ZDZ 80 Tuning Questions
 

Everybody (I apologize for the lengthy comments, but I appreciate any help that you can provide),

I have some tuning questions for my ZDZ 80 in a Comp Arf 2.3M.
I have had this 80 for almost 3 years now, and I have at least 35 gallons of fuel through it.
It has ran fantastic in 2 different airplanes, and now that I have it in the comp arf there are some wierd tendancies coming out now.

From what I can tell I am having problems getting the low end to tune correctly - I can get it set on the ground so that it transitions fine and sounds really good, but once it gets in the air the mid throttle range is very rich.
It has been to the extent that my idle will drop several hundred or more rpm's and it gets wors as I go farther through the flight.

I found that the idle problem was pretty well fixed by leaning out the low end, but after adjusting this the transition sounds lean on the ground (it cuts out slightly as I raise the stick), but it is still rich in the air.
The rpm's of half throttle on the ground are a lot higher than half throttle in the air.

I have also noticed that the motor does not want to run up properly when inverted - i.e. pushing out of a downline and going half throttle it does very little, but if I roll it upright without changing anything on the throttle it comes back up right away.

The top end runs great and will easily pull the airplane vertically unlimited, it is just the low and mid throttle range that I am having problems with.

I am thinking that there may be a pressure or airflow issue/problem in the cowling.
I was told by a friend that he had this same time of problem on a motor (inverted versus upright running), but he could not remember the fix that he did for it.

The motor is mounted on standoffs and the carb is a little behind the firewall.

Here is what I have done as of last night:
1. I took the motor off and cleaned the carb filter screen (there was nothing to clean) and verified that the diaphrams were in good condition which they appeared to be.
2. I replaced the fuel tank with one that I know has worked with this motor previously without issues.
3. I checked the fuel lines and filter and verified that everything was fine there. The fuel lines have been replaced 2 times already in tracking this down.
4. I reset the high and low needles to 1 3/4 turns out and tuned the motor from there.
If I remember right the low end went a little leaner from that, and the top end went a little richer from that to get a good transition and top end.
This tuning was done with the cowling off, so this may change slightley once the cowling goes back on.
I have not flown the airplane with these settings yet.
5. I closed off (with tape) several openings in the engine dome that are right above the carb - this is where I am wondering if the pressure/airflow difference is coming in.

The motor seemed to transition and run very well last night.
I am not thinking that the ignition, plug, ignition battery, so on need to be replaced as the motor starts and runs fine for the most part.

I can post some pictures that I took last night later if needed.

Anybody have any ideas?
Am I missing something completely obvious?

Once again - thanks for any input that you can give.

-- Kevod

RE: ZDZ 80 Tuning Questions
 

Maybe the old carb diaphram problem?

Funny pressure waves of air around the carb making the diaphram push down and open the jet too much in flight?

RE: ZDZ 80 Tuning Questions
 

maybe has Bing carb - these were sensitive to that

RE: ZDZ 80 Tuning Questions
 

That is possible- the question is what is the fix?

Would enclosing the engine dome help with this?

RE: ZDZ 80 Tuning Questions
 

I forgot to post originally that is does have the Walbro carb, not the Bing carb.

I have read up a lot about the Bing carbs being kinda finacky, but I do specifically remember seeing that this was a Walbro carb.

RE: ZDZ 80 Tuning Questions
 

The answer will be to add a manifold or velocity stack to smooth the airflow into the carb. Maybe add a air filter and experimenting with tubing connected to the diaphram ambient airpressure port. (Hole in the plate covering the diaphram). Locate the tube end around the fuse till you find a spot that has the least pressure changes. Evan hook it up into the intake manifold. Same issues are currently being hashed out with BME and 3W's. Is the plane a Yak or sukoi?

RE: ZDZ 80 Tuning Questions
 

Altavillan,

The plane is a Comp Arf Extra 330L 2.3m

Do you know of a company that sells the velocity stacks/manifolds that I can look into?

-- Kevod

RE: ZDZ 80 Tuning Questions
 

before you go blowing money on stacks n stuff- get with one of the guys in Provo are who runs ZDZ-
if the setup - tank position - line vent position etc., is ok - this problem simply is rare to non existant on these engines
the early on carbs were fussy ( Bings) and I would suspect you did somethin g this time you don't suspect.

RE: ZDZ 80 Tuning Questions
 

Dick, how can it be blowing money on an airfilter?

Kevod, get them from http://www.aircraftinternational.com/ <---------Basically "the" 3W importer but, carbs are carbs and Gerhard stocks good stuff. Go to; products-motor parts, scroll down.

RE: ZDZ 80 Tuning Questions
 

as a device to improve the noted problem -
How would it help?
I do run airfilters -just simple snap on type from ZDZ but they have nothing to do with the problem noted

RE: ZDZ 80 Tuning Questions
 

Dick, does RCShowase have the walbro carb for this engine? I have the Bing carb and I have not had any problems with it, however, the engine has been sitting around for three years and I don`t know if that ruins these carbs.
Now, is it really that much of a difference between the walbro and the Bing? Can it be tuned right with the bing or do you advice to change it to the walbro?

Thanks in advance Dick,
John

RE: ZDZ 80 Tuning Questions
 

Our little floatless carbs are strange devices - they are so simple -you would think they are all the same
I have run Bings which are great -but some which are fussy about attitude.
the present Walbro (there are differences) as used on the current 100 ZDZ twin from RCShowcase--is my favorite - easy starting and not fussy and best power with tuned pipe.
If your Bing starts easily and does not easily go rich on inverted flight--- keep it.
The new Tillotsons are also good . but my favorite is the Walbro mentioned .

RE: ZDZ 80 Tuning Questions
 

I have one of the first ZDZ 80's to enter the country. I was never comfortable flying with it because it went rich when inverted. Now I find it was the Bing carb. Where do you get the Walbro replacement and what is the type no?

RE: ZDZ 80 Tuning Questions
 

Stretch the metering spring EXACTLY 2mm on the Bing 49 carb only. This was a factory authorized fix for inverted or negative G carb loading.
Thanks,