Fuel/oil ratio for Alpina

[LSMO]

My Model 85 is finally running after much advice from many of you.  Hearty thanks to all of you!

I'd like to know what gasoline-to-oil ratio you have successfully used in your bikes.  I'm seeing everything from 40:1 to 100:1 recommended for two-stroke motorcycles in general.  I'm sure that covers everything from pit bikes to high-level motocross racers.  What actually works with the trials and trail bike Bultaco engines?  My bike will be used in an amateur video production, so very low smoke output is important.  What works, gents?

[djr]

I have a similar age Ossa MAR that I use for trials , and have used either 40/1 or 50/1 at different times over the last decade, with a good 2 stroke oil( synthetic or semi synthetic)

Doesn't smoke much, and on strip down there was a nice film of oil in the crankcase , which was reassuring to see.

You will get varying opinions, anything from 25/1 to 100/1.

something like 25/1 may have  been the Bultaco recommended ratio when the bike was new and mineral oil was the main option.

If it was me, I would be happy using your alpina at 50/1 for trials, and 40/1 for trail riding, light road riding , that sort of thing.

The theory is , the more RPM the engine is doing , then the more oil it needs.

 

 

[lemur]

It's a 1970's 2-stroke Spanish bike and in the 1970's when I rode my Montesa Cappra 360VA the oil I used was Belray MC-1 at 80:1 mixed with the highest octane pump fuel I could buy at the time which was the equivalent of todays leaded race fuel.  Cappra was fitted with a single dykes ring piston and I never had a piston or ring problem for the entire life of the bike.  MC-1 was rated for up to 80:1 and provided the closest thing to a no smoke 2-stroke as you could get.  

The product did have a shelf life and when it turned from blue to brown in colour that meant you should discard it or risk gumming up your piston and ring.  Found that out by trying to use up some old fuel/oil mix in a chainsaw which was a bad idea.

I go by the leanest recommendation written on the product packaging, although I see more and more they don't even print the recommendations on full synthetic oils.  

[LSMO]

Very much appreciate you both taking to time to give me some guidance.

[woody]

Being an old style cast sleeved cylinder 50:1 is the leanest mix to use, modern bikes have plated bores so are fine on leaner mixes like 80:1 or 100:1

As someone else mentioned the spec sheet mix ratio is for mineral oils used at the time the bikes were manufactured. Just use any modern semi synthetic 2-stroke oil at 50:1. Castrol Power 1 is a decent brand that doesn't gum up rings or silencer packing

[LSMO]

Thanks, woody.

Seems strange to me that you have made 4030 posts yet you're still considered a newbie.

[djr]

It's an old air cooled , iron liner engine, not a modern water cooled plated cylinder engine,  so its up to you if you want to go as lean as 80/1,  100/1 ( which is fine in modern engines, but maybe a risk in older engines ?)

Short term it will probably run okay on just about any oil, at any ratio that has been mentioned,  but good oil mixed at a sensible ratio should give the best long term life for engine wear.

I once accidentally mixed up fork oil with my petrol ( picked up the wrong silkolene bottle)  and rode a trial with no problems before I realised , But I don't recommend it ! 

 

 

[majesty]

15 minutes ago, djr said:

It's an old air cooled , iron liner engine, not a modern water cooled plated cylinder engine,  so its up to you if you want to go as lean as 80/1,  100/1 ( which is fine in modern engines, but maybe a risk in older engines ?)

Short term it will probably run okay on just about any oil, at any ratio that has been mentioned,  but good oil mixed at a sensible ratio should give the best long term life for engine wear.

I once accidentally mixed up fork oil with my petrol ( picked up the wrong silkolene bottle)  and rode a trial with no problems before I realised , But I don't recommend it ! 

 

 

Did the forks work OK ?

[LSMO]

Once all the video shots are done, I can drop back to a ratio that will give good longevity.  For now, I must reduce the smoke.

[djr]

31 minutes ago, majesty said:

Did the forks work OK ?

Yeah, forks were fine, and the engine was running well on the fork oil pre-mix.

It was the new/different exhaust smell that alerted me to my silly mistake.

At the time I thought I was the only person in the world who had run a 2 stroke on fork oil pre-mix, but later I read a story about Joey Dunlop at the IOM TT.

It was said he had run out of fuel while practicing on a 2 stroke bike, a spectator gave him some petrol and he apparently drained one fork leg into the petrol can , gave it a shake , filled the tank and took a steady ride back to pits.

No idea how true the story is, but it is the sort of thing I can believe he did.

[lemur]

My 360VA was an air cooled iron liner engine not unlike the Bultaco in most ways except it didn't have a chain primary drive.  

MC-1 was one of the first full synthetic oils, it's too thick to even run in 2-stroke oil injector systems, at 50:1 you are going to have a blue contrail and black mung oozing out the lowest part of that Alpina muffler, then you will know there is too much oil in the premix because it won't all be getting burned up inside the combustion chamber.

[feetupfun]

12 hours ago, LSMO said:

Once all the video shots are done, I can drop back to a ratio that will give good longevity.  For now, I must reduce the smoke.

Modern premix and injection two stroke oils for road use are designed to be "low smoke" to avoid making visible emissions and they achieve this by resisting burning during combustion of the fuel, but the penalty paid is that they condense/accumulate within the exhaust system as a gooey liquid.

If the fuel/air mixture is well managed on your Alpina and you run a modern premix oil at 40 to 1 or 50 to 1, the exhaust gases will be invisible. If you want to get the best fuel/air mixture control, run with a new modern carby jetted correctly. I run a 26mm OKO from Mid Atlantic Trials on my Alpina and it runs super sweet with perfect jetting straight out of the box.

[feetupfun]

15 hours ago, LSMO said:

Thanks, woody.

Seems strange to me that you have made 4030 posts yet you're still considered a newbie.

Yes something weird happened a few years ago that changed that. It previously showed if you were a financial supporter of Trials Central or not. Now we are all just Newbies!

[LSMO]

Loads of interesting and useful information.  Thanks to all for your contributions.