Hi all happy new year...I have been looking at past forum material but can't find anything on fuel mix. I have been told that it's ok to run the M20 on straight unleaded fuel won't harm it. Another said don't use fuel additives for side values as it fuses to the exhaust valve. Yet another says use a cap of two stroke oil in every tank. And yet another says use a cup of diesel. Does someone have the ultimate mix for unleaded fuel for the old M20s?

Basically anything that we get today is way, way better than the rubbish they had in the 40s which is what they were designed to run on. So just fill her up and don't lose any sleep about it!

P.S.
Back in the 60's when I ran out of fuel once filling up from the lamps used to light roadworks got me home!

I run 'straight' unleaded fuel, though I have had a hardened exhaust valve seat fitted...

I did experience some problems with valve face failure...Having fitted a hardened valve seat from the outset when the engine was rebuilt there were no problems there..

I have read that running at constant higher engine speeds has the potential to do more damage and it was certainly the case that my bike did a fair bit of this type of work when used for touring...

Ultimately I replaced the exhaust valve as well with an upgraded one and have had no further problems...

I have rebuilt a lot of other M20 owners engines in the past and those doing shorter runs or more local work don't seem to experience any problems at all running straight lead free...

Whether deterioration of the valve seat and/or valve becomes apparent after higher mileages only time will tell, but even on leaded fuel seat 'maintenance' is required more frequently on a side valve than a cooler running OHV engine...Ian

email (option): ian@wright52.plus.com

For Gawd's sake don't use a cup of diesel oil in every tank. Your rings will be gummed up in a couple of hundred miles.
Remember how we used to have to strip the engine to decarbonise every 10,000 miles? Absolutely no need to do it now with modern fuels. Engine should only need taking apart for normal mechanical maintenance.

Since I acually got around to fitting the speedo I have done 15,000 miles on my M20.
Now I had been riding this bike regularly for 12 years previously and am about to do the 3rd re-ring ( hopefully without a rebore )so i would be guessing it has done around 60,000 miles since I have had it, if not more.

Run it on strait fuel.
Only problems fuel wise was when it wore a 930 conentric carb which made it very fuel sensative at idle.
Now running a 626 concentric on whatever is available at the time, E 10 , unleded, premium , even 2 stroke mix when I grabbed the wrong can.

Never ever had any problems with valves that is fuel related. just plain old wear.

Only thing fuel wise that does make a big difference is running the engine dry.
Unless the bike is going to be restarted in less than 15 minutes I always run the engine dry to prevent contamination on the plug.

email (option): bsansw1@tpg.com.au

How do you guys feel about about 10% ethanol based fuel? I run non ethanol fuel in mine just because of the carburetor.

I run mine off unleaded, BUT, I dumped some of those leaded pellets into the tank to give it a bit of a helping hand.Used to run my old Beemer 1000cc boxer on the same and she towed a trailer around Europe without a hitch :-)

email (option): fozzie001@hotmail.com

email (option): ronpier@talk21.com

Not sure about ethanol in fuel, but I don't think it does my orange tank lining (whats left of it) any good. I always put a bit of lead replacement in my tank.

Also, I am not sure if it is my imagination, but when the only pump available is the higher octane fuel and I put this in, the bike always seems to run smoother.

Having said this, my bike needed a re-bore and a new piston some time ago, so running it in at the moment.

email (option): sacombsashtrees@hotmail.com

Run it on 98 octane or 95 in OZ only because it runs better than the 91. An egg cup of diesel once in a while not a cup was the suggestion I heard way back but its not needed for general use. I used to use upper cylinder lubricant now and again when unleaded fuel became the only available fuel but I found it didn't really need it.

Ron

I'm in Florida. We have non ethanol at a few gas stations. One station has recreational gas at around $3.99 (which I was using, just don't tell the tax man) Another just started carrying it for road use at $2.89 a gallon.

I usually use the higher octane unleaded on the basis that (I was told) this tends to have the lowest ethanol content, but have just bought some petrol additive that us supposed to combat the corrosive and water-attracting properties of ethanol. This is pricey so I am only going to use it for bikes laid up for a spell or used infrequently rather than for daily use.

Yes I do the same! I buy non supermarket super unleaded. Based on the principal that hopefully it's better stuff and even if it's not, it can't be any worse. I also give shots of ethanol treatment, again based that if it doesn't do any good, it can't do any harm.

Currently I am using 'Frosts Ethomix' but I've just bought a bottle of 'Briggs & Stratton' fuel stabiliser. After a conversation at a large lawnmower centre nearby, who informed me that B&S had to do something to combat customers problems with laid up machinery over winter. I've also been reading up on it on google and 'Miller Oils' have also come up with a stabiliser. These bottles range from £6 -£12 but the dose is very small meaning for the miles I do, even if I use two bottles a year, it won't break the bank.

Other products are obviously available, but I rather stick with names I know.

Ron

email (option): ronpier@talk21.com

If we all do more miles it won't be in there long enough to cause any problems... ....Ian

email (option): ian@wright52.plus.com

A similar conversation on many old car/bike sites .....

Probably just me (and a dozen mates on every thing from 90S BMW to '28 Rudge) but apart from problems with unleaded fuel left in carbs/engines etc. we have not had any valve seat recession problems -

Except for the 1926 Rudge who did the 2015 cannonball run across the USA (300 miles a day for ~12 days - diagonal across USA) - now that DID suffer - very badly. It also suffered very badly with the heat ..... which may be telling us something?
He's currently building a Triumph H for the 2016 Cannonball run - I've just built the crank with a 16H rod assembly and we are discussing the valve recession problem at the moment - but as no one i know has experienced it, not certain what to recommend ?

I do know a mini driver with +100,000 miles without problems - CI head without inserts.

One thing to consider - leaded fuels were not available pre-war, the biggest thing which allowed development of the Merlin/Griffon engines was the improvement in fuel ..............

An additional being that fuels banned in the '50's for being class 1 carcinogen's (Benzene, Toluene, etc.) are used in modern fuels to improve 'knock resistance'.

The idea of adding paraffin to pre-war bikes, was to REDUCE the volatility of the fuel, commonly used by Veteran/Vintage riders - nothing to do with lubrication or valve seats.

An M20 will run unleaded, e10, e25, kerosene , just about any liquid will go bang.
If you are running original WWII brass bits in the fuel system then there is a good chance if left in there long term you might get dezincifation of the brass as WWII brasses were not stabilized.

Apart from that nothing but nothing will cause any injury to your engine while it is running.
Valve resession on road vehichles is pure bull shit based upon research done into AEROPLANE ENGINES , so unless you plan on running you bike above 10,000 + rpm under lean burn conditions at 20,000 feet altitude, STOP WORRYING.

Worked race engines also so some problems, but again these engines are running at the limits of their designs, totall irrevelant to daily use vehicles.
Aws per usual some idiot with no idea about what they were reading got hold of the Air Ministery reports then extrapolated them to incorrectly cover every petrol engine ever built.
After that the unscrupulios set out to fix the non existant problems that people who did not know any better were convinced that had.

There are only two problems with modern fuels.

1) the composition of the brew will change from day to day so setting up carburettors can become a problem ON HIGH PERFORMANCE engines.

2) It does not keep well in all conditions so some times it will go off.

Other than that you get the same problems with modern fuels you used to get with real petrol. leave it in the carb for a long time then it evaporats and gums up the carb only with modern fuels it is worse.

So the long and short of it is ride the bloddy bike & stop worrying about it.
If you are not going to use it for longer than a month, run the carb dry and drain the tank.
Pour this fuel into your car and get some fresh fuel for your next run.

Forget about any addative.
Most will do nothing bebefitial to your engine at all.
And the ones that do actually work are unnecessary in your engine.

email (option): bsansw1@tpg.com.au

Yes I agree! Put fresh E10 into your vehicle and use it. My problem is, I have a collection of vehicles which I don't use regularly enough. I've already had to replace the brass float in my Morris Commercial which I've owned for over 25 years. I found that it had filled up with fuel after it had eaten through the solder joint.

Removing and replacing that down draught carb was a bastard of a job!! Ron

email (option): ronpier@talk21.com

bloody hell, common sense!

Yes all brass will tend to suffer from de-zincification (had to replace an entire central heating system, cos of it - cheap copper tubing !) - probably more due to an electrolytic effect than the fuel.

I did think the hysteria about it had gone away, but no (see B50.org site!!!).

and yes, i think the solution is to run the little darlings - unfortunately, like Ron i have several bikes i try to run each year, so i do tend to drain fuel from each as i use them .... hence the ES2 runs on 32:1 two stroke most of the time, as well as the B25 MX'er

Nothing intended by this, its left over from tougher Enduro's when i run the KDX - no other use for it since i've moved to electric garden tools.
Though i do hope it stops any run in my fuel tanks ?

One of the people I ride with had about a dozen bikes.
He also has about the same numbers ot stents so kicking for 20 minutes is not an option.
He has a couple of customised funnels in the garage and when he gets back from a ride he turns off the fuel ( normally a few yards down the street ) pops the bike on the side stand pulls out the correct funnel & a plastic fuel can slips off the fuel line at the carb, pops it into the funnel, then removes his helment & gloves.
He walks into the house, pops the kettle on and by the time he is back the tank is drained so the fuel line is done back up and by this time the kettle is boiled.
Just takes a tiny bit of dicipline.

email (option): bsansw1@tpg.com.au

All very well Trevor! Try doing that on the twin tanks of a Bren gun carrier or a Morris truck. I think the kettle will be boiled dry Ron

email (option): ronpier@talk21.com

In which case you try to only fill enough to do the trip at hand and keep a little in a spare can just in case you got it a bit wrong.

Another member who had his 50 A10 plunger from new ( thought to be the first in OZ ) only ever filled enough to complete the run.
Frightening bit is he was usually about correct generally going onto reserve a few miles from the end.

email (option): bsansw1@tpg.com.au