Carb replacement
 

I'm looking for a two needle carb that can serve as a drop in replacement for the airbleed carb on an OS 25 LA. I've been told that the old 25 FSR carb will work but my LHS can't get me one.

Any suggestions?

RE: Carb replacemen
 

Frank:

If you insist on replacing the carb on an LA engine, go to Conley Precision and get a Perry carb to fit. Go here:

http://www.perrypumps.com/

But you will spend another $40 for a good carb, and you can get a Magnum 25 for a little more, and you can find a fish to take your LA off your hands.

End result will be a good engine to go with a good carb, and depending on how much you get for the LA, it might even be cheaper.

And incidentally, while I've not (yet) used any, I'm hearing good things about the MECoA engines. Even less expansive than the Magnum - the MECoA 32 is just $50 with a trade.

Bill.

RE: Carb replacemen
 

I needed the very light weight of the LA, or I would have never tried it.

The low end screw of my LA is only in by about two turns. I pulled on the spring to lengenthen it to hold the screw from falling out. After an extended run at idle, I can put my palm right on the head, so it's still running way rich. I'm tempted to try and run it without a screw at all.

I had a 46LA years ago, and it was fine once set, but I do recall problrems with the low end screw.

At the Perry site, it lists the 25 LA as having the same size outer barrel as a few other engines. Maybe I'll find a used one of those somewhere.

Thanks for the info...

RE: Carb replacemen
 

Frank:

I have a bunch of small Perry carbs, measure your spigot diameter, I might have one to fit. You pay the postage and $20, it's yours.

Bill.

RE: Carb replacemen
 

Do yourself a favor and go with the Perry. Light weight and reliable as hell! One of the nicest features of the Perry is the plastic housing (trust me on this one:eek:) if/when you or your plane does a slam dunk....nose down[X(]... the carb breaks free and save the front housing of the engine!

RE: Carb replacemen
 

The diameter I'm looking for is .393 (Perry part #3600) according to the Perry site. There is also a .394 (Part #3601) that a piece of sandpaper would probably get to fit. The bore is .177. If you've got one, I'll buy it. $20 plus shipping is a very good price. If it's a go, can I send you a check, or would Pay Pal suit you better? If a check is OK, please PM me an address to mail to.

I ran a Perry carb on a Webra 120, and it did well. Many club members here have them on various engines. None have any complaints. Mine was pretty much "set it and forget it." I'm not one to dork around with a needle all year.

Thanks again,

RE: Carb replacemen
 

Frank:

Looks like I have only one you can use without an adapter sleeve, but it would still need a little work. It has a spigot diameter of 0.435, but in this case the spigot is an aluminum sleeve molded into the plastic. Could be turned to size without much trouble.

One thing that might possibly give you some trouble is the throttle bore. ALL the small Perrys I have are 0.219" throttle bore. That's 0.032" bigger than the 0.177" you have.

This carb ran well on a K&B 0.21, when the engine left the stock carb went back on it. If you think your LA 0.25 will run with the larger bore, it's yours.

Payment? It's up to you. I havea PayPal account if you'd like that, a check is acceptable also. But don't just pop whatever off to me, let me get it in the mail so we'll kniw the postage. After it's gone I'll give you a PM with my address and the total, but now I need your address to know where to send it. If you want it.

Bill.

RE: Carb replacemen
 

Well, before I come off the whompin' $20 price, I guess I need to know what potential problems the bore size could cause. I'd think that as long as the needles are able to flow enough fuel to maintain the proper mixture, based on the airflow, it would be OK. Is there something else to consider here?

Also, what kind of tool, or proceedure is needed for the turning of the spigot. I don't think the .042 difference is huge, but it's not exactly a drop in. I have only basic tools, so what is involved?

RE: Carb replacemen
 

Frank:

If you pull the throttle barrel out of the carb you can stick the carb body on a mandrel, chuck the mandrel in your electric drill, and use a hand file to cut the spigot while the drill spins the carb for you. That's no problem.

The increase in throat area is not trivial. Going from a 0.177" bore to a 0.219" bore is an area increase of 53%, and the air velocity through the carb, at the same engine speed, will be correspondingly lower. But the maximum power available will go up too.

Problem with the lower air velocity (weight of air taken in is the same) is lowered fuel draw at the same speed. Best case, the fuel draw will still be fine. Worst case you'll have to raise the idle.

Boring the carb out is the first step in hopping up any of these little engines, you will not be entering uncharted territory. Further, being equivalent to a two needle carb, you may well have no problem at all. Boring an air bleed carb, on the other hand, is usually a bear.

So while I can almost guarantee a healthy top end power increase, you'll have to take your chances on the idle.

Bill.

RE: Carb replacemen
 

Hi,

On post number 3 you state the screw is almost all the way out, but the engine still runs rich. Either I'm reading the post wrong, or I don't understand what was said.

Backin the adustment screw out will make the engine run rich, tightening the screw in, will lean out the engine.

Hope this helps,

Wayne Miller

RE: Carb replacemen
 

Wayne:

Sorry, you are thinking about a "Two-Needle" carb. On a 2N carb yes, backing the screw out goes rich, it is metering fuel.

The LAs (and some other engines as well) have an "Air Bleed" carb. On an AB carb the low speed mixture adjustment meters air instead of fuel, so the more open it is, the leaner the mixture should be.

Bill.

RE: Carb replacemen
 

Hi Bill,

Thanks for the explaination, I didn't understand it was the air bleed screw. Is there another adjustment to meter the fuel during idle?

Best regards,

Wayne

RE: Carb replacemen
 

Drill out the air bleed hole and you will be able to run the screw in further and lean the idel circut.

RE: Carb replacemen
 

Wayne:

An AB carb has only the one needle valve to meter the fuel. The idle is leaned by the air bleed. What it does is lower the vacuum inside the throttle barrel, thereby decreasing the fuel draw.

Frank:

Kent is right in his suggestion of drilling the bleed hole, but Ihad Ass-U-Med you already knew about that method.

Bill.

RE: Carb replacemen
 

I wondered if that might be OK, but how big to drill? 10% more... 20% more... Heck how about double? Like I said, the screw is only in about 2 or 3 turns.

I saw in a recent article that said a good starting point is with the screw actually covering half the hole. In my case, tempted to take it out and keep it in my pocket.

Like I said, I had a 46LA that was like this, but it finally did find a good set, and then was no problem. This 25 just want's tons of air to run.

Before I drill anything, think about this. First, this is not a stock muffler. It's a tongue muffler from a contrl line company. Any chance I'm making too much muffler pressure, as the C/L engines need not idle? Secondly, I'm running 20% nitro. Is this possibly a problem in the LA?

RE: Carb replacemen
 

Hi Bill,

I went back and re-read the thread. Sorry, the original question was for an OS LA, mine is an OS FSR which has the low speed fuel metering adj.

Thanks for bearing with me.

Wayne

RE: Carb replacemen
 

Frank:

If you go the drill route, just go one size and recheck, then if indicated, go one more. Always retest between drillings when you don't have prior experience with the same engine. Further, don't go any amount larger than the diameter of the adjuster screw. If you are getting that big try to widen the hole without making it higher, otherwise you'll reach the point where the screw wont richen the mixture when needed. It will be so much smaller than the hole it wont have much effect, if any. By going wide, the screw will still span the hole and be effective.

Wayne:

No problem. I thought I made a mistake last week, and then found I was wrong.

Haw.

Bill.

RE: Carb replacemen
 

Thanks Bill.

Hey Wayne, wanna sell me the carb off of the FSR?

Any thoughts on the muffler pressure or nitro % causing some trouble? Otherwise, I'm gonna go get the drill warmed up...

RE: Carb replacemen
 

Frank:

The tongue mufflers I've used generally do not give as much pressure as a conventional R/C muffler, and they usually aren't as quiet, either. And insufficient muffler pressure, of course, would make the engine go lean, not rich.

With higher nitro content you have to feed more fuel, so if the nitro percentage were at the root of your problem the idle would be getting less rich as you go to a hotter fuel. Practically speaking, if the carb works on 10% it will work at 30%, and 0% nitromethane.

Bill.

RE: Carb replacement
 

Good deal, I'm drilling then.

If I destroy this carb, I'll buy your carb.

RE: Carb replacement
 

Hi Tailtwister,

I just got the FSR from a swap meet, I wanted the engine for an old Midwest Das Little Stik (still in box) that I have. Sorry.

Good luck the the carb!

Wayne MIller

RE: Carb replacement
 

DOH!;)

RE: Carb replacement
 

Well, I got brave and went for the drill. The factory hole was a bit smaller than my smallest drill bit (1/16), so I figured I'd start there. I drilled the hole out to 1/16, and then gently moved the drill side to side "waller" out the hole from side to side. I did this only a hair's width to each side, then used sideways lateral pressure to "gut out the center" to an equal width. I now have an oval shaped hole, maybe in the 30% wider range. I figured I'd just done one of three things. I made an improvement, made no change at all, or destroyed the carb. With this in mind, I pulled out the Dremel tool and a carbide side cutter and opened the carb body throat all the way through. I also opened up the throttle barrel hole to match. I was using a TLAR brand micrometer, so a measurement isn't available.

Now on to the good stuff. I cleaned the carb really well with small brushes, 800 grit wet/dry, and some rubbing alcohol.

After I got it back in one piece, I ran the engine. Top rpm was recorded as 12,800 stable with a pinch yeilding 13,000 on a real tach, not TLAR brand. I'll take it! That's up a bit from the 12,500 stock. Next up the low end was set to a rough idle of 3,400 rpm. I was listening to hear the engine load up, and it did. The rpm went to about 3,000 but held there. That's not bad, I figured. I stood up, and counted off 60 seconds +/-, as I also used my TLAR watch for this experiment. And punched to full power. I got a blubbery "uhh uhh wahhhh" type of transition, but it did go. I repeated this three more times, each time getting an ugly, but complete, transition.

Then it happened...

I was standing up counting out seconds when the engine started to run much smoother. Rpm was climbing nicely and stabilized. I went for the tach to read and noticed my low end screw sitting on the ground. I slid the plane over and retrieved it. I puled the throttle trim tab back to get back to the 3,000 rpm idle, and the engine did a little better in transition to full.

Now on to the questions:

What is a realistic idle rpm for a 25LA. I like the sound of the 3,000 rpm, but is that too low? Next up, how much more should I cut out of the air bleed hole? Running well with the screw on the ground tells me that I could cut all day and do no better. What do you think?

RE: Carb replacement
 

I got brave again. I cut out more of the side to side oval. As I had the carb apart again, I better matched the barrel bore to the much larger carb body bore. With the carb fully assembled, I found that my first bore enlargement needed some work. It wasn't as round as I'd like on the first attempt.

The high rpm was pretty much unchanged, but I feel a bit better about the work now.

The low end idled right down to 3,400 rpm like before, but this time with the screw not visable in the air bleed hole, after a second or two the rpm started to climb. It went right up to 4,400 and had a "sing" sound to it. It was lean. I started in on the screw a bit and went back and forth until a good sound was heard. I pulled the trim tab back a click at a time and got back to 3,400, and worked the needle more. I now have an OK transition from 3,400 rpm to full. From 4,000 rpm to full is much better, so I'll probably use the lower rpm only on the ground and while on final. I'll up it a click or two just before take off.

So, for $69 and all of 8ish ounces, I am turning an APC 10x3 at 12,800 rpm with a fair to OK idle. It took some work, but it's done. If I figure in my hourly wage and a similar dollar figure for the help from here, the engine is probably worth about $300 by now.

Thanks for the help and some solid advice.

Yes Bill, this is now the loudest engine I own, by quite a bit. It is louder than my Super Tiger 51 with an Ultrathrust muffler (12.25x3.75 APC at 14,100 rpm). I'm lucky that my club does not have a sound level rule. This one would not make the cut. It's about as loud as the Rossi 53 I used to own. That was a real screamer.

RE: Carb replacement
 

Hi!
It sound strange that your OS LA.25 engine doesn't idle well...all OS LA engines I have run have run perfectly with instant throttle response...I mean really instant response...Wham! even if the engine in question have been idling for many minutes!
drilling the air intake hole in front of the carb is definitely not necessary...but could naturally be done if you like it ...it won't alter the already perfect idle much!
What is important with every engine is to run it with the correct fuel, glowplug and tank.
Your OS engine will run like a swiss clock if you use the following ...
Glowplug: OS 8 (mounted as standard on every OS engine) or a Enya 3 plug.
There is of course other glowplugs that will work too but these are the plugs that have proven to be good for sport engines running on low nitro fuel.
Fuel: 5-10% nitro...more is waist of money on all sport engines. Over 15%nitro and some engines will preignite due too high compression ...being very senitive to set...or impossible to set !
Oil: 20% castor or a mix of castor oil and synthetic....or just synthetic.
Prop for this engine in a highwinged trainer: APC 9x5-10x5 or 10,5x4.
In a lowwinged sport airplane with a span of around 130cm APC 9x5 or a 9x6 or a 10x4
Idle rpm would be around 2000-2500rpm with a APC 9x6-10x5.
Fueltank: 170cc (6oz) with the fueltank as close to the firewall as possible with lots of soft foam around it. And do use short silicon fuelines and use pressure from the muffler.
It is also vital that the fueltank is mounted correctly!
The centerline of the fueltank should be inline with the carb intake when the airplane sits horizontal. -Very important!


Regards!
Jan K
Sweden