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Author Topic: mikuni carb for dummies  (Read 5775 times)
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« on: June 20, 2010, 10:44:39 AM »

alright guys got a puzzle for ya.  1994 monster 900... mikuni carbs, ran fine until i pulled the carbs out and cleaned them up a bit.  now it spits gas out of the breather.... i'm about to pull them again and i'm a total noob so any help would be great.  what do i look for etc.  i think the float settings must be off..... let it sit overnight and it filled both carbs full and fouled my plugs.  i guess that would indicate the fuel diaphragm being messed up as well.  i'll post more detailed info after i get them loose again.
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ducpainter
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« Reply #1 on: June 20, 2010, 11:02:22 AM »

Replace the vacuum petcock for sure. Those things can fill the cases with gas if the diaphragm fails.

It could be that there is just some dirt on the float needles causing them not to seat.

I think the recommended float level is 14mm on those carbs, but do a search before you believe me.
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« Reply #2 on: June 20, 2010, 11:20:46 AM »

Replace the vacuum petcock for sure. Those things can fill the cases with gas if the diaphragm fails.

It could be that there is just some dirt on the float needles causing them not to seat.

I think the recommended float level is 14mm on those carbs, but do a search before you believe me.

+1

Factory Pro site has a good guide for tuning these carbs and setting the float level.

You could give the float bowls a tap with the back of a screw driver to help reseat the float needles and dislodge any dirt (lazy old timers trick). It's helped me out on the side of the road.

There have been a few guys on this forum who have fitted the alternate type OEM fuel tap or some nice on/off aftermarket types. Great when you want to work on the bike, drain the tank, etc.
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1995 M900 (Road)
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2010 HM1100 Evo (Adventure)
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« Reply #3 on: June 20, 2010, 03:30:35 PM »


     thanks guys,  can anyone recommend a good carb kit and setup for a pretty much stock bike.  i'm running stock airbox(hopefully going to pods when money isn't so tight.) with a cored stock exhaust.  before this whole fueling fiasco it was running really rough from 2000 to 3500 rpm.  been tinkering with the carbs and cleaned them out twice now (going to be thrice after tonight).  i really just want this thing to run, distance style.  in fact planning a trip to arizona in 1.5 months.  and love the factory pro sight thanks koko waytogo
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« Reply #4 on: June 20, 2010, 03:52:17 PM »

How many miles?

You should look at the needle jets if it runs kinda doggy at low throttle openings.

Personally I used a dyno jet kit because that's what my dealer used and had a good supply of jets. Many people rave about the factory pro kit.
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« Reply #5 on: June 20, 2010, 04:35:08 PM »

+1

Bugger! Twice now my replies evaporated.

Buy factory Pro needle jets when you replace them because they are stainless and will last longer (cheaper too).

Tell FP and DJ your plans and they will recommend a jet kit for your needs.

Is your bike due for a valve adjustment? Say every 6000 miles.

Dont fit pods or modify the air box untill you are fitting the correct jet kit. ( you reckon it runs rough now!)

Edit. If the bike has done 12000 miles on it's cam belts or if the cam belts are two years old, replace them before your long trip.

The bike will be a real pleasure when it's tuned and serviced.

Cheers

« Last Edit: June 20, 2010, 04:45:40 PM by koko64 » Logged

1995 M900 (Road)
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« Reply #6 on: June 20, 2010, 04:50:28 PM »

10,987miles on the odometer. so i guess it's gettin close.  tomorrow i'm gonna get a manual shut off and bypass the vacuum shutoff.  i'm very new to this sort of thing and really appreciate you guys and all the good info so far.  due to an extreme lack of funds at the moment i'm forced to do all my own work, i believe i read something in here about monsters turning riders into mechanics lol.  i don't really have a complete mechanical history on this beast but i do know it had a complete service about 1.5 years ago at a dealership in AZ.
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« Reply #7 on: June 20, 2010, 06:23:03 PM »

Do you know what was done at the service? Are you confident the bike was cared for by the previous owner? Any paperwork?
You got any pictures of your bike? Someone eagle eyed may spot something that needs attention.

Have you got a workshop manual yet? Haynes make an ok one. Maybe other books are out there that would help. This forum is great. There are threads about the servicing needs of your bike on this forum too.

For parts required check the sponsors on this forum. They seem like enthusiasts.

Good move on the manual tap. Manual fuel taps are better IMO.

On a real tight budget I would make sure the belts and valve adjustment are good and replace the needle jets. Belt failure is a Ducati owners worst nightmare. If you have any dough left over fit a jet kit that has enough jets to allow future mods. Dynojet and Factory Pro will advise you.

Besides that just the normal new owner servicing to be sure before the long trip, you know checking oil, chain and sprockets, etc.

Good luck and keep us updated on how you are going with it.

These bikes aren't mega horsepower but they are mega fun! Bikes that get you in.
Cheers.
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1995 M900 (Road)
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« Reply #8 on: June 21, 2010, 03:34:45 PM »

it's alive mwahahaa!!!  bout to take her for a test drive.

the carb for rear cyl was absolutely full of powdered rubber.... apparently i scraped the airbox gasket when re-attaching it last time.  the needles look brand new, no signs of wear.  i'll report after a short ride as to how she's running.
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« Reply #9 on: June 21, 2010, 04:49:11 PM »

  bang head
(insert explitive's here)

ran great for a short 5 mile run....  brought it back and shut it down for about 20 min.  then tried to start it again and it's flooded.  never had any trouble before i fixed the stinkin' vacuum leak on the front cylinder....  guess i'lll tear her down again tomorrow.  i have a sneaky suspicion this is going to go well past just the carbs....  gotta dig up the service record. coffee  maybe the vacuum pump is pushing fuel past the needle and seat....Huh?  aargh
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« Reply #10 on: June 22, 2010, 03:20:37 AM »

http://www.ducatisuite.com/jetkit.html

Might be helpful, jet change, float height etc.
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« Reply #11 on: June 22, 2010, 06:57:56 PM »

alright.... clean service record from tom hull ducati in az...   150 mains 40 pilot... set on 1st clip with a 2mm plastic washer..... floats are at 11mm(i think it's too high)..... anyone know how to figure float setting for my configuration with partially cored exhaust...
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« Reply #12 on: June 23, 2010, 12:38:23 AM »

Float height is 14mm, regardless jetting.
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« Reply #13 on: June 23, 2010, 05:17:28 AM »

http://www.ducatisuite.com/jetkit.html

Might be helpful, jet change, float height etc.


very helpful sight thank you.

i was under the impression that larger jets required more fuel which means raise the floats( which is backwards on these things), am i incorrect in my assumption?  every day this exquisite piece of machinery sits in pieces breaks my heart. 

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« Reply #14 on: June 23, 2010, 12:34:25 PM »

Quote
am i incorrect in my assumption?
Yes.

Float height is f correct function of carbs generally.
Other jet sizes handles more/less fuel.
Just fix correct float height as f now.
« Last Edit: June 23, 2010, 12:45:04 PM by greenmonster » Logged

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