2 Stroke Lesson

[Grassbandit]

Working on a Ryobi 725R, had alot of issues and after addressing them all I'm stuck on the carburetor adjustment screws.
Can anyone give me any pointers on how I should go about getting the correct settings so that the engine starts?
Right now I'm hearing it pop but it just wont get up and run.
The muffler isn't presently installed.

 

[ILENGINE]

Depending on type of carb installed the setting could vary from 1 turn out to 2 1/2 turns out. Before continuing I would check compression and make sure you have 90 or more. Below 90 and it is a boat anchor.

 

[Grassbandit]

Depending on type of carb installed the setting could vary from 1 turn out to 2 1/2 turns out. Before continuing I would check compression and make sure you have 90 or more. Below 90 and it is a boat anchor.

thanks for the suggestion, I dont have a compression tester so I cant give exact numbers but I can tell its got enough.
I'm about to use it as an anchor so it better start before my arm gives out!

 

[Rokon]

Two strokes are similar to four strokes, in that you need: compression, fuel and spark. For two strokes other factors come in to play. Such as timing (do you have a sheared flywheel key) or an air leak somewhere in the engine.

Since you said you got a pop, I believe your problem may be timing related. Adjusting the high and low needles will have minimal effect until you get it to actually start.

You could even have a compression problem. Get the unit compression tested and go from there. In my experience with two strokes, a reading under 120 psi means too little compression to run.

 

[Grassbandit]

Two strokes are similar to four strokes, in that you need: compression, fuel and spark. For two strokes other factors come in to play. Such as timing (do you have a sheared flywheel key) or an air leak somewhere in the engine.

Since you said you got a pop, I believe your problem may be timing related. Adjusting the high and low needles will have minimal effect until you get it to actually start.

You could even have a compression problem. Get the unit compression tested and go from there. In my experience with two strokes, a reading under 120 psi means too little compression to run.

Thanks for the suggestion, I haven't checked the flywheel for timing. Messing with that trimmer is on my list of things to do today so I'll let you know what happens.

 

[motoman]

We have some good 2 stroke guys . No one has mentioned crankcase pressure which is required for pushing charge into combustion chamber. Pros have pressure gauges to check this . A pressure gauge is not that expensive if you go bare bones.

 

[possum]

Im not a good two stroke guy but here is a few. Pick it up by the starter recoil handle. If it holds then it more than likely has enough compression to start. If the rope all pulls out and the unit is still sitting on the floor then its got some real compression problems. If the compression seems all right then check for spark. If the plug is wet dry it off and clean the fuel out of the cylinder. If its dry put a few drops of gas on it and try to start it. If still no go look for air leaks in the case, carb, fuel lines bulb. Check your muffler for blockage and look the cylinder over from the exhaust. Some times you just have to take your carb off again and start over or get a new carb.

 

[Grassbandit]

Two strokes are similar to four strokes, in that you need: compression, fuel and spark. For two strokes other factors come in to play. Such as timing (do you have a sheared flywheel key) or an air leak somewhere in the engine.

Since you said you got a pop, I believe your problem may be timing related. Adjusting the high and low needles will have minimal effect until you get it to actually start.

You could even have a compression problem. Get the unit compression tested and go from there. In my experience with two strokes, a reading under 120 psi means too little compression to run.

It seems someone else worked on this trimmer before me and in the process they damaged the flywheel. Error on my part was assuming it was alright....anyhow the key slot on this flywheel was non-existent so whoever tried to fix it used a half moon key and forced the flywheel on. Which worked for a short time but as you can see in the picture eventually the space wore down.
Replacing the flywheel is the way to go, but since parts are virtually non existent I think I'll try making a new slot and using a key.

 

[Grassbandit]

Im not a good two stroke guy but here is a few. Pick it up by the starter recoil handle. If it holds then it more than likely has enough compression to start. If the rope all pulls out and the unit is still sitting on the floor then its got some real compression problems. If the compression seems all right then check for spark. If the plug is wet dry it off and clean the fuel out of the cylinder. If its dry put a few drops of gas on it and try to start it. If still no go look for air leaks in the case, carb, fuel lines bulb. Check your muffler for blockage and look the cylinder over from the exhaust. Some times you just have to take your carb off again and start over or get a new carb.

Thanks for the tip! I'll be adding it to my bag of tricks.

 

[Rokon]

View attachment 24748

It seems someone else worked on this trimmer before me and in the process they damaged the flywheel. Error on my part was assuming it was alright....anyhow the key slot on this flywheel was non-existent so whoever tried to fix it used a half moon key and forced the flywheel on. Which worked for a short time but as you can see in the picture eventually the space wore down.
Replacing the flywheel is the way to go, but since parts are virtually non existent I think I'll try making a new slot and using a key.View attachment 24749

You cannot make a new slot anywhere in the flywheel, if that's what your above statement means. Timing is critical for 2-strokes to run properly. Even slightly moving the flywheel from it's original mating spot on the crankshaft will advance or retard timing.

If this flywheel slot is truly gone, a replacement flywheel is the only solution.