M900 Coughing Issue

[ChrisK]

Is there any kind of discount/ free shipping or anything at CA-Cycleworks for being a member on here?

[ChrisK]

Actually, not that I look at the DJ spec sheet again, what is the term "fuel needles" referring to? Would those be the needle jets, or are they something else?

[ducpainter]

Ahhh I just assumed the kit would come with them because I just installed a DJ kit on my project Virago and that one had needles. But the Duc kit doesn't, here is the link to the spec sheet:



Interesting, so it looks like I could be looking at even more money, yay!........

The kit has needles...not needle jets. The jet is the tube the needle rides in, and is what wears causing rich midrange and lousy mileage.

[ChrisK]

So I got both the Dynojet and Factory Pro kits in. I tore the carbs out of the bike and re-jetted them according to the write-up on www.ducatisuite.com. Now I have a question. First, I believe the bike WAS rejetted before. The mains that I took out of it said 170. I followed the Dynojet kit instructions which said to install the 175's for a bike running cans and whatnot. Also, I placed the e-clip on the 4th notch, per the instructions. Installed the new needle jets and set the float levels.

Here's the tricky thing. The ducati suite write up said that the recommended pilot jet was a 42.5. The Dynojet kit didn't come with pilot jets. I unscrewed them to examine and they are 37.5's. That's my question? Should they be larger? I'm guessing numbered jets aren't the same from brand to brand, but again, I don't know. Will this setup workout? I'm asking this question before I go to the trouble of putting the carbs back in the bike.

ALSO, on top of the jet combination I'm sitting at right now. Two other possible culprits for my coughing issue: first, both float levels were at 10.5 mm, opposed to the recommended 14 mm. Second, there was a little gunk in each carb that needed to be cleaned out.

So again, opinions on those 37.5 pilot jets - combined with the 175 mains, new needle jets, new needles, etc. Again, for reference, open airbox with K&N Filter and Staintune cans.

[ducpainter]

FWIW...I have stock pilot jets in my 900.

The fuel screws are set to 4 turns out and it runs great.

[ChrisK]

Okay thanks, the kit recommended 3.5 turns out so I'll start with that. Anybody else have an opinion on the pilot jet/main jet combo?

[koko64]

Are the stock pilot jets 40s? They are down here for an M900. Different up your way? I notice that the DJ kit uses the stock pilot but the FP kit has options. If you're in Southern Cal then try the 37.5s but if it can get cold then the 40s. In Melbourne Oz you're screwed as it it goes into the 100s in summer and cold in Winter. You get lumpy rich in summer with 40s but winter is ok (except the carb freezing with our humidity), or nice and smooth in summer with the 37.5s but a pregnant dog in winter. You gotta test it. Maybe try the 40s from the FP kit (iirc).



Careful measuring float level, you dont want the spring inside the float needle to fully compress. The float settles in two stages, so measure at the the first, "higher" stage. Could make a few mms difference.


If that float was set too rich at 10mm it would have caused problems, but may have been set that way to cover the small pilot jet. Sometimes its fix a problem and cause one somewhere else in the rev range.

With open airbox and open pipes/cans, 175 mains (DJ) (165 Mikuni), needle #4 and 40 or 37.5 pilot jets sounds like a good start. Float at 14mm, check and recheck it. You should be very close and close enough not to care. I think the needle posn or pilot jet/IMS setting are what you will play with if you need to. The mains are pretty safe with those mods.

[ChrisK]

Great, thank you so much for the detail.

I live in northern Illinois, 100 in the summer, 0 in the winter. I'll just roll with the 37.5 and see what happens I guess. Thanks for the heads up on the float level sitting in two different positions. I believe I set it correctly, or at least got it really close.

[ducpainter]

It isn't any different here in central NH with regards to temps.

My bike has always been fine with the DYNO JET kit and 165's with a drilled airbox lid.

My opinion is the 175's would be too rich. I'd start with 170's for your open box.

[koko64]

Use DPs settings as our fuel has kangaroo poo in it

[Speeddog]

Use DPs settings as our fuel has kangaroo poo in it

Our fuel has cow piss in it.

Crap, just different crap.

[koko64]

  Green fuel (or brown fuel)?

DP, you meant DJ or Mikuni jet sizes? Ah I see. That's a big difference.


I remember Brad and I having a conversation about how the 155s in a Factory Pro kit (Mikuni size) were once fine with an open airbox, but for quite a few years now an open airbox has requred more like 165s (Mikuni size). Strange but true. I remember getting the Factory Pro kits but later requiring extra main jets.

[ChrisK]

Okay I need more help.

I got it all put back together but it's running terrible.

I barely got it to start, twist the throttle and it dies. I thought it might be the idle mixture, so I turned those screws out even further. It seemed like the bike started easier, but AS SOON as I twist the throttle it dies.

What would that lead to? Jet size incorrect? Can you think of something on the carbs that I might have forgotten to attach or attached incorrectly?

[koko64]

Check
All lines and hoses
Diaphragms seated correctly
Little o rings are under the caps
Springs in correctly
Needles going down the needle jets straight
fuel tap on

[ducpainter]

Green fuel (or brown fuel)?

DP, you meant DJ or Mikuni jet sizes? Ah I see. That's a big difference.


I remember Brad and I having a conversation about how the 155s in a Factory Pro kit (Mikuni size) were once fine with an open airbox, but for quite a few years now an open airbox has requred more like 165s (Mikuni size). Strange but true. I remember getting the Factory Pro kits but later requiring extra main jets.

Dyno Jet sizes