Poor Running Issue (VFR400 NC30)

[RickDonoghue]

Struggling to diagnose a poor running issue.

Bike fires up no problem but it seems to idle inconsistently and kind of bogs down when you begin to twist the accelerator. When the revs do pick up, and the throttle is released, the revs hang on for ages and the needle slowly returns to idle. I may put a video on youtube to show this.

I am yet to purchase some new spark plugs which I will be doing this weekend. Also worth noting is that I've had the plugs out and there's some severe oil fouling around the thread of the plugs when I take them out. I'm blaming this on a slightly leaky gasket, for now, which I think is creating a slight puddle within the spark plug chamber if that makes sense...

Someone has however mentioned that it could be worn piston rings? I've had the carbs off and have given them a brief once over, there doesn't appear to be any air leaks or anything which I have checked for when the bike is running. Looking through the history of the bike the air filter was also replaced about a year ago.

The choke cable isn't sticking and it has a relatively loud aftermarket exhaust. From looking in the carbs it has been re-jetted to suit an aftermarket exhaust - according to a PDF document by Rick Oliver I think it may have been...

Can anyone recommend ways in which I can eliminate potential causes of the poor running please? Basic tools available and limited skills but I don't mind getting stuck in and having a go.

Youtube link: https://www.youtube.com/watch?v=mF5cWhbvnbE
Photo of plug: [IMG]http://i65.tinypic.com/f9dp4h.jpg[/IMG]

Shown on the video here it actually appears to be running better than it is now...

[magg]

Sound lean on the pilot jets, how many turns out are the mixture screws?

[RickDonoghue]

I checked them and they were all slightly different so I carefully changed them to 2+1/4 turns out from fully in (gently). This is apparently appropriate if you have an aftermarket exhaust on. I might try them at just 2 turns out this weekend along with new spark plugs and see how I get on. Thanks for the reply!

[magg]

I suspect turning the mixture screws in will make the mixture leaner. Have you tried applying a little choke when opening and closing the throttle. If the response improves it would confirm that the mixture is too lean for some reason.

[RickDonoghue]

Ah yes that's what I mean - I haven't tried revving with the choke on yet. I had a sudden thought after coming across a couple of other forum posts yesterday... What's the correct/ideal starting procedure? I'm used to a more modern bike so I could simply not be warming it up correctly and flooding the engine or something?
I just put the choke on, click the starter, fires up straight away, then leave the choke on for a min or 2, job done?

[magg]

For me, a cold start: full choke, hit starter, when engine fires use throttle to lift revs to 3-4000 and then close choke while holding 3-4000 rpm. I prefer to close choke early to limit over-fuelling, as choke is fuel enrichment only, no preset throttle opening. Engine still needs time to warm up and will be a bit flat and unresponsive until warm but I tend to ride off within a couple of minutes to get temperature into the engine as quickly as possible.

Warm/hot start: no choke, hit starter, when engine fires blip throttle to lift revs to 2-3000 rpm and then engine should settle quickly to idle speed (1300rpm).

[RickDonoghue]

Thanks I'll have a play tomorrow and see how I get on!

[RickDonoghue]

well progress has been made! I had the carbs off so I could 100% adjust the screws correctly! so I thought lets not mess about and have them another half turn out each. put the bike back together and fired it up... immediately as I revved it bit the revs were returning to idle rapidly! however it soon died and the exhaust looked a bit smokey, too rich?... I didn't realise you could adjust the screws with the carbs on (fiddly) so I've just popped them back in a quarter turn but the neighbours have a baby so I best not disturb them now since it sets my brothers car alarm off in addition to being loud already! will report back tomorrow.