ORIGINAL: hsukaria
1QwkSport2.5R,
I have a couple of Super Tigres, a G51 and the other a GS40. Love them both.
I noticed that you said that you richened the HS needle 2 clicks from top rpm with no noticeable drop in RPM's. I am no engine expert, but I have always understood that the HS needle has to be richened from peak RPM's until the engine speed drops around 200 rpm's or more.
Once the top end is richened to 200-500 rpm below peak, get the throttle to idle and spike up the throttle. If the engine quits, the idle needle is too lean. It the transition stumbles and hesitates, then it is too rich.
Super Tigre manual also suggests pinching the fuel line temporarily at idle and waiting for the engine response. If the engine slows down or quits, then LS needle is too lean. If engine speeds up a lot after the fuel line pinch, idle is too rich.
You probably tried all these tricks, but I know all these were all I needed to get them adjusted. I did have to rotate the needle spraybar lately on the G51 since the transition was too rich. But that is the first and only time since I bought it 5 years ago.
Occassionally, at the beginning of flying season, I have to pump fuel through the carb at closed throttle and WOT to flush out the gunk from the carb. It helped a few times.
Thanks for the reply. I have tried almost everything on this bugger. The break-in on the stand was painless and it didnt act up hardly at all. The reason I did not richen down off peak RPM is to have the high speed mixture set to "perfect" as to not create a needle-compensation scenario. ie: too rich high speed and too lean low speed or vice versa. I wanted the main needle peaked and then get the idle mixture set for idle and good transition, then richen the high speed mixture to drop the rpm a little. Since this is in an airboat and not an airplane, The prop will never fully unload. This boat doesnt go much faster than 35mph so I'm not going to be running anywhere close to pitch speed. So...
I can get the WOT mixture set fine, and I can get it to idle all day long. When set for both of these conditions, the transition is horrible. Moving the spraybar has little effect on transition which I find odd. I went through the carb and blew it out (it was clean, not a speck of debris, nor any castor goo plugging anything up.) I changed fuel tanks, clunks, etc. Either I'm an idiot or there is something amiss here. I am no stranger to finicky engines, though they dont exhibit their fickleness until on the craft they are to power. That tells me vibration may play a role in it. I do get some small bubbles. If I rest my hand on the fuel tank and hold the fuel line to the carb while at WOT, there are hardly any bubbles. I will mess around with it some more later today maybe. Got a few more things to try. I wish I had another carb laying around that would fit this engine just to try once. I know its possible even with the crappiest of carbs to get some decent production from the engine, but this is the hardest time I've ever had getting an engine to run reliably. I am going to try some different fuel tank padding material and see if that makes a difference or not, as well as dropping the fuel tank centerline some to see if that does anything. Fuel does not flow from the tank through the carb and into the engine with the tank full and the throttle fully open so syphoning is not happening.
edit:
It seems to me that I'm not the only one with an S90/S90K carb that is a bugger to tune.. here's a thread about it: [link=http://www.rcuniverse.com/forum/m_8867384/anchors_8867384/mpage_1/key_/anchor/tm.htm#8867384]S90/K w/ Perry carb[/link] I will go this route if I need to, though I will keep working on the ST carb. My patience is thin though, as I've been through a similar problem with my K&B .65 - Mismachined carb parts makes the midrange so obscenely rich no amount of adjustment would clear it. Both of my .65's are getting Perry carbs when I can afford to drop $100 for 2 carbs. Since I have airboats with no method of retrieving the dead boat except a fishing pole, I'd rather have the engine running superb before going back to the pond because its NO fun casting out 20 times to retrieve the boat. Incidentally, I had better running from my K&B's. I could feather the throttle through the midrange to get it to not quit on me.
Blah.