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EI Timing for conversion engine

Old 04-28-2010, 08:01 AM
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flyrc100
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Default EI Timing for conversion engine

Im putting an EI on a Homelite 30cc. I set up the intial timing around 4 degrees BTC. It flip starts and idles just super, but it does not make Good top RPM, it gets to about 6300 and thats it, this with an 18x8 prop. A 30cc Homie ought to get 7000+ with a stock magneto. I tried another carb (My master carb, a carb I know to run perfect) and same result.

The engine appears to be in perfect condition and has excellent compression. I changed the initial to around 10 degrees BTC and the engine would not flip start any more. One thing I noticed was the base gasket between the lung and Block is missing. Someone trying to get more compression out of it I guess. I wonder if removing the gasket would change the port height enough to screw up the Power output??? Any ideas, and what should the initial timing be? Thanks
Old 04-28-2010, 08:50 AM
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Default RE: EI Timing for conversion engine

The total timing on all our conversion engines should be 28 degrees

The CH and RCEXL ignitions when moving the magnet past the sensor at the bench should both be 28 degrees before top dead center

A stock Homelite 30 with open muffler and a 11 mm carb should turn a 18 X 8 prop at 7400 rpm
Old 04-28-2010, 12:05 PM
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Twin Star
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Default RE: EI Timing for conversion engine

My Homie 30 also doesn't have the performance I expected. I am getting 6900 RPMs with a 17 x 8 prop opened stock muffler, stock carb and on magneto. It is starting to appear to me that the Homie requires more detailed modifications to extract it's potential.

My first and only other convert, was a Poulan whacker engine. I took it from 5700 RPM to 7200 RPM on an 18 x 8 just by changing some parts.
Old 04-28-2010, 12:21 PM
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Default RE: EI Timing for conversion engine

Yes, total advance should be 28 degrees @ high rpm.

Most all of the weedie engines I have converted have average power without further modifications to the intake/exhaust port timing ,and maybe the size of the bypass ports. Sometimes you're stuck with it because there is little room for modification, some engines are highly modifiable.

Rarely do I use the stock carburetor, they are almost always a little small.

Don't get me wrong, conversions are good, but 3D powerhouses they generally are not. Some of the better conversions I have done were from chainsaw engines, I think chainsaws are pretty tough duty and a weedie engine just wouldn't cut it, if you get my drift.



Old 04-28-2010, 12:29 PM
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flyrc100
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Default RE: EI Timing for conversion engine

This is to W8ye's Post-I agree the timing (total at WOT) should be around 30 degrees, but that does not mean you should set it up there, does it? Should it not idle at 4 degrees (or so) and automatically advance to 30 degrees as RPM increases?
Old 04-28-2010, 01:17 PM
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Default RE: EI Timing for conversion engine

I was recently told that most electronic CDI are at 28 degrees when first energized. They do not retard to 4 degrees until the engine is flipped or turned with a starter faster than 300 rpm. I asked how fast a good flip was and the comment was that he timed his flip and it was 600 rpm. So, the initial setting should be 28-30 degrees and the CDI takes over from there.

Sorry I can't find the post that addressed this, but it was from one of the highly respected electronic ignition wizards.
Old 04-28-2010, 01:55 PM
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Default RE: EI Timing for conversion engine


ORIGINAL: flyrc100

This is to W8ye's Post-I agree the timing (total at WOT) should be around 30 degrees, but that does not mean you should set it up there, does it? Should it not idle at 4 degrees (or so) and automatically advance to 30 degrees as RPM increases?
It depends on what kind of ignition unit you have, some are auto advancing, and some are auto retarding. Most of the EI setups I have are auto retarding, so the base timing is set at 28 degrees. I think my ZDZ engine is auto advancing, it is the only engine I have like that.

Old 04-28-2010, 04:05 PM
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Default RE: EI Timing for conversion engine

The retarding type ignitions when you are playing with them on the bench Unless you move the magnet past the sensor very fast are not going to retard.

So the static timming set up on your degree wheel on the work bench is actually 28 degrees before top dead center.

Then when the engine runs and is idling, it should be retarded at a point much less than 28 degrees. It will not get back to 28 degrees until on up around 4000 rpm.

The exact figure at 2000 rpm idle is somewhere around 12 degrees I think? The 4 degree figure is at no rpm and if it is at no rpm, it will revert back to full advaqnce of 28 degrees internally.

You may as well disregard the 4 degree figure?


http://www.ch-ignitions.com/CHinst.html
Old 04-29-2010, 05:16 PM
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Default RE: EI Timing for conversion engine

Well said Jim.
Old 06-10-2012, 05:06 AM
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pejuve
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Default RE: EI Timing for conversion engine

Hi, I just finished installing my engine conversion (poulan 46cc) on my plane, I set the timing 28 BTC, or very close, it is a RCEXL , when I flip the prop, it does a back-flip and wont start, some times it will but my arm has almost fell off. Do you have any suggestion on what I can do.
Thank you.
Pedro V.
Old 06-10-2012, 05:10 AM
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pejuve
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Default RE: EI Timing for conversion engine

Hi, I just finished installing my engine conversion (poulan 46cc) on my plane, I set the timing 28 BTC, or very close, it is a RCEXL , when I flip the prop, it does a back-flip and wont start, some times it will but my arm has almost fell off. Do you have any suggestion on what I can do.
Thank you.
Pedro V.
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Old 06-10-2012, 08:31 AM
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w8ye
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Default RE: EI Timing for conversion engine

The ignition triggers just as the magnet leaves the sensor. If you turned the crankshaft in the wrong direction when setting the timing, your timing will not be at 28 degrees before top dead center. It will be off 12 degrees total advance if you turned the crankshaft opposite the direction of normal rotation.


That means that in starting mode, your timing is probably some 8-10 degrees after Top Dead Center depending on your method of setting the timing?
Old 06-10-2012, 08:44 AM
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pejuve
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Default RE: EI Timing for conversion engine

Hi W8ye, I know that I right with the engine rotation, maybe I'm a little off with the BTC, I have been doing some research and the people say that in the BCT always has +/- 5 degrees on play.
Thanks
Old 06-10-2012, 09:34 AM
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w8ye
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Default RE: EI Timing for conversion engine

You want Top Dead Center not bottom dead center

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