muzzlemaggot

My Feedback: (7)

For the record, I've been flying ST .51s for years and have never encountered this before. Yesterday, and once a few weeks ago, my .51 would start up and act fine (initially). Then on occasion, as I'd max out the RPM to "clear it out" prior to take off, it would immediately quit AFTER being maxed out. I've tried changing the plugs, checked for air leaks on the back plate and around the carb, checked the head bolts, changed the lines, richening the high speed a tad, and have observed no bubbles in the line while checking for this. What I've noticed is it only does it once in a while, such as being fired up for the first time of the day after being stored for a little bit. And it doesn't matter what position the plane is being held in (level, upright, etc..) The weird thing is, it suddenly goes away after fiddling with it for a few minutes, threatening to stomp it, and cussing it out. Then it starts running like the trusty tigre I know. I have exclusively run ST .51s in most of my birds for several years and have never seen this. Ideas out there?

aerowoof

is this the ringed or abc version?if it is the ringed version,sounds like a sticky ring that loosens up after temperture rises or it gets lubed up some from the engine being run.only other thing i can think of would be dirt in the spray bar such as a hair

LANNYBOB

if you have a air compressor or know somebody that does have it blown out with air. start at the high needle valve inlet and blow whatever might be in their out. it worked for my evolution 46 a while back

muzzlemaggot

My Feedback: (7)

It's the .51 ringed version. I was almost thinking the same thing with a sticky or collapsing ring, as I've rebuilt this engine twice in the past. However, I've always taken caution when honing out the cylinder before replacing the ring. I doubt that it's hair; I always run a fuel filter and have checked it, and even blew fuel through the needle valve ass'y when it started acting up with no change. It's clean as heck. Thanks for your reply...anyone else??

BillS

The most likely reason for erratic behavior is a floater. (trash somewhere) Most of the time you will never see the floater.

Bill

TimC

muzzlemaggot, I had an engine giving me fits. I found the problem was a semi-kinked fuel line between the firewall and the carb. I was using a heavy filter on the line .It would run fine most of the time. Too fast a roll in one direction would close off the line. Could it be that prop wash is doing this in your case?

muzzlemaggot

My Feedback: (7)

Thanks, guys. Hmmm, I never thought of the semi-kinked line. I'll check it out and in the meantime blow out the carb guts with a compressor. I'm still perplexed as to why this is only doing it upon the initial start up of the day, though. Once it starts acting right, it runs like a raped ape with absolutely no problems.

muzzlemaggot

My Feedback: (7)

Okay, here we go again. Same engine, same problems, no resolution. I tore it apart, blew everything out with a compressor and flushed with alcohol, even tore apart the carb guts. Replaced O-rings, applied a light coat of silicone sealer between the carb/crankcase and crankcase/backplate. Even used a tiny amount where the spraybar ass'y goes into the carb. Tried new glow plugs and replaced all fuel lines and checked for kinks. Cleaned the fuel filter. Ensured all bolts were tight, with head shim in place. New fuel, running 10 nitro/20 oil. This fuel works fine in all my other engines, including another ST .51. Fiddling with the high speed gave me no results. Erratic running all the time now, not just on initial start up of the day. Would run good on one setting, only to have it act up on the next run as if a gremlin came in and changed everything while my back was turned sipping from my coffee cup. Even changed the tiny little O-ring buried deep inside the high speed needle. Good compression. I've run ST's for years and never had one act like this. Oh, yeah....almost forgot....I even changed the front bearing thinking perhaps it was wore a little around the crank, therefore enabling air to leak past it. I go to the flying field to fly, not fiddle fart with engines. I prefer to do that at home. If this engine didn't have such good potential like I know it's capable of performing, I'd either give it away or throw it away. Better yet, I'd throw it away because I wouldn't want somebody else to have the same issues. Does ANYONE have an answer?

k3 valley flyer

My Feedback: (18)

I believe you said you have another ST 51, switch the carbs and see if problem continues on the problem engine or goes to the other engine.

Danh4

My Feedback: (5)

I'm having what sounds like the same exact problem you're having. My S.T. .51 has always been finicky and hard to keep tuned, I finally decided to put some time into fine tuning it with some of the advice I found on this site and after an hour or so I had it running great. Took it out and flew it over 3 or 4 days and it ran beautifully every time. Until the next time I took it out, then it would abruptly quit every time I throttled it up. I started playing around with it and I finally came to the same conclusion- I came to fly, not screw around with an engine all day. I hadn't touched a thing on it so maybe it is just some crud in the needle valve, but I'm so annoyed with it that it might sit there until this winter before I waste any more time on it!