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Old 08-10-2017, 03:54 PM
Biffster is offline
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4 Cycle? What is 4 cycle? Thanks!

What is 4 cycle?

Thanks


Quote:
Originally Posted by Pro1Foam View Post
Thought I would transfer this over from tha Cirkus (RIP). It is a couple of articals that Xipp wrote in response to my engine tuning question that got a great response from the RC Community.

Xipp engine tuning method (Salsa)

Petrol (Gas) Engine Tuning
*** Carbs aren't too difficult to tune up if you know what you're doing. First of all, you need to know how the carb works and how the settings interact with each other. About 95% of all the gas airplanes I've seen at the field are somewhat out of tune. How can I tell this? Simple, at some point the engines "four cycle" in flight. Two Cycle engines are not supposed to "four cycle" PERIOD. This is caused by a rich mixture that is forcing the sparkplug to intermittently miss making it sound like a four stroke. This is not good. HOWEVER the good news is; gasoline two stroke engines are very tolerant of rich settings (most of the time) and will run fine. You'll just consume a little more gasoline than necessary, and create a little more oil mess on your plane. You may eventually foul your spark plug as well. So why do so many people leave their engines tuned like this? Simple answer, the engine will start much easier when it's cold AND there's little or no warm up time needed prior to flying. Those are pretty good reasons! But the fact is... the engine is not running like it's supposed to.

(1) The low end needle on a Walbro carb is ALWAYS the one closest to the engine, the high end needle is the closest one to the intake/choke.

(2) There is no fuel adjustment for idle fuel, only air feed set by the idle stop or servo.

(3) Both low end AND high end needles feed the top end fuel supply.

Let's tune up a Walbro!

Set the low end & high end needles to about 1 to 1 1/2 turns each. Choke the carb or prime it, until the carb is wet. Fire up the engine and let it warm up. Let's set the top end first since it's the easier of the two. Go to full throttle. Adjust the top end needle for peak RPM. Leave it wide open for about a minute to see if it changes any. Should the engine go lean, open the low end needle slightly, if this doesn't work... you will have to adjust the needle valve inside the carb.( I will explain this later) If the top end runs OK, then slowly pull the throttle down until the engine begins to "four cycle" hold the throttle there. Adjust the low end needle until the "four cycling" stops. Now lower the throttle more until it "four cycles" again, and adjust the low end again. Keep doing this until you reach full idle. Now, from full idle begin to throttle up until the engine starts to bog or hesitate. Open up the top end needle just enough to eliminate the bog or hesitation.

When this is done right, you will be able to set the throttle in any position and it won't four cycle, plus you will be able to transition from idle to full power without any hesitation at all. -Xipp, Flyingcirkus.com Member



Understanding a Walbro Carb
Ok this is for people who need a little insight into how a carburetor works in this case I will be using a Walbro for example.

Starting from the gas tank, the fuel is pumped from the fuel tank and enters the carb through the inlet. The fuel works its way through the fuel pump through a little diaphragm pump that's controlled by 2 one way valves (little flaps). The fuel then passes through a needle & seat that is controlled by the "float" diaphragm. This "float" diaphragm manages how much fuel is available for the idle, low-speed, and high-speed throttle positions. The "float" diaphragm opens & closes the needle through a small lever attached to the needle. The fuel is then "standing by" waiting in the float area for a vacuum signal at the various jets. The lever setting is very critical since it controls the available fuel to the jets. If the lever is too low, the engine will run lean, if the lever is too high, the engine will run very rich and will likely flood out at idle
The fuel starts its journey through the pump assembly first...



Then the fuel is regulated by the float diaphragm that controls the needle & seat.



All of these parts reside in the float cavity area as well as the fuel ready to be fed through the jets as needed. The amount of fuel available in the cavity is regulated by the lever and its relationship to the float diaphragm. So it's critical that the lever be set properly. Within the cavity, there are distribution holes that are managed by the low end and high end needles. Plus the idle circuit, which is a fixed size.

(Note) All Walbro carbs will run in any position, but they tune "best" as a side draft carb. The down draft position tends to run a little rich at idle, and the updraft tends to run a little lean at idle. No big deal though, it's easily tuned none the less.

This photo depicts one of Walbro's premier carbs, having a large bore and equipped with a high speed check valve and external fuel pump pulse inlet.



Now let's talk about the pulse signal for the fuel pump.



Your ENGINE will determine which pulse inlet type you need! If the engine "carb base" has a hole drilled into the crankcase you will use the STANDARD pulse port and the optional (if you have it) port must be closed off. If there's no hole drilled, you will find a fitting located somewhere on your crankcase. Use a piece of fuel line to connect the crankcase fitting to the fitting on the optional pulse inlet. There's no need to block off the standard port, as it's already blocked off by the engine mounting.

The carb must get a pulse signal from the engine! This signal "pushes and pulls" on the pump diaphragm which feeds the carb fuel.

Now let's check out the "float needle & seat" setting.



This is the single most critical setting on a Walbro carb! Walbro offers a "setting gauge" to properly set the height of the lever for your particular carb. If you don't have one, the setting will be a trial & error adjustment and a real pain in the butt since you have to open up the carb to make the adjustment. For general purposes, the lever will be almost perfectly parallel to the carb base. This will get you close. If the lever is too high, your engine will tend to run a little erratic at idle. If the lever is too low, your idle will be OK but it will tend to run lean on midrange and high end. It may also run the float cavity "dry" at full throttle and die, regardless of your high speed /low speed needle settings.

The needle valve seat is pressed into the carb base, and you should not remove this without having the correct tools and setting gauges. Do not remove it!

Typical PROBLEMS The engine stalls when accelerated: POSSIBLE solution: High end needle way too lean, or low end needle slightly lean
Engine goes rich in flight : Low end needle too rich, float diaphragm needle lever slightly too high
Engine goes lean in flight : High end needle slightly lean AND low end needle is rich, float needle lever may be set too low
Engine runs good, but no idle at all : There's crap in the idle jets, the carb will have to be removed and cleaned. You may also have an air leak at the base of the carb. The throttle butterfly could be damaged or worn out
carb leaks fuel when not running : float needle is bad or has crap stuck in it, or the float lever setting may be too high, or the float diaphragm is bad.
My engine four cycles momentarily when I back off the throttle, then runs normal : This is perfectly normal for carbs NOT equipped with a "check valve" high speed jet. If you do have the check valve, then your float needle setting is slightly too high, or your float needle is leaking a little
the fuel leaks back into the gas tank when it isn't running : Bad fuel pump membrane, or an air leak in the fuel line at the carb

NOTE 1:
A very common problem with cowled in engines is, the air pressure in flight changes the "natural" pressure on the float diaphragm. This causes the engine to run rich in flight. There are several possible fixes available. Most of the time you can simply tune your engine for flight by trial & error. However, the easiest fix is to open up the cowling around the carb area to lower the air pressure. You may also rotate the cover to different positions to see if that works. The "BEST" fix is to solder a piece of brass tubing where the vent is, and route the vent line to a better location. I normally route it into the fuse going through the firewall. It works perfectly every time! Plus, your ground tune doesn't change in flight!

NOTE 2
Carbs equipped with the high speed check valve are greatly superior for flying aerobatics, or flying whereby the throttle will be used extensively. The check valve prevents jet dripping when you back off the throttle. That's all it does...
Straight through (non-check valved) jets always drip a little fuel while the throttle is being backed off, and causes a momentary four stroking of the engine until the jet stabilizes to the new air flow rate. This is completely normal.
-Xipp, Flyingcirkus.com Member
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Old 08-10-2017, 04:54 PM
deadrobmusic is offline
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Biffster.

I suggest you try this thread. Use Terry's instructions and you will have success.

https://www.flyinggiants.com/forums/...194009&page=38
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Old 03-24-2018, 07:16 PM
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Iím new to gassers, mostly glow and electrics in the past. I now have 4 gassers and am beginining to get into the running/flight stages.. mostly in he 30cc arena.
I am thankful for the advise in this thread as I feel that I have a great starting place to begin.
Dam
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Old 03-25-2018, 04:23 PM
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Just wanted in on this thread.....good info.
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Old 07-26-2019, 09:20 PM
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dle tuning

Greetings all

I have a dle 40 twin, it has about 2 gallons of fuel thru it.

It has a good transition from low to high, but if I drop it below half even a couple of clicks I begins to run very rough.

am I lean or rich on the low end??

Thanks
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Old 07-26-2019, 09:40 PM
3DJP is offline
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Sounds like you are rich.. turn the low end screw on the carb which would be the one on top if you look in on it.. about 1/16 of a turn at a time until it gets better.. and make sure you fly it and get it good and warm.. don’t just run it on the ground.
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Old 08-11-2019, 01:01 PM
deadrobmusic is offline
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ANYBODY???

DA50 Trouble (0 min 41 sec)
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Old 08-11-2019, 01:15 PM
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Quote:
Originally Posted by deadrobmusic View Post

More detail
New/used?
Just started running bad ?
Factory settings?


Video lowest idle you can maintain for full 20 sec then slam throttle.
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Old 08-11-2019, 01:29 PM
deadrobmusic is offline
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Quote:
Originally Posted by Dangerous Dan View Post
More detail
New/used?
Just started running bad ?
Factory settings?


Video lowest idle you can maintain for full 20 sec then slam throttle.
Used motor. Has been one of the best gassers ever. Had on the old 78 extra and a Pitts. Ran great. Pu on this new 85" extra with a CF tuned pipe. Never had to touch the needles. Ran like a champ for 8 or more flights.

Yesterday AM I flew an 8 minutes into flight took an upline at WOT. Just as I leveled off at top it lost all rpm and started idling like you see in the video. I landed safely. I THOUGHT it got hot and waited for it to cool. Meanwhile I opened the high needle just a bit.

Still would not run any differently. I have since changed the fuel, cleaned the carb and replaced much of the parts in the carb (all I had). Still no change.

BTW the spark plug appears to be in perfect condition.

Also, the throttle servo and all parts of throttle assembly work correctly. You can see in the video that at full throttle it still will not gain rpm.
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Old 08-11-2019, 02:00 PM
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Quote:
Originally Posted by deadrobmusic View Post
Used motor. Has been one of the best gassers ever. Had on the old 78 extra and a Pitts. Ran great. Pu on this new 85" extra with a CF tuned pipe. Never had to touch the needles. Ran like a champ for 8 or more flights.

Yesterday AM I flew an 8 minutes into flight took an upline at WOT. Just as I leveled off at top it lost all rpm and started idling like you see in the video. I landed safely. I THOUGHT it got hot and waited for it to cool. Meanwhile I opened the high needle just a bit.

Still would not run any differently. I have since changed the fuel, cleaned the carb and replaced much of the parts in the carb (all I had). Still no change.

BTW the spark plug appears to be in perfect condition.

Also, the throttle servo and all parts of throttle assembly work correctly. You can see in the video that at full throttle it still will not gain rpm.
Good info

From my experience if an engine runs great then suddenly donít itís never ever the needles.

Iím thinking ignition but take s look at carb screen and reeds. If those are good hook a appropriate voltage battery directly up to Ignition. To see if there is s change.

You can also drain your tank from carb line and closely watch for air this will eliminate fuel delivery

Do you have another Ignition you can try?.
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Old 08-11-2019, 02:17 PM
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Quote:
Originally Posted by Dangerous Dan View Post
Good info

From my experience if an engine runs great then suddenly donít itís never ever the needles.

Iím thinking ignition but take s look at carb screen and reeds. If those are good hook a appropriate voltage battery directly up to Ignition. To see if there is s change.

You can also drain your tank from carb line and closely watch for air this will eliminate fuel delivery

Do you have another Ignition you can try?.
Yes, will be a pain but I can switch out ignition. Yeah it is NOT the needles. I have now moved them to every possible position and it makes almost no difference at all. Guess it could be ignition. I'll see about that.
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Old 08-11-2019, 04:31 PM
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Another vote for ignition since that's what the problem is if not an exhaust restriction or broken reed. Weak battery, defective switch, connection, wire broken inside insulation anywhere from battery to spark plug, defective sensor or module. And many new plugs make better fishing weights. New doesn't always mean good. Shiny things can always be defective but I doubt it here.
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Old 08-11-2019, 05:26 PM
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How does it behave when you first start it up,will it go to full throttle.If it will it's probably the ignition.DA's ignitions will heat up then stop working,whats the voltage going to the ignition.
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Old 08-11-2019, 05:55 PM
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Just switched ignitions (did not switch hall sensor). Same results. ALSO while I was at it I got rid of the tech aero IBEC and plugged directly into an A123 battery. No difference.

TO be sure we all understand. It cranks up easily. I can use transmitter to cause throttle to go to wide open, but I only get like maybe 3,000 or 3,500 rpm out of it. It does not get better or worse as it warms up.

So it is not the ignition.

Maybe the hall sensor???? Don't see how that could have failed in a way to achieve these results?

I took gas tank out and tested for air leaks....Negative.

Waiting on new spark plugs to show up. But again, I never known a spark plug to act this way unless it was fowled. This one is not fowled.

The plane was flying great one second and the very next second it went to idle and that was that. What ever happened occurred in an instant.
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Old 08-11-2019, 06:02 PM
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That's at least a 9
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Where the reeds ok?

Dan
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