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Old 22-12-17, 01:20 PM   #14
Join Date: Jun 2016
Location: NE Lincs
Posts: 407
Default Re: Curvy Cold Starting Needs Running Start

Originally Posted by machulnyy View Post
Can the rings be changed? Where do I find them?
What I was trying to say was that normal engine wear is probably what is causing oil in airbox - only if it's excessive would you need to investigate the issue. Trying to decide what is excessive on an internet forum is...difficult.

You also asked what running rich meant: engines are designed to run with a certain air to fuel mixture, it is usually set on the lean side (more air less fuel) for emission and fuel economy purposes. A cold engine does not like running on this lean mixture so you have a choke which restricts the amount of air entering so the fuel to air ratio changes - it becomes a rich mixture (less air more fuel). Once the engine is warmed up it doesn't like the rich mixture which is why you release the choke. If you left the choke on for a while, stopped the engine and examined the plugs they would look "sooty" - caked with a soot residue. If a plug has not been firing constantly it may look wet - what do your plugs look like?

An engine will not generally backfire on a rich mixture, it usually backfires on a weak mixture. A badly adjusted carb can cause a backfire as can an air leak, particularly between the carb and the inlet manifold or less often between the airfilter and the carb.

An air leak is more common on older bikes because the rubbers between the carb and the inlet manifold can perish with age. Is yours backfiring (banging in the exhaust) or missing (an uneven stumble when idling)?

So, after this ramble, we haven't progressed much - the backfiring could still be fuel or spark related.
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