mikuni carb conversion problem

bavarian · Post by **bavarian** » Mon Jul 17, 2006 5:18 pm

I have a 1988 Ducati 750 Paso that I converted to 38mm Mikunis with dynajet stage two jets and Uni pod filters. I have searched the entire site and even the lenghtly write up I found about the conversion doesn't address my problem. The entire conversion went smoothly, that is until I turned on the ignition and fuel started pouring out of both float bowl overfill drains. I even installed a fuel pressure regulator and no fix. I removed the float bowls and cleaned everything out and even removed the floats and needles which were clean. I reinstalled it and I still have the same problem. I have the fuel line from the regulator hooked up to the the upper line, and the bottom line is hooked to a drain line as per the aforementioned lengthly write up that covers the conversion on this site. I hope somebody can give me some insight as to what I did wrong or need to check. Thanks!

Post by **paso750** » Mon Jul 17, 2006 7:30 pm

did you connect the returnline to the tank, there should be a Y connector in the line coming from the fuelpump to the carb (I used a T piece) ? That should solve it.
No pressure regulator required.

Gerhard

Post by **paso750** » Mon Jul 17, 2006 7:49 pm

I found another old text I once put together. Just posted it in the 750 technical FAQ section

G.

bavarian · Post by **bavarian** » Mon Jul 17, 2006 9:17 pm

I didn't connect the return line. Which spigot on the right side of the tank does the line need to be attached to; the forwrd or aft one? Thanks!

BikerBard · Post by **BikerBard** » Tue Jul 18, 2006 1:17 am

Be sure your fuel lines are correctly connected to the carbs themselves. I had the order reversed and almost went crazy trying to figure out why gas was pouring out of the **** things!

Post by **paso750** » Tue Jul 18, 2006 8:14 am

copied from a recent post in the mailing list:

"On my 906, the rear pipe is indeed for the fuel return, the front pipe is the breather."

G.

bavarian · Post by **bavarian** » Tue Jul 18, 2006 4:40 pm

I now have everything hooked up according to the site and still have the same problem. I even installed the pressure regulator in where the Y splits off and goes to the carb inlet. Could the floats be bad? They aren't full of fuel so I don't think they leak. The carbs came from a '95 900ss. I can hear the fuel being pumped into the tank so it definitle is bypassing some fuel? What could I be missing here?

Duc750 · Post by **Duc750** » Tue Jul 18, 2006 8:37 pm

Take the float bowls off and check the housing where the overflow drain screw fits
If you or a previous owner is particularly ham fisted these can crack quite easily which gives exactly that effect.
(I speak from experience

)

Have you checked that your floats do actually still float ?
You can do that quite easily when you have the float chamber off

Post by **paso750** » Wed Jul 19, 2006 7:56 am

you connected the fuel line from the pump to the upper front connetor of the carb right, not the bottom one.
If that`s all correct I`m also afraid it could be the the drain screw. I also had that once.

G.

bavarian · Post by **bavarian** » Wed Jul 19, 2006 1:15 pm

I'll check the drain screws, but wouldn't it always leak if the the bowls were cracked? They only leak gas with the pump on, the bike will run fine with the pump off until it runs out of the fuel that is in the float bowls. I'm going to check and see if the floats actually float as well...

Duc750 · Post by **Duc750** » Wed Jul 19, 2006 2:57 pm

Just a hairline crak in the housing of the scre might be enough to make it leak past under pressure but not without the pressure there :umm:

pikey · Post by **pikey** » Mon Sep 11, 2006 6:42 am

this may be a supid suggestion but have ypu measurd the float hight?
I have had similar problems on many japanese carbs and alot of times float hight adjustment has saved the day.

bavarian · Post by **bavarian** » Mon Sep 11, 2006 2:55 pm

I would like to measure the float height, but as yet nobody on this forum has come up with exactly how float height is measured and what the exact specs are. Until then I guess I'll keep fumbling around in the dark until the day a say forget it and slap the old webers back on. It sure would be nice to ride it this year...

pikey · Post by **pikey** » Mon Sep 11, 2006 9:23 pm

I have used the straight side of a digital caliper to measure the float hight on my cb 750. you can get a honda float gauge from various websites, and it will work just as well as any other. I dont know the correct float hight for the mikunis, but I can find out for you. you have to turn the carb sideways so the float is hanging straight down, and the bottom edge of the float must be perfectly straight with the the surface that the bowl touches. then measure the hight between the surface that the bowl touches and the bottom of the floats. now you know your float hight. once you know the correct hight (which I will try and find the correct hight), you can adjust float hight by gently bending the tab which the floats connect to, either up or down to compensate the diference.
Now with that said I have never been inside my mikuni 38mms
but my good friend, the previous owner, has. I will ask him the correct float hight, and if there are any special tricks for those carbs. I hope this helps.

good luck!..........pikey

Harigeharry · Post by **Harigeharry** » Tue Sep 12, 2006 8:21 am

bavarian wrote:I would like to measure the float height, but as yet nobody on this forum has come up with exactly how float height is measured and what the exact specs are. Until then I guess I'll keep fumbling around in the dark until the day a say forget it and slap the old webers back on. It sure would be nice to ride it this year...

This might help:

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

It was a great help with my build up:

http://forums.ducatipaso.org/viewtopic. ... pic&t=1105