M900 Coughing Issue

[koko64]

Thats four jet sizes difference. Definately the kangaroo poo.

[ducpainter]

Mine is also stock compression

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.

When you say 4th notch...from the top, or bottom?

[brad black]

on my 900 i think i went down to 37.5 pilots to help the fuel economy.  40 or 42.5 would have been std in our euro versions.

up to you, really.  if it is lean just off a closed throttle go bigger on pilot.  the more you play with them the mroe you realise they're hamstrung by their design.

[ChrisK]

4th notch from the top (fat end).

I know the diaphragms and o rings seated correctly when I put the carbs back together.

I have two mysteries: first, towards the front of the carbs (front as in front of the bike) there are two plastic nipples that clearly are meant to have hoses placed on them. One of them, I've gathered, is the fuel delivery hose, and I have that one all hooked up. During the re-install though, I got done, looked down, and said "shit." I had an extra 6 inch piece of hose laying on the ground. Now, I'm guessing that goes to the other, similar plastic nipple near the fuel delivery one, but I don't know where the other end attaches to. When I had the bike running no fuel was spraying or even leaking.

Second, I found what appears to be a tiny filter laying on the ground after the re-install. I definitely did not take it out of anything on purpose during the tear down. It is about 3/4 of an inch long, made of orangish plastic with a fiber membrane - kind of cone shaped. What the hell is it? lol

[ChrisK]

If you guys, my exalted Desmodromic expert technician consultants... can't come up with a definitive solution, I'm thinking I might just re-jet back to the 170's. I pulled 170's out of them so I'd basically be sitting with the exact same setup just new. If it still doesn't run right, then I know that I'm reassembling something wrong.

That said, I find it hard to believe that changing from a 170 to 175 is having this large of an effect on it. Went from very rideable and very fun, to can't even pull out of my driveway.

[Speeddog]

The small conical filter goes in the fuel infeed fitting, likely it got dragged out when you pulled the hose off.

Short piece of hose goes from the bowl vent fitting to the left pod.

Main jet change wouldn't produce the symptoms you describe, something else is wrong.

[ChrisK]

Speedog,

I believe my left pod doesn't have any hoses going to it, if I remember correctly. My right pod has two hoses coming to it, both from the bowls.

[Speeddog]

Right pod should have two hoses coming from the diaphragms.

[ChrisK]

Ah, yes, diaphragms. lol. Sorry about that.

Okay, I will check on the left pod and running that hose over there. Am I correct that where it connects to the carb is real near where the fuel comes in? And that it looks very similar to where the fuel comes in?

Thanks again, guys.

[Speeddog]

Yes, the vent fitting is right next to the fuel infeed fitting.

[ChrisK]

Okay, thank you. Still though, without that hose hooked up it's unlikely that it's causing the bike to run that poorly, correct?

[Speeddog]

Okay, thank you. Still though, without that hose hooked up it's unlikely that it's causing the bike to run that poorly, correct?

Yes, it's something besides that.

[ChrisK]

Well shit, lol, what is it?!

The throttle blades move like they should. I have the two diaphragm breathers hooked up, the two bowl vents hooked up. Fuel hose hooked up, other hose near that hooked up and ran to the left pod. No leaks at either end of carbs. Needles were slid in aligning their notches. Float height set to 14 mm. Jets seated like theyre supposed to. 175 mains and 37.5 pilots. Just trying to rattle off known variables.

[ChrisK]

Bike won't start with the air filter off. Starts barely with the filter on. Can't give it any gas with no joke, can slowly rev it up when choke is cracked a bit.

[SpikeC]

 It sounds like you have an air leak somewhere.