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HomeRC & Power✈️Aircraft🚁HelicopterEngines Plugs Mufflers Fuel › Can't get my OS .91SZ-H PS to run well...
08-24-2008 12:47 AM  12 years ago
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wings19

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Tucson, AZ

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Can't get my OS .91SZ-H PS to run well...
I'm having a heck of a time getting my OS .91SZ-H pumper to run good... I was running Magnum 30% fuel with all of the head shims and ended up frying the piston/ring/sleeve. I recently switched to Wildcat CY 30% and I am using two .2mm shims for a total of .4mm (.016".

From what I understand that is the correct shimming. However, the engine seems to run lean all the time no matter what I do to the needles. Either that or it is detonation I don't know how to tell it apart.

Today I ran mid needle 1/2 open and high needle almost 2 turns open and still running to lean.

Should I add the other .1mm shim and run all 3 like I was on my Magnum fuel?
Nick
If the wings are traveling faster than the fuselage, it's probably a helicopter
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08-24-2008 12:52 AM  12 years ago
RCMed-x

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westpalmbeachflorida usa

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It sounds lean but did you check temp . It might be rich and sounding lean.A good teacher is a good listening student !
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08-24-2008 01:02 AM  12 years ago
wings19

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I touched the engine with my finger and couldn't hold it on there for more than a second. We did temp it a few minutes after I shut it down and it was at 220-230F at the head. It seemed real hot but I should be that far open on the needles I don't think.Nick
If the wings are traveling faster than the fuselage, it's probably a helicopter
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08-24-2008 01:12 AM  12 years ago
RCMed-x

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Open mid more . I know that most people run mid closed or 1/2 turn but try opening more . Start with 2 turns on mid and high and get high close then go to mid and get transition smooth then fine tune.A good teacher is a good listening student !
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08-24-2008 02:24 AM  12 years ago
wings19

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I should also add, I did not have much smoke either.

Also, the engine would bog and didn't have the power it should.
Nick
If the wings are traveling faster than the fuselage, it's probably a helicopter
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08-24-2008 01:01 PM  12 years ago
RCMed-x

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Take carb apart and clean you could have a little piece of O ring or dirt stuck in carb .A good teacher is a good listening student !
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08-24-2008 06:05 PM  12 years ago
wrobijns

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Swalmen, the Netherlands

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I had the same thing and finally I found it.
It was my tank-fuel nippel thingy, to fuel it up.
It restricted the fuel flow too much.
A friend had a filt-clunk wich was too restrictive.

Remove all of your filters, filt-clunk, everything except the fuel-line.
When I did that it ran slobbering rich. (Wildcat 30% btw)
Walter Robijns, 3D rules !!!
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08-25-2008 01:19 AM  12 years ago
RCMed-x

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nippel thingy
My wife has one of these
A good teacher is a good listening student !
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08-25-2008 12:36 PM  12 years ago
Spacey

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Pretoria, South Africa

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nippel thingy
My wife has one of these
RCMed-x: Oh dear! What happened to the other one? Ok TBH only one is better than six, that would have had me VERY worried.
Today I ran mid needle 1/2 open and high needle almost 2 turns open and still running to lean.
wings19: I'd also say that right there is you problem. Do like everyone suggested though and check out the fuel supply, also ensure you've got the backpressure from the muffler rigged up proper. You have to get fuel into this sucker, don't bluff yourself into thinking the pump will take care of all this. If you got too small fuel tubings, restrictive connections, small filters or a combo of any of these you'll have a problem. BUT definitely get that midrange needle more open! From my experience and three SZ-H's all wanting the same, tuned by two different pilots the midrange on these motors actually needs to be much more open than the normal HZ. Ours end up at more like 3 1/2 turns out when the high end needle is optimised at 1/2~1 turn out whichever it needs.

If you're lean on the midrange you'll see all sorts of troubles. Motor causing a vibration, fuel foaming making it all worse and and and.
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08-25-2008 03:23 PM  12 years ago
wings19

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Tucson, AZ

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update
I removed the inline filter to the pump, replaced fuel lines and richened both needles. Runs ok but it is too rich to make good power. I can't even tic-tock without the engine coming way down. That can't be right.
Nick
If the wings are traveling faster than the fuselage, it's probably a helicopter
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08-25-2008 03:39 PM  12 years ago
Spacey

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Pretoria, South Africa

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NOBODY can tell you turn the needles to this and this setting and all will be dandy? Not on one single motor out there, doesn't even work with electrics.

You have to tune your motor run right in your conditions, barring everything else in the setup is perfect. But fine, now the midrange is at least running rich and the motor's reliable. Now you can start bit by bit by tuning the top end needle going leaner or even richer depending on what the heli is telling you when it's flying. Once you get it to make good power on the top end and the top end is perfectly adjusted then you have to go back to the midrange and lean that a few clicks at a time untill it's happy and not sloppy rich or too lean and cackling when you unload into midrange.

Not making good power, smoking alot, fuel making alot of waves, oil dripping out the muffler, heli just downright bogging but still reliable when punching out are all signs of too rich on high end. But in order to check this you have to get the motor to full throttle on the carb. Motor cackling, heating up and and is of course signs of too lean.

The same applies exactly to the midrange. Except you now need to get the motor to around half throttle to see what it's doing. Typically this one's adjusted while hovering and typically the motor wouldn't get nearly as hot as it would after a chuck around. The motor gets less cooling around the midrange so it would need more fuel (A little richer is good here). You will also see midrange kick in when you unload upstairs in idle up, it should pour out a bit more smoke than on the high end needle but it musn't start cackling or missing a beat at all.
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08-25-2008 03:51 PM  12 years ago
wings19

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Thanks for the reply Spacey, and I do understand how to tune an engine. It just gets frustrating when you drop $400 for an engine that doesn't run well unless you pour fuel into it and then it doesn't make any power because its so rich. I know the engine is capable of more. It ran well at IRCHA before I switched fuel and changed shims.Nick
If the wings are traveling faster than the fuselage, it's probably a helicopter
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08-25-2008 05:10 PM  12 years ago
Flying Tivo

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Monterrey,NL,Mexico

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Im running stock shim and CP30%
My needles are 1.1 on high and 1/2 on mid.
No problems whatsoever.
I do run free vented not pressurised tank.

Felipe
If life throws at you lemons......Squirt some lemon juice in the eye of your enemy!!!!
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08-25-2008 09:14 PM  12 years ago
RCMed-x

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wings19,Dont take this too personal we are trying to help. Its not that you dont know how to tune but take the time to let things set in .If you have pitch and throttle curves out (transitions)you will be ahead of throttle with pitch so motor will not keep up . Now you have running rich lean out high end a little at at a time to get more power then lean out mid until it gets better .Then go back to high to fine tune if you lose power then rich-en back up keep an eye on temp.A good teacher is a good listening student !
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08-25-2008 09:47 PM  12 years ago
wings19

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Tucson, AZ

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I'm not trying to take anything personal but it gets frustrating ya know. You dump a lot of money and you want it to perform like it should.

I am using a GV1 with JR 8717 on throttle, also on cyclic.

I had it running good at IRCHA after Botos flew it. I changed fuel and am now using .016" shimming instead of .020" and it sucks now. I think a .91HZ is in my future
Nick
If the wings are traveling faster than the fuselage, it's probably a helicopter
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08-25-2008 10:42 PM  12 years ago
Kevin Dalrymple

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Indianapolis

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I had that problem recently. It was the pump. I need a new one. My pump pumps but not enough flow and th eengine gose lean.
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08-25-2008 11:17 PM  12 years ago
wings19

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Tucson, AZ

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That is what Matt Botos told me... He gave me a pump but it wasn't a new pump. It was one he had lying around so maybe that one doesn't work either Nick
If the wings are traveling faster than the fuselage, it's probably a helicopter
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08-26-2008 12:45 AM  12 years ago
RCMed-x

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Bypass pump use regulator and pressure from pipe I liked using mine this way . If you can tune this way pump might be your problem .If it seems to be pump I might have one lying around I will give you .I will look .I baught 91 pumped and took pump off new using reg .A good teacher is a good listening student !
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08-26-2008 02:40 AM  12 years ago
wings19

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That would be very kind you you RCMed I will try to bypass the pump and see what happens. I would have to drill and tap a new hole for a pressure nipple and I messed up the other hole when I tried to get the old nipple out(which was red locktited) to put a screw in since I am not using muffler pressure at the moment.Nick
If the wings are traveling faster than the fuselage, it's probably a helicopter
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08-26-2008 08:10 AM  12 years ago
Spacey

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Pretoria, South Africa

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Wait you're not using muffler pressure at the moment!?! I've seen alot of guys do this like Scott but I'm not sure if they use the stock OS pump in this configuration. And then also they run OMI mods on the motors if I'm not mistaken.

Either way if the muffler pressure pipe on my motors come off the motor just doesn't run worth a darn like it should. It's a got a complete mind of it's own. Hate to say it but I'm thinking part of your problem could by lying right there. Sure alot of guys modify the motors to not use muffler pressure at all but reading the symptoms you speak of I have to say it wouldn't hurt getting the muffler pressure back into the tank to help push more fuel and a more consistent flow of fuel to the carb.

I'm also trying to establish if you might have a shimming problem on the motor now that you've switched fuels but it's impossible if you're not re-tuning the motor proper. You have to go about re-tuning it for max performance so we can see what you end up with. If it's running rather hot when you get it to make power and is extremely sensitive on the needles then we need to get another shim in there. If it's going the other way, running great temp wise etc and easy to tune but not making power when you get it set right (not too lean or rich, running happy) then yes you got a shim too many.

Changing fuel can cause all sorts of fun things. You're going to have to start eliminating one thing at a time.

I don't have my money on the pump being the problem just yet, if it was it wouldn't run reliably at all from my experience. All the pump failures I've seen (And yes these pumps do have a rep to be toast after you destroyed a piston and had the motor get up to melting temp) the motor would seem fine but always want to cut as soon as you start trying to get it to pick up RPM or go to "full throttle". You say the motor is reliable and all nice and rich right now so that makes me think the pump might be good.

Get that muffler pressure back on if you can and let's get this motor tuned, we can later bypass the pump because yes you can check if the pump is the problem this way but from my experience the motors just don't run anywhere near like they should without the pump either.
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HomeRC & Power✈️Aircraft🚁HelicopterEngines Plugs Mufflers Fuel › Can't get my OS .91SZ-H PS to run well...
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