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HelicopterEngines Plugs Mufflers Fuel › OS 91 PS get's lean in the hover
06-04-2004 06:53 AM  13 years agoPost 1
maddog72

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Gran Canaria

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Hallo!

I use an OS 91 CSpec-PS in my Rappy 90. The engine has a lot of power and on high rpm it works fine.
My problem is the hovering. At the beginning of a flight the engine runs very good and rich in the hover. When the tank is about half the engines get's leaner and leaner. There's no more thinking about hovering without beeing scared about crashing the engine. The high rpm runs rich at this time without problems.

I thought with the pump there'd be constant pressure until the last drop of fuel?

Does anyone know this effect? What can i do? Change to the YS?

My equipment: OS 91 C-Spec PS, MP II, CoolPower 25%, OS 8 Plug
The low-needle is about 90 degrees open (like i read on cj's page) the high needle is adjusted that the engine runs in high rpm, abot (360 degrees).

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06-04-2004 08:57 AM  13 years agoPost 2
RotarSoft

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St Leonards On Sea UK

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A lot depends on where you have the feedback pipe from the carb. If you have it going back to the inlet of the pump you'll have leaning problems as air bubbled get introduced to the fuel line.

You must run the feedback pipe from the carb back to the main tank to avoid air bubbles. This will stop any leaning problems.

Everyone I know whos run the fuel line back to the pump input has had leaning problems because of air bubbles. Rerouting back to the tank works a treat.. and is also what is recommended in the manual.

However if you have already done that.. Fly the model until it leans out and then check for air bubbles in the fuel line. You might well be sucking some air up from the tank once the fuel level goes down.

Cheers

Mark

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06-04-2004 11:41 AM  13 years agoPost 3
maddog72

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Gran Canaria

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Hi!

Thanks for the tipps so far.

I forgot to wrote down, that I use the fuel management like it's in the manual (feedbackl back to the main-tank).

I use a header-tank. The header is full until the main-tank is really amty. So i don't think there'll be air in the fuel line.

I think' I'll bypass the header for a test. Is it possible, that the pump-system doesn't work correct with a header-tank?

@Mark: I think, we'll meet in Bitburg (EC).

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06-04-2004 08:13 PM  13 years agoPost 4
AndyH

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Rockledge, FL

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You know I'm having the same problem with my Cspec PS! Starts out just fine and happy everything ok - go fly around - everything's happy and engines nice and cool, but when I bring it down and put it in normal it starts going really lean - any ideas? Do I run the return line straight back to the main tank.

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06-05-2004 12:43 AM  13 years agoPost 5
RotarSoft

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St Leonards On Sea UK

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You shouldn't need a header tank. Header tanks really only mask problems elsewhere.

I've flown my PS today with the carb routed back to the main tank and there has been no leaning problems.

When your engine leans out... land it and check the pipe really quickly for any air bubbles.. it should not be leaning out at all.

The only other thing I can suggest is try a different fuel. I am running 16% nitro, 18% oil, no header tank and an OS 8. The main needle is about 1 turn open and the engine runs great tank after tank...

Cheers

Mark

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06-05-2004 01:09 AM  13 years agoPost 6
maddog72

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Gran Canaria

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Hi!

The only thing, I'll try is to bypass the header-tank to see, what happens then.
@rappyluv: Do you use a header-tank, too?

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06-06-2004 06:33 PM  13 years agoPost 7
steverobertsuk

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London, England

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Hi,

I run a header tank on my model but do have the return line going back into the main tank and it runs great with no leaning out problems. Mark will confirm this after seeing it on Saturday.

Steve

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06-06-2004 11:57 PM  13 years agoPost 8
Barney

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Inverness Scotland

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Mixture problems with PS. I have problems with an extremely rich mid-range..OS8/Enya no3/Firepower 5 through to 7's..tried them all.. MP2 running 8.27..fuel from straight to 30% ..still not as good as it should be.. tried bottom end needle in every concieviable position & anything from11/4-3/4 on main & every combination in between.

Is it possible to change PS carb to 3 needle & fit an in-line check vale instead?

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06-07-2004 09:02 AM  13 years agoPost 9
steverobertsuk

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London, England

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I left my bottom end as it was out of the box (1/2 way) and have just gradually closed the top over 2 - 3 gallons of fuel (Bekra 16%) and it seems to be just right across the whole range.

I have seen pictures of a PS with a 3 needle carb. I think it was the 60k from the original c spec but dont see why you would want to change it as I think the PS carb is much easier the tune.

Steve

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06-07-2004 02:32 PM  13 years agoPost 10
AndyH

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Rockledge, FL

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Yes, I do run a header tank and after looking at the problem again and some twiddling with carb settings I think I wasn't seeing leaness in the midrange but over richness producing simliar symptons. I agree with Barney.

My guess is it has to do with the pump pumping too much when I go back down to Normal and the check valve's just not keeping pace. I will continue to twiddle but as I leaned the midrange my problem started to go away.

Ooh - I'm running a Viper head too.

Hope this helps!

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06-08-2004 03:07 AM  13 years agoPost 11
Bushy

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Tucson, AZ

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According to Curtis Youngblood, remove the pump pressure adjust setscrew, carefully remove the coil spring behind it and stretch it to twice it's original length. Reinstall and set the screw with about 1 thread showing. No deeper than flush with the case. This is how he runs his to make them work with the 91.

I watched a fellow this weekend with a cspec in a Fury that leaned out everytime he dropped in from a high altitude. He would have to pump the collective to get it to run right again. I told him about this "mod" and he did it on the spot. The Fury then ran great for the rest of his flights.

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06-08-2004 05:10 AM  13 years agoPost 12
AndyH

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Rockledge, FL

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I was told that they fixed that problem with the pumps on the PS - If it becomes an issue again I will try it!

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06-08-2004 05:35 AM  13 years agoPost 13
maddog72

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Gran Canaria

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Hi!

I solved the problem for myself. I ordered a YS 91. With this engine I never had such problems.

I heard about a lot of modifications on the PS here in Germany: Use a 60K-Carb with some mods would help for example. Using a kline regulator without the pump-system is another thing. But no one seems to use this engine out-of-the-box. It's hard to see, that one should spend a lot of money for an engine with that problems. Maybe we all are to stupid for it...

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06-08-2004 01:14 PM  13 years agoPost 14
Barney

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Inverness Scotland

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If you study CY websight..Ask Curtis..With the PS..He says that the spring should NOT be stretched as the engine or pump system is matched from the factory.

Correct me if I am mistaken but stretching the spring increases the pressure & would further agravate the problem anyway?

The next thing I plan on doing when I get a chance..is to remove the check valve & fit a 3rd needle to my PS carb from a STD 'C'spec & fit an in-line perry one-way in the fuel line. Has anyone done this?

cheers

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06-08-2004 03:11 PM  13 years agoPost 15
dunbare

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Oak Ridge, TN

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Barney is right about the stretching of the spring at Curtis's site. That was in reference to the pre PS engine, when people were taking the O91's and installing the pump themselves.

I'm having the same problem with my PS leaning out at about half of a tank, from talking to others running this engine, this has been a common problem. I've heard that the Viperhead helps a little. One of the people I talked to suggested just buying a regular C-spec and having the cline modification done.

Frenzy 50, T-Rex SE, T-Rex 600N Pro

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06-09-2004 02:32 AM  13 years agoPost 16
benben

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Taipei

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Maybe you should get the optional midrange needle for the PS carb. I saw it in a Japanese RC magazine. You turn the needle in to cure the lean midrange problem and turn it out to adjust overly rich condition.

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06-09-2004 04:07 AM  13 years agoPost 17
Bushy

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Tucson, AZ

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Hmmmm. Stretching the spring to increase the fuel flow/pressure on Phil's PS did cure his lean running though. Must have the tolerance specs of a capacitor +50 or -20%.

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06-09-2004 06:48 AM  13 years agoPost 18
Unbalanced

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Melbourne, Australia

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I saw a photo of the Japanese 3D guy (aren't I specific!) who had modded his c-spec ps with the standard carb/return. This week I'm fitting the pump from my old ps (rip) onto a standard c-spec - have bought the perry check valve and will run the return back into the tank.

I expect it will be good - time will soon tell. I had problems with a rich midrange on the ps so I'm going to use the standard 3 needle carb.

Jeff

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06-09-2004 03:52 PM  13 years agoPost 19
Akio Miyata

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Rondonópolis-Brasil

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I am using the third needle here in the japan really she improves the operation well, because here most doesn't use the pump due to difficult carburetion

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06-10-2004 03:27 AM  13 years agoPost 20
benben

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Taipei

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Akio,
Do you have the part # for it?

Thanks

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HelicopterEngines Plugs Mufflers Fuel › OS 91 PS get's lean in the hover
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