Till a couple of weeks ago I thought I was at least proficient at tunning engines but now I'am starting to wonder. I finished A Sig Something Extra about 6 months ago and installed a old but nearly unused OS 46SF figuring that would be plenty good to fly the Sig SE, well so far it hasn't. With an 11 X 5 apc prop the engine turns just under 11,000 rpm (not to good) and at full throttle the RPM will constantly vary by about 500rpm and throttle response is slow. I have also tried this witha an 11 x4 apc and the results are the same. This has given me so pretty good dead stick practice since at least 1 flight during the day winds up a dead stick. With a 10 x 7 apc prop (which makes the SE fly like a bat out of hell) the engine runs more reliably although I have never tach'd it with this prop. This engines seems to refuse to turn a larger prop apparently there is a BIG difference in power between the older .46's and brand new ones. I don't believe this but a guy at the field who is more knowledgeable about engines than I am says that because the 4-5 pitch props are nearly flat and cause a lot of drag they may be more work for a engine to turn than a higher pitch prop of the same dia. I am thinking that a 10.5 dia props would be a good fit but they are hard to find around here.

You might need to flush out the carb with the needle removed - richen a couple of clicks of the needle - should be able to turn an 11x5 or 12 1/4x3 3/4 or 12x4. Those props should fly the SE good with a 46sf. Is it broken in and fresh fuel as well?

The OS 46 SF or newer FX should both scream thier heads off with a 11X5. That is the combo I have used for years. I have that on my Kyosho Cap232 and it flys the pants off of it. They do drink the fuel with such a flat prop in a hurry and that high fuel flow helps keep them cool. If you are certain that you are not too lean, you might consider the bearings. Steal cranks in aluminum cases to tend to rust rather quickly. When you run them after sitting for prolonged periods, the rust breaks loose. It seems to find its way to the bearings and lodge there. Some poor bearing winds up skidding around and gets a flat spot and pooka, and engine that won't run worth a darn. Often the engine will have a sick sound, sort of whinning. And sometimes they sound normal. You have to play with the engine in your hand. Turn the prop back and forth sveral times and see if you can feel the bad bearing catch. It is a very small sensation, so you must pay attention when checking. Don't expect to feel it with each revolution. Bearings are one of the weak spots of these little engines because of the dissimilar metals and oxidation states of the metals. They act almost like a battery.

I let a friend borrow a OS46SF I was not using at the time for his Sig Something Extra and it flew it great, I would take the advice delman gave you, it should be plenty engine for that plane.

Dauntae

It sounds very much the state of your particular engine that's causing your issues, and is unindicative of the SF on general.

The SF is inarguably less powerful than the its supercedent FX/AX and alternative equivalent TT Pro, but it does punch out power sufficient for the larger sized props you mention. I've had running reliability problems with a next to new OOTB but old SF myself. The problem will prove to be either the bearings, rubber (gaskets) &/or carb contamination (gum or dirt) ....possibly a combination of all three. Though it's had little running, it needs an overhaul. So does yours by the sound of it.

The SF throws an APC 11x5 with authority, as it does a APC 10x7. Throttle response should be crisp & smooth in the usual OS fashion. I go up ½ inch in diameter and slightly broader heavier blade in a Bolly prop for the FX/AX and Pro.

Once overhauled, a 11½x4 Bolly if they make it in that pitch sizing (?) or 11x5 APC should work a treat with that engine in SIG's SE. A 10.5x5 Bolly or 10x5 APC is too small for that engine IMO.

Your real decision is whether to overhaul that engine or triage it to the bin and buy a Pro 46.

The 46 SF was available in both ABC type and ringed versions. You mentioned the engine was very low time. If the engine is ringed and not run in all the way it will also give the running conditions you describe. As others have said the 46SF should have plenty of power for a Sig Somthing Extra.

Don't listen to these bozos .......

Box up that old OS 46 SF and send it my way.

I will even give you 20.00 dollars for that paperweight.
Most guys would charge YOU 20 bucks to haul off that junk.

Just tryin to help a fella out.
Greg

Thanks for the good advice guys esp. from Sigrun and Kingwood Barney and sorry Av8raa your not getting my paper weight just yet. Since I didn't have anything better to do this evening I decided to fiddle with my engine and try to chase down a few gremlins. I also spent about 5 minutes turning my prop to see if I could find a rough spot in the bearings I never could find one. I did change a few things around before starting

Prop was 11 x5 apc now 11 x 4 apc
Glow Plug was Fox RC short now OS A8
Fuel flitter removed for this test
Fuel was the same: Cool Power green 10% nitro 18% oil

Engine started right up but was running way rich useing my tach I leaned it out max rpm wich was almost 13k then riched it up a few clicks till it tached 12.5k I say about / almost xx rpm because the only tach I have is an ancient ACE R/C analog tach. I also had to move the low speed needle a little to get a good power transition. I ran nearly a full tank of fuel through the engine with no problems . The next tank of fuel I replced the fuel filter and the engine rpm dropped a good 500-700 rpm and the needle valve needed richend up a few clicks, my max rpm never exceeded 12k with the filter on. So that was part of my problem the filter (which was new) was restricting fuel flow.

These numbers while maybe not ideal are a big improvment over what I was getting out of this engine. I am guessing that this engine produces max power at around 12k so I am thinking a higher pitch prop would lower the RPM's to much. Thanks for the help guys looks like3 I am cleared for take off.

Since it is a very interesting to know filter makes drop of power,can u pls.post a picture of your fuel filter or describe it simply I can
compare it with mine.Then I will have a decision to remove it or leave it.

Its a small hexagonal shaped fuel filter made by du-bro and has been anodized a red color. I have always tried to run my engines with a few filter on but have found that most of the time they noticiably restrict fuel flow. I have another plane powered by a Enya 60xf although the engine runs great no matter what without a fuel filter with the fuel fiter on the engine will cough and die EVERY time the plane is flown inverted or during a violent snap.

Thanks for info.

Did you confirm if your SF was ringed or ABN? The ringed engine does require more break-in, which could also contribute to the better rpm numbers you're getting with the engine.

Daryl, try a Dubro "Final Filter" (Tower stock# LXD742, $3.39). Enough fuel flow even for a Jett .90L at full noise.

Its an ABC engine.

I'd trade in that green stuff for Omega which has some castor in it. The short Fox won't work too well in this engine. I use a standard long or Miracle plug. The #8 os is a great plug for most engines, just more expensive. I filter my fuel going in the tank but do not use a filter between the tank and carb. Good luck with your SF. I'm running a .61SF that I pieced together from a helicopter engine and an airplane model that was crashed and its running great on 10% Powermaster (castor/synthetic blend) and the OS #8 plug.