ignition timing

So if I had crazy port timing and/or planned to run 12k or more rpm then do I still time my e50 to 2mm btdc? Seems like I would advance it more as the rpm went up but people say retard to make the pipe hit harder. What do I do?

Re: ignition timing

Retard it, to tune it right. Like I said in Ryan's port timming post, if you raise the exhaust port, like you want to, then retard it. You can squeeze those extra rpm's like you want. Brent

Re: ignition timing

) Cupermcnewbster ( /

How much should it be retarded?

Re: ignition timing

So 2mm before tdc is stock right? Thats already pretty close to tdc imo... I retard it to avoid detonation at high rpms because the supercharge effect of the pipe? Wont that put the flame down into the pipe wasting power and cooking my pipe? Isnt the explosion power sposed to be harnessed by the piston? Can anybody tell me why I should retard it? I wouldn't be a dirtyrottenstinkingbiker if I blindly followed whatever anybody said would I?

Re: ignition timing

I'd say advance it till you can see through your piston, buy a new piston and make sure it wasn't a fluke, no one will accuse you of blindly following then

Re: ignition timing

Nobody had accused me of blindly following I don't think... Oh right.. That must be your special way of saying you don't know why either right Jesse? ;) Maybe I'll see you riding around here in Louisville sometime..... You can tell me more. I kinda wish I had an inner rotor setup just so I could change the timing while it was running... even while Im going up the road, under load... That would be a good way to figure the amount of advance it would seem

Re: ignition timing

If, you raise the exhaust port with porting, you will have to retard the timming, to squeeze those extra rpms that you are trying to achieve. If you advance the timming=loss of power. Or, just don't raise the port, and only widen it, then just leave the timming where it is. Good luck on whichever way you go!

Re: ignition timing

Thanks for the replies... Can anybody tell me why retarding the timing is the thing to do with a raised exhaust port? Is it only because it sends a more powerful pulse to the expansion chamber because it hasn't finished burning (still expanding) resulting in more pipe effect??

Re: ignition timing

nobody knows lol

Re: ignition timing

here. shut up.

AFFECTS OF THE IGNITION TIMING

Here is how changes in the static ignition timing affects the power band of a Japanese dirt bike. Advancing the timing will make the power band hit harder in the mid range but fall flat on top end. Advancing the timing gives the flame front in the combustion chamber, adequate time to travel across the chamber to form a great pressure rise. The rapid pressure rise contributes to a power band's "Hit". In some cases the pressure rise can be so great that it causes an audible pinging noise from the engine. As the engine rpm increases, the pressure in the cylinder becomes so great that pumping losses occur to the piston. That is why engines with too much spark advance or too high of a compression ratio, run flat at high rpm.

Retarding the timing will make the power band smoother in the mid-range and give more top end over rev. When the spark fires closer to TDC, the pressure rise in the cylinder isn't as great. The emphasis is on gaining more degrees of retard at high rpm. This causes a shift of the heat from the cylinder to the pipe. This can prevent the piston from melting at high rpm, but the biggest benefit is how the heat affects the tuning in the pipe. When the temperature rises, the velocity of the waves in the pipe increases. At high rpm this can cause a closer synchronization between the returning compression wave and the piston speed. This effectively extends the rpm peak of the pipe.

Re: ignition timing

Thanks Shay! I tried to help him, but doesn't want to listen. Granted I didn't go into all that, cuz I wasn't sure how to word it.But maybe he will take this advise now. Thanks Shay! Brent

Re: ignition timing

another important thing he mentioned there was the tendency to have high pumping loses at high rpms. which is why high output engines run around a 7:1 corrected CR. not static compression (trapped volume at TDC/total volume at BDC) which is why having high comp heads and advance timing limit the rpm ceiling of 2-strokes and therefore the top speeds on mopeds.

Re: ignition timing

oh i cant take credit for that. i copied and pasted from this site after i searched a website called "google" (which our friend here apparently isnt familiar with) for "retarding ignition timing, exhaust porting two stroke"

Re: ignition timing

No problem. I'm just glad he got his info.

60+mph out of my Puch, I had to be doing something right.

Re: ignition timing

I just wanted to know why thats all.. Thanks for the replies

Re: ignition timing

You just wanted to know why, but you were being an asshole about it, and accusing other people of not knowing their shit. It's fine to ask people how they know things, but it's much less cool to be a douche about it.

Re: ignition timing

that's it 60mph on a 18/28 gearing? nothing to brag about with that gearing. 60+mph can be obtain with 18/36 gearing

Re: ignition timing

It hasn't been GPS run. It has been next to a car at 64mph. 60+ has always been safe in saying. And yes I know there has been peds going that fast with 18-36 gearing. We bought one in 1980, with 18-36 that did 73mph. Thanks for your comment. Brent

Re: ignition timing

I'm sorry if I offended anybody.

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