grind2tenths

My Feedback: (17)

I have an older 90 with the two needle carb that just will not maintain any reliabe runs. I think I have the low speed needle so far out of whack that I need some idea of how to get it back. It is mounted in a U-Can-Do inverted with a 15-4 APC wide blade with 15% Cool Power Fuel and a Fox miricle plug. I took the carb off and cleaned it and it is still not any better. Help me out before I take it off and mount it sideways instead of inverted.

Flyboy Dave

My Feedback: (21)

Put the low speed screw at 2 turns out, and go from there. It will
probably be rich, but it will run.

FBD.

iflyj3

My Feedback: (7)

Heck, if it is like one I have, all this means is it will run poorly on its side.

I have two and one runs fine but the second one I cannot get adjusted. Idles and runs fine wide open but will not transition without spuddering.

Hobbsy

My Feedback: (102)

Have you rotated the spraybar, this is a tuning option on ST engines that relly works. Just rotate it a few degrees, preferably in the direction that suits the nipple position best, because it doesn't matter which direction you rotate it. Rotating the cat eye in the spray bar reduces the fuel draw in the mid range. Best to do this with the carb off so you can see the position of the cat eye.

iflyj3

My Feedback: (7)

Thanks for the suggestion. However, been there, done that.

I am going to replace the engine, I just haven't decided with what yet. I'm looking at the new Elvolution 100.
My hobby is flying, not trying to get contankerious engines to run.

Rudeboy

J3,

I have an older 90 too, and it has always been one of the most reliable engines I have ever had. It would only dead stick on me when I ran out of fuel... it had the common rich midrange thing too, but that didn't seem to hurt anything.

Try this:
Adjust your throttle linkage so you can completely shut the throttle barrel.
Put a length of fuel tubing on the fuel nipple... long enough so you can blow into it.
Open the high speed needle 5 to 6 turns.
Blow into the fuel tubing, and adjust the idle needle until air just starts to escape when you have the throttle set at an idle position (about the opening of a modelling pin). When you close the throttle barrel completely, the airflow should stop.

This procedure will get your idle needle back into the ball park, or even close to perfect once you get the hang of it, but it will need further adjustment to get it perfect.

iflyj3

My Feedback: (7)

Thanks Rudeboy,

I have done that too.

ronwc

My Feedback: (404)

Change your glow plug to one with an idle bar, I like the K&B. Crank and get full throttle set first, come down to a normal idle for about 30 seconds then open throttle quickly. If it is too lean on low end it will cut off quickly, if too rich it will sputter. Many times just changing to an idle bar plug will take care of it -

Flyboy Dave

My Feedback: (21)

Last resort....put a different carb on it. I, and many others put different
carbs on the S.T. 3000.

FBD.

grind2tenths

My Feedback: (17)

Thought about the carb change but I hate to rob one of my OS engines to make this one run. I had a older ST 61 that was one of the best engines I ever had. I will try a different plug and adjust the low speed needle. I have a swap meet coming up in Nov. I may let it be someone elses problem.

loading

I kinda had the same problems you are describing with my ST 90. Although, I think part of my problem stems from only having about 3/4 of a gallon through the motor. I was using an OS #8 plug. No matter what I did, I couldn't get it to transition worth a d. It would only idle for about 30 seconds before quitting. I put more than one #8 in it, so I know it wasn't just that one plug. Eventually I ran out of #8s trying to get this motor to tune and I put an OS A3 plug I had in it. It was like it was a totaly different motor. I don't know how hot the Fox plug it, but the A3 is the hottest OS makes. I know its kinda contrary to what you would think, but it worked for me.

tIANci

I have noticed that my G90 sucks on 50% throttle ... I think perhaps I need a hotter plug. Its mounted on a WMSuper Chipmunk and I fly at 50% throttle ... then engine sounds so rich! Transition is decent or fine but somehow its not that great at half speed. Time to try what LOADING says ... a hotter plug. I got mine to idle as low as 1,800 RPM on a 13x6, it will just idle almost all day and still throttle up decently.

iflyj3

My Feedback: (7)

Thought of that. I just have a hard time putting a $70 carb on a $130 engine with no guarantee that will fix it. The phrase "Throwing good money after bad" comes to mind.

I think $70 toward another engine with a warranty would be a better choice at this point.

Flyboy Dave

My Feedback: (21)

Dan,

....if it's the 10mm spigot size, the $28.95 Magnum carb will fill the bill.
This 3000 was almost unuseable with the wimpy original carb....

....now it's a one flipper ! [sm=thumbup.gif]

FBD.

Bax

My Feedback: (11)

If you mount the engine on a test stand, how does it run upright? If it runs well when it's upright, then it's the inverted installation that's causing the problem. Inverted running can be problematic with some engines, and the only solution may be an on-board glowplug battery that lights the plug at low throttle settings.

We'd consider a 15 x 4 prop to be a bit large, especially the wide-blade variety. We normally run a 12 x 8 prop and tach the engine at full throttle for about 12,000 RPM. The engine is ported for RPM, and doesn't like running low RPM. We'd not want to run the engine below mid-11,000's when leaned to peak on the ground.

iflyj3

My Feedback: (7)

Thanks, I may give that a go!

Hobbsy

My Feedback: (102)

Here are just two examples of what happens when I get my hands on those SuperTigre carbs that have made other owners unhappy. They make my unhappy engines happy.

tIANci

Hobbsy ... most controversial! Hahahaa ... perhaps its all in the tuning ... patiently tuning the engine.

Kweasel

My Feedback: (29)

The blow through method works well if you know what your looking for. Otherwise Install an idle bar plug, this will let the engine run ritcher without dying, start it and set the high needle. Then start pulling the power back slowly. It should start sputtering about half throttle. All ST 60-90 carbs will be a little rich at 40-70% throttle if the slow idle is set right. Lean the slow needle until it dies out at low idle, then back it out 1/8 turn. It should idle several minutes with a slight sputter when full throttle is applied.