I'm going to ground my airplane until I get to the bottom of this. I can
tune it on the ground and it will run just fine all the way from idle to
full throttle. I get about 5300 rpm at full throttle at 29 in hg. MP. I
have 12 hours in the air so far but can't get past this issue. Other
than this, the plane is an absolute joy.

When  I get off the ground, when I go through around 5400 RPM, I start
to get stumbling and engine roughness. At this RPM I am about 18 inches
MP. Just below this point, I am making about 50% power and the engine
will run smoothly.

I went to another airport and had a lot of roughness on takeoff, but I
am used to it and so continued on my way to my home airport. When I got
back I found out that someone at the other airport wanted to report me
to FSDO because he thought my engine was going to blow up, but he didn't
get my tail number.

So, I thought I had it sorted out before I flew today, but it's back to
the drawing board. I've tried both leaning and enriching the mixture at
all throttle settings, but to no avail. At and above 5400 rpm I start
getting all sorts of roughness so I think that it has to be an ignition
issue. My injector wiring is separated from my coil wiring, but could I
be getting inductance between the different coil wiring?

I have a 93 13 BREW normally aspirated, 2.85 RWS redrive, EM2, EC2, 88x
74 CAtto Prop. This is getting to be really frustrating. It's got to be
something simple that I'm overlooking. I don't know anyone with an
ocilliscope, and have never used one.

Brian Trubee


Does the intake system still look like this?  If so remove
the large right angle pipe before the throttle body and fly it again.
Don't worry about where it is getting the intake air. There are probably
enough
leaks in the cowling to supply enough air for the engine.

That pipe is resonating somewhere in your RPM range. Probably around 5500
RPM. I
don't know for sure if that is the problem but it is worth a quick try.

Is there an opening in the cowl on the bottom for the intake air?
If so take some pictures of it.

---------------------------------------------------------------------

I am looking for a different response Brian. Without the pipe
it still may run rough so it will need to be re tuned for that
configuration. In principle it is a good idea to keep the length
of the intake tract up to the throttle body as sort as possible.
That means an air intake some where near the throttle body
on top of the cowl.

I am sorry but every time I hear about these kinds of problems I get
angry.
If I put on my programmers hat I know that Tracy's EM2 engine monitor
could be ten times better if only he added a USB port and sent all the
data to a net book, tablet or God forbid even a recent cell phone.

Back in the
early days of the personal computers and the Apple II we immediately
discovered that less than 80 characters per line and 25 lines was not
a viable user interface. The EM2 screen is a far cry from this minimum
required user interface. Now a days we can have 100 characters and 100
lines on a high resolution color net book or tablet screen.

Here is the problem. You can not see a complete map of the mixture as
a function of RPM and intake manifold pressure on the EM2 screen.
This makes it far more difficult to trouble shoot these intake manifold
problems.

As an illustration of what I am talking about here are a couple of the
possible tuning screens on a Megasquirt system. The Megasquirt has an
USB port to talk to a PC, tablet, net book, notebook, etc., etc.

I am not advocating Megasquirt as it is not optimized for aircraft use
and it has a steep implementation and learning curve despite its open
software and hardware. I am advocating a much higher res EM2 display
screen and or a USB interface.

Tracy's computer already has one or more serial interfaces that
can be converted to USB ports. Here are some examples of cheap hardware
that can do it. The PC software can be programmed in something
simple like Visual Basic.

It would be way less of a tuning problem if everybody built P-ports.
That is the closest thing we have to a standard intake manifold
configuration over a wide range of 13B engines starting in 1973 up
to the current RX8 engine.

Unfortunately there are a lot of engines still out there with
all sorts of variations on side ports not to mention some with turbo's.

The side port engine can be a nightmare if there are two or more resonant
intake systems in series. The stock RX8 intake manifold is a classic
example.

Paul Lamar



Can the engine be carefully run without a prop?  That would allow
checking
higher rpm. Though some problems only show up with load.


Matt-


Tracy's system is highly dependent on prop load.

Paul Lamar



ALL SYSTEMS ARE HIGHLY DEPENDENT ON PROP LOAD. Even using points and a
carb.
Bill Jepson

I'm going to borrow a smaller prop and do some more ground runs

Brian Trubee

What about the pictures of the intake scoop? :)

Paul Lamar

Do you want pictures of the cooling scoop or the engine intake scoop?

Brian Trubee

The engine intake scoop.
A smaller prop will change the load on the engine and you
will have to do a total retune.

Do you have any friends that are good with electronics?
Could they handle hooking this up? You can tell what is happening
by recording the intake manifold pressure at 1000 times a second
at various RPM's.

http://www.hytekautomation.com/Products/IUSBDAQ.html

What year or model is your computer?
Do you have auto tune?

Paul Lamar

Hi  Brian,    I am not a rotary expert, but, if you have tried
varying the mixture when it is missing/stumbling, it would have to be
ignition, you would not have a sudden change in intake tune to the
extent to cause a miss, lowering of power output yes, but not missing to
the extent that a witness on the ground thinks your engine is about to
blow!! my two bobs worth.  Try replacing your ht leads from the plugs to
coils with solid copper wire ht leads,(old style), cut the lead about
the middle slip some clear plastic hose over the lead and leave the
copper wire about 40/50 thou. apart, run the engine and you can see a
regular stream of sparks run to the rpm band while watching the sparks
when it starts missing you should notice a flutter in the spark stream.
But be very carefull, that prop is VERY CLOSE.
    John Burey.

-
I'm going to try to borrow a prop which will allow higher RPM on the ground for
ground testing. The first variable is to remove the inlet pipe from the throttle
body and put just a filter or a screen "air Strainer" there and try to replicate
the stumbling. Then I'm going to do a run on just the primaries and then
secondaries. Then I'll try separating all my coil leads to see if I am getting
inductance.


At that point. if I have not found the issue, I'm sure I will have thought up
more potential causes and test for those.


Brian Trubee

It is a mistake to do more than one thing at a time.
Take off the intake  pipe.
Re tune if necessary to get it to run well up to static RPM at
5300 RPM. Leave the upper range over 5300 RPM as is in the mixture
map for now.

You have a long runway for 747s. Tell the tower you may abort
the take off. Get it up to take off speed. Prop RPM should start to
increase at around 60 MPH. Then abort if necessary if the engine
starts to stumble.

The air intake scoop is critical. Please take a picture before
you do anything else. NACA did a lot of R&D on this for the P51.
The prop slip stream has a large effect on scoop mounted on cowls.
The prop slip stream is fundamentally different when the aircraft is
moving quickly.

Paul Lamar


Yes, sorry I was not clear. Each one of those changes is to be done separately
and then tested. I want to borrow prop that will allow a full rpm run on the
ground for this testing,

I've got 12 hours on the plane so far. I was flying it with the theory that once
I got up in the air, I could then troubleshoot a few miles to the west over an
airport on South Whidbey island. I can retard the throttle

to about 45-50% throttle and the engine will run smoothly. This will give me
speeds of around 110 MPH.  Above that, people on the ground start making phone
calls, and I don't blame them.


I am no longer comfortable flying like this, I think the smarter approach is to
kick this problem on the ground. I am becoming weary of doing serious soul
searching prior to every flight.

I need to resolve this on the ground.

The plane flies just fine otherwise, I've done some loops and barrel rolls, it
handles fine in the air and on the ground.

Brian Trubee

Well if it is truly a coil problem Tracy has changed the dwell time
over the years. If the dwell is too long the coil will misfire.
Scopes should be cheap to rent as the price has come way down
in recent years to the PC scope.

http://www.amazon.com/100MS-Based-Digital-Storage-Oscilloscope/dp/B002Z34QUA

Handy for checking dwell time and looking at your 3rd gen crank angle
sensors. You can also use it to look at the pulse width on the
injectors.

Ask Tracy what the dwell time is for your computer.

What coils are you using?

From the pictures they look like early chevy coils.


Paul Lamar

How about a dwell meter?

http://www.amazon.com/gp/aw/d/B00062YUUS/ref=redir_mdp_mobile/176-6354762-0803467


Matt-