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Old 21-12-17, 10:42 PM   #11
machulnyy
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Default Re: Curvy Cold Starting Needs Running Start

Hey guys. Been a while...I came off on that weekend before I had the chance to try everything! Sad times as am still waiting for the shifter to arrive from America..

But here is the interesting part...

Before I came off, I had the chance to check the airbox (thought would start with the easy stuff before getting to electrics). And after removing it I find petrol (edit: could have been oil...forgotten by now!!) inside. This could explain the choke issue right? But how could it have gotten in there??! So i cleaned out the liquid from the airbox and run a bit of fuel system cleaner through it and rode out to my friendís. The next morning it had trouble starting again but did eventually, I rode for 5 mins and came off. Took it back to his where it is now. Came back a week later to have a look at it and it started first time without problems! I think this is because the connection in the starter motor jolted back into place or something?? But now the exhaust sounds different...more muted and not as crisp and raspy as before and backfires every now and then on idle. Yet another mystery to solve.

To sum up: I think Biggles is right in that there were/are two problems: starter motor and choke.

The choke issue seems to be something to do with the presence of petrol/oil in the airbox (is this what running rich means?). Ordered a new filter. But how did it get there? Whatís the cause?

The starter motor issue (as my car mechanic friend explained) could be something to do with worn out brushes which causes motor to short (im paraphrasing but he seemed to be sure of it as soon as I described the symptoms). The fall may have shifter the position of the brushes which is why it now starts well again. But have Ordered the back part of the starter motor to replace.

If these fail, will get to examining the electrics.

But now, the issue of the backfiring...does anyone have any ideas?
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Old 22-12-17, 09:33 AM   #12
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Default Re: Curvy Cold Starting Needs Running Start

a little oil in the air box is not unusual often caused by wear on the rings/bore, it gets there by the engine breather. The worn rings cause the crankcase to pressurise and the crankcase breather, which alleviates the pressure, is fed into the airbox.

Backfire? either the mixture is wrong or the plug isn't firing every time and when it does fire it ignites the unburnt fuel in the exhaust. Were you running it without the airfilter (this would cause a weak mixture). How old are the plugs - what do they look like: wet or sooty or light brownish-white (should be the latter).
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Old 22-12-17, 11:02 AM   #13
machulnyy
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Default Re: Curvy Cold Starting Needs Running Start

Quote:
Originally Posted by Seeker View Post
a little oil in the air box is not unusual often caused by wear on the rings/bore, it gets there by the engine breather. The worn rings cause the crankcase to pressurise and the crankcase breather, which alleviates the pressure, is fed into the airbox.

Backfire? either the mixture is wrong or the plug isn't firing every time and when it does fire it ignites the unburnt fuel in the exhaust. Were you running it without the airfilter (this would cause a weak mixture). How old are the plugs - what do they look like: wet or sooty or light brownish-white (should be the latter).
Can the rings be changed? Where do I find them?

The plugs were changed not a week before the crash. Brand spanking new.

No I put the old filter back in prior to riding it.


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Old 22-12-17, 01:20 PM   #14
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Default Re: Curvy Cold Starting Needs Running Start

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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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Old 24-12-17, 10:21 PM   #15
johnnyrod
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Default Re: Curvy Cold Starting Needs Running Start

Hmm my money on the backfiring - which I'm guessing is more of a pop than a gunshot - is a stuck choke and it's all running rich. Nothing to do with oil in the airbox - mine gets this now and again if I cane it, it builds up slowly really. You need to check the cable for kinks and make sure it has enough slack in it. Also check where it splits as this little box is easy to break. You could do with getting the plungers out and checking for rust etc. build-up on the seats. If you follow the cables to the two carbs, you need to undo the single screw of the retaining plate, and carefully pull out the plunger - if in doubt, pull the choke lever right back first and nothing will fall off. Check the recess for crud, repeat for the other carb. The screws and be stuck fast so use a good-fitting screwdriver and try not to chew them.
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