New Nitro Engine Revving Up and Down
 

Hello,

I just purchased a Hangar 9 Alpha 40 with the Evo .52 engine. I've started it with brand new fuel, but when start to rev up the engine starts to rev up and down quite a bit. It will often take a few seconds to either rev up or slow down, but it does this consistently. Because of this, it is almost impossible to tune. I have put about three tanks through it. Originally, I had it set too lean (I think) because it would die when I'd point the nose up. Also, I tried a couple take-offs and it would die right when it got enough speed to take off. My biggest frustration is that it revs up and down, so I'm kinda blind with the tuning. I believe I started with the HSN 1.5-2 turns out.

Ideas???

Nitro engines need some break in when new.

What did you do to break it in?

I ran one tank through it on the ground (the book on the engine said nothing about break-in). It was at half-throttle max until the end of the tank. Then I took it to the field and an instructor had me run a second tank through on the ground between half and full throttle. That was when the issues started happening. Since then, I've tried to fly it, but these issues have continued. Should I run it on the ground some more and just set it rich?

Thanks!

Welcome to the wonderful world of Evolution! When an engine doesn't respond to the needle valve changes consistently, there is another problem. I'd look first for an air leak. The carb o-ring, backplate, and fuel lines are the most likely culprits. An air leak can cause that up and down running condition as the engine cycles between rich and lean due to the way the leak happens. Being set slobbering rich is probably part of the issue as well. I had one that had to be set crazy rich just to stay running and would go up and down like you're describing at full throttle. If I tried to lean it out, it would snap straight to too lean and die. It had a bad front bearing from the factory allowing it to suck air.

Try leaning the idle jet. If you adjusted it, you may have gone a little too far.

Thanks for the replies!

Iron Bottom--that needle has a weird setup that does not allow it to be over adjusted. I have been messing with it, so I will set it between the two points for starters. Thanks!

Jester_s1--I will look into every potential area for a leak. Is there a trick to finding out whether it's the font bearing or not? I suppose the o-ring and backplate would be fairly straightforward. I will start tearing things apart and hopefully find something!

Now I know why OS is so popular!

It could be vibration from an unbalanced prop foaming the fuel, bad fuel, bad plug, out of balance spinner, fuel lines kinked, muffler pressure blocked, holes in fuel line in the tank, switched tank lines, leaking head or backplate, loose motor mount, leaking needle valve, too much prop, too cold to run well (well that might just be here today a 5 degrees). You do need to run an engine a lot richer than just not dying when the nose is vertical.

I just spoke with Horizon Hobby. If it is more that an air leak with the HSN o-ring or carb o-ring they want me to send it in--which I will do since I don't want to compromise whatever warranty comes with it. The fuel lines are solid with fuel when running and the engine seems smooth all-around. I just remembered that it ran good for a short time when I moved the HSN closer to the carb. Maybe it's not sealing right again and is sucking in some air there.

Thanks for your help!

How did you move the HSN that made it run right? Do you mean you adjusted it or do you mean you pushed on it?

To answer the bearing question, you can only eliminate other causes and then replace the bearing to see if it helps.

Hi!
It's easy! Every time the rpm goes up and down You are running it too lean! Open the high speed needle some! And remember...when you are about to fly...hold the planes nose up high and adjust the high speed needle a little rich. That way you are sure the engine won't stop when you climb up.

Bingo! You beat me to it. One other clue to look for if too lean is the color of your oil resido that comes from your muffler, if its extremly dark black then chances are your too lean.

Several years ago fuel manufactures started using an anti foaming agent in our store bought fuel. I have tried to make it foam up like it used to and haven't been able to get it to foam. I started hard mounting my tanks and still haven't been able to get it to foam.
It does sound like the carb is adjusted too lean but the EVO engines do very often develop air leaks, often just a loose screw holding the carb or back plate. Fatten the engine up a bit and test it, if it still does it then check all the screws. If all else fails send it into Horizon for repair or replacement. I haven't seen an EVO in a while but they used to put a cap over the low speed needle so it couldn't be adjusted. Good idea but they often came new out of the box out of adjustment so that cap had to be removed to get at the needle.

Jester_s1--We physically moved the HSN from the remote location to right by the carborator. The instructor was thinking that would help. It seemed to run better, but some time later it started running funny again. I just tore things down and checked both o-rings. They look fine. However, I'm noticing a strang amount of nitro leaking from the front bearing. I think you're onto something there. Will start today and see if it runs any different.

Gray Beard--Thanks for the input! When I tore things down, I made sure everything was tight. Hope it fixes things! May have to send it back as you mentioned.


Thanks!

Fuel leaking from the front bearing can be a real problem. I rebuilt a OS 120fs and the front bearing I got wasn't seating right, like a lot wrong and fuel was flowing out pretty fast. It fixed the problem when I got another set of bearings for it. Your engine is under warranty so if you have a bad seal on the bearing then just send it in for replacement or service. No reason to be chasing down a problem like that on a new engine. Horizon is pretty good about things like this and they know there EVO line isn't the best on the market. This is a good time of year to send it in too.

Evolutions run well when they run, and have the best throttle response I've ever seen on any engine. But their quality control sucks. At least they do service their products so they'll likely fix yours.

For future reference, any time you have an engine that is simply inconsistent, look for leaks. An engine that isn't leaking air and has good fuel and a good glow plug will respond very consistently to needle valve changes and will be fairly straightforward to tune. Blocked fuel passages from debris in the fuel or congealed castor will cause similar troubles. You may see issues like a fat midrange or frustrate yourself trying to get the lowest possible idle, but if everything is mechanically right the engine won't be inconsistent or unreliable.

Jester_s1--Thanks for your input! That makes a lot of sense. Will definitely remember this experience!

Sending the engine out tomorrow. Hopefully you won't see a post about it again! =D

Thanks again!

[QUOTE=mike_r;11677537]Hello,

I just purchased a Hangar 9 Alpha 40 with the Evo .52 engine. I've started it with brand new fuel, but when start to rev up the engine starts to rev up and down quite a bit. It will often take a few seconds to either rev up or slow down, but it does this consistently. Because of this, it is almost impossible to tune. I have put about three tanks through it. Originally, I had it set too lean (I think) because it would die when I'd point the nose up. Also, I tried a couple take-offs and it would die right when it got enough speed to take off. My biggest frustration is that it revs up and down, so I'm kinda blind with the tuning. I believe I started with the HSN 1.5-2 turns out.

Ideas???

Hi there,

I have a similar problem with trying to tune my idle, engine keeps making chirping noise and constantly have to adjust the idle screw. My glow plug area appears to be always damp and notice air bubble coming out of the glow plug gap. Even tightening down glow plug, still erratic. Any ideas?
https://cimg6.ibsrv.net/gimg/www.rcu...0276526c0.jpeg
Notice bubbling from the glow plug area, air leak that causing impossible to tune idle, it would chirp after idling for less min and ramp up/down.
https://cimg9.ibsrv.net/gimg/www.rcu...1eeb3a68f.jpeg

[QUOTE=HueyC;12813790]Is the copper gasket on the plug? If it is it could be damaged. Glow plugs shouldn’t have to be cranked down to get a good seal. Do you have a spare plug to try? Also make sure the head bolts are tight enough.

[QUOTE=HueyC;12813790]Is the copper gasket on the plug? If it is it could be damaged. Glow plugs shouldn’t have to be cranked down to get a good seal. Do you have a spare plug to try? Also make sure the head bolts are tight enough.

How much nitro do you use?