Wont start until its left a while

[2wheelsteve]

I have recently altered the mixture on two carbs ( four of ) since they where running rich ( coked plugs ) and since then it can be difficult to start, tonight at the garage filled up then it wouldnt start.
I left it about five minutes then great it started, next I turned it off as I needed to stop to make a phone call, wouldnt start atall,
I took the plugs out but they all looked fine and then ofcourse with the time it took to do that it fired up no problem.
Very misty tonight so all was soaking wet though I dont think thats anything to do with it I thought its worth mentioning,
The bike is now running lean if anything but adding choke doesnt help either.
I will get fired into it tomorrow but any thoughts of a possible reason would be appreciated, thanks
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[0l0dom0l0]

This problem is very often caused by moisture in the plugs.

I had exactly the same problem with my bike after it had been sitting for a while. Basically, what happened was moisture had gotten into the plugs, and it would start without any problems from cold, but as soon as it had been fully warmed, if you went to start it again, it just wouldn't go. I found it would bump start though, strangly!

Apparently if there is moisture in the plugs it will stop them firing when warm, as it condenses on the electrode or something.

Changed the plugs and never had the same problem again. Try that first!

[st3v3]

Surely adding choke to a warming up bike is not helping? Once its nicely running, i wouldnt imagine the choke being in the equation.
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[luckylarry]

I've had similar issues as well and found replacing the spark plugs helped. Also it may be that you're not getting full compression as when the engine warms up the metals will expand. When its been running from cold for a while does it begin to feel like its struggling?

[N cee thirty]

[stinkwheel]

Remember, fiddling with the mixture screws only affects the mixture at maybe up to 1/4 throttle.

I'd suggest that coked plugs after normal riding are probably due to the fuelling at larger throttle openings which would be adjusted by needle position or main jet diameter.

Mighty suspicious that it starts playing up after twiddling with the carbs. I'd put them back to their pre-twiddle position (which you of course checked and noted down before you started twiddling against just such an eventuality ) and check that it now starts properly.

I would then go ahead and try to sort out the running rich problem. A 4-cylinder bike suddenly starting to coke up 2 plugs smacks to me of an electrical problem causing a misfire, altered timing or a weak spark. Especially if they were on a pair that shares an ignition coil (1&3 or 2&4). I'd start at the plugs and work back from there.

If it was 1&2 or 3&4 I'd be more inclined to go down the fuelling route to find the source of your woes and would start with the air filter.
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[2wheelsteve]

Yeah interesying replies, the compression could have something there,
if I take a ride til the engine is well warmed up thats when it wont start, inlet manifold air leak is a possibity i think, the choke was incase its now running too lean so thats why I did try a bit of choke needless to say it didnt help.
The guy I bought the bike off I reckon he increased the fuel mixture because of this problem.
Its got newish plugs in it, I may consider hotter plugs but that has a risk factor, umm no easy answer
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[2wheelsteve]

[2wheelsteve]

Sorted.
I narrowed the plug gaps from .07 to .06, altered the tickover at the carb tickover screw, added a quarter turn of fuel mixture to pot two and guess what, it sorted itselft out all on its own
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[0l0dom0l0]