Experimenting With Timing

BOYGOFAST said:
piston ring worn cylinder ports the top of the exhaust port will likely go first the rest will follow until the engine stops running if it does not explode or break a crankshaft minuets before that happens ,only a guess......
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Just curious. How is this pertinent to this thread? Just asking.

Tom
 
maniac57 said:
Still need a magneto for the juice cannonball. Would need a battery at minimum for points to work.
Good idea though, should allow more adjustment range with only points under the cover if running off battery. Might be worth a try
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I was thinking of mounting the breaker plate assembly over the existing magneto and using it as the power source for the point conversion. Simply ground the black wire and run the blue to the ungrounded side of the points. The condenser could be mounted up at the coil for space saving. Wouldn't be too hard to use a commonly found small point set and mount a cam lobe to the existing rotor.
 
This has been stated before, but there are a couple of different Magnets, with different keyway locations.
From what I have been told 20 deg is the sweet spot.
Building a CDI with variable settings seems the best way to experiment with different timing.
 
I almost bought a variable CDI, but figured a stock engine wouldn't benefit much from it. That was a wrong conclusion! You are right Theon the keyways were in slightly different locations between the GT5 engine and the Flying Horse The GT5 was a bit more retarded and took much less out of the keyway to see the same results. Finding one of these rotors would be a good starting point. Problem is you hardly ever get what you are shown in the picture of the part.

Im thinking the CDI has a fixed timing and does not vary. If I hadn't thrown my old timing light in the recycler thinking it was obsolete I could check it. Maybe some one out there could. I have heard there is too much advance in the CDI at high revs. So if the running is improving by retarding the initial timing Im concluding it must be a fixed value, or it has too high a starting point. In all the years of changing timing this is the first time I have seen timing improve by retarding, starting from the manufacturers base point. Somethings gotta be off!
 
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exactly. the stock cdi has a good timing curve but the starting point is variable.

since we are retarding it. the rotor keyway needs to be widened and rotational forces will hold it in the retarded direction along with the fastener.
 
Relying on electronics to do the advancing/retarding is too fixed.
What would be ideal is to have timing controlled by either centrifugal weights and vacuum as old style distributors had. At least they would be adjustable by anyone with a basic mechanical understanding. Changing springs or weights would allow advancing based on crankshaft RPM and engine load.

Newer cars use computers to do it and they are making constant adjustments. We don't have that luxury. And I still stand by the reliability of the stock CDI when it comes to performance. I've yet to see proof of any gains from the aftermarket wonders.

Tom
 
but when the ports wear out the timing will advance the only correction is to lengthen the stroke by adding a head gasket or two or three under the cylinder head ,no ? anyway the engine is only cast aluminum why attempt correcting timing or adjust beyond minor repair
 
there's no way the timing could be off even one degree mechanically if the piston is at top dead and magneto or magnet is centered @0 degrees at the same time in the rotation the spark travels faster than any percentage of a 360 degree measurement the loop would have to be the size of brick oven
 
BOYGOFAST said:
but when the ports wear out the timing will advance the only correction is to lengthen the stroke by adding a head gasket or two or three under the cylinder head ,no ? anyway the engine is only cast aluminum why attempt correcting timing or adjust beyond minor repair
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Nothing you can do will "lengthen the stroke" except altering the throw of the crankshaft rod journal. Stroke is a product of how far from center the rod bearing is from the center of the crank. Nothing else will change stroke length. Nothing.

As for being no way for the timing to be off based on piston position, the indexing of where the keyways are cut in the rotor and the crank have everything to do with it. You might not see two three or four degrees difference but when you use a dial indicator to find exact TDC and then compare different engines, you will see a difference in rotor position verses piston position.
I've examined too many to believe otherwise.

Tom
 
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Agreeably centrifugal advance would be ideal like the older Honda and other M/Cs had. However fixed timing is a good compromise when the range is acceptable in both directions. Theons suggestion of 20 degrees sounds good. I honestly don't remember what small engines run at, seems like 24/26? I have set timing as I said earlier as high as 28 degrees on hand start engines, over 30 you are asking to have the starter handle jerked out of your hand. Problem is we are in the dark as to where the actual timing of the CDI is. I need a timing light. Im gonna scour the neighborhood and see if I can borrow one. I have a rotor on the way. I will mark the point where Grubee says they fire and see first if that's a fact. I have a dial indicator set up some where to read the piston drop before TDC. This will tell exactly where the CDI is firing. Resetting the CDIs start point mechanically with the rotor to an acceptable value will also lower the ultimate advance, which is probably good. Got some stuff to find!
 
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I have all the parts here to build an adjustable CDI as well as parts and a circuit for a small LED timing light. I think that if your timing is right, aftermarket CDI will not help. However a lot of these motors obviously do not have the correct timing and this is were an aftermarket CDI may help.
My friend Jim, who is a retired electronics 'engineer', has done a lot of testing for Screaming Roo, He has found very little benefit from altering timing from the 20 deg sweet spot.
But I guess it all depends on the rev range your after, still, my thought is that any deviation from 20 deg would only want to be in the range of 2 to 4 deg.
When I get around to putting this together, plan was to have initial timing at around 22 deg. with around 18 deg at higher revs. Apparently a good quality plug wire will help give a little retard increasing with revs due to inductive properties of the wire? But not sure how much.
The Rocket CDI appears to have low quality components compared to what Jim has given me, The HD has been epoxied, so can not be modified. Building an adjustable CDI is not hard, but would likely be a bit hit and miss without a timing light to monitor adjustments.
I'm probably not at liberty to share Jims Designs I'm afraid.
But really from what he has told me after many hours of testing is that standard CDI at 20 deg with good lead, is hard to beat.
 
I'm currently doing some serious testing of several popular aftermarket CDIs (& magnetos) for spark timing & total spark power, (at the plug).

I'm doing 'side by side' testing of the HD Lightning, Jaguar, Screaming Roo & several stock Chinese units.

I'll post my findings in the next few days when I'm finished testing. (^)



So far, the most powerful spark I've been able to produce on a coil voltage tester, came from a 100% stock Chinese CDI & magneto!!! (They beat out all the others)!! :eek:


I'll post more soon! ;)
 
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I am also waiting on the weather to break to allow testing of the new Screaming Roo coil CDI combo. I already have the Lightning and plenty of stockers laying around.
Be aware there are now two DIFFERENT CDI boxes coming in kits, they are slightly bigger boxes and the newer ones have MUCH better plug boots as well. Not sure if the bigger boxes are internally different due to epoxy potting, but the better cap and wire alone make them a good addition.
The Screaming roo CDI is slightly bigger than the largest stock CDI and the coil is said to be wound for more power. Testing miles will tell if there is a seat of the pants difference between the three.
So far my fav is the lightning due to better low end and smoother running motor. No power difference over stock.
 
Thanks for all the input Guys maybe we can get somewhere with a few people working on this.
What I am trying to determine is where give or take the stock engine is timed. Only way to know for sure is dynamically with a timing light. This will verify if the stock CDI has a fixed or variable curve, and where it starts. I have found in the past a 2stroke will run with way advanced timing(where a 4stroke wont) but not well. If the rotor and mag signal the CDI to fire with a dead on say 20degree advance and it does perfect! If the CDI throws an additional 10degrees in that's not good! Might be ok for max rpm but not all through the range. The adjustable CDIs from what I can tell move the ranges, but not the curve? Im not sure on this. If that's the case its not very adjustable, you can do that with the rotor. In practice I know its easier to do with the CDI, but cheaper with the rotor.
I have both a stock CDI and an aftermarket non adjustable unit. Both responded with better running from retarding. Im not wanting to discuss the merits of various CDIs, according to all they seem to run the same. Thats kinda my point they also run(or will) equally as bad due to the improper initial timing.
Its plain and simple if our engines run better overall from retarding theres just too much advance somewhere. If the CDIs base line is fixed, initial timing has to be adjusted mechanically.
 
I just wanted to offer myself as a guinea pig, I will gladly test any ignition system sent to me and give an unbiased report of my results. Joking aside, I will try filing the magnet to the retarded side and see what that does. My motor is running stronger than ever, I want to let it actually break in first though so the results will be more clear. I have never actually let it fully break in a set of rings before taking it apart and reworking something.
 
I'm not interested in a power gain so much as I am a smoother running engine at my normal speed range. I don't really care if one gets a few hundred more top end rpms, I hardly ever scream my dolls guts out so who cares?
I want a nice smooth engine that pulls from idle without popping, four stroking, or cutting out and that will run out at least as far as the stocker.
That is why I like the Lightning over stock so far...smoother low end and better manners.
I am hoping for more of the same from the Screaming Roo unit with hopefully better coil reliability as well...
 
LSR, establish a good baseline of performance before you make the rotor mod. That way we will know what effect it had. If it does nothing but improve bottom end that's gonna be a plus for your situation.

I checked around the hood and timing lights are all gone these days. Still looking. My plan is to make a very accurate mark on the rotor aligning with the cranks keyway, shoot it with the light and try to get an accurate mark on the mags laminations where the cranks mark aligns. The difference from that mark to the 12:00 position of the cranks key is the advance. This will also give me a chance to see if the CDI is an advancing of fixed. This requires a stock rotor which I have ordered.
 
Ugh, I had an inductive timing light laying around for a devious reason.I will dig for it tomorrow and if I find it I will mail it too you Cannonball. I can't promise, it's been a while since I have seen it but if I find it I will P.M. you for an address to send it too.
 
No need to mail it, you can do the testing, I can talk you through it if you like. Its quick and simple. To get max out of your LSR engine timing is going to have to be known. Especially if you go to fuel, it will allow more advance.
 
I would try and get a couple of magnets, I have 3 different style of magnets, and have noticed a difference with the 'better' ones.
The good ones have the keyway at about 1.00 as opposed to say 12.05.
They generally have a shiny appearance like SS , the others are a plainer metal. Some have a Y stamped on them.
Failing that, I have made 'Rocket' keys before by getting a wider key and filing it to a stepped shape.
I found the magnets with more advance wouldn't let my engine rev as well, not much difference other wise, but I don't put around, I'm wanting it to run it's best from 5000 to 10000.
One motor whilst running a slant head (min deck height so hi comp) in hot weather, would ping at about 8G, swapped magnet, got another 500 RPM. Still pinged, Swapped head, much better. First step to getting a motor running its best is get the compression up, (and a center fire head), then ignition changes may make more of a difference.
 
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