so far, i know how to clean a carb and other maintenance stuff, install a metrakit, kinda know how to trouble shoot, and am familiar with most of the parts but i don't know anything about timing.
what is the importance of timing and what does it do?
the importance of timing?
Re: the importance of timing?
Ignition timing in a combustion engine is the process of setting the time that a spark will occur in the combustion chamber (during the power stroke) relative to piston position and crankshaft angular velocity. Setting the correct ignition timing is crucial in the performance of an engine. The ignition timing affects many variables including engine longevity, fuel economy, and engine power.
Re: the importance of timing?
if your timing is off, it wont spark at the appropriate time during the piston stroke, and it can cause flooding due to it not igniting fuel at the right time, thus not allowing the bike to start and/or run or die out
Re: the importance of timing?
Timing advance is the number of degrees before top dead center (BTDC) that it sparks the air-fuel mixture in the combustion chamber during the compression stroke. Timing retarding refers to the number of degrees that ignition is delayed after the point that would have resulted in creating the most
Re: the importance of timing?
here's a good link to review the idea of how to set timing
Re: the importance of timing?
that's all jibberish to me. haha.
Re: the importance of timing?
lol, well you asked...and there it is!
here's another example
bikey-san spaaahka atta wwong time no ghood to make bike whuuk! need spaahka splita second before TopDeadCentaah
Re: the importance of timing?
OK, here's the deal. Maybe this will make it easier.
When your piston is moving up in the cylinder it squishes the gas/air mixture in to a smaller space or volume. You want spark when it's all squished as you get more power out of the explosion. Most Puchs are set so that the spark fires at around 1.5 mm before the piston reaches the very top of its travel or Top Dead Center (TDC). It sparks just as the piston is reaching the top and everything is super squished. When it sparks, all hell breaks loose and pushes the piston back down to get more gas/air mixture and do it again. If you're timing is set too late, then the spark might be firing when the piston is already on the way down. Not cool. If it's sparking too early, then it kinda slows the piston down as it is on its upstroke. Does that help at all?
Re: the importance of timing?
yes. that helps. but...how can you trouble shoot that? what are the symptoms of timing that is firing too soon or late? can you only tell when you start your moped? or is this something you can tell when riding it? or both?
Re: the importance of timing?
Backfiring is a symptom of bad timing. Sluggishness can be a symptom of bad timing. If you take out your spark plug and stick a pen in there and look at your points at the same time, you can get a rough idea of what is going on. Turn the flywheel and look at the points through one of the holes in the flywheel. When the points _just_ start to open stick a pen in the spark plug hole. When the points just open is when your spark plug sparks. Your piston should be almost to the top of its travel. Keep turning the flywheel and watch the pen. Does it move out more than 1.5 mm before it starts to move back down? If so, your timing is too early. Does it not move out at all before it starts to move back down? If so, then your timing is too late which means that the spark is happening when the piston is already traveling back down.
"Here's a great thread about a tool you can make to assist you with setting your timing.":http://www.mopedarmy.com/forums/discuss/7/75554/75554/
Re: the importance of timing?
thanks! that helped a lot
Re: the importance of timing?
2 stroke timing is very important. too advance and you are putting the flame into the crankcase, too retarded and it lights up the fuel as the piston leaves where it can make power and shoots everything down the exhaust.
Re: the importance of timing?
Can timing just go bad all of a sudden?
Re: the importance of timing?
Someone posted this in GD and i didn't want you to miss it.
Re: the importance of timing?
Yumster, I see you're not a Moby person so don't read this. Bryan, here's my chance to ask you about something that's always bothered me. Isn't our Moby timing a combination of both the setting of the points and the orientation of the cam on the crank? I mean if the cam is not where it was in the beginning (at birth) then there's only so much one can do with adjusting the points to get that 2mm. If the cam's been removed and imprecisely re-installed how can you ever get correct timing and correct gap? And some have commented that with our worn engine we would be better off with 1.5mm. I've spent hours fiddling with this.
If I'm out of line on this thread or this forum, please forgive me.
Re: the importance of timing?
Sure, the cam or stator plate could change position if loose or if the flywheel rotates on the crankshaft.
Re: the importance of timing?
you are better off with the timing set closer to 1.5mm then 2mm on a moby
Re: the importance of timing?
Well, OK then, if timing is troublesome, you remove the cam and re-install. but isn't just lining up the holes with the bolts rather crude? I mean, don't you have two variables to adjust simultaneously--the cam on the shaft and the points opening at 2mm? It all seems circular to me.
Re: the importance of timing?
This is how I do it. I spin the cam loosely on the flywheel to get the biggest gap in the points. Adjust the points to the desired gap. Then I go and put the piston in the desired position before TDC, whether it be 1.5 or 2.0 mm. Then I loosely turn the cam so that when it makes contact with the points and they _just_ start to open, I leave it there. Give it a whack with a hammer and a socket to "set" it. That's all I do. Sometimes it doesn't quite work out and I have to do it again but it seems to be close enough. How are you doing it? I'm no expert at Mobys but that seems to have always worked for me.
Re: the importance of timing?
I've been trying something similar--except when setting the rubbing block on the highest point on the loose cam, I try to have the elongated slot of the points set about centered on the tightening down screw. My thought was then I had max adj. available in either direction. I don't understand the Moby experts who say they can set the timing in 3 minutes. And this means that nobody can set timing without a cam puller if it's ever been moved. And lots of folks don't pull the cam. (a couple of mine have heavy plier marks on them, either the PO used water pump pliers to rotate the crank or was trying to pull off the cam). Maybe I'm missing something. If it wasn't freezing out I'd try 1.5 for awhile.
Re: the importance of timing?
Another thing that usually happens is the points themselves wear down on the cam contact side, since that side rests on the cam as it rotates. Thousands of RPM for hours on end wear it down after a while. On Bosch and Iskra and maybe a couple more they have the little piece of felt in there that touches the cam. That piece should be oiled so that it keeps oil on the cam face to help prevent wear. It doesn't take too long to remove 0.38mm.
Re: the importance of timing?
Fory the Mobylettes out there (I don't theink the original poster was doing timing on a Moby)...
OK, if the rubbing block (the part of the points that rides on the cam) wears down, all it will do is reduce the point gap. If you open the points to the maximum and reset them to the proper gap you have compensated for that wear.
A few weeks ago I used a ruler and an ohmeter to set the timing as accurately as possible. A couple things I can tell you - the points are actually opening before it is apparent to the eye. If you're setting them to where it looks like they're just opening you're probably too late.
My little testing also showed that the quick method really does work, and you can set the timing in under five minutes easily (assuming you can get the cam off - a puller helps!)
Take out the spark plug and use something (like na allen wrench) to indicate when you are at TDC. Slip the cam on with the riser toward the top and the holes pointing towards about 10:30 or 11 o'clock. While holding the crank at TDC, rotate the cam towards about one o'clock (which should be opening the points) and line up the holes on the cam with the axis of the cylinder, or just slightly to the left.
In the picture below you can see how the holes relate to the cylinder axis at TDC, and this is with the timing set to 2mm TDC very accurately. Setting to 1.5mm would put it even more in line with the axis. So yes, the "quick and dirty" method of putting the piston at TDC and aligning the cam up this way really does work!
Re: the importance of timing?
Looking at the picture, if you want to be even more accurate, put the piston at TDC and place some type of straightedge in line with the cam holes. For 2mm TDC have the ruler line up with the rivet on the left side of the tag on the cylinder head. For 1.5mm TDC have the ruler line up with the middle of the cylinder # tag. Quick, easy and accurate!
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