Comments? Thoughts?

[reveeen]

For the sake of trying to expand my knowledge I'm looking for comments and thoughts on spark plugs.

I have a vertical Minarelli (Yamaha), 50cc, ported, piped, and just about worn out (but compression is still good). As is, it's a 40+ mph machine, and I've seen 55 with a tail wind.

1) is there any advantage to "indexing" the spark plug?
(pointing the plug gap at the exhaust port)

2) is there any reason it prefers a "7" plug, rather than an "8"?
(no matter what jetting changes I make, it simply runs better/pulls harder with a "7", than an "8")

[mccanic]

well the 7 plug is hotter then the 8 plug. i don't belive that pointing the plug in any direction will do anything. i remember seeing something about that in one of my old mans hot rode mags, where people tryd that and didn't see any difference?

[tango]

I've never heard of indexing spark plugs. I'm curious to know exactly how it is that the fitter can make that happen. Even if the gap position is marked on the ceramic portion how can it be guaranteed that the proper torque can be arrived at while keeping the gap pointed at the exhaust port. Additionally I can't see what benefit that might have, particularly since the spark plug is not functioning during the exhaust/intake event.

[reveeen]

The way my engine is configured I appear to be having flame travel "issues" that are covered up by the hotter plug.

Really, the whole issue is moot, as I am preparing for a rebuild (with different stuff), but I was curious if anyone else had seen this, and if this was a missed tuning opportunity?

Hot plug rich mixture vs cold plug vs leaner mixture, or timing?

I can also source Bosch plugs that seem to fall in between a "7" and a "8".

[tango]

Something just came to me, as you mentioned flame travel issues. I wonder if there are any plugs out there for 2Ts that are of the multi-electrode type? That would certainly create a more circular flame front. Another question to those that are into porting, etc. Could the shape/position/size of the intake port be a factor in that flame trvael issue? I mean if the port is not flowing or directing the charge properly could it not allow a higher concentration of charge towards one area of the chamber? If that's so then that would be reasonable to assume that fuel isn't being burnt homogenously and thus the flame front is crooked. I'm still learning this 2 stroke thing and I may be thinking too much, but I would be interested to hear from some experts on this.

[90GTVert]

Aug 9, 2011 8:45:34 GMT -5 tango said:

I've never heard of indexing spark plugs. I'm curious to know exactly how it is that the fitter can make that happen. Even if the gap position is marked on the ceramic portion how can it be guaranteed that the proper torque can be arrived at while keeping the gap pointed at the exhaust port.

You mark the spark plug and then use indexing washers (a set of washers of varying thicknesses) to make sure the plug is positioned how you want it. The other option would be to try multiple plugs, but the washers are cheaper. On multi-cylinder engines, some folks will move plugs from cylinder to cylinder till they find which combination aims them best.

I've never tried it, but most of what I have read says there's no real benefit from indexing plugs in most cases.

[jmkjr72]

indexing wont do much good unless the spark plug is off set from the center of the bore

on multi cyl 4 stroke engines at the track it can make a big diffrence when you are trying to get every last drop of power out of an engine