Mikuni experts, your answers please...

discussions specific to the 906 Paso
lane1feathers
Posts: 258
Joined: Thu Sep 20, 2012 11:48 am
model: 906 Paso
year: 1989
Location: Perth, West. Australia

Re: Mikuni experts, your answers please...

Post by lane1feathers »

Ok, progress report....

Mikunis from the Yamaha worked...but the cables coming in from the rear did not. They fouled on the tank and made the steering feel stiff. Enter Gerhard :D he kindly donated a set from a Ducati so the cables came in/out from the front. Unfortunately this was not a quick fix either, as the cable bracket had very little room before the radiator cooling fan housing. The throttle was very stiff as the cables were bent as they came out, mainly the return (throttle close) cable. I removed the return cable as the spring on the carb is strong and was snapping shut. I had to use the original Paso twist grip as it has the stopper bar inside as its designed to run 1 cable only.
Image

Also, the cooling system hoses and T piece I installed were too high and the cable bracket stopped the carb from being seated on the inlet tubes. I had to re-route hoses and modify T piece to lower whole system :banghead:
The coil for the hor. cyl. was in the way too, so I had to move it forward. Make sure you remove the paint from both surfaces to get a good contact as its now only secured with one bolt. :thumbup:
I removed the electric fuel pump (gave to Giscard) and installed a vacuum pump in its place (Thankyou G.) I mounted it in the same spot but had to use spacers and a home made bracket.
Image
I power the pump from the inlet tube closest to it.
I supply vacuum to digiplex from the other inlet tube.
I have the fuel line going from tank to filter to pump to T piece to carb. The other leg of T piece returns back to tank with a restrictor jet in the line. There is also an overflow line from the mikunis that goes to a little catch tank. I have also mounted another little triangular,black, plastic tank from a monster which the diaphragm breather tubes go into.

Once it was all plumbed in I started it up and went for a ride. It took a little while for it to start but that was expected. It ran ok for a km or so but then started running like a pig and then died altogether. After pushing it home (she's stretching the relationship right here) I pulled it all apart and noticed that the diaphragms were slightly too small and were not seating properly in their grooves under the black covers. Luckily the ones from the Yamaha mikunis were a little bigger and seated perfectly. The jetting set up is as follows;
Dynojet (stage 2 for 900M) Needle jets with the circlip on the 3rd rung down from the top and the nylon ring under the circlip.
Dynojet springs
75 (mikuni) Starter jets
170 DJ Main jets
45 (mikuni) Idle jets
Idle screws set at 3 turns out
Adjusted idle to 1200rpm
Installed UNI foam pod filters, put the tank and seat back on and went for another ride. Pretty much runs perfect now with this set up :thumbup: There are a few little indiscretions every now and then (read; farts :fart: ) :mrgreen: but I think that's more to do with a balance issue as I only balanced by eye on the bench (made sure the butterflies were moving in sync and were at the same point at WOT) I will be making a balancer from some tubing later today and will fine tune now that I have the basics done.
I have a bad oil leak which needs to be fixed before going on a long ride anyway. I have traced this to the oil pressure switch which I'll be replacing when I get back down from my next work commute in a couple of weeks.

I hope this helps anyone who is looking at doing the mikuni conversion in the future. This set up works for me. I am in Australia at sea level. You may have to play with your jetting to suit climate and altitude.
I apologize for sounding like I know what I'm talking about (coz I don't :D ) I am only stating the steps I took to get where I got, and managed to pull it off. Thankyou to all for your help along the way...you know who you are :thumbup:
Last edited by lane1feathers on Fri Jul 26, 2013 2:10 pm, edited 1 time in total.
Lane
89 Dark Blue 906 Paso
Ducati Paso, It's an 'understanding'....
User avatar
paso750
paso grand pooh-bah
Posts: 5558
Joined: Sun Jul 18, 2004 12:00 am
model: 750 Paso
year: 1987
Location: southern Germany

Re: Mikuni experts, your answers please...

Post by paso750 »

There are throttle cable bends like these. Maybe there`s something matching or you can make one yourself.
Image
Image

they sell all parts
http://www.venhill.co.uk/Cables_-_Compo ... E_KIT.html

Do you still have the Yamaha throttle cables ? Are they the type with a bend on both cables like these:
Image
In that case you could shorten them and make your own custom cables.

G.
lane1feathers
Posts: 258
Joined: Thu Sep 20, 2012 11:48 am
model: 906 Paso
year: 1989
Location: Perth, West. Australia

Re: Mikuni experts, your answers please...

Post by lane1feathers »

Yeah, those cable bends look like the go. I might have to invest in some of those :thumbup:
Lane
89 Dark Blue 906 Paso
Ducati Paso, It's an 'understanding'....
koko64
Posts: 95
Joined: Sun Feb 24, 2013 11:14 pm
model: other
year: 1999
Location: Melbourne Australia

Re: Mikuni experts, your answers please...

Post by koko64 »

Hey Lane. :thumbup:
Great job, obviously the aircooled motor is easier to do it with.

I just split two pairs of Mikunis so I can run them on short manifolds. Im using the carbs with the throttle cam to make it easier. There is a step and lip in the transition from the carb mouth to carb throat due to the way the carb is bored. To improve airflow, I "ported" the carb mouth to create a good radius at the transition from the carb mouth to its throat just in front of the CV slide. I also put a radius on the front, bottom edge of the CV slide to improve flow.
They will go on a P750 or E750, whichever I find first!
Organzing the short manifolds, hoses, fuel inlets and cables will be a pain in the arse, but it's something I've wanted to try for a long time.
2013 M1100 Evo Street
2004 GSXR750 Track
lane1feathers
Posts: 258
Joined: Thu Sep 20, 2012 11:48 am
model: 906 Paso
year: 1989
Location: Perth, West. Australia

Re: Mikuni experts, your answers please...

Post by lane1feathers »

...there's nothing like having a project :thumbup: almost as much satisfaction as riding.
But definitely most satisfaction when riding something you've had a hand in building/resurrecting :beer:
Lane
89 Dark Blue 906 Paso
Ducati Paso, It's an 'understanding'....
lane1feathers
Posts: 258
Joined: Thu Sep 20, 2012 11:48 am
model: 906 Paso
year: 1989
Location: Perth, West. Australia

Re: Mikuni experts, your answers please...

Post by lane1feathers »

lane1feathers wrote:The jetting set up is as follows;
Dynojet (stage 2 for 900M) Needle jets with the circlip on the 3rd rung down from the top and the nylon ring under the circlip.
Dynojet springs
75 (mikuni) Starter jets
170 DJ Main jets
45 (mikuni) Idle jets
Idle screws set at 3 turns out
Adjusted idle to 1200rpm
I had balanced the carbs but couldn't get rid of the bucking on deceleration. I wound the mixture screws right in to lean off the mix. and dropped the needles one rung. That helped to smoothen out the deceleration but now the idle was hanging around 2000rpm and causing a flat spot mid-range.
I swapped out the 45 idle jets for 42.5's and put everything back as above. Now it's running like it came off the showroom floor. I was expecting to have to fine tune a little more but this set up seems to be perfect. I'm at sea level.
I initially used the 45's as they came with the carbs and I had open cans etc. but should have gone with a smaller size as suggested and saved time and grief :truck:

I thought I'd better update the thread incase anyone's using the info for their own conversion. :thumbup:
Lane
89 Dark Blue 906 Paso
Ducati Paso, It's an 'understanding'....
Andrew2
paso grand pooh-bah
Posts: 574
Joined: Thu Oct 27, 2011 7:47 am
model: 750 Sport
year: 1988
Location: Wollongong,Australia

Re: Mikuni experts, your answers please...

Post by Andrew2 »

Good stuff Lane.Happy days ahead :choo: .

Cheers
Andrew
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