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I am trying to figure out what exactly I need to do to make this bike run perfect. Its a carbed 99 m750. I have cut the airbox and put in K&N pod airfilters, also using a stage 1 jet kit and I have also changed to a Staintune exhaust. I tried adjusting the fuel mixture myself but I have to change it every time the temp changes 10 degrees. It takes a long time to get it to maintain idle and not stall. Also when it is finally running smooth, it is horrible at low speeds...your either on or off the gas, there is no middle ground,. It feels like it bucks if your trying to maintain a little throttle in first or second. I know this bike will never be as smooth as my BMW r1200...but I think it can be a lot better than it is. Any ideas or tips on what you think might work??? I don't know if I can afford to toss in a upgraded carb. but I would still like to know if that would solve a lot of my problems, hopefully the pictures will show up below
 

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u4ric blues said:
I am trying to figure out what exactly I need to do to make this bike run perfect. Its a carbed 99 m750. I have cut the airbox and put in K&N pod airfilters, also using a stage 1 jet kit and I have also changed to a Staintune exhaust. I tried adjusting the fuel mixture myself but I have to change it every time the temp changes 10 degrees. It takes a long time to get it to maintain idle and not stall. Also when it is finally running smooth, it is horrible at low speeds...your either on or off the gas, there is no middle ground,. It feels like it bucks if your trying to maintain a little throttle in first or second. I know this bike will never be as smooth as my BMW r1200...but I think it can be a lot better than it is. Any ideas or tips on what you think might work??? I don't know if I can afford to toss in a upgraded carb. but I would still like to know if that would solve a lot of my problems, hopefully the pictures will show up below
You need a stage 2 jet kit for that set-up. It will solve those issues.
 

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ducpainter said:
You need a stage 2 jet kit for that set-up. It will solve those issues.
+1

Make sure you've got everything else that might be adding to the problem set right first too, get the carbs balanced, make sure you're using new plugs and a clean fuel filter, check the fuel pump, check the valve clearances (though they'd need to be a long way out to cause tuning problems).

I'd also recommend paying for a few dyno runs - get someone to do you some runs at 10%, 25%, 50%, and full throttle and chart the air/fuel ratio across the rev range on each run (the actual throttle opening isn't critical, you just want a few constant throttle runs at apporximately those sort of openings to see whats going on with each jetting circuit so you can identify pilot jet, needle, and main jet problems).

big
 

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bigiain said:
+1

Make sure you've got everything else that might be adding to the problem set right first too, get the carbs balanced, make sure you're using new plugs and a clean fuel filter, check the fuel pump, check the valve clearances (though they'd need to be a long way out to cause tuning problems).

I'd also recommend paying for a few dyno runs - get someone to do you some runs at 10%, 25%, 50%, and full throttle and chart the air/fuel ratio across the rev range on each run (the actual throttle opening isn't critical, you just want a few constant throttle runs at apporximately those sort of openings to see whats going on with each jetting circuit so you can identify pilot jet, needle, and main jet problems).

big
+1 again - I've ended up with jetting way different even to that recommended with pod filters....
 

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You should be able to get the idle tuned in by adjusting the idle mixture screws on the outside of the carburetors. I don't know what the setting is for an M750, but for the M900 the recommended setting was 3.5 turns out and both of the ones I owned worked best at 4 turns out.

Start off by figuring out what the screws are set to now, then try a few different settings, like 2.5 turns, 3 turns, and 3.5 turns to see how it works. You should be able to get the low speed tuned right without opening up the carburetors.

Oh, and count by half turns when turning those screws. It's a lot easier that way.

Here's a photo of the brass screws on the left side.
 

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I had the same problem though I was stock. Turned out the emulsion tubes were worn. Also, the idle mixture is important, and also the progression holes just after idle mixture. These holes are dependent on float level so you'll likely need to tweak that with all the mods you've done. When you check float level make sure you check the same side of each float- the pontoons are not symmetrical. There's a footnote about this on the Factory web page somewhere, I think under the 900SS page.

jim
 

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With any miles on them the Emulsion tubes should be replaced. The pilot circuit needs major changes when the airbox is opened or removed.
It will require some work and dyno time to get them to work properly.

Fred tells me that someone called and asked him about that last week and he told them that there is no power to be gained by it and it is a tuning nightmare.

Doug
 

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moperfserv said:
Fred tells me that someone called and asked him about that last week and he told them that there is no power to be gained by it and it is a tuning nightmare.
If you're referring to cutting the airbox, that's the total opposite of my experience. My carbureted 97 M900 was stronger everywhere after cutting the airbox and rejetting. And it wasn't all that hard to get the jetting right on.
 

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Pods are worth it for the sound and looks alone! Cut out the variables as suggested above - new emulsion tubes, fuel filter, check pump, plugs, valves etc. - then start from recommended baseline settings and see how it goes! (and be prepared for a bit of trial and error - I think Scott was very lucky as it's taken me a lot of fiddling and I'm still not sure if I'm there yet. I think each bike and location calls for it's own setup when it comes to carbs, but if you don't enjoy the fiddling about bit you just have to pay someone else....) ;D
 

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Scott, your 900 probably did have big increases when you cut the lid open, but my experience and Fred's is that the 750s don't respond like that.
The airbox volume relative to the cylinder volume is quite a bit different between the two.
I did a couple 750s 3 or 4 years ago, but Fred recently did the test where he jetted it with the airbox and snorkels, then re-jetted it with the top removed, and got no increase in power. I noticed the same thing but didn't do quite as thorough a test.

Doug
 

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I had much the same trouble with my Mikunis after installing aftermarket exhaust and BMC filter on an open airbox. Off-idle it was ragged and jumpy -- fouled plugs like crazy. But in midrange it was too lean. Had the airbox on/off fourteen times doing various things to try to fix. Mark at Factory Pro was very helpful -- even sent me some special needles -- but I just couldn't get the Mikunis to work decently.

Finally gave up and bought a set of FCR 41s from Chris at CA Cycleworks. They worked perfectly right out of the box. YMMV, but my advice is to junk the Mikunis and put on the FCRs before you waste any more time and spoil any more rides.
 
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