Ducati Monster Forum

so i have a 96 M900 that i'm trying to rejet after some upgrades and i'm not having the best of luck.  without a dyno it's very difficult for me to follow the factory pro tunning instructions since i kinda need to tune the bike well enough to idle in order to take it down the street and evaluate the bike "after 10-15 minutes of hard use".  but if you read the FP instructions, fixing the idle is their last step...

so i guess i'm looking for some sort of a sanity check on my main jet selection.
I went from a stock setup to K&N pods and a set of Mark's (motocreation's) BoomTube straight pipes.  i tried both the 145 and 155 main but i can't really tell the difference on the streets near me (no real place to open it up, f-in suburbia)

is 145 definitely too small?

could people with similar setups/experience chime in with their viable configurations?

Oh man, having just finished about 40-60 hours of trial and error jetting hell school on my '81 Moto Guzzi Monza, I feel for you.  Unfortunately I can't really offer anything but moral support. 
I will offer this.  It was a bit more appropos for the Guzzi, as it has Dellorto's, but the theory is all the same, especially the part in the back about CV carbs.  I'd suggest you read it a couple of time until you understand all the sentences (not casting aspersions, it took me three or four times.  :o)  It will make the process easier.

http://www.thisoldtractor.com/gtbender/mg_manuals/dellorto_manual.pdf (http://www.thisoldtractor.com/gtbender/mg_manuals/dellorto_manual.pdf)

I'd also suggesting asking the same question of whomever you bought the pods from.  I'm sure they've answered your questions countless times.

If it runs good :IE no popping on decel, and no coughing on accel, run it for a few miles ( a hundred or so ) and read or post pictures of your plugs. Black is rich, light brown is optimal, and white is lean.

that seems to be my primary problem.  it won't idle/idles on the rear cylinder. on part throttle the front cylinder fires, but the rear cylinder after-fires.  it hesitates on accel and pops on decel.

and it does this basically no matter which main jet i have installed.

the carbs are clean.  i completely broke them down and dipped them.

the emulsion tubes are new.

the engine has compression. ~135-140psi on each cylinder

could it be the rubber and plastic bits in the carb? does someone make a rebuild kit with o-rings and such?

Have you synced the carbs?

um, no...
can you sync them without the bike being able to idle?  i have always synced with a warm idling bike.  how do you sync when you first get the thing back together? running with the enriching circuit on?

My solution would be to turn the idle screw in untill the engine will run on it's own. Then sync the carbs, lowering the idle as necessary while doing so.

It's best to sync them at a warm idle, yes.
Having recently chased jetting on a carbie Monster (futile effort that was solved by syncing  [roll] ), I'm thinking that it may be your issue with the idle quality.

It's more difficult to sync when it's running poorly / not idling, but it can be done.

Alternative is to give the sync screw a quarter turn one direction, and see if it helps.
If it gets worse, try going the other direction a half a turn, so then you're a quarter turn the other way.

Or, you could take a stab at the pilot jets, go a step richer and see how it likes it.

Carb tuning is as much art as science and will definately drive you to distraction at times.

sync the carbs first.  sounds like a plan to me!

i also managed to track down a cheap carb rebuild kit at https://www.carbkitscapital.com/carb_kit_list_part.php?make=Yamaha&cat=Carb_Kit (https://www.carbkitscapital.com/carb_kit_list_part.php?make=Yamaha&cat=Carb_Kit)

the same kit is used on the FZR, XTZ, and TDM as is used on our Ducatis.  my gaskets all have a crustiness on them and one of my o-rings has a burr.  for 20$ shipped i figure it can't hurt.

For a 1997 M900 with open airbox, I had excellent results with 155 main jets, needle one clip leaner than the middle position, and 4 turns out on the idle mixture screws.  Springs and pilot jets were whatever came in the Factory Pro jet kit.

There you go. 

And back to Speedog's question,  you mention you've had the carbs off/apart?  The first step to all this is making sure there is slack on the throttle/choke cables.  If I'm following Speedog, I agree that one of your carbs is working sooner than the other.  I had the same problem with the Guzzi until I noticed the one of the throttle cables was routed incorrectly.


Nonsense.  It's a black art, plain and simple.  Only pain and suffering in purgatory can free you!  ;D

i was wondering when you'd chime in Scott.   [thumbsup]  you always had good carbie advice on TOB.

i've been working on this the past 4 nights in a row and i need a break.  luckily i have first corner tickets to the F1 Canadian GP.  i'll check back in after i return from Montreal and put some MORE [bang] time into it.

yeah...  so i got back to the bike FINALLY after waiting for the rebuild kits (i forgot i needed 2) to arrive.

install the new gaskets and float valves from the kits and try and fire it up so i can sync the damn thing...  still misbehaving, but on one of its smoky coughs i noticed that instead of coming out the top of the carbs there was smoke below the battery box...  now isn't that peculiar.

turns out that my fuel pump's vacuum hose had been torn off its nipple by the starter cable.   [roll] ugh...  quickly repaired that with some spare fuel/emission hose, synced it up, and what do you know! no more flames out the tail pipes!

went for a ride and it's running at least as well as it was before, if not better.   [moto]
155 main, 42.5 pilot, middle clip, and 3 turns on the idle mixture screw, which is the FactoryPro recommended setting for open intake/free flow exhaust.  plugs are nice and tan now, but i'm sure i'll tweak the clip or idle after i get a few rides in to characterize it's cold to warm transitional behavior.

Soud right on w pods. [thumbsup]

so what drove me to futzing with my carbs in the first place has decided to rear its ugly face again, though not nearly as bad.

previously i had power delivery problems when cruising at higher speeds (higher loads) and higher engine speeds.  scenarios like 80MPH in clean air (not drafting).  if in this scenario i will periodically experience a brief loss of power either upon gentle throttle application or simply cruising.  it used to feel like hitting a brick wall, now it's more of a hiccup.

i had thought that this was needle clip position related, and hence probably how i managed to break my fuel pump vacuum hose with the starter cable by removing my battery box to get at the slides.

does anyone have other ideas about what this could possibly be?

Perhaps your fuel pump is getting a bit marginal on delivery.

Is it the original?

you know, that was my FIRST impression also.  so i ordered the rebuild kit and installed.  no dice.

so i thought maybe my tank is flaking rust into the system.  so i ordered one of those tank sealer systems, flushed all the lines, the pump, and completely broke down the carbs, dipped them, and put it all back together.  no dice.

somewhere along that journey i ripped open the fuel pump vacuum line and the last thing i did was fix that hose and i'm kinda back where i started...  although not nearly as bad. :-\  hey, at least it's rideable

so after a day or so the bike began to have issues holding an idle.  it would run on one cylinder and intermittently.  the plugs looked a little too sooty so i decided that it was running too rich and changed out the main jet to the 145 that came in the factorypro kit. 

so far the 145 is really making a big difference!  there is definitely more power and everything seems to be behaving, for now.  i only went for a short ride to lowes for holesaws, i'm building a reef tank, but throttle response was much crisper. 

i'm going to have to get it out on the highway this week to see if this jet change solves my high speed cruising issues.

Just a random comment here, on jetting.  I got the Factory kit, and eventually wound up with good plug color with 130 mains, 70 starter, 40 pilot, 60/1.4 pilot air, y-2 needle jet, factory springs, 3 1/2 turns on idle screws, and needle is 2 from top.  This is on my 94 900SS.

for whatever reason the 900ss likes smaller jets than the m900.  take a look at the example installs about half way down.
http://factorypro.com/Prod_Pages/prodd09.html
then look at the m900 page sample.
http://factorypro.com/Prod_Pages/prodd12.html

and the instructions that come with the kit give 2 more examples for the m900 and both recommended the 155 with an open airbox and high flow exhaust.

i guess my setup doesn't flow all that great after all.  i have always known that straight pipes and pod filters weren't the best performers, no scavenging, but i guess i just didn't want to believe it.

took it in to work this morning...

it started easily enough, but idled a little rough, intermittently dropping a cylinder.  it was doing this before, but it would do this after it warmed up.  now i'm intermittently dropping the one cylinder only when it is still a little colder.

so my best guess is that my idle was a little rich, and now is a little lean.  i'm going to ride home and check plugs before i make any adjustments though.

oh, it is also definately running a little bit warmer than it has been.  i'm also going to try and duplicate this observation on the return trip.

I would agree with this  ;D   142.5 main 4th clip from top (richer) and a 40 pilot

what's your setup (intake and exhaust) on this jetting Printman?

open air box and stock exhaust

Would really die off at 9000, cause of the long intakes


FCR's have it running strong on top  ;D

i really wish i had a tach...

this just helped me alot. thanks y'all.

i'm glad it helped someone...  i couldn't quite get mine dialed in and i needed new tires mounted anyway, so i am having my local shop dyno tune it while it's in for the tires.

i'll definitely post the settings that come back on it though.

i'm in the middle of doing mine right now. i hope it all goes well...