Petrol/Oil ratios

Moto Rumi technical problems or solutions
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mjpound
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Joined: Tue Oct 20, 2015 12:04 pm

Petrol/Oil ratios

Post by mjpound » Sun May 26, 2019 9:00 pm

Both the Formichino and I are about to take to the road after a 51 year break. Having a newly rebuilt engine (by Ken Brittain) I'm a little uncertain about what petrol/oil ratio to use. Originally it was 16:1 but I've heard of ratios of up to 50:1 with modern oils. Recommendations, please, including which brand to use. I have some Halfords two-stroke oil for garden machinery - date I use this?

Mike

greasy-fingers
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Joined: Thu Jan 07, 2010 11:36 pm

Re: Petrol/Oil ratios

Post by greasy-fingers » Mon May 27, 2019 7:41 am

I have used exol ultima fully synthetic at 33/1 in everything two stroke I own = rumi,s / maicolett,s / velocette viceroy,s / and all my two stroke work tools for the last 5 years without any issues. it can be purchased through ebay, if you buy a big tub it is delivered for a price cheaper than most basic mineral oils. you will be told that synthetic will gum rings etc but this has never happened to me however I do use my rumi,s as the designer intended "with enthusiasm", if you are going to pootle about you may be able to reduce your ratio to 50/1 with this type of oil.

greasy-fingers
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Re: Petrol/Oil ratios

Post by greasy-fingers » Mon May 27, 2019 7:52 am

oh yeah!. if you do decide to use your halfords oil it will be fine but I would mix it at 25/1, whatever you do don,t venture out onto todays public roads at 16/1 = you will be chassed down by mobs of sandal wearing unwashed vegans on push bikes :shock: . you will then need to flush the tank clear of mineral oil before using synthetic as they are not compatible.

greasy-fingers
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Re: Petrol/Oil ratios

Post by greasy-fingers » Mon May 27, 2019 8:12 am

exol "optima" not ultima.

formic
Posts: 195
Joined: Fri Jan 08, 2010 3:52 pm

Re: Petrol/Oil ratios

Post by formic » Mon May 27, 2019 12:56 pm

I also use Exol Optima and I fully concur with everything the last bloke said.
Michael.

hugomez
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Re: Petrol/Oil ratios

Post by hugomez » Mon May 27, 2019 10:48 pm

Hi Mike, I use “Stihl hp ultra” at 3% (32:1)
Very high quality to use at the fuel mix in 2 strokes engines that get high revs.
Greets,
Hugo
My little Formichino here: http://www.formichino.com/pictures1.html

greasy-fingers
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Re: Petrol/Oil ratios

Post by greasy-fingers » Tue May 28, 2019 10:11 pm

I had a chat today with a respected uk rumi owner/restorer/crankshaft builder, who said I should mention that my rumi,s all run caged roller big and little end conrods, and that owners still running with old fashioned uncaged big/ bushed little end type conrods may be better off with a 25/1 two stroke mix.

hugomez
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Re: Petrol/Oil ratios

Post by hugomez » Mon Jun 17, 2019 8:14 pm

Hi All,

Here two images very useful that probably you will find interesting.

Thanks Ian for send it to me.

Fuel Lubrication Chart:
Fuel-Lubrication-Chart.jpg
Fuel-Lubrication-Chart.jpg (113.07 KiB) Viewed 982 times
Ratio mix percentage:
Ratio-mix-percentage_02.jpg
Ratio-mix-percentage_02.jpg (38.26 KiB) Viewed 920 times
My little Formichino here: http://www.formichino.com/pictures1.html

greasy-fingers
Posts: 498
Joined: Thu Jan 07, 2010 11:36 pm

Re: Petrol/Oil ratios

Post by greasy-fingers » Mon Jun 17, 2019 9:05 pm

I have been looking into this a bit recently. Comments from many owners of D and LD Lambretta,s "caged big end / bushed little end" have been running their machines for many years and thousands of miles on between 4% = 25-1 and 3% = 33-1, using mostly semi and fully synthetic. I am not sure of the ratio of oil used by people using the Rumi engine weak link uncaged big ends, but the French club have in the past advocated the use of 3% mix on the literature of their sortie road runs, however many French owners sensibly use upgraded caged big and little end bearing cranks.

formic
Posts: 195
Joined: Fri Jan 08, 2010 3:52 pm

Re: Petrol/Oil ratios

Post by formic » Mon Jun 17, 2019 9:15 pm

Hello all,
The engine in the RUMI that I use most was assembled by me but I really cannot remember whether the small ends are rollers or not.
I will carry on until it seizes.

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