Dellorto MB22A (Rumi Sport)

Moto Rumi technical problems or solutions
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hugomez
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Dellorto MB22A (Rumi Sport)

Post by hugomez » Tue Jul 09, 2019 8:04 pm

Hi all,

In the last days I have been working a bit in my Rumi Sport. Since I bought it, I only start the engine a few times and finally my first ride was a few days ago (around the building because it still hasn't Dutch documentation)

Among other problems that this motorcycle need to get fixed, I got carburation problems. It was extremely rich in the mixture.

I've check the "Rumi Dellorto Carburettors Specifications" table that Ian Skinner made for us years ago (You can see it at the next link: viewtopic.php?f=23&t=177 )

This is the result of what I found in my carburetor:

Float: 6.5 gr
Float needle length: 60mm
Main jet: 90 (It should be 100)
Atomizer: 265
Idle jet: 45
Slide: 50 (It should be 70)
Slide needle: E3 (It should be E1)
Slide needle position: Middle 2

Searching among other carburetors that I have around, I found a main jet 98, I could not find 100. I will give a try with it.
About the needle for the slide, I found the correct one, an E1
Last thing was the slide. I found two number 70, however one of them do not have the "hole" for the "bar" of the choke :shock: The other slide 70 that I found has the hole for the choke, but the "bar" of the choke of my motorcycle do not fit in it. I have to say that the choke of my Sport is activated with a lever at the handlebar, so it use a cable, however the replacement slider 70 I got, was in a carburetor that activate the choke without cable, but with a little push stick as the one at the UA15S of the Formichino.

I wonder if depending of the type of way the choke is activated, there are different type of slides, however I found this very strange if that is the case.

A solution would be reducing the size of my the choke bar, or make the "hole" at the slide bigger, however before removing any metal from any part, I want to ask your advise to be sure that I am not doing anything that I shouldn't. I don't want to ruin anything.

Please advise :)

Thank you very much in advance!!

Dellorto-choke-bar-comparison.jpg
Dellorto-choke-bar-comparison.jpg (88.37 KiB) Viewed 109 times
Dellorto-Slider-hole-too-small.jpg
Dellorto-Slider-hole-too-small.jpg (82.77 KiB) Viewed 109 times
My little Formichino here: http://www.formichino.com/pictures1.html

hugomez
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Posts: 3534
Joined: Thu Jun 11, 2009 10:05 am
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Re: Dellorto MB22A (Rumi Sport)

Post by hugomez » Tue Jul 09, 2019 10:45 pm

Here the measurements of both "choke bars".

The problem is the wide, because the long and high are very similar.

Dellorto-Choke-bar-measurement-01.jpg
Dellorto-Choke-bar-measurement-01.jpg (141.22 KiB) Viewed 94 times
Dellorto-Choke-bar-measurement-02.jpg
Dellorto-Choke-bar-measurement-02.jpg (122.48 KiB) Viewed 94 times
My little Formichino here: http://www.formichino.com/pictures1.html

hugomez
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Posts: 3534
Joined: Thu Jun 11, 2009 10:05 am
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Re: Dellorto MB22A (Rumi Sport)

Post by hugomez » Thu Jul 11, 2019 10:58 am

Hi,

This all is very strange.

The slide 50 I had in the MB22A with the "thick" choke, is original, but as mentioned, the choke doesn't fit in the also original slide 70 I want now to use in that carburettor.

Comparing in the Eurocarb website, I see the choke (for cable type), look different as mine. (See photo below)

Can anybody do me the favor to measure the choke (cable type) to compare with mine? I would really appreciate it, to try to clarify what is happening here.

(Maybe at the end my slide 50 is not as original as I think (and the choke (cable type) neither)
choke-dellorto.jpg
choke-dellorto.jpg (41.28 KiB) Viewed 64 times
My little Formichino here: http://www.formichino.com/pictures1.html

hugomez
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Posts: 3534
Joined: Thu Jun 11, 2009 10:05 am
Location: Amsterdam
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Re: Dellorto MB22A (Rumi Sport)

Post by hugomez » Thu Jul 11, 2019 8:12 pm

Thank you Rudolf for sending me the measurements of the choke (cable type) by Whatsapp.
It is a mystery why my slide (number 50) and the choke (cable type) that is coming with it, are different as the rest of Dellorto slide and choke, even if the look is basically the same with the exception of the size of the choke (and obviously the size of the "hole" at the slide to accommodate the choke). No worth it to carry on trying to find out.
To end with this story I will just order a new replacement choke (cable type) and the carburettor will be ready for test.
My little Formichino here: http://www.formichino.com/pictures1.html

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