much good^^^^^^^^^.
That’s interesting, thanks. I guess that could explain why when the actual carb body has warmed up it expands a bit and seals. I’ll look at this, thanks !
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