engine runs rough

[Slyfox]

new engine installed 4th month of 2009. has 750 hours. 912uls.
My kitfox has been running poorly for quit some time, first sign was rough running on take off. thought it was fuel pump, nope new one, went through carbs, nope still there. what it will do is act like it's running on 3 cylinders for about 2 seconds. todays flight it did it randomly for 3 times. got back to the airport and did 2 touch and goes, on the second one it seemed a little rough in the mid range on down I ran the runway and took back off and it did it after hitting the throttle full throttle for more than 2 seconds. came back around cus it quit doing it and landed. on taxi back to the runway was running poorly, pulled out the enrichment and didn't get better. pulled out more and the engine wanted to quit. I feel this is not fuel. I turned on my electric fuel pump and it will do this with it on.
Now when did this really start. Thinking back I put in the earthx battery with the b and c regulator. first flight went out 15 minutes, on the way back seems more vibration than normal. next flight it reared it's ugly head. my thought is the earthx or b and c or both. my thought now is to put my original regulator back on and fly. if that doesn't do it, put the odyssey battery back in. thoughts

[Dave S]

Hi Steve,

I can offer a couple thoughts although diagnosis via e-mail leaves a lot to be desired.

Considering that engine running troubles can be roughly divided into 1) cylinder health (compression), 2) Ignition and 3) fuel/carburetion the symptoms don't sound much like compression (barring a sticking valve or broken valve spring) and you have pretty well gone through the fuel/carburetion. Might be good to think about the ignition system.

The random symptoms don't really sound like what a fuel problem would do, assuming the fuel flow is not interrupted from time to time for whatever reason.

On the ignition, I'd not suspect the modules since they either work or don't, or they don't work when cold. My first thought would be to check the cheap stuff first - grounds for the modules need to be solid. A cracked wire inside the insulation can hide so manipulating the ground wires to search for an internal break is important. If I recall, the original 912 installation in a IV moved the carbs/manifolds to opposite sides and some sort of provision needs to be made to re-establish a separate ground from each module to the manifold. It seems that some instructions had both grounds going to single fabricated bracket which if it cracked could interfere with both modules. P leads and switches are something to look at. Integrity of the harness to flywheel pickups as well as solid and correct mounting of the pickups another possibility.

Don't know if that helps, but I'd start looking over the entire ignition system.

[rv9ralph]

Another area to check is the carb boots for cracks. They are part of the 5 year rubber replacement recommended by Rotax. (although I am more of a believer of "replace on condition".)

A crack in the boot will result in an induction leak causing a lean condition in those two cylinders.

[AvDES LLC]

No bueno to hear another 912 is on the struggle bus. I will state that I had a similar issue and in speaking with Hal he pointed at the ignition boxes. If you have the old ones that have maybe 3 inches of wire coming out of them and directly mounted over the engine, it is possible that one of the wires has an internal short / break that is intermittently connecting and disconnecting when vibration sets in. I had chased these issues around the plane for months and finally had enough of it - swapped over to programmable ignition modules and never looked back. The new modules also have a few feet of wire on them to allow for mounting in cab away from the heat - bonus.

[Slyfox]

tell me more about this. willing to spend whatever to fix this. about a year ago I changed one module to a newer soft start with extra wiring for the soft start. the other one only has a cold start up problem that works itself out after I start the engine, generally will start working when the rpm's are over 2000. I left it alone with 1000 a pop. I've run on one mag while flying and no change going between the two. But a programable module does sound interesting. give me the web site or something for this. thanks

[AvDES LLC]

If you’d like, I have one of my old cdi boxes that I can send your way for you to swap out with your others to see if the problem goes away. That way we can narrow it down to the ignition before you go spending a ton of money. It will be the one that doesn’t have the broken internal wire - promise! Haha. If that solves the problem and you want to go the programmable cdi box, we (AvDES) sell them along with a mounting kit to bring them into the cab. That said, I’m not a paying sponsor on the site (yet), so I cannot openly discuss the kit in the forums. Touch base with me in pm and I’ll shoot you my phone number if you’d like to discuss your problems more.

[Slyfox]

right now my plan is to rip the coil-module assy out and check all wiring and do a test on each coil with heat. if that passes than yes I'll consider it. thanks

might be a few days, been working hard and I'm going fishing this weekend. lol

[AvDES LLC]

right now my plan is to rip the coil-module assy out and check all wiring and do a test on each coil with heat. if that passes than yes I'll consider it. thanks

might be a few days, been working hard and I'm going fishing this weekend. lol

sounds good! And lucky man! I’ve been trying to escape to a fishing hole for months now. Good luck!

[Slyfox]

a little update on this. I cleaned the plugs, they were quit black. started it up, and it ran very good on the right mag. left mag, ran like it was not on all 4. problem is in the ignition. I had my spare cdi and installed it on the left side. switch that is. not sure at this time which coils that one runs. will find out though. I have the rotax heavy duty manual so I have the wiring diagram for this. I replaced that cdi about a year ago with a soft start. the original cdi quit working when cold. installed that cdi and ran the same, so it is working. I am starting to think coil at this point. I need more time to dig in and find the problem. let you know.

[AvDES LLC]

Good to hear the troubleshooting is going well. If it ends up being a coil I HIGHLY recommend reaching out to Hal. He has a stash of them and will save you big bucks.

[Slyfox]

like I said I need to find out which side I'm working on, a or b. I know which side is which on the diagram not on my plane yet. going to rip the system off the motor mount and dig in maybe tonight. I was way excited that it turned from an intermittent problem to a hard problem. I'm sure I'll find it.

[Slyfox]

well it tested positive for a bad coil. I ordered one and I hope this is the end to this saga.

[AvDES LLC]

Great to hear you’ve isolated the issue. Keep us informed when the new coil goes in if the problem is solved!

[Slyfox]

the saga continues. I did put that coil on, didn't fix it. I got me a timing light and put it on t1 and it wasn't firing. checked t-2 and it was firing. what the heck. that's on the same coil. can't be the trigger it runs both on or should I say fires the coil with one trigger for t1 and t2(let me know if I'm wrong) . so back to the cdi module. this is the new one I got about a year ago with soft start. my thinking is this thing is bad. so what I'm going to do now is take the module I took out and put it in the freeze for an hour and put it on ice and take it to the airport and install it and hopefully be able to start the plane. you see it failed and wouldn't work until the engine has 2000 rpm. it is said it will start working if put on ice for a bit. this is a green label cdi. I will see if it will start and have the timing light on that plug. got me baffled for sure. I did check the ohms for the triggers, they are all the same so should have good wires going down to the triggers. wish me luck, cus that is what this is turning into.

[AvDES LLC]

sorry to hear the frustrations continue. It’s odd as a single coil is triggered by a single trigger wire from the cdi. If one of the plugs on that coil is firing, the trigger from the cdi is good. Have you changed out the spark wire and plug boot to see if those have an internal short? Napa auto parts will have some 7mm wire you can pick up for a few buck to make a test wire.

[Slyfox]

it now has a new coil for that t1 t2, came with new secondary wire and I bought new end caps. I did change to the other plug in for the triggers and that made that t1 fire on the timing light. if it is in the cdi it will be a total weird happening, things like that happen to me. lol anyway I'm going to try and install the old cdi and see if it will fire with things hooked up normal for the A circuit. Hope that does good. I'm not going to buy another cdi, they lost me on that one. factory anyway.

[sturdee]

Check your connections too each plug cap! Found one that was not into the centre wire and caused a right huntdown, symptoms as you had

[Slyfox]

update:
I replaced the spark plug in no. 1 top. I now have a running engine. I cleaned the plugs as they were black from ground runs. starts nice and flew for an hour in the pattern. I have a slight vibration from 3400rpm on down, idles just fine. Not sure if this is normal or not, the cowl will vibrate at the front section when it does it. plenty of power. I've done everything you can think of on this thing. the idle circuit set screw was set a 1/2 turn out and I increased it to 1 after landing. I didn't want to pull the choke for that has fouled the plugs in the past, but if I need to I will the next time I fly. there was no fall out of cylinders on climb out at all, just running with a little vibration under 3400rpm. what to do, not sure. on a mag check at 4000rpm on the ground, both are equal. with a drop of about 150 or less.

[henrysamson]

Model IV with 912 ULS with 540 hours. I've always had a little vibration in the 3000-3500 RPM range. Is your vibration at 3400 RPM new? I have been led to believe that mine is due to harmonics in that range. I had a dynamic balance done right after I completed phase I and it is smooth from 2000 RPM to about 3000 RPM and over 3500.

Henry

[Slyfox]

Model IV with 912 ULS with 540 hours. I've always had a little vibration in the 3000-3500 RPM range. Is your vibration at 3400 RPM new? I have been led to believe that mine is due to harmonics in that range. I had a dynamic balance done right after I completed phase I and it is smooth from 2000 RPM to about 3000 RPM and over 3500.

Henry
I'm going to say it's newer. I've also had vibration at that speed you mentioned, but this seems a little bit more pronounced and goes down a little lower.

[sturdee]

May have mentioned this before, when balancing carbs I do idle and cruise power settings and then check mid range, the twin throttle cables are the best the springs are not as strong going too full throttle, but are very necessary, if you look at the arm as it travels from closed too full throttle it goes in a slight arc, if there’s any lack of smoothness they lag thus imbalance. With the electronic carb mate balancer you can see if this is occurring, remember throttle must be closed when using choke for start,
If you open the throttle even a quarter the choke become ineffective. Always check the springs are secure on that choke as well.
there’s no voodoo in balancing the carbs, if you want too change the idle , turn both idle stop screws the same amount, please stop the engine before adjusting anything, one slip or lack of consideration of what that whirling prop will do is not worth the cost.props are live always! treat so,
even with those mags off!
That’s why a dead cut check during shut down confirms the sucker is grounded,
stay safe,

[Slyfox]

May have mentioned this before, when balancing carbs I do idle and cruise power settings and then check mid range, the twin throttle cables are the best the springs are not as strong going too full throttle, but are very necessary, if you look at the arm as it travels from closed too full throttle it goes in a slight arc, if there’s any lack of smoothness they lag thus imbalance. With the electronic carb mate balancer you can see if this is occurring, remember throttle must be closed when using choke for start,
If you open the throttle even a quarter the choke become ineffective. Always check the springs are secure on that choke as well.
there’s no voodoo in balancing the carbs, if you want too change the idle , turn both idle stop screws the same amount, please stop the engine before adjusting anything, one slip or lack of consideration of what that whirling prop will do is not worth the cost.props are live always! treat so,
even with those mags off!
That’s why a dead cut check during shut down confirms the sucker is grounded,
stay safe,
yup agree with all that. I was thinking of the springs as well. I was considering ordering the spring set up that vans has for the rv12 with the 912uls. thanks

[Av8r3400]

Steve - Did you try new spark plug wires or boots? ( got mine from the local fleet-farm store in the snowmobile parts aisle)

Also, I have found gapping the plugs to .021-.022" (.53-.56mm) is far better running than the Rotax spec.

[AvDES LLC]

If you’re getting rough vibrations as you pull out power I am going to go out in a limb and ask you if you’d mind tinkering with your idle fuel screws a bit. Try setting them to 1/2 to 3/4 turns out from fully seated and do a full power run up before flight. If all goes well in run up, lap in the pattern and on the decel on downwind note if the vibrations improve or get worse. If they improve, your needle circuit and idle circuit may be wayyyy too rich a I’ve seen most people report. That idle fuel screw is a quick means to diagnose.

[Slyfox]

If you’re getting rough vibrations as you pull out power I am going to go out in a limb and ask you if you’d mind tinkering with your idle fuel screws a bit. Try setting them to 1/2 to 3/4 turns out from fully seated and do a full power run up before flight. If all goes well in run up, lap in the pattern and on the decel on downwind note if the vibrations improve or get worse. If they improve, your needle circuit and idle circuit may be wayyyy too rich a I’ve seen most people report. That idle fuel screw is a quick means to diagnose.
this is with idle mixture at 1/2 out. was going to try 1 turn out.

[Slyfox]

going out on a limb. has anybody had the guts of your exhaust fail. meaning did it come apart. I was thinking of pulling the muffler and looking inside

[AvDES LLC]

this is with idle mixture at 1/2 out. was going to try 1 turn out.

you planning to attend the KF factory fly in? I may be bringing the dual monitoring exhaust setup I made to display and we can strap it in and ground run it to see where you’re at.

[Av8r3400]

going out on a limb. has anybody had the guts of your exhaust fail. meaning did it come apart. I was thinking of pulling the muffler and looking inside


I’ve had two fall apart. The blast tube rots away leaving the stinger unsupported then the housing cracks.

I usually smack the stinger on preflight and listen for a rattle to tell…

I have one on my workbench to rebuild right now. Will make a new blast tube and retrofit ball and socket joints to hopefully make it my last exhaust system.

[Slyfox]

I’ve had two fall apart. The blast tube rots away leaving the stinger unsupported then the housing cracks.

I usually smack the stinger on preflight and listen for a rattle to tell…

I have one on my workbench to rebuild right now. Will make a new blast tube and retrofit ball and socket joints to hopefully make it my last exhaust system.

thanks Larry, I had one do similar on my io360, ended up cutting out all the baffles inside for both mufflers and made them straight pipe. I also thought of banging on the muffler real quick, but I think I'll pull the muffler and take a look. On the outside it looks great. I do understand the rotax needs back pressure, correct me if I'm wrong.

[AvDES LLC]

thanks Larry, I had one do similar on my io360, ended up cutting out all the baffles inside for both mufflers and made them straight pipe. I also thought of banging on the muffler real quick, but I think I'll pull the muffler and take a look. On the outside it looks great. I do understand the rotax needs back pressure, correct me if I'm wrong.


I’ve had two do the same thing. The last one I just gutted and called it a day. Plane has been running fine without the baffling in the pipe.

and the back pressure claims and 4 strokes are kinda funny. The back pressure term when discussing exhaust really only pertains to two-cycle engines in which there was nothing more than a gateway opening exposed by the post on during the engine cycle. This resulted in a need for a tuned exhaust and back pressure needs to ensure the engines would perform at an economical operation range.

4 strokes don’t really need back pressure in this way due to the inclusion of valves. There are claims that slight back pressure on a 4 stroke engine results in slightly better economy, but these are claims and I have yet to see anyone actually perform the experiment and record their results.

in looking at the internal “baffle” in these pipes and all of the holes etc etc, I’d argue that the back pressure within that system would change very little with it without that little holey tube inside.

[Slyfox]

checked my muffler last night, took the two front pipes off and the inside looked like new. outside looks like new, no cracks. back to lookin.

took and reset the plugs to .022 last night. Number 3 cylinder was very clean on both, the others looked slightly wet and brown, little black on the outside ring. Doing some reading that might be normal for idle back to the hangar.

My thoughts if this continues is to remove the prop and tear into the gear box. check the hubs for wear, that's really all that's left. I have an IVO medium prop and I'm at 800 hrs. I removed the magnet plug and it's got just a light film of black. sorry to say, it's the first time I've checked that magnet. so judge on that for material. I've read that even with wear on the hubs that magnet will still be clear. I also use Amzoil 10-40 motorcycle oil, have since first start. opinions. Yes I know, it's time to do the gear box.

[Slyfox]

pretty sure I found my problem. Now let me say this, I usually find my problems to be unique. Well here you go. I removed the top of the right carb and guess what, that diaphragm was pulled in on a section on the outer edge, major leak. I ordered the stage 2 kit that comes with orings gaskets and two diaphragms.

[AvDES LLC]

pretty sure I found my problem. Now let me say this, I usually find my problems to be unique. Well here you go. I removed the top of the right carb and guess what, that diaphragm was pulled in on a section on the outer edge, major leak. I ordered the stage 2 kit that comes with orings gaskets and two diaphragms.

heck yes simple fix! Congrats!!!

[Av8r3400]

pretty sure I found my problem. Now let me say this, I usually find my problems to be unique. Well here you go. I removed the top of the right carb and guess what, that diaphragm was pulled in on a section on the outer edge, major leak. I ordered the stage 2 kit that comes with orings gaskets and two diaphragms.


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