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View Full Version : Ironhead who juts sets timing to the highest/smoothest speed attainable w/out predetonation?


1982ironhead
20th September 2009, 00:18
well i have mastered setting timing with a light and statically, so now im thinking just set the run speed at about 2000-2500 rpm and tune the Dyna ignition to the highest and smoothest idle i can get without getting predetonation to get the timing the bike "wants"

i read of guys setting timing as low as 30 degrees advance, well mine is set at the factory mark, stated in the book to be 40* advance, if i tune it like i am thinking and end up with 42-45* advance without predetonation, will it be fine to run like this? the old 900's ran 45* i believe b/c of a smaller bore and the flame front traveled quicker acrossed it before ping occured with no ill effects to the mechanicals, so if i get 45* with my 1000, mechanically it should be fine to run like this? all assuming i get no ping.

i have not done it yet but i do like messin with my bike:p

Bob F
20th September 2009, 00:26
i have not done it yet but i do like messin with my bike

Back in my Chevy hotrod days we'd keep tweaking the timing until it "felt" like the most power. As long as you don't have detonation "go for it."

GA_Ironhead
20th September 2009, 00:39
Same testimonial as Bob F.

1982ironhead
20th September 2009, 04:06
any specific RPM you guys tune at in particular? or just as long as your at full advance already?

ericfreeman
20th September 2009, 04:10
I static time both of my Ironheads, one electronic and one with points, at the factory setting and then back them off to eliminate pinging. So far, with both bikes I've had to retard the timing a bit to get rid of that high load detonation, such as when hitting the throttle hard to pass slow traffic. Once I'm assured there will be no detonation, I'm happy. I've never bothered to check the timing with a light to see just what the exact timing is since the engine's performance tells me everything I need to know.

Eric

1982ironhead
20th September 2009, 04:20
I static time both of my Ironheads, one electronic and one with points, at the factory setting and then back them off to eliminate pinging.

both bikes running 10:1 pistons as well? i only have 9:1

ericfreeman
20th September 2009, 04:38
both bikes running 10:1 pistons as well? i only have 9:1

My '78 has the 10:1 pistons while the '77 has stock 9:1's. I've had to back off the '77 a bit so I can pass in the mountains without worrying about detonation. Didn't take much and now it runs like gangbusters!

Eric

1982ironhead
20th September 2009, 04:45
what are you jetted at? im running a 69 main and .265 int, i like riding through lake lure out bat cave, up #9 and up to Mt Mitchell and back down hwy 80 towards marion good long curvey roads of WNC. what altitude does mt mitchell get to?

racerwill
20th September 2009, 04:59
that's how we've been setting the timing on the hot rods for years...... once you start changing pistons, cams, compression, head flow, and ignition the factory timing no longer applies...... we know about where to start and then just "season to taste" from there...... when I finally come up with the "best" spot, I write it down on the intake so we can just go right back to it.

Ww

ericfreeman
20th September 2009, 05:02
My jetting will be meaningless since I'm running vintage Mikuni-Solex 2 barrel sidedraft carbs on both of my Ironheads. Fell in love with these carbs back in the '70's when I fitted a new one to my '77 XLCH. Carb/manifolds were marketed by Jerry Branch in Long Beach, CA and I bought one directly from him at the time. Superb performing carbs but most parts are hard to find these days. I've managed to acquire 4 of the carbs and manifolds and rebuilt them all. Nothing like a few spares for the future!

Eric

jstme61
20th September 2009, 06:11
I've never bothered to check the timing with a light to see just what the exact timing is since the engine's performance tells me everything I need to know.

Ditto!!!!....:)

MDT
20th September 2009, 13:37
Never use a timing light. Static timing on both my bikes. Kick starting and performance tell me where they want to be.

1982ironhead
20th September 2009, 17:10
would .010-.020+ pistons make any difference in what timing is needed gennerally?

1982ironhead
20th September 2009, 17:12
with .010 over pistons, what is the total cained cc overall on a 1000 xlh? just curious and cant find the equation i used to use. i dont think its much, between 5-15 cc i think. anyone know?

biknut
20th September 2009, 18:01
well i have mastered setting timing with a light and statically, so now im thinking just set the run speed at about 2000-2500 rpm and tune the Dyna ignition to the highest and smoothest idle i can get without getting predetonation to get the timing the bike "wants"

i read of guys setting timing as low as 30 degrees advance, well mine is set at the factory mark, stated in the book to be 40* advance, if i tune it like i am thinking and end up with 42-45* advance without predetonation, will it be fine to run like this? the old 900's ran 45* i believe b/c of a smaller bore and the flame front traveled quicker acrossed it before ping occured with no ill effects to the mechanicals, so if i get 45* with my 1000, mechanically it should be fine to run like this? all assuming i get no ping.

i have not done it yet but i do like messin with my bike:p

I have to keep in mind you have a Iron Head which may have different timing requirements than my bike. My bike stock had 40 degree total timing, but my motor isn't stock anymore so that's out the window now.

I used to be strongly in the camp that said you'll make the highest hp from the most advanced total timing you can get away with and not detonate. In the last 2 years I've run my bike on a dyno about 125 runs, and found that that's simply true at all. My bike turned out to make the best power from bottom to top, with the least initial advance, the least aggressive curve, and the least total advance, but it wasn't having a problem with detonation with lots more advance. The dyno just said it didn't make as much power that way. Roll on testing on the road confirmed the same result.

This has been very hard to understand after a lifetime of believing in something that just wasn't true. It's almost like a religion. It has been one of the most eye opening things I've learned about tuning so far.

Will your bike be the same? I got no idea. You'll have to find out for yourself, but keep these things in mind while you do.

1982ironhead
20th September 2009, 20:29
The dyno just said it didn't make as much power that way. Roll on testing on the road confirmed the same result. very interesting, what was the end result for total advance?


i wander if anyone has tried this on an ironhead. i know of a shop that has a dyno, i know he does cars but not sure about bikes, do they run on the same dyno? is 50 bucks/half hour about normal cost, and how much tuning can you get done in a half hour? a few jets and maybe a couple timing settiong? or when adjusting timing on the dyno can you set the bike to run 3000 rpm and go for the highest torque number , adjusting timing with the bike running?

GA_Ironhead
20th September 2009, 21:24
Dynojet differentiates between auto and motorcycle dynos.

Find a Dynojet dyno in your area: http://www.dynojet.com/dyno_centers/list_motorcycle.aspx

1982ironhead
20th September 2009, 21:30
cool thanks.

biknut
21st September 2009, 00:27
very interesting, what was the end result for total advance?


i wander if anyone has tried this on an ironhead. i know of a shop that has a dyno, i know he does cars but not sure about bikes, do they run on the same dyno? is 50 bucks/half hour about normal cost, and how much tuning can you get done in a half hour? a few jets and maybe a couple timing settiong? or when adjusting timing on the dyno can you set the bike to run 3000 rpm and go for the highest torque number , adjusting timing with the bike running?

Usually bike shops have Dynojet model 150 or 250 dyno's. $50 is about what I pay each time for 15 to 20 runs. Dyno's are a great tuning tool, but they look at the tuning very closely so be prepared to find out things you didn't know were happening. You can do anything with a dyno.

bustert
21st September 2009, 01:28
the old iron is like a lawn mower engine and can tolerate wide timing values but that does not mean that it is optimum. ideally, the flame should end in the exact same spot in degrees of rotation but that is not the case as many variables come into play.
hd says 40 degrees and that gives the best all around performance for what they engineered. can a builder do better-sure!!!

timing needs change for environmental conditions, fuel characteristics and condition of tune both mechanically and volumetric effiency. that is why the iron has a mind of its own, some days it will run like a scalded dog and other days a one legged man on a schwin will pass you by.

i would error to less advance. too much advance will cause heating problems. i doubt that you will be able to detect abnormal cylinder condition until they are severe enough to be heard but damage is cumulative even at less detectable levels. on a auto engine, they use a frequency sensor to pick up abnormal combustion and the computer dials back timing until it stops. when hd came out with their electronic ignition, they used a voes switch to dial back timing at low manifold pressure but allowed full timing at normal range for best throttle responce and mileage. the newer ignitions will also dial back timing but do so with a variable curve (not off/on).

point being is: unless you have the equipment to see how the engine is doing, i would be less aggressive. one more point is i do not think butt dyno's are accurate enough to do any good.

1982ironhead
21st September 2009, 01:33
i guess im set ok right now, i can go from a 850rpm idle to 3000+ in under half a second..... with no load.


would you get close optimum timing by setting throttle to 3000rpm, or any RPM enough to fully advance the weights, and tune timing for the highest idle?

biknut
21st September 2009, 01:36
point being is: unless you have the equipment to see how the engine is doing, i would be less aggressive. one more point is i do not think butt dyno's are accurate enough to do any good.

This is oh so true. You got to be very careful what you think the butt dyno is telling you. It'll play you for a fool in a heartbeat.

biknut
21st September 2009, 01:38
i guess im set ok right now, i can go from a 850rpm idle to 3000+ in under half a second..... with no load.


would you get close optimum timing by setting throttle to 3000rpm, or any RPM enough to fully advance the weights, and tune timing for the highest idle?

Mine doesn't fully advance till 5200 rpm. 28 degrees total