Basic engine tuning.
- Thread starter Terryscustom
- Start date
49dimes
Damn I'm hungry
Just a couple of pics to show what can happen to carbs and reeds even when the engine is not running. I'm going to run an air filter now. This was a caused by a dead stick landing in soft sandy dirt. Thankfully none of it reached the crank case. But boy if I had not disassembled and inspected and just did the "wash down" in place??? The carb plate picture is poor. It does not show all the hard particles of sand covering the entire surface.
edgewise
30cc
Wow your carb really sucks....Lol
It's amazing what can get in and cause all kind of headaches. All it takes is a piece of dirt in the wrong place to cause problems.
N-O-V8-R
50cc
jhelber08
Try and take a pliers and pinch the ring so it is smaller in diameter and try it. Simple enough to do, but you will need to tuck one end of the ring under the other to get it small enough.
I have solved a buddies problem with identical problems. It was all in the cap fit.
When the buddy throttled up, there was so much noise that the throttle servo started jittering around half throttle.
Thought for sure it was a motor issue. Tightened ring on cap and all problems disappeared.
Noise was also getting back to RX thru the throttle servo lead and causing other issues.
Was the jitters on any other control surfaces?
Other little thing to consider:
1.) Make sure there is no continuous metal in the throttle linkage especially if it is closer than 12" to the CDI Box/HT lead.
A metal link with Plastic ball-ends doesn't count. It still acts like an antenna. Sames goes for Choke servos, if present.
2.) Move your IBEC as far back as the ignition wire will let it go.
3.) Run your IBEC wire on a separate side or away from your throttle servo wiring, especially if you have your throttle servo in the motor box area.
Please keep us up to date on the IBEC issue, as I haven't heard of a failure, yet.
Re:
I think alot of people (just from reading other forums) are under the conception that ibecs isolate interference from ignition to the receiver when really it is just a filtered signal. Theres a big difference between isolating vs filtering
My guess is that it is coming from the RX to the IBEC, not the other way around, unless you are closer than 6" to the HT lead.
Just some things to try. Hope they help!
Try and take a pliers and pinch the ring so it is smaller in diameter and try it. Simple enough to do, but you will need to tuck one end of the ring under the other to get it small enough.
I have solved a buddies problem with identical problems. It was all in the cap fit.
When the buddy throttled up, there was so much noise that the throttle servo started jittering around half throttle.
Thought for sure it was a motor issue. Tightened ring on cap and all problems disappeared.
Noise was also getting back to RX thru the throttle servo lead and causing other issues.
Was the jitters on any other control surfaces?
Other little thing to consider:
1.) Make sure there is no continuous metal in the throttle linkage especially if it is closer than 12" to the CDI Box/HT lead.
A metal link with Plastic ball-ends doesn't count. It still acts like an antenna. Sames goes for Choke servos, if present.
2.) Move your IBEC as far back as the ignition wire will let it go.
3.) Run your IBEC wire on a separate side or away from your throttle servo wiring, especially if you have your throttle servo in the motor box area.
Please keep us up to date on the IBEC issue, as I haven't heard of a failure, yet.
Re:
I think alot of people (just from reading other forums) are under the conception that ibecs isolate interference from ignition to the receiver when really it is just a filtered signal. Theres a big difference between isolating vs filtering
My guess is that it is coming from the RX to the IBEC, not the other way around, unless you are closer than 6" to the HT lead.
Just some things to try. Hope they help!
jhelber08
70cc twin V2
All good tips! I only got to play with this for about 10 minutes before leaving to go out of town that day so I still have some things to look at when I eventually get back.
- Jitter was only on left elevator. Jitter went away when I disconnected ibec from ignition and plugged in life battery to ignition. I need to look at the extension on the left elevator and see where it is in relation to ibec or throttle extension. If I remember right either my throttle extension or extension to ibec was pre made from a different plane and was a little long, so there is some excess tucked in there by the rx.
1) My typical throttle setup is as such. I use ball links on both ends. On the servo side I use a 1" hangar 9 turn buckle (for easy length adjustment) that goes into a golden rod/nyrod to the throttle arm. I typically cut a 1" 4-40 all thread or bolt to connect the nyrod to throttle ball link. Any how, no continuous metal linkage.
2) Ibec is as far back as it will go.
3) I typically follow this rule of thumb but will have to double check on this one. I think I had the throttle servo wire and ibec wire together from the rx to the ibec. From there the ibec wire goes straight across the fuse opposite of throttle servo wire and then up to the motor box and ignition.
The plane is a pau edge, i put two of them together back to back with nearly identical setups. Wiring layout is identical. Only difference is some of the equipment (servos, smoke pump, etc). This is what my typical setup looks like.
Truckracer
50cc
A small screw type hose clamp around the base of the plug cap removes all possibility of it being loose. In fact, on a couple of my planes where removing the normal cap is difficult, I remove the usual wire spring around the base of the cap and just use the hose clamp. Extremely secure and much easier to remove in cramped spaces.
jhelber08
70cc twin V2
Well finally got around to tinkering with my 120. Found 2 issues. Definitely an issue with the ignition and also a big issue with the idiot (me) that rebuilt the carb before putting it on the plane. I took the carb apart today to look at the rebuild kit I put in and found that in my haste I installed the wrong diaphragm from the rebuild kit on the inlet side...luckily I still had the old one to look at. I also had the gasket and diaphragm backwards thinking it went in the same order as the metering diaphragm and gasket. Put the correct one in and bam she would go to full throttle sort of just fine but surfaces still twitched like crazy and it sounds like one cylinder is misfiring. Put the new ignition on and she purrs like a kitten now with no control twitches. I'll be sending the ignition back to DA to get some new cables and caps put on rather than messing with it myself.
Robert lyman
30cc
Petrol (Gas) Engine Tuning, I used this for years.
*** 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.
*** 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.
