Monster 900 Carburation Problem?

**ijr900** · 06 Mar 07, 02:46 AM

ive a problem with my 900 monster, rough running at small throttle openings, accelerating hard in third or fourth it coughs then clears up and runs cleanly. closing down on overrun it pops and bangs in the exhaust pipes. drawing in air a bit due to poor sealing on downpipe but this is worse than i would expect.theres a bit of firing back through the carb now and then, when shutting of for roundabouts its like hitting the kill switch. power cannot be fed in with any finness at all,thumping in with a jolt. have taken carbs of and its got a 165 main jet instead of a 140 with circlip second groove from top. air box has been drilled out and its got aftermarket cans.booked in next week for a dynojet session but does anyone know the main jet size for a bike with these mods.thanks ijr900

**zimbo** · 06 Mar 07, 08:39 AM

I think from memory the 900 main jet is 175 or so as standard, if you have a dynojet kit fitted though they use a different numbering system. Does sound like it's running lean though. The fact it runs fine on full throttle opening indicates the main jet size may be ok, most likely the needle position is wrong, lifting the needles a groove or two will probably sort it. The Dyno will reveal all though!

**ijr900** · 17 Mar 07, 01:08 AM

the bike went today and it looked awful on the dyno,at 2500 rpm it was jumping up and down.the unburnt hydrocarbons where 10 times what they should have been,it was too rich at the bottom end and too lean at the top end.the verdict was (possibley) the 165 jet was too small and the needle has been lifted to compensate,left it to have dyno kit fitted,worth 225 pounds? ill let you know when i get it back

**ijr900** · 21 Mar 07, 09:29 PM

picked up the bike from the dynojet shop on tuesday and i can say yes it was worth 225 pounds,the bike now runs smoothly,accelerates cleanly and needs the choke to cold start9(LOOK OUT FOR THIS ONE if THE choke is not needed it may be running rich.).25 pounds for the diagnostic run,this showed problems up straight away,no pressure to have the work done and helpful advice.damo has just set up in keithley,west yorkshire tel 07801589678 i will post the before and after printouts next week when his printers working ijr

**ijr900** · 28 Mar 07, 06:42 PM

dyno results ,look at the torque curve ,nasty

**ijr900** · 28 Mar 07, 06:52 PM

blue is before the dynojet kit ,red is after,you can see now how it was so bad to ride,the torque curve is very rough,a needle that has the correct profile for an open airbox was fitted along with all the other bits,the bike is now transformed.ijr