acceleration problems

[darkduc7]

ok, so i know the problem i have could have many causes, but im hoping someone has a eureka for me. im having major acceleration issues with my carbed M900. it idles perfect, and pulls pretty well until right around 4500 to 5000 rpm. then it hestitates, pops through the intake sometimes, and just plain falls on its face. this happens most noticably when i chop the throttle and try to get back on it, it just bogs horribly and you can just hear it sucking air. even when in 6th gear on the highway, as soon as i hit 4500 rpm, its like i have a governer on it, it just stops going!! fml. im thinking maybe main jet in the carbs? could the ducati dealer i had do the belts recently have the timing off? my plugs look good, both cylinders are firing. fuel pump? filter? valve clearances? timing not advancing? i dont know which direction to go with this and im hoping not to tear the whole bike apart to figure it out, i just built this bike. (part of why i cant narrow it down, EVERYTHING has been apart.) thanks for any advice/ideas.

[Howie]

If the bike was fine before service you need to go back to the dealer.  If the carbs were not touched main jets are an unlikely cause.

[darkduc7]

well, see, this is a new motor to me, and the carbs came installed on the motor. so i have no way of knowing if they performed well prior to me putting it in my bike. (yes i should have cleaned them first) i have found several other things the dealer installed incorrectly, so i wouldnt be suprised if they messed up my timing too. not impressed at all with a certain nh dealer that had a decent reputation among others.

[bobwithboobs]

sounds like the bike is being "choked " out in one form or the other.  try replacing the easy stuff..  fuel filter and spray some carb cleaner and see if it makes a difference.

if its miss firing and popping at hier rpms (like it feels like it cutting in and out)  most likely due to something being clogged and not getting enough of something. ( air \\fuel  or wrong mixture)

Just my experience. I never have to deal with bad timing but other then in cars . If its off you should notice it quite easily , it would feel like your missing a whole powerband and be quite sluggish. and it will back fire or afterfire. i believe there is a way to check this just by seeing how the pullies are alligned in relationship to each other .. there should be timeming markings on the pullies.

[bobwithboobs]

also if timing was off it wopuld have the tendency to pop at constant rpms and or more on downshifts (  just car experience Fuel  injected)

[ducpainter]

if the belt timing was off the bike would have stopped running by now. The valves would have hit the piston.

Check the plugs. If one or both are black...

Check the vent hoses to the carb diaphragms.

[64duc]

 How many miles on the engine, and do you have carbon cans or open airbox?

[darkduc7]

ducpainter, which vent hoses do you speak of? the fuel tank's? 64duc,  i do have an open airbox and sil motor exhaust. would that throw off the fuel mix that much? i know it does some, but i didnt think it would have such an extreme effect. i guess it could be that, ive been thinking so deep into things maybe i just overlooked the fact that i never tuned the carbs to my intake/exhaust setup. duhh . im not very familiar with carbs at all...but i might have to do some research and do it up.

[wiggy_nz]

If you are running an open air  cleaner and a K and N filter it will be running lean.  This will have it mis-behave in the higher revs and feel as if you are hitting a wall at those reves.  Are you running standard jets?

[darkduc7]

i believe i am running standard jets, but i havent gotten a chance to tear into the carbs to check. i just installed this motor in the bike, which was a huge project for me in itself, so some of this stuff fell to the wayside. i was kind of hoping things would just fall into place haha. the bike def hits a wall at higher rpms, so maybe jetting is the issue. i was aware that it made a difference, i just didnt think it would be so extreme!

[ScottRNelson]

You really should have put in a jet kit before putting the motor in there.  It seems like 90% of the work is getting the carburetors out and reinstalled.  Opening up the float bowls to set the float height and change the jets is the easy part.  It would have been totally easy to do before the motor was in place.

Here's a description of proper jetting for an M900: http://www.ducatimonster.org/index.php?page=showpage&section=faq&item=faq_jetkit

Go buy a Factory Pro jet kit and start off with all of the settings that I listed in the jetting description.  At least that will put you at a good starting point to figure out what else needs to be done.

[darkduc7]

yeah, in my haste and excitement of putting in the motor, i overlooked the fact that the carbs were probably oem and wouldnt perform correctly with my setup. oh well, when i put it up for the winter, i'll tear it apart again. 

[grunte]

darkduc, I had the same EXACT problem with my 96 m900.  It ended up being the fuel line from the tank to the engine.  the nozzel off the tank that the line connects to is at a weird angle when the tank is down, thus, it gets pinched not allowing the proper fuel flow to the engine.  When you hammer on the throttle it just dies but you can hear the engine trying to suck in air...exactly what you stated.  I went to NAPA, got some longer fuel line.  I think took a piece of black velcro and tied the line to the trellis frame so that when the tank was down the line was snug and would not move.  this fixed it.  Let me know if this helps   

[darkduc7]

well, i checked for kinked fuel lines. no luck. i ordered a stage 2 jet kit, i'll install that and see what happens. where would i get the needles? im assuming they dont come in the jet kit. also, should i tear into my vaccuum pump...maybe that's acting up? ive heard the diaphragms cause issues from time to time. or should i wait and see what the jet kit does?

[ScottRNelson]

well, i checked for kinked fuel lines. no luck. i ordered a stage 2 jet kit, i'll install that and see what happens. where would i get the needles?

If you had purchased a Factory Pro jet kit, you would get the needles in the kit.  With Dynojet, who knows?