M900 Coughing Issue

[Howie]

I'm going to add that with the CV carbs all the circuits affect each other.

While the main jet is solely responsible for the wot circuit, it also affect the midrange, and to a lesser extent the idle. Same for the needle. It is responsible for the midrange, but fuel does flow through the main jet and therefore the needle jet at idle.

None of the circuits shut off at a particular throttle position.

True, but, IMO main and idle need to be at least close to correct first.

[ducpainter]

True, but, IMO main and idle need to be at least close to correct first.

I agree on the main.

It should be determined before you even think about the needle.

I'd get the needle close next, because as long as the pilot jet is close you always seem to adjust the idle mixture when all else is said and done.

[Howie]

I agree on the main.

It should be determined before you even think about the needle.

I'd get the needle close next, because as long as the pilot jet is close you always seem to adjust the idle mixture when all else is said and done.

Agreed.

[ChrisK]

Doesn't it sound like my main and idle jets are 'at least close'? Since it idles fine and rips at WOT?

[ducpainter]

Doesn't it sound like my main and idle jets are 'at least close'? Since it idles fine and rips at WOT?

If that's the case then yes.

How are your needles set up now?

How's the off idle throttle response?

[ChrisK]

I only changed the needles to the most rich setting. Didn't touch the floats because I could adjust the needles without taking the carbs off the bike. It runs great.

[danaid]

 

I'm learning a lot from reading this thread and helping out my friend with a similar problem with his KZ650 he is building, but I'm glad my bike has fuel injection.     

[ducpainter]

I only changed the needles to the most rich setting. Didn't touch the floats because I could adjust the needles without taking the carbs off the bike. It runs great.

Have you ridden the bike at a cruise?

I would think with the needles in the richest setting it would get horrible mileage and run rich.

It may be OK on acceleration like that, but it is definitely not a 'normal' setting.

[ChrisK]

Have you ridden the bike at a cruise?

I would think with the needles in the richest setting it would get horrible mileage and run rich.

It may be OK on acceleration like that, but it is definitely not a 'normal' setting.

I rode 20 min to a neighboring town at 65 mph and 20 min back last night. It seemed to be running great. But I'll tell you what, it's raining today, but then after Wednesday we're going to have dry weather so I'll fill the tank up Wednesday and run it till it's bone dry and report back what kind of mpg I get. I live in a small town so I don't do a lot of city riding - more cruising on country roads.

[ChrisK]

In the mean time, just words of advice to people embarking on a similar, uneducated journey. Definitely give it a shot, it's a great feeling knowing that you know how to work on your bike. Only change one variable at a time. I made the mistake of changing two at a time and it made it difficult to pinpoint the culprit. Don't be in a hurry and forget to do something. Have attention to detail. This came back to bite me twice on this project, the biggest being yesterday: I changed the needle position and was so eager to test it out that when I put my gas tank back down I forgot to unkink the fuel hose loop. The bike ran great for a while and I was excited, then when the gas in the lines had run out it started running terrible and I thought the worst. Got it back home and had a 'doh!' moment.

[ChrisK]

An update:

I haven't had enough time to do the mileage test yet, but I'll report back when I do.

What I have noticed - I have a small gas leak happening. I was suspecting it so I placed some cardboard under the bike overnight, in the morning there was a spot about the size of a softball. So not a whole lot but it's there. I THINK the culprit is an aging float bowl gasket, but in addition to that it seems like there might be some gas coming out of the idle mixture screw hole. Is there an O-Ring around the base of that screw that could be bad? In addition to the leak, I'm assuming a tiny air leak in a float bowl gasket could be causing some strange issues?

I can't decide if I want to just buy two complete rebuild kits for them or if I can do it cheaper by sourcing parts from a TDM850 from the local Yamaha dealer (no Ducati dealer within a 2 hour drive).

ALSO, there are four black plugs about the size of a dime that are supposed to be on these (2 per carb). They're on the bottom of the float bowl. What the heck, if anything, do those do?

Thanks.

[ducpainter]

The plugs are to plug e holes for float bowl heater lines.

Not sure about your leak.

[ChrisK]

Thanks for the information, I think the leak has to be the bowl gaskets, picking up new ones at the local Yam dealer tomorrow.

[ChrisK]

So since I was putting in new float bowl gaskets. I tried to give the 14 mm floats and 175 mains another shot. Also moved needles to the fifth slot. No go, wouldn't even start. So, I'm back to 13 mm and 170 mains. The thing that worries me, is that I have to have my idle mixture screw turned out 6 the s and the needles on the sixth position for it to start and run. Obviously not normal, so I'm worried. Just did a mpg test today, mostly cruising 60-65. Completely filled the tank and ran it all the way down till when the low fuel light came on at 127 miles. So still some gas left, don't know how much. What do you guys think?

[ChrisK]

Earlier I forgot to add that 50 of the miles were done with two people on her.

Also, I just went back out and road more before filling up. Ran the total to 145 miles. Brimmed it with 3.7 gallons. That's 39 mpg and some change, I figure it'd be we'll over 40 w/o the two up riding.