Why not use ignition advancer?

[juno]

I recall reading a post sometime back (in one of the million ignition advancer threads) where someone stated that it is bad to advance the ignition.  What are the negatives, if any?

[sprint_9]

As far as I know there arent any, the advancer only affects rpm's below like 3 grand, I think, so there shouldnt be any top end loss.  You get better response below 3 k, and no loss up hi.

[cummuterguy]

the topic you read was a warning about advancing ignition too far, combined with the stock lean jetting advancing too far could cause detonation.

Not likely to happen if you use an advancer, either Bob's or V&H's. But definataly a hazard if you go the DIY method and grind too far.

But you've already re-jetted the bike anyway, right? :mrgreen:

[JeffD]

Well the ignition works as follows.

The piston gets the air/fuel mixture.
The piston then compresses this mixture at which time the spark plug fires.
Then the gasses expand and push the piston back down.
The used air/fuel mixture is then expelled and a fresh air/fuel mixture is put in and the cycle continues.

For sake of reference imagine the piston at 90 degrees is when the piston is all the way at the top (TDC).  At idle the spark usually fires at about 96 degrees, which is slightly before the piston reaches TDC*.  The reason you have to spark before it reaches the top is because this will ensure complete combustion of the fuel.  When the engine rpm increases the spark will advance itself by some means.  So at 9,000rpm the spark might fire at 115 degrees. (I dont know for sure)  This is because there is a time delay between the spark and combustion.  Therefore to ensure complete combustion you have to give it time to burn.

OK ok...  All an advancer will do is make the spark fire at 99 degrees or 105, or whatever at idle and even earlier at high rpms.  This will increase combustion time and should lead to more torque all around.  However since the combustion is taking place before the power stroke you will use energy to compress the already combusting mixture.  Finally if you fire the spark too early you will lose power since you will be using so much power to compress the combusting mixture.

[John Bates]

I would think that all rpms are affected by changing the relative positions of the rotor and pick-up.  What would retard the timing above any certain rpm to cancel the 5 deg. advance?  

My understanding, from Haynes, is that the ignitor module further advances the ignition based on rpm.  The timing spec. is 12 deg. BTDC at 1200 rpm and 40 deg. BTDC at 4000 rpm.  So by adding 5 deg. advance, the new spec would be 17 deg.  and  45 deg. respectively.  This is for a non-Calif. bike.   A Calif. bike after advancing by 5 deg. would be 10 deg. and 45 deg. respectively.

[Shadowhawk]

The only warning I know of is that your bike will use(burn) more oil.  There is a mention on this site of how much it should advance CA and European bikes, but I don't know how that will affect them.  I do know that my bike(with the DIY advance done prev. to me) does burn a noticable amount of oil, but it isn't much more than the 1983 GS450LD I gave my fiancee this year.

Don
Shadowhawk
:mrgreen:

[number1]

can you still buy the timming advancers or do you have to do it yourself.

[davipu]

once in a while you will see the original aftermarket ones, the stock ones can easly be modified though.