Maybe I just don't see it, but is there only one needle on an OS .25 FP?

Xray328,
That engine's carb has 2 needles on it. The big needle is for the high speed adjustment. These engine use an air bleed adjustment for the low speed adjustment. If you look at the front of the carb you will see a small hole up towards the top of the carb. This hole is the air bleed low end. There is a scree that extends from the hole out to the side of the carb. This screw is the low end adjustment. Refer to attached picture.

One note, be very easy when making adjustments on the low end. A little turn goes a long way to make adjustments. Turn it as little as possible for each adjustment.

Hope this helps

Ken

The FP series has an air- bleed type carb. That means the carb only has a high speed fuel adjustment. The low end is adjusted by a small screw on the front of the carb body. This opens or closes a hole through which air is sucked into the engine at idle. Since this screw controls air, not fuel, the adjustment is opposite to the high speed needle. To lean the idle, you open this screw more. To richen the idle, you close it more.

IMO, the hole should be drilled out to the next larger drill size to allow sufficient air for proper leaning of the low end.

Dr.1

If you want to know how I feel about this, get a carb with a low speed needle instead of the air bleed. I've had exactly one FP engine with an air bleed low end. It took 2 months worth of tinkering to finally get my low end correct. I'll never have another one, that's for sure.

Ken

Hi!
As has been said earlier the OS FP series of engines uses an airbleed carb.
That means the carb has a highspeed needle...and a lowspeed screw . The lowspeed screw is a small screw that regulates the incoming air through a small (around 2mm in diameter) round hole up front on the carb.
The standard setting for this low speed screw is to have the hole half way open, but most of the time a little more is needed.

All OS air bleed carbs/engines are very reliable and very easy to set and they are excellent engines for scale airplanes and twins where outer most reliability is required.

Any enlarging of the air bleed hole is not necessary...at least in my 31 years of using these engines have I ever encountered such an engine.

Regards!
Jan K
Sweden

Must say that RCKen gives excellent answers. The post with the pictures is superbly complete and detailed.

But . .

I have been using air bleed carbs since 1966. Currently own 6 engines with them. Currently flying four of those.
In the past 10 years, I have acquired four engines with the "better" carbs. They work great, too. I believe RCKen is infering that these can be tuned more finely. If that belief is true, Ken is absolutely correct again. If I'm wrong, he is propably still right.

Dr1Driver's post gives you the info to tune an air bleed carb. Not much of it needed to achieve the purpose for which the thing is made. I have never drilled the hole.

If you are wanting precision tuning, get an engine with true low speed needle. Most will also have ball bearings, higher compression and much more power.

As you did not say what plane you are using, I will not suggest the proper propeller. That will also make a difference in tuning these carbs.

Ken, AMA 19352

Its on a SPAD dogfighter.

Thanks for thingfo guys!

Ken,

Wouldn't that be kinda like putting diamond earrings on a pig?

Dr.1

You've got to be friggin kidding me [:@][:@][:@][:@]

Whats wrong with this picture???

Stupid Ebay!!![:@] Stupid me!!![:@]


Whats that gonna cost???

How in the world do I get that out?

New carb needed?

The problem with trying to replace the carb is that it's a discontinued part, so getting an new one may be hit or miss. To get out the broken screw you might consider letting a local machine shop try getting it out. Or if you're good with a drill and a tap you could take swing at it yourself.

Ken

Maybe you should have asked some questions BEFORE you bought the engine, xray238.

From what I understand, dogfighting is done at 1/2-to-full throttle, so the idle really isn't that important.

What's gonna hurt you is you won't have the power of your opponents who have stronger engines, like the OS .25FX, .32FX, the ST .34, and the Webra .32.

Dr.1

Looking at your pic: The barrel stop screw, on top of the carb at the rear, is not stock, and I see plier marks on the prop drive washer. Unless this engine runs great (and I don't know what terms the auction offered) I'd send it back. It looks like it's been crashed.

Dr.1

If you try removing the screw and re-tapping the hole remember the screw is probably Metric. It's hard to tell why the screw broke off. Siezed, damaged in prior crash, heck- it may have been CA'd in for all we can tell from the pics. As for having a machinist take it out - a lot cheaper to replace it with a better carb or at least a new one like that.

Part list
http://www.osengines.com/parts/xr12331.html
and carb:
http://www2.towerhobbies.com/cgi-bin...00&FVPROFIL=++

Good luck

http://www.osengines.com/parts/xr22381000.html

The plier marks are mine.

Maybe all is not lost, the transition seems ok. But then again I'm pretty new at this. I let it idle for 30 seconds then went to WOT and it didn't bog.

It starts right up, I just touch the prop with the electric starter and off it goes.

Again though, I'm very new to tuning (or anything else related to glow engines for that matter.)

I paid $25 for it.

As far as the power goes, I'm sure there are bigger and better engines out there, but this is only my second SPAD and first combat plane. I don't need to win, I just need to get up there and play a little.

The plane is 3lbs 9 3/4 oz. Is this motor enough for that?

Maybe I got lucky and it broke in a good spot (tune wise).

$27 for a $25 motor. Geez.

I'm going to a much more experienced flyers house tonight for him to look at it, guess I'll find out then.

Thanks again guys.

Xray,
It's hard to see in the picture, but is there any of the low end screw sticking out or is it broke off flush?? If there is a little sticking out you could try cutting a slot in it so you can use a screwdriver to remove it. One thing I would worry about leaving is that the original screw has a spring on it to keep the vibration of the motor from causing the screw to back out. I'm a bit worried that it might back out in flight.

Ken

Hi!
It's an easy fix!
Just take a Dremel cutting disk and cut a slot in the remaining screw (don't worry about taking some of the carb housing away)and just screw the remains away and replace it with a new screw.

Regards!
Jan K
Sweden

Thanks.

LHS will order it for $1.99

I'm leaving it until the new one arrives.

Thanks guys!

If it sticks when trying to remove it, take the carb off and heat it up a little with a heat gun. The carb body metal enlarges faster than the steel screw and it should loosen up.

Xray -- you hit the important point... that the engine starts well and transitions well. That's what an FP is made for.

When someone talks about things like enlarging the air bleed, that's to trade a little reliability for a little added performance... which is to say it's trading what this engine was designed for to get some of what some other engine was designed for. That kind of trade-off is for engine designers -- the other posters may be engine designers, but I'm not. I buy engines that are designed by someone else to do what I want them to. And the engine you have is a top-notch example of being able to do that -- without anyone changing it.

I have at least one or two copies of most sizes of OS FP engines because I can grab any one of them, bolt in into an airplane, and go fly without messing with carb settings. Does that give me max performance? Well, if you measure performance in terms of power alone it doesn't... but I measure performance partly in terms of being able to focus on flying and safely forget about engine adjustment. Measured that way, my engines' performance is unbeatable -- and so is yours, even just the way it looks in the photo. I repeatedly go a whole season without once needing to adjust a needle on those engines and that's why I paid the prices I did (more than any similar engine) when they were new.

I'd leave the thing just the way it is unless something about how it runs tells you that it needs to be changed.
Most of the guys at the field don't believe that a plane can fly without the carb setting being changed each time, but with a good engine that is just not true.

"When someone talks about things like enlarging the air bleed, that's to trade a little reliability for a little added performance"

Don't assume you know why I do what I do, Al. Whenever I enlarge the airbleed, it's to acheive a reliable idle. I've never seen one that didn't need modifying. If you know that much, you should know that changing the idle mix will not give any "added performance".

Dr.1

Some (dr1driver)have nothing but negative comments to say so maybe they should just move on to a topic where they can contribute something of benefit.

To each there own I guess. I appreciate everyones input.

Anyone know what the FP stands for?

Dr1 --

Sorry 'bout that. I meant to imply the differences between different peolple's uses and requirements and that one man's performance is another man's <whatever else>.

When my head is together, I personally define performance as something along the lines of meeting requirements effectively, efficiently, and reliably. I think I lost sight of that in my last post, and of the fact that what works at my location, elevation, humidity, temperature, altitude density, etc. may not do it for others. You're right, the enlargement may improve the air bleed's ability to do its intended function at conditions other than what I'm used to.

That's still a performance enhancement in my world (i.e. an improvement in its ability to do its job), but it's not the trade-off I painted as. I didn't think that through, but I sure didn't mean to mislead anybody or to misrepresent anybody else.