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Author Topic: Resetting Stock Idle Speed  (Read 7786 times)
koko64
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« Reply #30 on: August 11, 2020, 07:50:07 AM »

Sharp tapered needles are not stock for a 900 or 750 so are aftermarket and may have markings. The fatter needle with a slight taper is most likely stock and it may have a Mikuni insignia stamped on it.
Does the air box lid have the snorkel? If not, then stock 140 jets may be a little lean.
Worn needle jet tubes will make cruise/midrange too rich.
What do your plugs say?
« Last Edit: August 11, 2020, 07:58:10 AM by koko64 » Logged

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« Reply #31 on: August 12, 2020, 05:47:31 AM »

Thanks koko, you're correct they do have markings.  Y218's or something close to that (I can't recall the last 2 digits). 

No snorkels, and the lid is "swiss cheesed"  I masking taped the DIY holes to better emulate stock.

I have also a set of needles with mikuni markings on them that have only one position on them.  I tried these last night with both the 140s and 150 main jets.  same results each time: starts and idles fine, dies at the first crack of the throttle.  I'm thinking super lean.  I cant for the life of me figure out why the stock needles are giving me such lean results... maybe the pilot air jets with the side holes were appropriate after all?  (I switched these out for jets without side holes when I discovered them, presuming this to be a modification).

I went back to long skinny needles at 4th position last night.  This time I removed the washers (shims?) at the bottom of the slides and moved the washer on the needle to the topside of the e-clip.  This needle is consistently giving me the best throttle response so far.  Looks like I need to sync again though; the the slides are not rising evenly anymore.  Left side lags and backfires into the airbox when I watch it run without the lid (does this indicate rich?). 

At this point I'm considering coughing up the change for a stage 2 dyno kit... unless I can emulate it by just buying 165 main jets?
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« Reply #32 on: August 12, 2020, 07:49:03 AM »

Update: these washers are indeed Sudco carburetor needle shims.  Pictured here under the mikuni N208.099 press-in main jets:

http://www.pjmotorsports.com/mikuni-jets.html#main%20jets
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koko64
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« Reply #33 on: August 12, 2020, 12:36:45 PM »

The pilot's without the bleed holes are correct. 40 is in the ball park.
The bikes were on the lean side in the midrange (needles) when dead stock for emissions, so no snorkles is having an effect leaning out some more.
The stock needles were often replaced to add some fuel if nothing else was. Lean US needles were substituted for not so lean EU needles or an aftermarket kit was used.

You have a concurrent issue with the slides not rising together and correctly as ducpainter mentioned. It doesn't take much for a diaphragm to not seal correctly. Pinching a lip with cap is common and a ring not seating happens. Test before fitting by blowing in the vacuum hoses and manually lift for even spring return.

The tape would bug me as is not sustainable. I'd commit to an open airbox or a stock one. Drilled de snorkeled lids need  sporty needles and 150-155ish main jets, open lids 162.5- 165's, stock 140''s, but local fuel varies. Ducpainter ran a drilled or partial lid so try his jetting if you want to remove the tape but not chop the lid.
« Last Edit: August 12, 2020, 12:39:20 PM by koko64 » Logged

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« Reply #34 on: August 13, 2020, 04:26:46 AM »

Thanks Koko, this is helpful.  I'll make sure that diaphragm is rising evenly before I move on.  got any idea where I can find Ducpainter's jetting configuration?
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« Reply #35 on: August 13, 2020, 10:31:14 AM »

PM him or ask the question here.

What markings does the sporty needle have?

When in doubt, start with the middle notch on an adjustable needle.

If you can identify that sporty needle, there will be a guide to its setting for your mods.
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« Reply #36 on: August 14, 2020, 05:10:32 AM »

Groovy, thanks koko, I'm getting close.  Ordered 165 and 170 mains and sent him a PM.  I'll check the markings when I get a chance to open up the carbs again-- I recall it starts with Y2 and there are 2 more digits I don't recall after the 2. Is there a site you use to find these guides?
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koko64
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« Reply #37 on: August 14, 2020, 09:22:35 AM »

Look up Dynojet for their US kits.  I lost my link but the instructions for each kit are on line. The fat needles are stock so go with the sporty needles.

By 165 mains I take it that you're going to open the air box lid. Try a needle position midway or a notch richer, so how many notches on the sporty aftermarket needles?
« Last Edit: August 14, 2020, 09:37:23 AM by koko64 » Logged

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« Reply #38 on: August 14, 2020, 02:52:17 PM »

My drilled air box lid...

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« Reply #39 on: August 14, 2020, 02:53:51 PM »

 waytogo

https://www.dynojet.com/jet-kit-for-1998-1999-ducati-m900-monster-7209/
Click on the download for the installation instructions.
« Last Edit: August 14, 2020, 02:56:34 PM by koko64 » Logged

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« Reply #40 on: August 14, 2020, 03:13:09 PM »

waytogo

https://www.dynojet.com/jet-kit-for-1998-1999-ducati-m900-monster-7209/
Click on the download for the installation instructions.
The kits for the earlier bikes were the same except for the nnedles. Probably due to the smaller valves in the 98/99.
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« Reply #41 on: August 14, 2020, 04:10:19 PM »

Yep 729 Vs 730 needles. You're correct, the 729 needle was also used in the 750 which adds up. waytogo

Shows that valve size and cams have as much to say as displacement.
« Last Edit: August 14, 2020, 10:09:46 PM by koko64 » Logged

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« Reply #42 on: August 24, 2020, 04:38:19 AM »

Awesome, thanks folks--

Got my hands on some 165 and 170 mikuni mains from the aforementioned site, still not sure what the exact specs are on this tapered needle since it has no markings, but I've got it running strong!  Final jetting configuration:

165 main
70 secondary
Pilot air screw 4 turns out
long skinny tapered needle 4th position down + 1 needle shim (so ~4 1/2 down)
40 pilots without bleed holes

My airbox is drilled just about identically to ducpainter's shown earlier, and I'm running stock exhaust.

Thanks to everybody who helped out with this! The plugs look great and bike is extremely fun!

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« Reply #43 on: August 24, 2020, 04:46:16 AM »

 chug
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