How to set Timing on Rotax 185

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Postby Bill R » Fri Sep 24, 2004 8:06 am

I followed Shannon's suggestion and set the points to open/close at 0.17" BTDC. Both of Dave's engines are set that way and they start well and run quite smoothly.
I have one of my engines set at 0.15" and the other one at 0.17". The set to 0.17 had 100 RPM more than the one set to 0.15". The Left one is 0.15" and when I measured it last year it ran 5600 RPM static with the biprops. The Right engine is set to 0.17" and it will turn 5700 RPM static with a biprop. I find that the right engine idles rougher than the left engine. Every thing else being equal, which they are not, I'll explain later, I would expect higher RPMs with the 0.17" setting providing you do not get knocking, Predetonation.
To further complicate the experiment the right engine has the spinner backplate but no spinner. The left engine has neither the spinner nor the spinner backplate. The carb on the right runs a little richer at times even though I try to set them for max -1/4 turn The pump works better on the right engine. I need to do some maintenance on the Left pump/carb
Both engines run well enough that I did a 140 mile crosscountry on Saturday and they ran like swiss watches.
My 2 cents worth, Bill
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Postby rayjb60 » Fri Sep 24, 2004 4:56 pm

Thats great Bill, and thanks for some hard numbers confirming your settings and rpm.

Looks like the Magic number is about 0.16" BTDC.

Its good to know how reliable those little devils are, given a bit of TLC and a fighting chance.


About that Xcountry, was that on a single tank of fuel?
Where did you go?
Any pics from the trip?
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Postby Guest » Wed Sep 29, 2004 10:57 am

Bill R @ Sep 24 2004, 08:06 AM wrote: I followed Shannon's suggestion and set the points to open/close at 0.17" BTDC. Both of Dave's engines are set that way and they start well and run quite smoothly.
I have one of my engines set at 0.15" and the other one at 0.17". The set to 0.17 had 100 RPM more than the one set to 0.15". The Left one is 0.15" and when I measured it last year it ran 5600 RPM static with the biprops. The Right engine is set to 0.17" and it will turn 5700 RPM static with a biprop. I find that the right engine idles rougher than the left engine. Every thing else being equal, which they are not, I'll explain later, I would expect higher RPMs with the 0.17" setting providing you do not get knocking, Predetonation.
To further complicate the experiment the right engine has the spinner backplate but no spinner. The left engine has neither the spinner nor the spinner backplate. The carb on the right runs a little richer at times even though I try to set them for max -1/4 turn The pump works better on the right engine. I need to do some maintenance on the Left pump/carb
Both engines run well enough that I did a 140 mile crosscountry on Saturday and they ran like swiss watches.
My 2 cents worth, Bill


Just to clarify. The recommendation to try 0.17" BTDC was originally given by Peter Corley and handed down. There is no guarantee that an engine will run better with the points set to 0.17" as there are many "non-ignition" complicating variables with attaining peak engine performance. If anything I would say 0.17" is the "starting point" to find the best setting for a particular engine. On average however .017" works great on most engines.

Just as important as the ignition settings is proper set-up of the carbs. To get started it is imperative that proper (L) "low-side" tuning be done with a tachometer. As stated in the Series 3 operating manual page 11 section 8 the (L) adjustment controls the mixture for 80% of the engines rpm operating range. After 80% Rpms both the (L) and (H) adjustments are working in unision to provide proper mixture. There may be a misconception that the (H) adjustment alone controls mixture. The point being that the (L) must be set correctly to get proper (H) adjustment.

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Postby lazairiii » Wed Sep 29, 2004 12:50 pm

Excellent advice Shannon. I am very close to finally getting fuel into the engines. I have followed the handed down timing proceedures and will pull out the manual to make sure I have proper (L) and (H) settings.

Thank you for taking the time to educate us on the finer points of engine tuning, something I didn't know very well with my first Lazair years ago. I'm looking forward to flying with finer tuned engines and P-tips.

George
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Postby lazair3ca » Tue Jan 18, 2005 8:41 am

This post is to answer Ray's question from September:

The cross country trip in September was a multi leg trip. I had a ground crew, Dave and Michel, who helped a lot. I landed at a regular airport after the first hour to pick up fuel. Since CYRO only sells 100LL Dave and Michel had fuel in Michel's van. the next leg to Alexandria took 1.6 hours. With 5 gallons on board at liftoff I do not plan for more than 1.75 hours before coming down for fuel. The burn is probably 1 gal/hr/engine at cruise. I have to get some better numbers or increase my tank size to be comfortable flying over 2 hours. I refueled at Alexandria and did some flying with Karl and Tyler (series 2 with pod and p-tips and a 2 place) Then I filled up for the trip home. The north wind was now a head wind and it took 1.9 hours to fly to Kars. By this time I was cold and we only had 1/2 hour of daylight left. My ground crew arrived after I had the plane tied down. I had decided there was not enough daylight left to make it home. Kars does not have fuel so again I had to rely on my very efficient ground crew to provide fuel. I made it back to CYRP two days later when the winds had dropped. The flight home was another 0.9 hours. I had to do a few orbits while waiting for my ground crew.

So in short the total flight hours was around 5 hours. I will need bigger tanks to stay up that long. I hope the CDI ingnition will extend the airtime per tank. But I don't expect to get 5 hours from 5 gallons. :)
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Postby lazair3ca » Tue Jan 18, 2005 8:44 am

I have set up 7 Rotax 185s in the area. Now that we are converting some of them to CDI I will will have more time to fly rather than spending time cleaning and setting points. But then the weather is more of a factor than the engines. :-)
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Postby lazair3ca » Tue Jan 18, 2005 8:46 am

Ray,

I did take some pictures but they were from the ground and most of them were of Tyler's 2 place. I can post them if you are interested.
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Postby rayjb60 » Tue Jan 18, 2005 3:53 pm

The more pictures the better, I would like to see any pictures you've got if its not too much trouble.
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