Ignition Timing & modern Fuel

[BigEd]

I was also wondering about the ethanol content and RON spec of the fuel available in Australia. I spent last December in SA and had a look at the pumps in Gawler when my son-in-law was filling his car. I couldn't find the ethanol content displayed on the pumps.
My experience of using ethanol as fuel was years back when my brother was racing my vintage Sunbeam. We used alcohol for a couple of seasons and needed bigger jets and different ignition advance. Is 10% ethanol enough to need jet/ignition adjustment?

If a higher spec fuel like BP Ultimate works you may later be able to tweak jets and ignition to get 10% ethanol content to work too.

Martyn, before fiddling with the timing why don't you run a tankful of BP Ultimate or Caltex Vortex 98? Most 91 RON petrol in Australia contains a minimum of 10% ethanol which is a waste of both petrol and ethanol. Shell 98 is also OK as long as you don't let it go "off". It takes less than a month for it to go off.

 

[Albervin]

Eddy. my old herringbone lines disintegrated with the ethanol fuel. The outer layer just peeled off and what was left was very spongy. New lines and only no-ethanol fuel seems all OK after 2 years. If I have old fuel in the tank the beast is a beast to start but top up with fresh stuff and first kick start. Same goes with the old Riley, hates stales fuel and positively protests at the 91RON garbage.

 

[clevtrev]

Eddy. my old herringbone lines disintegrated with the ethanol fuel. The outer layer just peeled off and what was left was very spongy. New lines and only no-ethanol fuel seems all OK after 2 years. If I have old fuel in the tank the beast is a beast to start but top up with fresh stuff and first kick start. Same goes with the old Riley, hates stales fuel and positively protests at the 91RON garbage.

Why be surprised, fuel has only a shelf life of 7 days. Then the oxygenators disappear.

 

[vibrac]

Ethanol...

http://www.youtube.com/watch?v=OfZgDkRwAUk&noredirect=1

 

[Paul Ennis]

Love it! That'll make my fuel stops a bit longer!!

 

[Chris Launders]

Having finish work this spring i've done a considerable bit more riding this summer and have found the three bikes i've been using all run noticeably better on super rather than regular unleaded as a comparison they are:
1950 rapide with ported heads,mk3 cams, 32mm mk1 concentrics ,BTH mag single plug heads at 34 BTDC
Norvin, ported heads, mk2 cams, 34mm mikuni's, twin points, twin plug heads, dyna coils at 25 BTDC
1933 Brough Superior 11.50,1100 SV with a single type 29 amal, lucas mag at 38 BTDC
Even though the Brough was built (I think) before the introduction of leaded petrol it runs smoother on the higher octain stuff,given it's a sidevalve on 4.5:1 compression and 80 years old the ethanol stuff must be really poor.You can literally feel the difference if you go on a long run and use one tank of regular say,then the next refill with super and continue on.
Chris.

 

[derek]

Comet ignition timing

I have had trouble getting the timing correct on my Comet, I tried Pazon sure-fire electronic, reverted to magneto, and I am now trying distributer points/coil. I am also thinking of fitting mechanical wire pull to add/ret ignition while underway. If it is thought that 28deg is OK now, why was 39deg always given in all original information? Why was vacuum advance never used on motorcycles? Interestingly classic cars with similar engine parameters use the following timing, idle 5deg BTDC, maximum mechanical advance to 28deg BTDC and then for fuel economy depending on engine load, vacuum advance up to 39deg BTDC.

 

[greg brillus]

Hi Derek, When these bikes were being manufactured the fuel available had an octane rating of about 80. A vacuum advance unit would have been perhaps a bit complicated for engines with only one or two cylinders....remember that the vacuum advance assists with a flat spot just off idle which multi cylinder engines with only one centrally mounted carburretor need, as well as an accellerator pump to enrichen the off idle mixture. And also the fact that most all car engines were/ are liquid cooled verses a bikes air cooled engines which run much hoter. The fuel available now burns much faster, so if the original timing figure is used, the engine will most certainly detonate.....I run twins at around 34 deg and singles 30/32 deg at full advance and around 4 deg in the retarded possition or else the engine will run hot and be a little harder to start. As an aside.....I did a run this Sunday just gone on my Rapide, this being a fairly hot 34/35 deg celcuis day, and when i got home after a couple of minuts i checked the temp at the top of the crank cases with a digital thermometer and it read 137 degrees celcius..........Cheers......Greg.

 

[alscomet]

With a standard ATD you just can't mess about with the timing ,its a fixed ratio if you set the timing to 38deg BTDC on
fully advanced on the firing stroke at retard it should automatically be 4 deg BTDC or the bike wont start. You need to check both Advance and retard figures to see what the ATD is set at. If you set it at any other figure of Advance BTDC it will retard approx 34 degrees on starting.Unless you have a manual mag and then you can please yourself. at 26 deg Advance the bike shouldnt start and advance to run correctly.

 

[A_HRD]

With a standard ATD you just can't mess about with the timing ,its a fixed ratio if you set the timing to 38deg BTDC on
fully advanced on the firing stroke at retard it should automatically be 4 deg BTDC or the bike wont start. You need to check both Advance and retard figures to see what the ATD is set at. If you set it at any other figure of Advance BTDC it will retard approx 34 degrees on starting.Unless you have a manual mag and then you can please yourself. at 26 deg Advance the bike shouldnt start and advance to run correctly.

Absolutely right. Which is why the ATD needs to have bits welded to the ears to limit the range of movement. This what I did on my Rapide (4 to 34 BTDC) and father's 636 Comet (4 to 27 BTDC).

Peter B
Bristol, UK