nned some help getting b12 engine running right

[virusjohn]

some of you may remember pictures ive put up on the facebook page, Got a bandit 1200 engine in my gsx600f ratfighter now.





got a few running issues though.

For informations sake heres the full spec:

97 b12 engine, running with 95 gsx500f ignition pickup, loom and cdi.
stock carbs with 150 mains, needles on 4th clip down, stock pilot jets, mixture screws set to 2.5 out on 1+4 (2+3 are siezed)
K+N dual filters, stock downpipes with a kerker s system can (no packing) fitted.


wether hot or cold the engine will pop from the exhaust regularly (not just on overrun)
once the engine has warmed up it wont idle below 2/3k (a guess, i have no tach)
when warm the exhaust will pop about a second after hitting the killswitch
i dont know if its me just coming from the 6 with its revvy screaming nature or im just not used to the rumble of a 12, but it almost sounds like its only just running on 4.


I did a plug check today, 1,2 and 3 seem fine, if a little on the lean side, 4 however was erring on the rich side. cyl 4 lead checked with a different plug and it sparks, plug swapped with no 2 so i can plug chop after a ride tomorrow and see if its riched up cyl 4 plug again, if it hasent then i know its a duff plug.

other plans include spraying the carb rack with brake cleaner when its running to see if its got an air leak, but the rich no4 makes me suspect otherwise, as if it was leaking i thought it'd be 4 (i replaced the throttle shaft and butterfly, however was slightly suspicious of the seal)

has anyone got any ideas? Id like to sort this out myself and tune it as best i can before getting it dyno'd, saves more cash for petrol.


Cheers
John

[mcleanracing]

are all the valve clearances correct?

[robbo64]

If no. 4 is your problem, the carb might have a split diaphragm might be worth whipping the top off the carb and having a look?

[virusjohn]

valve clearances done before the motor went into the frame, there isnt enough space to remove the cover with it in frame.

I think today im going to systematically swap parts fron cyl 4 to 2 to continue testing, i'll give the diaphram a check but i would have thought a torn diaphram would stop the slide lifting, causing a lean condition not rich?

I'll have a look anyway, checking everything i can think of this weekend.

Cheers
John