I feel like I have been down this path before. I have ryobi conversing (previously a 725 weed whacker) with a zama carb that I had mounted on a test stand and found it hard to start. The culprit turned out to not enough RPM at start up. Once I was getting enough revs-the engine started easily.

Since then I have mounted it on my big pink and have no luck starting it. Not even a pop. I can see a spark when I hold the plug outside of the engine and ground it, and I can get fuel to flow and I have primed it by squirting sam gas into the cylinder or by sucking some gas through the primer bulb valve. I'm just sort of surprised that I get no ignition at all.


I only have two guesses of what might be happening- the gas is not recent (although it does start up in my weed whacker) and it is cold outside (about 40 degrees).

Anyone have any clues?
Thanks,
Steve

Put Electronic Ignition on it then you can hand start it. RC Ignitions has them for around $75 dollars and a good warrenty.


smallplanes

So you think that my problem is that I am not getting a real spark which would be solved by going electric?

I wonder if my engine was just really flooded.

SB

Are you using the same system and getting the same rpm?
Try some fresh fuel, fresh plug. Remove the plug and clear the cylinder by spinning prop, put the plug back in loosely and try to start with reduced compression. If it goes let it warm up, shut down and tighten the plug and see if it will start. Worked for me. but a royal pain... Elec ign made life much easier.

sboxer;

Your info is a little short. Are you hand starting it? or using a starter?. Some of the modern coils are very reluctant to produce a spark at lower rpm's. A combination of being mounted on the plane, being lower than bench height or just too cold to give it a good flip may be all that is wrong??????????????. If you are not doing so, try a starter first to get those extra rpm's.

Peter

I am using a sears 19.2 cordless drill will a miller big cup on the end. It seems to twist that prop faster than my little starter.

SB

A drill should do it. I have done so in past and had no problems. So you now can look elsewhere. The ignition on these small motor's is quite simple. Coil, magnet, spark plug or ignition lead (wire). This is just a total shot in the dark......... could you have a broken spark plug wire inside the jacket and the cold or reposistioning of the wire is giving intermitant contact? When you got this spark, was it when you were outside, or on the bench?. Sometimes the cold will contract metal pulling a break in the lead apart.

If you have spark and you have fuel, the only other thing I can think of would be, is there a chance that your flywheel has no key and when installing it on your plane you reposistioned the flywheel and changed the timing?

Just a couple of guesses. Peter

I think the key issue is very possible. Between the time I had the engine on the test stand and then mounted on my model, I sent the flywheel out for balancing. I believe that I slipped the flywheel back over the notch on the shaft and I certainly see the piston going up and down. What else should I look for?
Thanks for giving me something to work with.
SB

Another issue I haven't seen addressed here is the magneto gap.
Have you checked it?
Should be a business card's thickness or ~0.01 inches

Btw, my cheap tower starter ($20) starts my Ryobi fine

Pete Johnson

Yup-I checked and doubled checked the gap with a business card early on in the process.
SB

Take the spark plug out. It will then spin over real fast with electric starter or drill. Just let the sparkplug set on top of cyl head and watch for spark. A blue spark is better than a faint orange one. Good luck... Capt,n

I did that-I get a blue spark.

SB

You might have the carb to lean richin the high end and the low end and try that. If your getting that good of a spark it should crank unless your not getting enuff fuel. I ran my weedy motor today on my plane and it has EI on it and it would not hardly crank,so i riched the carb and it cranked up. I then had to richin it up about a half a turn to get it to turn up some rpm's. I then tryed to fly it when it all went wrong. I forgot i was on the wrong model in my futaba 9c radio when i pulled up it was fine but when i went to make a fast turn she rolled over and hit the ground. It did not hurt the fuse but it did break the sheating on the top of the wing but i can fix that so i guess it was not to bad. It was my own dumbness. You win some you lose some.

Thanks
smallplanes

I wonder if timing is messed up. I just checked the engine and this is what I found:

1) the flywheel is sitting nicely in the notch on the shaft
2) With the spark plug out, I can see that when the piston is at the top of cylinder, the flywheel's magnets are sitting right on top of the magneto (points?)

Does that sound correct to the ryobi masters here???
Thanks,
SB

The first ryobi I converted gave me the same problems you're having. Worked on the test stand, but not in the plane. I found I had to raise the tail of the plane till the fuse was level. Full choke, full throttle, ign. off and turn over engine with elec. starter for about 3 seconds. Drop the tail, throttle at 2 clicks above idle, ign on, fires right up with starter. That is pretty much my starting proceedure for my gas bandito now.
Edwin

Edwin made an excellent comment re the aspect of the plane, good staring routine!

Good tip and thanks.
Does anyone have any imput on my timing?
SB

Oops, forgot about that. If this is a stock ryobi conversion, its pretty hard to get the timing wrong since its fixed. I initially had a .050" gap and an intermittant spark. Using the business card got me a good spark. Unless the shear key is broke, timing should be ok. Since it runs on the bench, I wouldnt work it from a timing issue. Is it inverted? Is the plug getting wet when you prime?

Edwin

I must be wrong- but is it possible that the shaft rotated when I replaced my flywheel?
I rememver that when I replaced the flywheel I had the engine opened up to look at the guts.

SB

You timing should be fine as Edwin mentioned.

I have Ryobis some with A) a physical metal key (about 1/16" wide) which fits the slots in the shaft and flywheel; some of the others B) have a cast key protrusion in the flywheel taper which fits into the slot in the shaft (about+-1/8" wide) Unless the was not installed in A or B) cast key has been sheared off, it is almost impossible to put the flywheel on out of time.

Is your engine mounted in the plane with the head(and plug) on the bottom (inverted) or top?

????? Is it possible that you have the fuel lines connected correctly? That primer bulb is designed to be on the downstream side of the fuel flow through the engine.

If you 1) set full throttle, 2) choke the air intake with your thumb, 3) rotate the prop 10 or so times you should have a wet thumb. If not you have a fuel supply /air leak problem in the fuel delivery system.

Try some starting fluid ( ether ). Works for me. Get it at the local auto parts store, or Wal Mart.

John

Forgot about the primer bulb. I didnt use it. Caused too many problems on the test bench. I just the tube on the carb with some fuel line and a fuel dot. I know others that can make those work, but I just couldnt do it so I gave up.
Edwin

Thanks!
I will give up on the timing issue. The more I thought about it-the clearer I was wrong.

The engine is upside down (as it was on the test stand). I used the primer bulb to suck some gas into the carb and my guess is that I flooded it from the get go.


Also-my gas was a month or more old and 91 octane with a 1/32 mix of 2 stroke oil. Maybe that is too rich?

I am assuming that flooding it and the poor gas and the cold weather resulted in my problems.

I did take the plug off and rev up the prop to clear the flood, but I guess that did not help.

Toward the end-i did see some gas drip from the muffler. I thought these little engines like to start wet!

If I do use some ether to jump start it in cold weather-i assume that I just squirt a small amount in the spark plug hole and make sure no one is smoking?

Thanks again!
sb

Oil! I have to run mine at 28:1. I use klotz, for no other reason than just cause the hobby shop had it. I started at 50:1 and had overheating problems in the cowl. At 32:1 it would run ok but would have occasional problems. Ran good without the cowl but I didnt like that. 28:1 solved it and has run great for 2 seasons now. My ryobi is a 12 year old wore out retired weedeater motor. But still runs great, 6700rpm with TF 18x8.
Edwin

wet yes, drowned no!
The primer bulb should not flood the engine. Its function is to fill the carb passageways not to put fuel into the engine. The choking (creating a vacuum on the intake is what allows fuel to pass the internal needle (check valve)
RCIGN explains carb functions to where I understand you may want to spend some time searching. A starter:
http://www.rcuniverse.com/forum/puls...339703/tm.htm#

Check your plumbing on the primer bulb. Shorter, side port on the primer bulb goes from the top of the carb to the primer. When you press the primer, the fuel should go from the tank clunk fitting) to the bottom of the carb, then from the top of the carb to the primer (short port) and then from the primer long port to the return to the gas tank. Any leaks in the lines will prevent it from working.

You need to get a wet thumb or plug the spark plug.