rcmodelflyer2010

hi there,i too have just bought the 26cc engine from hobby king and i did like you said and low needle set 1.25 and high needle 1.30.would not start at all.
im still having issues with getting the needles set right,ive started it up ok but its running like a four stroke engine.with the engine being new i dont want to lean it out to much so i was going to ask you if i could have the settings that you have used on yours just to give me a head start as this is my first gas engine.

thanks for your time in reading this and i would be so greatful for any assistance

sdherington

Keep opening the low 1/4 turn until you get it to start. Once you get it to start easily then you can go through the break in and setup. Needle settings are approximate. It all depends on the grind of the needle and the taper on the seat. Once you get a consistant idle you can start tweeking it leaner 1/16th turn at a time. I let mine run rich for about 2 hours before dialing it down. Be careful how far you take it down because it takes both needles for the high end. If it seems to be starving at the top end then open it back up a little. Watch the head temp also.

sdherington

I found my Walbro set up. Like I said needle turns are relative.

I had recently copied this from the ****** forum from Xipp. This may help,

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 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 intermittantly miss making it sound like a four stroke. This is not good. HOWEVER the good news is; gasoline two stroke engines are very very tollerant 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 lowend needle on a Walbro carb is ALWAYS the one closest to the engine, the highend 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 lowend AND highend needles feed the topend fuel supply.

Let's tune up a Walbro!

Set the lowend & highend 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 topend first since it's the easier of the two. Go to full throttle. Adjust the topend 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 lowend needle slightly, if this dosen't work... you will have to adjust the needle valve inside the carb.( I will explain this later) If the topend runs OK, then slowly pull the throttle down until the engine begins to "four cycle" hold the throttle there. Adjust the lowend needle until the "four cycling" stops. Now lower the throttle more until it "four cycles" again, and adjust the lowend 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 topend 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.

Ok this is for people who need a little insite into how a carburetor works in this case i will be useing 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 amout 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 lowend and highend 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 sidedraft 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 highspeed 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 highend. It may also run the float cavity "dry" at full throttle and die, regardless of your highspeed /lowspeed 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 accellerated: POSSIBLE solution:Highend needle way too lean, or lowend needle slightly lean
Engine goes rich in flight : Lowend needle too rich, float diaphragm needle lever slightly too high
Engine goes lean in flight : Highend needle slightly lean AND lowend 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" highspeed 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 highspeed 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 completly normal.

I have the associated pictures in a Word document but it is too large to post here. Maybe Xipp will redo a thread like this for us.

Jim Blair
<Lame Post

rcmodelflyer2010

hi there,thankyou for getting back to me so quick :-) wow the info that you have given me all makes sence now and the reason ive not been able to set my needles correct is because ive been fighting with them against each other instead of working with then together haha i will try this today if the weather stops raining and with abit of luck i will get a nice flow from low to high rpm.

i too have heard alot of planes running 4stroke rich when infact there only 2stroke!
anyway thankyou for the info mate and i will post later on today to let you know how i get on :-)

sdherington

You are welcome

rcmodelflyer2010

hi there,i used the info you gave me and my engine is running alot better now although i do get an engine stall now and then but i guess this is because of the engine being new.

ive ran about 4 ltr of fuel through the engine at this time and feel the engine idles alot better now.
just a couple of questions,my first is black oil coming out of the exhaust? is this because ive been running rich? and also how would i check my spark plug to make sure its gapped properly plus when i checked the plug today it also was black?

ive just built a sig four star 120 for this engine to go in but i think im going to carry on bench running until i have a reliable engine or should i say when i can tune it better lol

thanks again for your time

sdherington

That sounds like the oil mixture being rich. What oil are you using? Mixture ratio? It might be time to go to Amsoil. You will get some residue even after the engine is broken in and running great. Mine runs better every flight.

Sonny.C

My Feedback: (23)

I installed one of these RCG-26 engines in my CMP 120 size corsair and was suprised, and very pleased, with the starting ease and power of the little engine. I didn't have a tach, but it turned an 18/6 Zinger Pro well enough to pull the Corsair around the sky with authority. I can't know how well it will hold up, but after 6 tanks of fuel run through it the performance is improving in both power and idling.

Didn't have very high expectations, but did have high hopes and the engine performs as good or better as hoped for.

Now am very tempted to give the RCG 50 a try in my YA P-47.

rcmodelflyer2010

im on mineral oil at the minute at 25:1 ratio,do you think that i should go on to full synthetic oil at 40:1 ratio?

regards

rcmodelflyer2010

sonny i am to impressed with the engine and its got so much power and i too am thinking of the 50cc engine and im going to put it in a giant scale p51 mustang,after ive built it of course lol

i was just saying to sdherington that im new to the petrol engines and the tuning seems to be a little different to glow engines but with a little guidence im starting to get the hang of things.

does your corsair have movable wing ends or they just fixed? i do like the style of the corsair.im a bit nervous about the maiden flight of my sig four star 120 as i need to make sure the engine is in tip top condition as i dont want 14 lbs of plane coming down lol
i guess thats what makes this hobby so exciting and special haha

sdherington

I would finish out what you have on the mineral then convert to synthetic. No need to waste the gas. Are you using aviation fuel? I use high octane auto and add a fuel stabilizer with my oil. It will keep the internals of your carb in good condition. I have used aviation and it works great and could be worth it if the price ever goes back down.

rcmodelflyer2010

im just using standard petrolium from the gas station mixed with 2 stroke oil,what is aviation fuel? is it keroseen? and what price is it per litre.is the stabilizer to stop the oil floating in the fuel?

sdherington

What we call "regular" (89 octane) is fine to use. Aviation fuel would be available at you local airport for small aircraft. You don't have to use it but it burns much better than gasoline for autos. Fuel stabilizer would be available at your local auto parts store. It keeps the fuel from "breaking apart" chemically over time. We have had some problems in the US with the oil gelling in the fuel and clogging the fuel filters in the carb up. This can happen over time. It has been found that the fuel stabilizer helps or can eliminate this problem all together. You might try some Coleman fuel as used in camping stoves. It is very high octane and burns extremely clean. Kerosene is jet fuel and it does not burn well in these engines.

rcmodelflyer2010

we have a local airport but i think it may be better for me to stick to normal petrolium fuel lol can you recommend any oil for me to use on my engine ie: fully synthetic or semi?and would 40:1 ratio be ok in 1 gallon of fuel?

thanks again for your help its made a big difference :-)<br type="_moz" />

sdherington

I use Amsoil synthetic in 60-1 ratio. GREAT STUFF! You can get it over the internet if you can't find it locally. I would check with your local hobby shop to see if they can get it. I have heard of some using it as high as 90-1. For me the 60 works well. I do get some spots of residue to clean up but it is better than nitro and much less expensive on the fuel. Get the highest grade of fuel you can get at the pump. It doesn't cost that much more and will run better.

On a side note: You have said you are putting this engine in a Sig Four Star 120. Try a MA 16-8 3 blade prop. It will tug that one around great. That is a great flying plane. If you put this type of engine in a cowl you will have to set it up all over again. Also watch your airflow as it is critical to keep the cylinder cool for long engine life.

Good Luck and enjoy.

rcmodelflyer2010

had a really bad day today with the engine,really stressed out with these needle settings.when i open the throttle full it splutters and bogs until i shut it down also ive got my idle screw all the way in at the minute and it wont idle then it got to the stage where the engine sounded the same whether it was on low throttle or full and lots of smoke.i checked the plug again today having cleaned it yesturday and it is really black again.

do you think i should come off this mineral oil at 25:1 and go on fully synthetic at 40:1 im guessing that for the first 20 mins the engine runs fine and then because im using 25:1 ratio im getting oil build up which is making the engine play up and fouling the spark plug,does this sound about right to you?

regards rcmodelflyer2010<br type="_moz" />

sdherington

Calm down and breathe while counting to 10.
I would say yes it is time to change to synthetic. I would also say you need to tear the carb down and clean the screen inside. I bet you will find the gel that I talked about earlier or another form of contamination clogging it. You will have to do the adjustment proceedure completely again. We need to work on nomenclature. Idle is controlled by the servo. I remove my "idle" screws completely. You have a "low" needle and a "high" needle. It takes both to provide the correct fuel to the engine. My Father was in the Army and as a drone mechanic in the 50's. He told me the school was 16 weeks. 12 of those were on carbeuration.

Clean the carb by carefully removing the side plates in such a fashion that you do not damage the diaphram or gasket. Use a good carb cleaner to flusgh all the ports out. Be careful because carb cleaner makes neoprene swell. Greasing the gasket will make it shrink back some. Check to see in the pump diaphram in neoprene of mylar. If it is not mylar I would get one on order as the neoprene will deteriorate with todays gasoline. Inside you will find a cupped screen made of very fine mesh pressed into one of the ports. If you can clean it without removing, do so as it is a real pain in the butt to reinstall and it is very easy to damage. After it is all cleaned then reassemble.

rcmodelflyer2010

i think ive just found out why my engine is running poor and my trying to fight with the high and low needle settings,ive just took out my fuel tank to find the fuel pipes in the tank have x4 in size and have split also the clunk has come off too.this could explain the spluttering noise ive had today.
this is not the first time this as happened and the piping is ment to be for petrol.when i got my engine i ordered with it a fuel tank and it came with some fuel pipe which i installed and twice it has swollon and come off.the out side pipes that run to the engine are ok just the breather pipe and the fuel pick up in the tank were damaged.they must not be proper pipe for petrol more like gloww fuel pipe if you ask me!

i will do the carb clean anyway as im sure its picked up alot of gunk or do you think there is no need now that its more like the fuel piping.thing is im only good at basic mechanics so if i can avoid taking the carb to bits then would sooner leave it lol

thanks for your time

rcmodelflyer1020<br type="_moz" />

sdherington

Aha
Fix the fuel lines first. Buy good quality lines. I use the sullivan yellow.

rcmodelflyer2010

right,ive changed the fuel line to the yellow tubes i took them out my petrol strimmer so i know they will work and also ive cleaned all the carb as you were right there was quite a bit of gunk in there more so in that little mesh filter.all i did was flush it all out with some petrol in a sringe so everything is looking ok now also ive ordered a 3 blade 16x8 prop which i should get tomorrow.
if all goes well tomorrow i will maiden flight the sig four star 120 on sunday and will try shoot a couple of videos to post.

thanks again for your advise and will update on sunday with some good ,i hope lol<br type="_moz" />

sdherington

It was my pleasure to help. Good luck.

rcmodelflyer2010

hi,well what can i say but thanks for your advise and the four star 120 maiden flight today and it took off like nothing ive seen before,total weight is 14.5 lbs and i gave it a long run up before pulling back and it almost took off its self.the handeling is also really good.i do think maybe a 30 or 40cc would be better in this plane because of the weight but still the rate of climb on my 17x8 prop is still good and flys at a good pace on half throttle.maybe once the engine is fully run in i may get some inverted climbs.
anyway since you told me what to do about the carb cleaning and engine tuning it is now running like a dream and dont even need to touch the needles.

my next project is going to be a 80'' p51 mustang with maybe a 50cc or more engine.do you know where i can buy the kit from as i want to build it from scratch ready for the forthcoming winter.

thanks again for your advise you have not only made my day but have also prob saved my plane from distruction as the engine defo needed that tlc :-)

regards modelflyer2010

sdherington

You are welcome. Glad to be able to help. The engine will get better with each flight. It breaks in much better in the air than on the stand.

I think you will find much better performance when you change the prop. My Texas RC Pawnee was the same before I changed the prop. THe extra 500 rpm made a big difference.

There are several manufacturers of Giant Sale planes. If it was me I would get one from Yellow Aircraft, Wendel Hostetler, or Dave Andersen. Not neccisarily in the order. Put as large a powerplant in it as you can. The DL 55 is a great motor. I have one of the older DL 50's in a Skyshark P-40 and it flys OK. Check out SOLO Props for a Scale flying prop. They are ground adjustable on the pitch which is real nice for tweeking. They also have individual blades for replacement. Sierra makes great retracts and Down and Locked can make them electric for you. Much more reliable than pnuematic. I am beginning to sound like an advertiser for these guys. I am just letting you know the ones I have used.

At one time SIG made a Giant Scale P-51. One of our club members has one and is running a DA-85 in it.

rcmodelflyer2010

well on my sig four star ive ran almost a gallon of fuel on a 16x8 prop and now im on a 17x8 prop for maybe another gallon and then i think the engine recommends once break in is done a 18x8 prop would you say that sounds about right?

many thanks,rcmodelflyer2010

sdherington

Give the 16x8 a shot in the air. I bet you will be surprised.