Moto Rumi Sport - 1951 (Fixing some problems)

Moto Rumi technical problems or solutions
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Moto Rumi Sport - 1951 (Fixing some problems)

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
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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
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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
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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.
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Forks Rumi Sport - Dismantling

Post by hugomez » Sun Jul 14, 2019 12:09 pm

Hi,

The forks bushes of my Rumi Sport are worn and need replacement (WATCH video):



Today I started dismantling the forks, but when I was loosing the center nut of the fork I stopped, because I don't know how much pressure the springs are putting to the upper yoke, so I afraid that if the center nut is completely removed, the upper springs and the upper yoke are going to eject like rockets.
I don't have the special tool for the dismantling of this fork, and not experience with type of forks either. The type of forks that my Bicarburatore & Scoiattolo mount is the later model, not this earlier model.

At this point, can anybody advise me what should be the next step to do this correctly and as safe as possible?

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Thank you very much in advance.
Hugo
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Re: Forks Rumi Sport - Dismantling

Post by hugomez » Sun Jul 14, 2019 1:33 pm

Thank you Rudolf for the tips by Whatsapp!!!!!! :D

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Re: Moto Rumi Sport - 1951 (Fixing some problems)

Post by hugomez » Sun Jul 28, 2019 10:06 pm

Some news about the Sport.

By parts:

Forks:
Rudolf helped me bringing a brand new lower yoke (including the bushes) and a used upper yoke with the bushes in pretty good condition. With his original Rumi tool for the assembling of the forks, the process was pretty fast and now this problem is solved.

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Carburettor:
After replacing several parts (jets, needles, slider, etc, to the correct sizes, I tested the bike and it was running very well. So carburation problems are solved. (Still pending to receive the choke from Juan Nizio, and the carburettor will be 100% perfect)


Unexpected problem (but not too bad at the end):
After testing the Sport I decided to visit a friend at the other side of the city and during the way back home, at the end of a long straight road (around 400 meters), the engine lock. Then I check the kickstarted and was frozen. In that moment I thought the worst, so I walk home with the bike at the side. At home and with the engine cold I check and it was not frozen anymore, however I start dismantling for a further inspection. Then I confirmed how lucky I was, realising that very little damage happened in the right side piston and even less in the cylinder.
With a little manual work I will have them ready to assemble again, luckily the damage doesn't need machining.

Probably I was too fast for too long in an engine that didn't have completed the running-in period.
I will be definitely more careful during my next rides.

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Rumiroma
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Re: Moto Rumi Sport - 1951 (Fixing some problems)

Post by Rumiroma » Sun Jul 28, 2019 11:51 pm

Hi the damage you have is not from lack of running in,
Yes I am a newcomer to Moto Rumi but have been building engines for over 50 years.
The damage that I can see is either from something coming in from intake, or something from crankshaft seal, bearing cage, etc.
Michael

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Re: Moto Rumi Sport - 1951 (Fixing some problems)

Post by hugomez » Mon Jul 29, 2019 8:22 am

Rumiroma wrote:
Sun Jul 28, 2019 11:51 pm
Hi the damage you have is not from lack of running in,
Yes I am a newcomer to Moto Rumi but have been building engines for over 50 years.
The damage that I can see is either from something coming in from intake, or something from crankshaft seal, bearing cage, etc.
Michael
Hi Michael,
Whatever caused the problem, I hope doesn't happen again. At this point I guess the right thing to do is just assemble the cylinders, once the little marks are removed from piston and cylinder, and ride carefully for some time.

If you have a better suggestion please let me know, I would like to know what you think.

This is how exactly happened. After the long straight road (400 meters) and riding in 4th gear to 3/4 of the throttle, I was arriving to the end of the road, when I was reducing before taking the curve, then that happened.

Greets,
Hugo
My little Formichino here: http://www.formichino.com/pictures1.html

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Re: Moto Rumi Sport - 1951 (Fixing some problems)

Post by greasy-fingers » Mon Jul 29, 2019 8:52 am

Hi Hugo, to me jpeg 2 and 3 look like classic 2 stroke nip-up, the fact that it happened when you closed down after a run would suggest that your carb is running lean on pilot, jpeg 4 is a little more worrying due to the score being in line with the ring peg = I would give the condition and security of the ring peg and piston ring ends a good examine as it does look like something has travelled down the piston in that area. graham.

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Re: Moto Rumi Sport - 1951 (Fixing some problems)

Post by hugomez » Mon Jul 29, 2019 9:19 am

greasy-fingers wrote:
Mon Jul 29, 2019 8:52 am
Hi Hugo, to me jpeg 2 and 3 look like classic 2 stroke nip-up, the fact that it happened when you closed down after a run would suggest that your carb is running lean on pilot, jpeg 4 is a little more worrying due to the score being in line with the ring peg = I would give the condition and security of the ring peg and piston ring ends a good examine as it does look like something has travelled down the piston in that area. graham.
Hi Graham,

Thanks for your reply. Yes, the most worrying part is the area of the lower ring peg. Seem that a little bit of it move along the piston and cylinder. I check and still the remain of the ring peg that is there make the work and avoid the ring to turn around the piston. Seem that the damage caused at the piston and at the cylinder will be possible to remove. I will work on it and show photos once is done. I have to buy a "Norton India" stone for the piston and a "3-arm brake cylinder hone". Once I receive them I will try to fix it.
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Re: Moto Rumi Sport - 1951 (Fixing some problems)

Post by Rumiroma » Mon Jul 29, 2019 9:56 am

Hi, if the ring peg has a bit missing look inside the piston to see if you can push the remaining part out as it may be loose.
I would not start this engine up until I have found the problem. The long score made from? Ring peg part would have tightened up the cylinder to smoke the engine seizure, you must clean out crankcases, as this a mistake most people make, as everything goes down before it goes up
Michael

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Re: Moto Rumi Sport - 1951 (Fixing some problems)

Post by hugomez » Mon Jul 29, 2019 10:08 am

Hi Michael,
Thanks for your reply. I will clean well the cavity between the crankcase halves (where the con rod moves). If there is any little trace of metal there will be gone after I clean it.

Greets,
Hugo
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Re: Moto Rumi Sport - 1951 (Fixing some problems)

Post by Ian Skinner » Mon Jul 29, 2019 11:19 am

Hi Guys

Just a reminder of my 'Strange Looking Conrod' item, some years back. Seems appropriate!

Ian

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Re: Moto Rumi Sport - 1951 (Fixing some problems)

Post by hugomez » Mon Jul 29, 2019 1:42 pm

Very interesting reading here:
https://cdn2.ms-motorservice.com/filead ... _51730.pdf

Greets,
Hugo
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Re: Moto Rumi Sport - 1951 (Fixing some problems)

Post by greasy-fingers » Mon Jul 29, 2019 2:21 pm

That article looks to be aimed at 4 stroke petrol and diesel engines, but interesting all the same.

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Re: Moto Rumi Sport - 1951 (Fixing some problems)

Post by hugomez » Mon Jul 29, 2019 8:54 pm

Hi,

After a closer inspection to the ring peg, I can confirm that the lower one is the same size as the others two, for some reason yesterday I thought it was damaged, but now I see it is not (luckily)

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Re: Moto Rumi Sport - 1951 (Fixing some problems)

Post by hugomez » Wed Jul 31, 2019 9:01 pm

Hi,

This is the result after honing the cylinders barrel. I hope I did it right because is the first time I do it. Lubricating it with oil every 10 to 12 seconds. Slow speed at the 3 arms hone tool attach to my driller.

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Re: Moto Rumi Sport - 1951 (Fixing some problems)

Post by hugomez » Mon Aug 05, 2019 7:11 pm

Today I received the "Norton India Stone" to fix the piston.

This is the result:

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Norton-India-Stone.jpg
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Re: Moto Rumi Sport - 1951 (Fixing some problems)

Post by arthur lewthwaite » Mon Aug 05, 2019 8:02 pm

Hugo the honing of the cylinders looks good, but the amount you needed to clean pistons skirts I would look at replacement pistons. Not sure what others may think.

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Re: Moto Rumi Sport - 1951 (Fixing some problems)

Post by hugomez » Mon Aug 05, 2019 10:17 pm

arthur lewthwaite wrote:
Mon Aug 05, 2019 8:02 pm
Hugo the honing of the cylinders looks good, but the amount you needed to clean pistons skirts I would look at replacement pistons. Not sure what others may think.
Hi Arthur, I've already assemble the cylinders and probably tomorrow I will do a test checking the compression to see how many psi both sides give me.

Most of the time I listen and react accordingly whatever experienced members of the forum advise me when I get problems with the bikes. This time several people told me that they think the stuck piston/cylinder was caused by some external small object that maybe now is inside the cavity of the crankshaft/conrod, however for me to check that probable theory I would have to open the complete engine apart, and honestly I don't feel like doing this now, so I am going to gamble and hope that this is not the case.
In case they are right and something external was inside, there is the possibility that once I removed the cylinder, it felt out and now there is nothing inside.
Either case the cylinders are now assembled and soon I will probably ride the bike and see what happen once I fix another problem with the front tyre.

Greets,
Hugo
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Re: Moto Rumi Sport - 1951 (Fixing some problems)

Post by hugomez » Tue Aug 06, 2019 5:38 pm

Hi,

I just test the compression in both cylinders and the reading is the same, between 80 and 90 PSI.

Thanks Rudolf for explaining me how to fix the damaged cylinder and piston :D


Moto-Rumi-cylinder-compression-test.jpg
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Spokes for the 21inch wheel (Sport)

Post by hugomez » Tue Aug 20, 2019 10:10 am

Hi all,

Do you know which motorcycle spokes would fit the 21inch wheel of my Sport?

The other day, after removing the old tire, I add some WD40 to all spokes nipple to afterward try to adjust them here and there to see if I could fix the rim that is not going very straight, however after playing a bit with a few of the spokes, I broke one :(

I am not going to carry on playing with those old spokes, so either I find one spoke to replace the broken one, or I try to find new full sets that would fit on that 21inch rim/hub and replace all of them in both wheel, that second option I think would be the best, maybe that way I manage to get the rim a bit more straight.

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One curiosity here to show you, once I remove the old tire I saw that the inner tube had 9 patches on it!!!!!, fixed and reused 9 times. Long and hard live that this inner tube has :lol:

Inner-tube-for-21inch.jpg
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Last but not least, here a photo of the front original 21inch tire. The crack that goes from side to side is very scary, that is why there is no way I can ride with this tire, too dangerous. We all know how difficult is to find a replacement for it. Unfortunately I didn't find yet the correct one with that road pattern to replace, so in the meantime (who knows for how long), I am going to mount two brand new Pirelli ML14 in size 21 x 2.25. They are trial tires, not road tires, so it is going to look a bit strange, but if I want to keep the 21inch, this is the price I have to pay. I will show the result once it is all assembled.

If any of you have a "Superflex" available (even if is used, but still in a reasonable condition), please let me know.

Pirelli-cracked.jpg
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Re: Spokes for the 21inch wheel (Sport)

Post by arthur lewthwaite » Tue Aug 20, 2019 8:53 pm

Hugo, for tyres try Gualtiero Tonelli in italy. Its his Italian phone number 337989524

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Re: Spokes for the 21inch wheel (Sport)

Post by hugomez » Wed Aug 21, 2019 8:25 am

Hi Arthur,

I contacted him already some days ago. He doesn't have anymore.
He used to have some of them when I visited him a few years ago, but at that time I was not interested in 21" tires, so I didn't buy, pity.
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Re: Spokes for the 21inch wheel (Sport)

Post by arthur lewthwaite » Wed Aug 21, 2019 4:11 pm

Hugo you can buy spokes on eBay and cut to length and thread yourself. Just check the die of spoke, also threading tool can be obtained.

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