Engine trouble
 

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!

RE: Engine trouble
 

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.

RE: Engine trouble
 

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?

RE: Engine trouble
 

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

RE: Engine trouble
 

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

RE: Engine trouble
 

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.

RE: Engine trouble
 

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.

RE: Engine trouble
 

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.

RE: Engine trouble
 

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

RE: Engine trouble
 

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.

RE: Engine trouble
 

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.

RE: Engine trouble
 

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.

RE: Engine trouble
 

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.

RE: Engine trouble
 

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.

RE: Engine trouble
 

Maybe its a bad carb? Just a guess.

RE: Engine trouble
 

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.

RE: Engine trouble
 

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?

RE: Engine trouble
 

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.

RE: Engine trouble
 

has the plane been crashed? thought i'd ask

RE: Engine trouble
 

yes, but not a bad one at all.

RE: Engine trouble
 

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.

RE: Engine trouble
 

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.

RE: Engine trouble
 

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

RE: Engine trouble
 

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

RE: Engine trouble
 

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.

RE: Engine trouble
 

Except it doesn't occur for quite a while, and the symptoms are of a RICH condition once the engine is been on for some time.

RE: Engine trouble
 

for the cost of fuel tubing, replace all the lines. even the one in the tank. while your in there check to see if the clunk has come loose or is stuck forward. check the stopper in the tank for leaks as well as the pressure fitting. make sure it is not pinched or plugged. if none of that solves it, run the engine up to temp, and see if the carb gets loose. you may also want to check your throttle connection, see how much vibration you have. good luck and let us know what you find...

RE: Engine trouble
 

If, after all that has been suggested above, your engine doesn't perk up, it may be worth un-mounting it and checking the backplate screws for tightness. Loose backplates can cause many strange problems that are difficult to diagnose.

Really, tho, I think if you replace your fuel lines and verify that the carb is clean and retuned from the start, it should work out.

RE: Engine trouble
 

The engine runs flawlessly the first time he flies it, for about the first 3/4 tank. There-after even if the tank is re-filled, he has this problem.

The clunk is NOT "stuck".

Since running the engine down to 3/4 of a tank takes more than 2 minutes ( which is about what is required to fully warm up the crankcase of an engine in flight ), this is unlikely to also be an issue with the carb getting loose, though it's a remote possibility.

The problem takes long enough to develop that this is more likely a issue with something that takes far longer to warm up, e.g. the fuel tubing or something surrounding the engine.

A leak should manifest problems in the first 5 minutes.

RE: Engine trouble
 

Sorry for all of the misunderstanding, and once again thanks so much for all of the help. I found last night that the fuel lines are good, and even tested the line between the high-speed, and the carb..fine. It has to be the low-end, we are currently adjusting the low end needle now, (which we found was screwed well into the carb, which would I guess result in more fuel than air or a rich condition. We have leaned the screw by 2 turns and are now seeing some improvement. I am letting the engine cool now so we can do another test run. It ran on full throttle enough for me to finally tune the high end needle but died from what I guess would be overheating. I pulled the plug to check and see if it was still ok after the dying of the engine, and it was and by the way very clean. I will let you know how the rest goes!

RE: Engine trouble
 

On my LA .46 I had to fully turn OUT the screw until the bleed hole was completely uncovered.

Even then the low end was far too rich, so I ended up doing as suggested, and slightly enlargening the hole.

This permitted the engine to run reliably, but the engine is still too rich in the low end.

I left it this way so as not to risk ruining the carb.

I'll bet that if you turn it out as far as you can, it will be much better.

If you do this, take out the screw and add a bit of locktight to the threads, so that you don't end up loosing the screw with engine vibration.