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 Post subject: Mikuni Carbs
PostPosted: Sun Mar 01, 2020 8:21 am 
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Joined: Sun Dec 29, 2019 11:30 pm
Posts: 3
Location: New Zealand
model: 750 Paso
year: 1988
Has anyone got some info about setting up Mikuni Carbs on a Paso 750 Limited, (I'm not sure if LTD means much but has been suggested it might have racier cams and bigger valves).
This would explain it's running rich and "popping" sounds like piping in the carbs, the plugs indicate running rich, & I've dropped the needles down to their most lean position, the next step will be re jetting .. (after a fast ride on a good day,) i only have to wait 8 hours ...hehehe

I've setup the tubes, pump, return and filter, they're running nicely now ,,

Anyone got any anecdotes & tips to share


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 Post subject: Re: Mikuni Carbs
PostPosted: Mon Mar 02, 2020 9:35 pm 
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Joined: Tue Jan 17, 2006 12:00 am
Posts: 331
Location: Lower Hutt, New Zealand
model: 750 Paso
year: 1986
Hi Stepaso,
What air filters are you using and what sort of exhaust pipes?
With foam pods and Conti mufflers a Dynajet Stage 2 kit worked a charm, nice steady idle and great throttle response.

Cheers,
Fraser

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1980 Moto Morini 500 Sport
1979 Moto Guzzi V1000 Convert


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 Post subject: Re: Mikuni Carbs
PostPosted: Tue Mar 03, 2020 12:18 pm 
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Joined: Sun Dec 29, 2019 11:30 pm
Posts: 3
Location: New Zealand
model: 750 Paso
year: 1988
The air filters are UNI foam pods, and the exhaust is aftermarket, Alloy in bulk & rear with SS on the bit that goes to the exaust, no brand indicators. ( I can't figure out how to put pic's up )

I see you're in Lower Hutt, I'm in Henderson Vally in West Auckland, I was in "the Hutt" last week of January and had the most stunning fast ride up the Rimatuka hill, good light, late afternoon, no other traffic, dry road, pure NZ bike riding magic ..


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 Post subject: Re: Mikuni Carbs
PostPosted: Tue Mar 03, 2020 7:17 pm 
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paso grand pooh-bah
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Joined: Wed Dec 05, 2007 12:35 am
Posts: 1701
Location: Newzealand
model: 906 Paso
year: 1990
Yee ha , another Kiwi.

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 Post subject: Re: Mikuni Carbs
PostPosted: Wed Mar 04, 2020 4:52 pm 
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paso grand pooh-bah
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Joined: Sun Jul 18, 2004 12:00 am
Posts: 5366
Location: southern Germany
model: 750 Paso
year: 1987
Quote:
I can't figure out how to put pic's up

That is simple. Below the editing field in which you write a post there's a red bar saying 'upload attachment'. Click 'search' and select the file from your computer, then click 'add file'. You may have to resize the picture as a full resolution several megapixel large Image having 5MB and more won't work.
If your picture is hosted somewhere else you copy the link into the editing field, mark it and click on 'Img' which you find just above the text field.


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 Post subject: Re: Mikuni Carbs
PostPosted: Thu Mar 05, 2020 6:05 pm 
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Joined: Sun Feb 19, 2006 12:00 am
Posts: 137
Location: Bolivar, Ohio USA
model: 750 Paso
year: 1988
Hi Stepaso,
I have a LTD but cannot confirm or deny the internal modifications - just doesn't seem to be enough info out there and I have never opened up the engine to measure and compare with other's non-LTD motors. Anyway, I have Dellorto carbs on mine and when I bought it from the prior (2nd) owner the carbs were installed but so was an unmarked aftermarket 2-into-2 exhaust with large aluminum "mufflers". I put that in quotes because they were open straight through with no baffling/noise reduction so didn't muffle anyting. Bike ran horrible - cough, backfire, ran rich, no low rev power, just unbearable. And it was freaking loud and hurt my hearing too. Fortunately I did get the original Silentium "off road" exhaust setup/mufflers that were stock on LTD's (and different than non-LTD models) with it and when I put those on the bike was transformed. All the bad qualities went away - the bike literally went from unbearable to loveable - so I have to think the carbs were setup with the stock mufflers and the prior owner added the aftermarket exhaust because it "sounded better". So I guess the moral of my story here is that it may be your exhaust is not helping your bike to run well but also that the carbs/exhaust should be matched to each other. I will admit to not being tuning experienced so would be great if others here with that experience could chime in.


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 Post subject: Re: Mikuni Carbs
PostPosted: Mon Mar 16, 2020 1:21 am 
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Joined: Sun Feb 24, 2013 11:14 pm
Posts: 79
Location: Melbourne Australia
model: other
year: 1999
If they are used Mikuni BDST38 carbs then the needle jets, also called emulsion tubes are likely to be ovaled out. The oem brass ones are soft and get sawed into by the needle. If they are brass coloured they are oem which dont last long. Slight ovalling lets a lot of extra fuel thru. Factory Pro make harder needle jets that last longer. What jets and kit are in it?

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 Post subject: Re: Mikuni Carbs
PostPosted: Mon Mar 16, 2020 12:49 pm 
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Joined: Sun Dec 29, 2019 11:30 pm
Posts: 3
Location: New Zealand
model: 750 Paso
year: 1988
Thanks WhitePaso, secretly I think the LTD was just a marketing idea, (some would call it a scam) but I'm open any knowledge available on this..
I have been told they have hot cams and big valves, which is all very well but people don't always want to drive their bikes between 6 & 8K RPM all the time, riding "way up there" is downright dangerous.. Although in saying that while on a ride last week the Paso performed amazing at the top end, I went up to 115mph in a snap, everything felt happy as up there. I'm struggling with flatness in the 2 to 5K range,

This Paso, Pantah engine & Mikuni carbs are new to me and learning curve, all my past Ducati experience comes from a bevel drive,

I "spat the dummy" with the whole thing last week, I went for a ride and when coming up to an intersection it coughed and stalled,, I wasn't slipping the clutch, it lurched forward, I lost my footing on some loose metal and over we went.
The bike rolled onto a curb, scratched and broke some fibreglass on the left side, as well as the left indicator mirror.. It took a bystander help to pick the bike back up as petrol poured out of the overflows and made the road so slippery I couldn't lift it by myself..

I was going to go down the back country road twisties for the next hour in the afternoon sun, but instead had a very grumpy plonk home on the motorway.

Pissed off, I put the Paso into the back room and shut the door for a week...

A week later.... Being a happy Ducatisti, I soon got all that behind me and got on with the business of turning myself into an A1 mechanic ..
A weeks worth of research and thinking, watching the summer slipping away and I'm happily back on the case.

I pulled the carbs apart and cleaned everything putting it back together, I fixed a range of issues re-routing the fuel line to reduce the pressure, and shifting the needles to the top position after a few days I've got it to run quite nicely.
Written on the side of the carb and barely legible is DUC75 T1 Y1, from what I've read on this site thats should be used for racing and should be changed, but that is yet to happen and I need to understand more before they get changed.

One of the gems I found on this site is those tubes coming out near the top of the carb, one pointing backward the other pointing down, these are the breathers for the bowls and need to have tubes on them leading to a pressure free place, I made mine the same length (about 800mm), put some insulation (plastic wool) in the ends to stop dirt getting in and ran them along under the seat. Those two "vents" had been bugging me for ages as it was obvious the pressures would be different but I had no idea what they did.

Some of the tools I used might be helpful to others,
I made 3 lines for the overflows one from each carb and one for the T between them. On the end of the lines I placed small plastic pill bottles, this allowed me to see any fuel and which outlet it came from, this system really works as I started with an overpressuried pump (solved using a by pass) and one carb got some grit in it, (from the by pass) then flooded, it was all easy to see where the fuel was coming from.. and these can stay to be checked if I feel the need.
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A useful tool I created for balancing might be of interest to others, it's cheap and accurate

get 2 big glass bottles, 2 plastic caps with 2 holes in them for plastic tube, build it so there is long tube to transfer the water between the bottles, this joins the bottles together so when vacuum is applied to bottles water flows one way or the other, coil the tube inside the bottles ..
the other tubes connect the manifolds one to each bottle.
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add water (make sure you don't fill more than a third of a bottle, if you put too much water in there is the danger of sucking water into the engine)
put a light behind it if you want to get sophisticated or stylish

Start the engine and set to a fast idle, you want to balance at 3500 - 4000 rpm, watch whats going on, the water will pass from one bottle to the other, when you tweak the carb adjustment the water will slow, speed up or reverse flow. I found the most precise adjustment was obtained by letting the water run from one bottle and fill the transfer tube with bubbles, by watching the movement of the bubbles in the tube the adjustment was really sensitive but accurate.. (rather than the water levels inside the bottles)

The adjustment difference would have been 1/8 of a turn (if that) between the bubbles going one way, stopping then flowing back, play with this for a while and you will realise how accurate a technique this is ...


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 Post subject: Re: Mikuni Carbs
PostPosted: Thu Mar 19, 2020 1:24 pm 
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paso grand pooh-bah

Joined: Thu Jun 21, 2007 12:00 am
Posts: 1475
Location: Gothenburg, SWEDEN
model: 907 I.E.
year: 1991
https://www.ducati.ms/attachments/ducat ... ng.322161/

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M900 -97
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