Ignition timing advice

[Joachim]

So…..

I checked the timing yesterday statically (LED on the Trispark) and made some markings. Turned out I was riding around with 20deg for a while. I then rode at 32deg and 27deg. No pinging, similar performance.

Today on the Dyno:

I made a direct comparison between 22deg, 27deg and 32 deg. 2 runs each. No significant difference in power across the rev range. The best performace was at 27deg.

Then I changed the plate back to 27deg for the carb adjustment. Later I checked static timing again and it was actually 26deg. I didnt have enough time to do everything meticulously. In the end the power and torque results were very satisfying at that setting.

I will make another post summarizing the testing, the whole point of the test was a comparison between stock and modified engine.

What I take away. Ignition timing doesnt seem to make a massive difference. And dont trust your perception about power too much.

 

[Fast Eddie]

Falls in line with my experience for sure.

I think it’s because, when compared to modern engines, the combustion’s chambers on old bikes just aren’t very efficient. So such fine tuning is kinda lost on them.

But the other part of my experience is that old bikes can benefit enormously from a big fat spark. Dunno what coils you’re running but if they’re 50 year old Lucas jobs, or cheap shit Far Eastern jobs, you might find an advantage going to the high output cNw coil, or Tri Spark high output coils, or similar.

We tend to think ‘a coil is a coil’ and ‘they either work or they don’t’ … neither of which is true. Cheap shit crap coils give weak sparks, old coils break down and give weak sparks. A weak spark could easily lose you more power than you’ve gained with your engine mods. In fact, the higher the engine tune = the more critical the big fat spark becomes.

 

[Onder]

Which is why one of our members bangs on about mags....

 

[Joachim]

I use the twin coils which I ordered with the Trispark. Not much on my bike which is original anymore.

 

[cash]

The Norton twin I was comparing it to had flat topped pistons

Sorry, I picked up on the 500 and surely that had big humps on its pistons?
Dave

 

[Fast Eddie]

I use the twin coils which I ordered with the Trispark. Not much on my bike which is original anymore.

Twin Trispark coils? If so they should be fine IMHO.

 

[Joachim]

Maybe Tri Twinspark. Dont remember.

 

[johnm]

Sorry, I picked up on the 500 and surely that had big humps on its pistons?
Dave

Not really actually. They were just GPM pistons. About 10.25 to 1.

Bit of a dome but not a big lump at all.

My thought on advance was more about diameter. I did a little bit of advance testing but didn't find dyno performance impacted much at all by changes of 3 degrees or so. But I did see a bit of speckling in the white porcelain which Gordon Jennings attributed to oil specks coming past the rings as the very first indications of detonation and too much advance.

See Gordon Jennings old articles on spark plugs and advance. I found this particularly useful when I changed the bike to methanol which requires between 3 and 6 degrees more advance over petrol. I found 3 to 4 degrees best for the 500.

Also very interesting are the engine advance and fuel experiments made by Gordon Blair published in his Design of Four Stoke engine text. He published lots of graphs of combustion chamber pressures.

 

[cash]

I changed the bike to methanol.

I bet it drank the bloody stuff.
Dave

 

[johnm]

So…..

I checked the timing yesterday statically (LED on the Trispark) and made some markings. Turned out I was riding around with 20deg for a while. I then rode at 32deg and 27deg. No pinging, similar performance.

Today on the Dyno:

I made a direct comparison between 22deg, 27deg and 32 deg. 2 runs each. No significant difference in power across the rev range. The best performace was at 27deg.

Then I changed the plate back to 27deg for the carb adjustment. Later I checked static timing again and it was actually 26deg. I didnt have enough time to do everything meticulously. In the end the power and torque results were very satisfying at that setting.

I will make another post summarizing the testing, the whole point of the test was a comparison between stock and modified engine.

What I take away. Ignition timing doesnt seem to make a massive difference. And dont trust your perception about power too much.

Hi.

I'm not familiar with the advance curve on the Trispark.

You state the static advance. What is the advance if you strobe it at say 5000 rpm?

 

[johnm]

I bet it drank the bloody stuff.
Dave

Methanol consumption by volume is about 2.3 times petrol consumption so yes in longer races you had to checked the tank volume carefully.

The biggest problem is actually getting big enough hoses and fittings plus the internal carb passages. At the end of a long straight it's easy to get fuel starvation. Easier to solve with a twin than a big single engine.

 

[acotrel]

Combustion conditions depend on a balance between four factors - fuel octane ratio, compression ratio, fuel/air ratio and ignition advance. Advancing the ignition usually has a similar effect to leaning-off the jetting, if you change nothing else. Most Commandos use Amal carbs which offer a choice of only two sizes of needle jets, so most are probably jetted slightly too rich. If you advance the ignition timing the balance in combustion conditions can improve.
The 28 or 29 degrees ignition advance which is specified for the Commando when it runs on petrol, is probably for low octane fuel. If you get the carburation jetted right, the motor will probably be as good as it would ever be without changing to a different ignition timing, regardless of the octane rating of the fuel you use.
If you are running higher comp. ratio, the better octane rating of the fuels which are now available will probably be enough compensation without changing the ignition advance. If you lean off the jetting, you might get better performance, but the tuning will become more weather-dependent. It is better to tune your motor when the weather is cold. If you tune it when the weather is hot, when the cold weather comes, it will run slightly too lean - in cold weather your bike might become a pig. Slightly too rich on hot days does not matter.

 

[acotrel]

Methanol consumption by volume is about 2.3 times petrol consumption so yes in longer races you had to checked the tank volume carefully.

The biggest problem is actually getting big enough hoses and fittings plus the internal carb passages. At the end of a long straight it's easy to get fuel starvation. Easier to solve with a twin than a big single engine.

Tuning with methanol usually gives more power because it hides up the tuning errors. But getting it jetted lean enough is as important as it is with petrol. Fuel starvation is usually due to constriction of the tank breather, as long as the float needle seat is large enough.
With my 850 on 9 to 1 comp. I run 0.116 inch needle jets with 6D MIkuni needles in 34mm Amal carbs The motor goes like buggery. With 0.117 inch needle jets, it is too slow. I make my own needle jets. I use 33 degrees of ignition advance.
Try it !

 

[johnm]

Tuning with methanol usually gives more power because it hides up the tuning errors. But getting it jetted lean enough is as important as it is with petrol. Fuel starvation is usually due to constriction of the tank breather, as long as the float needle seat is large enough.
With my 850 on 9 to 1 comp. I run 0.116 inch needle jets with 6D MIkuni needles in 34mm Amal carbs The motor goes like buggery. With 0.117 inch needle jets, it is too slow. I make my own needle jets. I use 33 degrees of ignition advance.
Try it !

Hi. Thanks for info

I havnt raced the bike for over ten years but
I just used the off the shelf methanol conversion for amal mk 1 concentric carbs and worked well. (Needles, Jets, bowl and slides etc)

I used 31.5 degree advance on a 500 twin with 10.25 compression. Thats 3 degrees more than for 98 octane petrol. I determined this by first going 6 degrees which is one end of the text book recommendation and then going back to three degrees inspecting the plug as per Jennings. This gave a good plug appearance and no sign of soot from detonation. Fitted large bore taps and dual pipes etc.

Methanol is indeed a very easy conversion. Just follow the usual recommendations. I never dynoed the bike on methanol but going by laptimes against Mcintosh Manxs and the Gold star Chris got a 100 mph race average on at the Manx it will be in low mid 50s I'd guess. On petrol the bike got 51 bhp at the dyno.

First race on methanol we got second place in the NZCMRR Senior TT at Pukekohe. Lap times came down by about 1 second compared to petrol to around 1 min 11 sec for the old Puke circuit. A good laptime for a Clubmans rules bike converted to methanol. And it even had a drum brake ;-). As per clubmans rules.

It's not relevant for the OPs question but my bike has a maģneto so number one issue is to check both cylinders fire at EXACTLY the same time. This is absolutely critical with a mag

 

[Joachim]

Hi.

I'm not familiar with the advance curve on the Trispark.

You state the static advance. What is the advance if you strobe it at say 5000 rpm?

The Trispark goes to full advance at 3500rpm.
This can be checked dynamically by strobing at >3500rpm or statically by slowly rotating the engine by hand and checking when the LED on the stator plate comes on. When I compared static and dynamic in the past it was always close enough. I just dont have access to my strobe light at the moment.

 

[gortnipper]

Hi.

I'm not familiar with the advance curve on the Trispark.

You state the static advance. What is the advance if you strobe it at say 5000 rpm?

Commando Timing Advance Curves Compiled

I've taken the liberty to compile existing advance curves from different sources and plot them on the same graph. I'm obliged to Ludwig, who supplied the TriSpark curve and much private information, and Dave Comeau, who posted the AAU and Boyer curves on his website. 1. The AAU. The AAU...

www.accessnorton.com

 

[johnm]

Commando Timing Advance Curves Compiled

I've taken the liberty to compile existing advance curves from different sources and plot them on the same graph. I'm obliged to Ludwig, who supplied the TriSpark curve and much private information, and Dave Comeau, who posted the AAU and Boyer curves on his website. 1. The AAU. The AAU...

www.accessnorton.com

Thanks. So on the basis of that curve if you strobe the Trispark at 29 degree at 3500 to 4000 rpm I suspect you will be about perfect. Maybe up to 31 with your lower CR than my experience. In that range for a street bike without heaps of work tuning other components like cams exhaust inlet tract I think you will be just fine.

Then just tune the carb and your done.

 

[Fast Eddie]

The Trispark goes to full advance at 3500rpm.
This can be checked dynamically by strobing at >3500rpm or statically by slowly rotating the engine by hand and checking when the LED on the stator plate comes on. When I compared static and dynamic in the past it was always close enough. I just dont have access to my strobe light at the moment.

I find that LED timing light so useful. It’s so accurate that these days I don’t bother strobing.

 

[MexicoMike]

The advantage to strobing the first time you install an ignition system is that you can see at what RPM the maximum advance occurs. It should be all in by around 3000-3200 (as does the OEM and the TriSpark in the graph). Of course, if you have done that once with whatever ignition system you have, you know what it is from then on...assuming no electronic gremlins have intruded!

Obviously a strobe is the most accurate way to check/set timing but even in the old days, I usually just used the Norton owners manual method! With my Trispark, as FastEd noted, I just use the LED if I'm doing anything that requires re-timing.

 

[gortnipper]

I use the strobe with my TS to make sure I am not a dumb ass. Well, at least regarding timing.