I have a farely new Super Tigre 40 that just won't run. It starts but won't idle and when I advance the throttle it runs at the same RPM even with the throttle wide open the RPM doesn't change. I have readjusted the high and low end needles with absolutly no change. It's driving me crazy. I have used Super Tigre engines for years and this is the first one that has given me fits. Any ideas?
Jay.

When you say that it runs at the same RPM, is it High or mid range RPM?

Just a thought if you have more of them swap the carb, If that shows no improvement check the the cylinder is in the correct position and not rotated. I do not remember if they use a pin to keep in the right position or not. If a pinned liner thats not the problem
I assume your O ring is ok between carb and engine martin

Look for air leaks. Air leaks where the carb mounts on to the crankcase. Check the cover on the back of the crankcase. Check for any obstructions in the fuel system, like in the needle vavle assembly. Take the carb apart, soak it in alcohol, clean it up and reinstall it.

You did not say if it was a new engine or an old one stored for a long time.

Good luck.

Chip

Sorry for not getting back to you all promptly but I've been sick the last few days.

Question #1- "High or Mid range RPM". It's mid range. Any advance of the throttle shows no increase in RPM and any attempt to go to idle shuts the engine down.

Question #2- "Air leaks". I find no air leaks at all and the O-ring is in good condition.

Question #3- How new is the engine? When I said fairly new I ment that it has set in the box untouched for about a year and a half and the only time it was ran was now. This engine is doing this right out of the box.

Now I will dissasemble the engine and check the internals for obstruction. Thanks for the suggestions everyone.
Jay.

Hi!
What you should check first is the ball bearings...having been laying for a year or more, un-run and perhaps being run on castor oil, surely means oxidized, gummed up ball bearings.
Also check cylinder liner for scratch marks.
Regards!
Jan K
Sweden

I thought he said it was NIB until mhe tried to run it recently.

Sounds now really like a carb or fuel problem .Put a piece of fuel ine on the carb close the needle all the way should not be able to blow through it open the needle about 3 turns it should hiss as the air goes through open the low speed needle about 1 turn out you should get a hiss ( at idle position on the carb). I do not know if you are doing this on the bench or in the plane , best to bench it
If ok one the bench then check the fuel system in the plane lines, clunk, etc. getting back to the carb if you do not get results you
have junk in the carb clogging the orifice martin

Sounds like a fuel restriction somewhere. Maybe in the spraybar?
Also, ensure the spraybar is positioned correctly in the carb body.

He should also check the spray bar to see where the opening is pointed. It should be pointed down at the crank opening.

Ed Cregger

You maybe running backwards too. On a windy day that is sometimes hard to tell with prop blast. Super Tigre has a great carb tuning section on their website.

I like dieseldan's advice. It helps me to know the carb and tank are doing what they're supposed to. I'm always blowing into fuel lines when I'm working with a balky engine.

Some of the MDS 40 engines left the factory with improperly set bearings. That could cause the symptoms you describe. The fix is to reset the bearings (reinstall). If it's not a fuel delivery issue, you might look into this possibility.

I helped someone last year with a new ST90 that wouldnt behave. Constant dead sticks and irratick running. Not your problem but his turned out to be the muffler. It had a severe restriction. Put an aftermarket pitts on, readjusted and its been fine since. Its the second bad ST muffler I've seen in several years. There are a LOT of ST in our club.
Edwin