Mudbay

I'm looking for some glow engine wisdom, being a relative newbie in the glow side of the sport. I have fallen into a couple of used Thunder Tiger Pro-46 engines, one of which is powering a 4-Star 54. Parts for these engines seem to be incredibly hard to come by, most specifically, carburetors. Can anyone tell me if the Perry carbs are good units, and if they're compatible with the Pro-46? The Perry site indicates a 1200 carb should fit the "Pro-45", which may be a typo or may be referring to the Magnum Pro-45. Any perspectives from the experienced in this fun sport will be much appreciated.

1QwkSport2.5r

Perry Carburetors work well - I have a few. The only caveats to them is they are a little more sensitive to debris getting stuck in them and causing issues with getting the mixture set correctly, and the o-rings can leak causing similar problems. As long as they are clean to start with and fuel is filtered well, they will work well. The idle mixture is set via the mixture disc and adjustments must be made in very small increments. The main needle is set in the same manner as any other carburetor - set the high speed first, then adjust the idle mixture. In some cases the high speed mixture may need a tweak after adjusting the idle mixture - sometimes but not always.

Square Nozzle

My Feedback: (1)

All you can hope for is to find someone selling a used engine and then scavenge the carb from it. I went through the same search a few months ago. Thunder Tiger no longer produces the .40/.46 line of engines and spares. The market is going dry and guys (including me) with those engines are holding on to them.

Mudbay

That explains my experience, Square. I occasionally see used carbs on EBay, but it's hard to spring for the money they're asking for a used carb that is likely no better than the one I have. In other aspects the engine seems very good, bearing in mind that I have very limited experience with glow engines so far.

Mudbay

Thanks for the advice, 1Q. I may well go that route. I shall have to improve my fuel handling system, though, in an effort to improve cleanliness. So far I'm in Entry Level mode when it comes to glow flying. Time to up my game a bit!

Square Nozzle

My Feedback: (1)

Why do you feel you need a replacement carb? Unless you broke the body or lost a part, typically there should be nothing wrong that a good cleaning can fix.

Mudbay

Well, you may have a point there. I'm new enough to the glow engine thing to know I'm dangerous, and that's about it. I've had a number of flights where the Pro-46 works perfectly, but lately I'm seeing more deadstick landings than I'd like. Perhaps it is just dirty. I've read a couple primers on how to tune an engine, and chased mixtures back and forth quite a bit, but continue to have in-flight shutdowns with disturbing frequency. My next thought was to try replacing the carb, but cleaning may be all it needs. What are recommended procedures?

Square Nozzle

My Feedback: (1)

From what you are telling us, I believe that you are simply not adjusting the needle valve properly. The engine may run fine on the ground when the mixture is set for peak RPM but when you get in the air there is ram affect pushing more air into the carb while the fuel flow remains the same. The end result is a lean mixture in the air. The engine gets hot and shuts down. Try this when you fly again;

Adjust the needle valve for max rpm on the ground. You should be able to hear the engine peak at max RPM. As you slowly turn the needle clockwise from a rich condition the RPM will increase to a point where it starts to drop off again. That tells you that you have gone to far. Now back off the needle tell you hear the engine RPM decrease a couple of hundred RPM. You now have a setting that should sustain power in the air. I run Thunder Tiger .46's and the needle valve is 2 1/2 turn open from a fully seated position. I rarely adjust the needle valve. There will be minor difference between engines but that should be a good starting point. Once you find the sweet spot, leave it alone. I have seen many modelers fiddle with the needle valve every time they fly. It's not necessary to adjust the needle all the time unless you fly in the high desert one day and in the artic the next.

1QwkSport2.5r

A good way to ensure the mixture is rich enough for flight is pinch the fuel line close to the carb briefly and not what the engine does. If the revs stay the same, you're at peak mixture. If revs drop, it's lean. What you want is a slight increase in revs when you pinch the line - not a lot, just a slight rise. Using a tachometer can be helpful as well - set your mixture for 400-500rpm rich of peak and go fly. It would also be wise to use a fuel with some castor in it as well. Omega or SIG Champion are good fuels.

Mudbay

Thanks again to both of you for the input. I've been running Omega 5%, and have been using the Pinch-the-Line technique for sampling the mixture at wide open throttle. I am beginning to suspect my idle mixture may not be set correctly, as many times the engine will quit in flight when the throttle is pulled back fairly aggressively. I have read that the pinch test should work similarly there: with the engine at idle or just above idle, the rpms should eventually rise a tiny bit before it dies, though that it should take several seconds for that to happen, whereas at WOT the rpm rise is almost instantaneous. Does that make sense to you guys?

I forgot to mention another possible symptom, and that is a rather slow response, or "stumble", to a rapid throttle increase. I don't think it's ever shut down in flight with a rapid throttle opening, but the sluggishness has seemed disconcerting, at least. Too rich? Too lean? Hmmm.

1QwkSport2.5r

I don't like the pinch test for setting the idle mixture because the results aren't nearly as accurate. I use the acceleration test to determine idle mixture. Idle for about 20 seconds and slam the throttle wide open. If it throttles cleanly with no burble or cutting out, it's set about perfect. If it burbles and stumbles before cleaning out, it's too rich. If it cuts out or revs slow and all of the sudden revs up, it's lean.

Sport_Pilot

Perry carbs are OK, but not as good as the original carb. The idle seems to take a bit more tweeking from hot day to cool day and it is a very small tweak so easy to overshoot.

captinjohn

This is the correct way....forget the pinch method...........

wcmorrison

My Feedback: (2)

Roger on the acceleration test from idle. That is the real thing to do. The idle is incredibly important setting and is most often abused. When adjusting it should be in very small increments, about an eighth of turn at a time. But once you get the snap acceleration test working, you got it right. Good luck.

SuperNash

The long idle period, before doing the quick throttle opening, is important. The longer the better, really. It gives the engine temperature time to settle down to normal idle levels, I guess, and maybe the element in the plug works a bit different after a while of idling... I'm speculating here though.

Whatever, the 20 or 30 second idle period is important.

1QwkSport2.5r

The idea (in my mind) behind the long idle is to mimick when you're on approach to land - in the event you need to take back off or do a touch and go, you don't want the engine to quit due to being too lean or too rich.

SuperNash

"worst case scenario"

Mudbay

Thanks for all of the great insights, gentlemen. From what I'm reading here, I've a really strong hunch now that I've never had the idle mix set correctly in the first place. It may all be connected to my failure to allow a significantly long idle period before snapping the throttle open. I've generally not idled it for more than 10-15 seconds, and often settled for a sluggish response. Now I just need time to hit the field and try out this new-found perspective!

1QwkSport2.5r

The Thunder Tiger pro .46 typically throttles instantly with its stock carb, it should with a Perry as well. The TT Pro engine is world renowned for being a fantastic engine - awesome for 3D work even. So don't settle for sluggish anything with one of these. If it doesn't throttle and behave perfectly, something is out of whack.

Hobbsy

My Feedback: (102)

Mud, I recon you've discovered that the idle mixture disc on the Perry is super sensitive, tiny changes make huge differences. My Perry's are all in a drawer.

1QwkSport2.5r

They are super sensitive, however once set, you rarely need to touch them. A friend gave me a Perry carb (.270" choke - old style) and an adapter for b-block Foxes. It works amazingly well - especially on diesel. The smaller choke makes a big difference in throttle response compared to the stock .330" carb.