Ironhead Detonation

Sporty77 · #1 8th June 2009

Hey guys,

I've been experiencing some minor detonation since the weather has gotten hotter. (Central Texas, so it's actually HOT!) Is there anything that I can do to prevent this. I tuned the carb (Super B) when it was about 70* daily so could this be a problem since we're hitting high 90*s? Does timing need to change in warmer environments?

The bike is overall running very well but I like things to be exacto. Thanks in advance for your help.

GA_Ironhead · #2 8th June 2009

Retarding the timing will reduce detonation. It may be related to a different gasoline formulation being used during the summer months.

jpironhead · #3 8th June 2009

Very Important - What RPM range is it starting to detonate at? Just off standing start?

Sporty77 · #4 8th June 2009

Actually yes. It detonates once just off of start. I'd say 17-1800 RPM range maybe.

jpironhead · #5 8th June 2009

Ok. I too run a B on my 79. And in S Texas. Couple things....and do only one at a time, look for change, if none then move to next. 1) I run ONLY premium gas (these machines were designed when gas was real.) This will increase the detonation point. 2) richen idle needle a smidge. More fuel cools the cyl walls and fights detonation. 3) retard ignition A COUPLE degrees.

Try those in that order......Let me know!

Sporty77 · #6 8th June 2009

This may sound a little back woodsy but which way do I need to move my plate to retard? Clock wise or counter. I don't have an adjustable timing light so I have to old school it with the plate moves X distance = 2*. I have a full tank of reg gas so I'll start with the needle and then move to the timing. By the time I rule in or out those two I'll probably need to refuel.

Of course, if I have no luck with the first two I will return everything to the initial settings and start over with the new fuel type. I've found that knowing your last known good setting is imperative when making changes.

jpironhead · #7 8th June 2009

turn plate counter-clockwise to retard. A little goes a long way! ALways mark starting point....I prefer the fine tip sharpie method.

IronMick · #8 8th June 2009

Read thru the Ignition Timing Sticky. At the end it has a calculation of how far to turn the plate. Note that 1/16" == 5` of timing. So you need to rotate it only a very small amount. Before moving it mark the starting location with a dot of paint - bright red or "crossing guard vest" orange.