Saito 82 Tuning

[arun 0]

Hi guys - struggling tuning my Saito 82B engine, appreciate any help those more experienced with four-stroke engines can offer (this is my first).

 

Propeller is a Graupner 13x7. Fuel is 15% nitro, 20% synthetic oil from Souther model craft.

 

I've followed the (extensive) run-in procedures to the letter, but in a nutshell I can't seem to get a nice reliable low-speed idle. The best I can manage is something that stutters and coughs, occasionally resulting in the engine backfiring and restarting backward!

 

I took a video of it showing speed through the range, effect of quick throttle change. At end of video (around 25 seconds in) you can see what happens when I close the throttle and let it idle ... not good.

 

Any advice where to go from here? I haven't touched the low-end needle at this point as was my understanding that is was fairly well set at factory. High-speed needle is open 3.5 turns which (with my unreliable tacho) gives my an RPM of around 9500.

 

Here is the video!

 

https://vimeo.com/63751899

 

Thanks in advance.

[shanemarsh28 11]

It looks to me like its running very very rich on the bottom end and its flooding on idle giving you a lumpy tick over and eventually stalling completely also, backfires are nearly always the result of too much fuel entering the venturi. The high end sounds OK, although you could probably get a little bit more - If you haven't touched the low end at all, I'd wind in the low speed needle 1/8 (but no more than 1/4-1/2 unless the engine is well run in) of a turn and try again. That should go some way to solving your tick over issues.

 

Shane

Edited April 10, 2013 by Guest

[Trevor 25]

What idle speed are you trying to obtain? I find my 82a won't idle slowly, min about 2200rpm. Whereas my asp80 will idle happily at 1800rpm. Have you got a tachometer?

 

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[arun 0]

Am aiming for ~2500rpm per the manual. I've got a tacho, it's currently showing in the region of 4000rpm for a stable idle without risk of backfiring - although I'm not sure I trust it 100% as the values fluctuate much more than I'd expect. I think Shane is probably right, bottom end (and probably top) can be leaned, but I've been being cautious as this motor is neither cheap nor tolerant of over leaning from what I read Any recommendations for a tacho, I have a Turnigy one but as mentioned am no convinced of its accuracy?

[Emay 2]

It seems both low and high ends are too rich. Have a look in here http://saito-engines.info/starting.html

 

Hope this helps.

[shanemarsh28 11]

Its always best to have a slightly rich bottom end if you can, helps with cooling on a new, tight engine. Of course eventually you'll want to tune it up a bit but If it was me i would just very slowly start to lean out the low speed needle, that should stop.it backfiring. Do the spit test on the cylinder head while its running at idle, if the spit boils the engine is far too hot and should be shut down straight away and allowed to cool before re starting. If you can get it down to 3000rpm or less without overheating or stalling? You'll be good to go!

 

Hope that helps,

 

Shane

 

Ps: I suspect your tacho is probably not that far off. Id just be careful about overheating. You really don't want to scorch the rings. If it does start to get overheated or liquids start to boil on the cylinder head as you start to lean it out, you'll just need to run the engine in for a little longer. Im sure it will be absolutely fine though.

[arun 0]

Thanks for the advice, I'm just very cautious with the Saito of over-leaning too soon. I'll probably guide the bottom end lean out based on restricting fuel flow to the carb and observing behaviour (e.g. speeds up quickly and quits = too rich). I've heard such good things about this engine once it is well run in I just don't want to ruin it by rushing...

 

I tested my tacho using a fluorescent light running on 50Hz mains. My tacho shows 3000 "rpm" which is correct, since 50 cycles/sec x 60 sec x 2 pulses / 2 blades = 3000rpm. I know that formula cancels down, but just noting that that fluorescent tube pulses on both the +ve and -ve part of the AC wave. So, nothing wrong there! My only guess to the wild readings was that I was outside (obviously) but the tacho lens was pointing at a patio door about 10ft away, possibly the reflections from this caused issues - I'll validate this on the next run but since it is raining now I doubt that will be today

[arun 0]

Haven't had time to do any more tuning, but I did find these very comprehensive notes on running Saitos. Might be of interest to others:

 

http://www.wamasc.org.au/pdf/technical/SaitoGeneral.pdf

[hotrod 0]

Is the Nitro too high at 15%? With both my J'en engines it was not possible to get a good tickover on 10%, the instructions said 5% and 5% was needed, as soon as I put the correct mixture in they both ran fine. It seems you can get preignition with a higher nitro content.

Just a thought

Rod

[arun 0]

15%+ nitro is very normal for Saitos and recommended in manual. I think it just needs leaning at both ends.

[Trevor 25]

For modern Saitos they recommend 10-30%. I use 10% and mine run fine

 

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[arun 0]

Made some pretty good progress with this. Can get an OK idle at 2700-3000rpm with WOT at 9000rpm (which is tuned down from a maximum currently possible at 9500rpm). I think I can improve the top-end speed a bit by switching to my APC 14x6 as currently on a Graupner 14x7. The latter allegedly loads up similar to an APC 14x6 according to Dave at Motors & Rotors, but I'm less sure as the top speed seems low esp. given 15% nitro.

 

So, some advice from Saito or other four-stroke owners please! Is it possible to lean-out the low end needle too much to the point that it causes damage? My intuition is that it is not and that the worst that will happen is that the throttle transition will be poor or even cut. I'm basing this assumption on that fact that damage due to leaning is presumably caused by heat due to excess RPM which isn't really an issue at the idle end. Am I right?

 

I don't want to fiddle much more at the low-end until am sure that further leaning isn't at risk of causing damage, but I do want to carry on tuning the low-end though as 2500 seems like a better target speed at this point in the engines life (approx 1 gallon in). With more running I hope I can get nearer 2000.

[Trevor 25]

I dont think it is possible to damage it with a lean bottom setting. As you say, it won't idle or pick up properly if too lean. Too lean a top end MUST be avoided and the needle should be set so the speed is 300rpm slower than highest speed by richening the mixture, so they say

 

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[arun 0]

Thanks Trevor

[Trevor 25]

One other thing to note in case you didn't already know, tuning an engine on the ground is one thing but when it is flying it is possible to over rev an engine by, say, a power dive and it is this that the engine should be tuned for, so that in these circumstances the richer setting on the ground becomes a "normal" setting in the air and you don't damage the engine. This is just stuff others have told me over the years and I am passing on.

[arun 0]

Makes perfect sense - I've observed the same effect on a windy day (no shortage of these currently) with aircraft pointed into wind and throttle held constant - when a gust arrives the revs rise noticeably. Thanks as always!

[shanemarsh28 11]

tuning an engine on the ground is one thing but when it is flying it is possible to over rev an engine by, say, a power dive

 

I seem to remember something about this somewhere, I believe its called 'unloading'?? Apparently It's a good thing and it makes the engine run cooler at high RPM as the load on the engine is reduced - as long as you say the engine isn't over revved. I'm not sure though .. I may be talking complete rubbish!!

 

Shane

[Bravedan 106]

Yes, unloading, but it can be good or bad!

 

And, don't forget it affects EP equally as well.

 

Tachometer, have two...........but prefer the Mk1 ear!!