I have a Ryobi 31 in a 4*120 and I got troubles. This is a brand new engine, and it's only turning about 6100RPM with a Zinger 16-10. I'm using 40:1 fuel and a C&H ignition. Battery is new. Brand new ignition. New plug. It's all new. Twin ring. No compression relief slots. Long shaft.

I switched out the stock Zama carb for a WT610 because the Walbro has a choke butterfly. The WT610 is the same size venturi as the opening in the backplate on the engine. It's about 15.5mm wide. It has a 34 stamped inside the carb throat. RCIGN1 told me how to read this number. It's measured in 64ths of an inch. So, 34 is read as 34/64.

I can get it started after a few flips on choke. It will idle and transition pretty decent, but it slows down and abruptly dies at about 1/2 throttle. I started with both needles 2 turns out. Richened the low speed so much that the engine started to slow down and load up a bit. Still won't go over 1/2 throttle. Richened the high speed--thinking that it was leaning out. No effect. It sounds to me like the engine is getting too much fuel and just drowning. I've richened the high speed to 4 turns out and it won't go over 1/2 throttle. Leaned the high speed down to where it won't even run.

Do I just have to much carb on it? I've had one of these engines before, and I put a carb on it that was the exact same size as the backplate opening, and the engine ran very well. I believe that was a WT438.

I can go back to a stock carb with a little bity 24/64 opening, but not getting much power out of it. One local guy who does a LOT of engine conversions told me that my engine is only turning 6000RPM on a 16-10 because it's brand new. Less than 1 gallon of fuel through it. Probably only about 5/8 gallon of fuel through it. He said it will break in over 5 or 6 gallons and pick up as much as 1000RPM. Do they really pick up that much when they finally break in? If so, then I'll stick the stock carb on it and just run it. But, it just seams low on power with the stock carb.

Is it possible that the WT610 is just too much carb for it, and I'm drowning it?

Thanks

Rcpilet, The carb you have is too big in my experience and opinion. The venturi is 13.49mm. My 50cc Echo conversions use that carb and scream with a 21/8 to 22/8 prop. I would start with a carb in the 11.11 range then maybe switch to a 12.7mm venturi if you think there is anything left to wring out of it. Also check out my recent posts on carbing engines. I developed a formula to determine the intake side sight unseen which is as you learned in 64ths of an inch. That is to take the venturi number and multiply it by 2.5 then round to the nearest whole number. You will almost always come up with the venturi number that is cast into the carb body. Reason I say this is that Walbro doesn't publish this number anywhere that I can find. When I put a carb on a new conversion, I open the needles about 1 3/4 turns then start the engine. Warm it up then adjust the high to max RPM then fatten it up just a little. 1/16 turn maybe. Adjust the low for transition then fatten it a little too. Now go back and recheck the high. Go fly and work from there. I prop my motors for about 7500 or so on the ground. If I were you I would be in the 15/8 to 16/8 range. Anymore and you will lug the motor and or over speed the plane. Also check your intake system for leaks etc. Good luck.

Tim

By the way the WT-438 has an 11.11mm venturi. Go to www.walbro.com and look around in Service and Aftermarket.

RCpilot
from what I have read on this site 15.5mm is too big ,recomended is up to 13.5mm and I
cant get that to work either same engine as you (short shaft)I had a single needle walboro
swaped it out for a stock size duall needle,ch ignition I'm turning 7500 on18x6 zinger
Ithink you may be over proped a little at 16x10 try 16x8 I tried a 10mm carb yesterday and
couldnt get a consistent rpm on hi rpms kept going up and down four stroke a littlethen run ok
then loose 500 rpms drove me nuts .I went back to the stock carb ,7500,rock steady I dont get it.
if you figure this stuff out give me a shout will ya my neighbors want to linch me for all the noise
and swearing ! really poco 242 said that he has used this zama that I have(13.5mm) with some
success on another ryobi and on his 25's ,ive gone through two so far with not so much success
it runs but I run out of needle trying to lean it out i need to lower the float some and try again
good luck let us know how it comes out


wow I got to learn to type faster
hey what saize tank are you guys using for how much flight time?

The tank on my Echo 44 and 50cc engines are 16 and 24 ounce. Fly for at least 20 minutes and usually have at least a third left depending on how hard I push. On the 23.6 Echo in the Eindecker I have a 14 ounce and that thing will fly for half an hour and I will still have a 1/4 tanke left. Even with the gas prices as they are you can't beat these engines.

Thanks a bunch guys.

You've confirmed the suspician that the carb is just too large.

I've got a couple carbs here. 24/64, 26/64 and 28/64. I'll put a stock Walbro 24/64 on it and try again.

Your saying that I'm over propped. I thought these engines were supposed to turn an 18-6? 16-10 is the same load as an 18-6.

Either way, I'll step down to a 16-8 for now and just see if I can get it running.

Thanks very much for the help.

My 50 cc Echo (BME clone) turns about 6700 depending on temp and humidity here on a 22/8 pulls well. Today I went back to the 21/8 and the RPM jumped back to 7250. Engine just winds tight very fast again. Measured the prop and there is maybe 3/8ths of an inch difference in the prop diameter. That little difference makes a huge load difference. However the plane lands a little hotter now but I will take that any day.

I would recomend that you check your exhaust duration timing, I have found some ryobi to have a very short duration timing on the exhaust at about 130 degrees I had to increase it to 145 degrees in order to get the desired performance I know for a fact that I am getting 8200-8300 rpms on an APC18x6W, so once again check the exhaust duration timing.

aero nut
my ryobi's piston goes past the exhaust port bottom should I drop the port by grinding
it down a little?even or slightly lower than the piston at bottom dead center?
this would give a few more degrees of duration correct?
how about sharing your exhaust timing from top dead center to port openingso I can compare
it with mine Iknow if I grind on the top of the port it will change the exhaust timing,I will if I have to
but it would be easyer if i had a starting point .8000+ rpm's is pretty darn good i wouldnt mind matching that

This is the way you measure the timing duration: with a protractor circle scale made out of poster paper or cardboard place it loose on the prop hub, now place a paper clip on topof the cilinder an make a bend as to indicate on the scale the location of the degrees next while looking at the exhaust port, turn your crankshaft counter clockwise until the top of the piston is level with the top of the eaxhaust port, this will be your ZERO degrees point on your protractor, now keep turning the crankshaft counterclockwise until the piston goes down and then it starts going up again until it reaches the upper edge of the exhaust port this would be your total exhaust duration (the time that the exhaust port remains open, the longer it remains open the
more the exhaust gets out the cylinder

The original carb on all the Ryobi's I've been around were a "20". A 24 will make them run a lot better but a 28 is max.

I put a stock carb on it today. I can't see a size number on it, but it's 13mm at the throttle butterfly. Engine runs good, but still not enough power.

17-8 Zinger--6100RPM

I'm going to just run it and try to put some more fuel through it. Still haven't even put a gallon through it yet. I should have cut weeds with this thing for a season before I slapped it in a plane.

Rcpilet, sent you a PM and some information. If you can only use this carb try a 16/8 or 16/6 prop. Your RPM will go to near 7000 I bet. However I think the carb is too big. Also think about the muffler too. The engine is just a little compressor and can only do so much. You can put all kinds of air and fuel to it but if it can't breath and or use all the air and fuel it won't go anywhere. Same thing with over proping. Basically the less load the faster it turns and the more power you will get. All you need to do is find that balance.

Tim

It's got a wackerengines aluminum muffler on it. More of an exhaust diverter. Pretty free-flowing and loud.

I had a 16-10 APC on it and got the same RPM.

I'm going to just fly it for a couple gallons and hope it breaks in. Kinda late to reassemble the weed eater and trim the lawn with it for a season. I threw the rest of the weed eater in the trash.

aerro nut
I get how to measure my exhaust duration, the timing is my question how many degrees from t.d.c. is your exhaust opening? this is the $64 question ,
I dont know how much I can change the timing and still be o.k. there is a little at the bottom of the port that could be removed .the piston at bdc is lower than the botom of the exhaust port this should give me increased duratioin without changing my timing, and improve the flow of the exhaust out of the port. but it all comes down to the exhaust timing

rc pilot
any progress? after opening my exhaust port up to 137 degrees with my dremel , and dropping the bottom of the exhaust port just below the piston top, smothing, and polishing the port I am happy to report 250-300 rpm gain!
on the stock carb.thats not to bad for a little elbow grease Im now at 7650 rpm's(I lost about 200 due to a replacement carb not as good as original) I may do a little more and see what happens
some new advice,LISTEN TO AERO NUT, he may just be correct about the exhaust port on your engine. I took off 1\2 mm, maybee and picked up at least 200 rpm.
140degrees duration, thats the ticket. at least measure your duration so you know what it is.aero nut tells how back a few replys its easyand its cheap!

aero nut thanks and now I understand about the timing thing on the exhaust any idea how far you can take this? 150degrees maybe ,If I remember correctly 160 degrees is tuned pipe time right?

No news yet. Terrible weather and a 2yr old thats been sick for 2 days--throwing up and he's got gravy in his diaper. [:'(] That's kept me pretty busy. I'm sorta disabled. Serious back problems. Multiple surgeries last year, and still not fixed. My wife works, and I'm mister mom.

It's Friday night, and as soon as she gets home, I'm going downstairs and start checking the timing with my degree wheel. I'll put the numbers up here pretty soon.

If I need to grind--whats the best bit to use on my dremel?

Rcpilot, Did you get the information I sent to you? Let me know what you think.

Tim

rc pilot
I just used a carbide cutter small enough to get inside like 1\4 inch diameter. its aluminum so it cuts easy be careful its real easy to go to far. I dont want to be responsible for you destroying your engine so let me explaine somethings to you to ease my concience.
you need to check the piston skirt at the exhaust port to make sure you have enough to work with BEFORE you do any grinding.
heres how I do it ,remove the back plate and muffler.bring piston up to t.d.c. draw a line on the piston skirt at the bottom of the port ,now bring the piston down so you can see the line you drew on the piston skirt ,this material below the line is what seals the exhaust port from the crank case,when you take material from the exhaust port floor you are moving this line down on the skirt ,please make sure you have enough to spare so you dont ruin your engine by grinding the port so low that the skirt uncovers the crankcase..the book i perchased says you need at min. 2 mm overlap for an efective seal .anyway,just take the least bit you can from the port so you dont have problems.
If you are going to grind on your port a word of caution ,GO SLOW,small steps ,be careful.I found its pretty easy to want to do "a little extra " when grinding because reasembling and checking it out is such a pain in the posterior.but resist the temptation dont forget to leave some material to smooth and polish.
while you have your degree wheel on the engine note how much you need to remove to obtain the durationyou want
how much metal do i have to remove before you pull the jug so you are not guessing when it is time to grind . the way I did it is to figure your duration as it is , lets say its 125 degrees we want 140 degrees that is a difference of 15 degrees I move the piston to the bottom of the port,even with the floor or use a feeler gage to find the piston top , rotate it up 15degrees then measure how much the piston is above the port floor with a feeler gage. I grind about 1\2-3\4 of this depends on how soft it is and how much is to be removed ,the rest I save fore smoothing and polishing operations and finaly dont forget to chamfer the port inside the cylinder lightly so you dont catch a ring on it.Ihave found that the emery cloth will get most of it for you as you smooth the port for polishing but dont forget to check just to be sure so you dont hook a ring on the port edge and seize the engine
So like I said, go slow, remember a little bit under is better than a little bit to much ,when it comes to grinding
GOOD LUCK. let us know how it works out for you.

Tim:
I got the chart. Can't open it yet. I don't have Excel. I'll have to download a trial version from Microsoft.

FlyJoe540:
I appreciate that info. I knew that there was a risk of opening the exhaust up too much and uncovering the bottom of the piston skirt when its at TDC. I agree that it would ruin the engine. Opening the bottom side of the case to exhaust gasses is going to completely ruin intake suction.
But, I have a question:
Why are you taking material off the bottom of the exhaust port? I always thought that you were supposed to only take material off the top.??

I got 128* exhaust duration when I checked it last night. [] I guess I'll open it up a bit. My local friend has a lathe. I might take it to him and have the cylinder knocked down a little to increase the compression ratio.

Whats the minumum squish band? .15? .20?

If I knock the jug down a bit, then it seams logical to me that I'd want to take a bit off the top of the exhaust port to at least get it back to 128* duration.

rcpilot
the piston in all 3 of my ryobi's goes past the bottom of the port durring the piston stroke .the theory is that the exhaust gas hit this edge of the port and creates an eddy of exhaust gas which disturbs the flow out of the engine and partially blocks the port to flow.
I dont think turning the jug shorter will help because of the transfer port timing if you shorten the jug then you move the ports lower delaying transfer port opening and shortening there duration they are open, you will get higher compresion but less fuel\air mix in the cylinder,also these ports aid in exhaust gas scavenging so delaying their opening also efects the way the exhaust is removed from the cylinder so it may in fact have the reverse effect
I have just finished my second cutting sesion on my exhaust port now it has 147degrees of duration will run it today and post the results later.
I think aero nut hit it on the head with the duration of the exhaust port I didnt gain as much top end as I would have prefered with my first cutting sesion but the engine is way more powerful and responsive to throttle input than it was ,we'll see in a little while

rc pilet
o.k. add another 50 rpm's almost 7700 on an 18x6 zinger , thats where I'm going to leave it for now .I'm pretty sure it will come up more as it breaks in and I tweak the carb some more.also have to try those 13.5mm carbs I got from poco 242 he had a suggestion on how to fix them so we'll see about that later .good luck .

anyone got a suggested idle speed for a ryobi

The piston SKIRT is at the bottom..Somebody tell me what the bottom of the piston has to do with the exhaust timing.....
The TOP of the exhaust port is what controls the exhaust timing...
A reed valve engine will take only as much fuel as the reed assembly will pass, no more, it can suck only so much fuel..This is controlled by the size of the transfer ports and the reed valve ....A great big carb on a little reed valve engine doesn't work as well because the air flow through the carb isn't enough to draw fuel through the holes in the venturi...You want more fuel through the engine, make the reed so it flows better..[8D]

Because if you drop the exhaust port too much, then the piston skirt will open the bottom of the exhaust port and expose it to the crankcase when the piston is at TDC. I know that you know this, but our discussion might not have been clear enough.

But, your right, it doesn't effect timing. It'll just screw up the engine.