Hey guys, I have a Dazzler with a used .40 LA OS engine. I have flown the plane a total of 4-5 times and have experienced this trouble the last 3. The engine runs fine the first 3/4 of a tank, and then any tank after that it idels fine but sputters upon throttle increase, what could this be? No matter what needle setting it stays the same.
Thanks!

Check the klunk in the tank. It sounds like it is running out of fuel therefore causing the engine to run lean causing the sputtering you describe.

Does it sputter and die, or does it sputter then rev up? Have you made any adjustments to the air bleed
screw, or are you only adjusting the main needle?

It sounds like a fuel system issue, I have had a bunch of these problems.

main needle. Sputtering and dying....if not interrupted by me throttling back.

your clunk could be flipped around to the front of the tank. Take the plane and give it a good shake. Im not kidding, thats all it takes to fix that problem if thats what it is. Before that youshould gently shake the plane to see if you can ear the rattle of the clunk and if you dont then thats what it is. or you could have a pinhole in the fuel line. If there arent any obvious leaks then it could be inside the tank.

Sputtering at idle, could be caused by a bad glow plug, improper mixture (too much fuel at idle).
If it sputters and cuts out without revving up I would have to think that an air leak isn't present.
Also you said you can throttle up and clear it out which is pulling me toward rich at idle.

Here is a link to the OS .40 LA manual http://manuals.hobbico.com/osm/40-46-65la-manual.pdf
Refer to page 25 for low speed needle adjustment. also you might want to go through an entire retune
as per the manual. I have found that when I get things a bit screwed up a new plug and a full retune from
factory needle positions is always a good starting point.

I haven't been on this bandwagon for a while but anybody can tune an engine perfectly but even many experienced rc'r have no clue. its too easy. If you get it right the first time, you don't have to mess with the low end at all in any given season.

The trick is all inthe low end needle. To start with, just tune it as best you can, then lets check to see if your adjustments had any effect. Since its on a dazzler, your engine should be exposed which makes this easy.

While the engine is at an idle, carefully remove or pinch off the fuel line and wait for the engine to quit. Listen to the rpms as this happens. If the rpms increase as the engine quits, low end is too rich. if the rpms just go down and quit, low end to lean. Adjust as necessary. I keep mine at a slight increase.

Now each time you make an adjustment to the low end, re tune the high end. This may take a couple tanks to get it right but then thats it, no more except for the high end each day.

I have not had a deadstick engine in so many years due to tuning. There is a reason for getting it perfect and that is if you do have an engine problem, tuning is the last thing you want to be fooling with. Look for other problems.

I have engine problems as much as the next guy but the issues have nothing to do with tuning.. I may have a plug go bad or and airleak somewhere. all the usually things which i usually find before it comes down to tuning.

No needle, it's an airbleed screw on this engine for idle mixture. OS .40 LA

When checking the fuel line remember to look at the clunk line in the tank. If that has a hole you will get the symptoms you you describe.

Very true.

If it runs fine when the tank is full, and only does it at 1/4 tank or less, my guess is either a hole in the clunk line, OR, it's very possible you're getting fuel foaming, but only when the fuel reaches a certain level.

Another possibility is that you could be just running out of fuel. You may have 1/4 tank, but that's not much. Any number of things could be keeping the fuel from reaching the carb.

Cyclic Hardover, please stop making those generic tuning posts. Also it is quite clearly not a tuning problem but a problem with the klunk in the tank, or you are simply running out of fuel.

Alex, C172152 said in a previous post "Sputtering and dying....if not interrupted by me throttling up"
which leads me to believe that if he gives it some throttle the doesn't die.

I will try to make everything a little mre clear for you guys. The engine will run fine on idle, but when fed any throttle, it sputters and later dies. No matter what tuning is done, there is no difference.It's not always at 1/4 of a tank, and the airplane always has plenty of fuel to run on. Hope this helps, if not I can try to be more specific.

Maybe its a bad carb? Just a guess.

Sounds like you have a problem with your clunk line, its not touching the back of your fuel tank is it? If so the suction could be causing it to come in contact with the rear of your fuel tank. Thus restricting fuel flow. From your symptoms you have described, it does seem you may have a very tinny hole in your line.

Yeah, all fuel lines are under 2 months old(except for inside the fuel tank and needle-carb fuel line.) think it's the clunk or the line?

if it only does that when the engine is idling and you rev it, it seems to me that your idling to rich which would mean that its not a fuel line or clunk issue. i've had that problem too once i had to move my fuel tank down and inch or so. the middle of the tank shouldn't be higher than the carb.

has the plane been crashed? thought i'd ask

yes, but not a bad one at all.

Assuming that you have the high speed needle set correctly you need to adjust the "bleed" screw. It (the idle) is too rich. On this engine you need to back out the screw to open the bleed hole which will allow more air in. If the "bleed" opening is fully open then you MAY need to drill the "bleed" hole a LITTLE larger. Go real easy and don't make it too big. Also take the carb off the engine first.

He stated that "the engine runs fine on the first 3/4" of a tank.


He states that every subsequent TANK of fuel he runs after the first 3/4 results in the run-up sputtering....

"and then any tank after that it idels fine but sputters upon throttle increase,"

It sounds like his engine is mistuned, but the mis-tuning is only apparent once it has warmed up fully.

Since it is likely that it takes far longer than 2 minutes to run through the first 3/4 tank, that indicates to me, that once the entire engine crankcase ( and surrounding areas ) are warmed up, fuel is flowing a bit better, resulting in an overly rich condition.

So something related to the fuel line is likely the cause.

Maybe the fuel line is too thin, or restricted.

Once the entire area warms up the line becomes more supple and able to stretch resulting in much better flow.

Since this doesn't happen at the beginning, but DOES occur on each subsequent tank full, it is likely NOT related to the tank or clunk itself, but occuring somewhere between the tank and the carb, or at the carb intake.

c172152, is opjose correct? Does this occur even when the tank is FULL?

hey minnflyer would you happen to know the guys at autosave (autowrecker)

Maybe his carb isn't sealed well to the engine? That would allow good idling but at higher vacuum would show up as a lean condition.