Ryobi RY253SS 2-cycle trimmer dies after about 10 seconds

[ttimtucker]

Trying to repair a Ryobi RY253SS 2-cycle trimmer. Starts up fine, runs for ~10 seconds and dies. It dies regardless of whether full/no-choke, full/no-throttle. Restarts right away, but exhibits same behavior (which leads me to think not an electrical issue). Here is what I've done:

• New 50:1 fuel in tank
• Dry compression: 80 psi
• Wet compression after dripping some oil into cylinder: 120 psi (so some leakage around rings? would this explain symptoms?)
• Cleaned passages in carb, gaskets/diaphragms seem in reasonable shape
• Intake and exhaust gaskets look fine
• Applied 10 psi pressure to carburetor fuel intake pipe and it holds steady
• Applied vacuum to fuel inlet tube going to tank, and it sucks up fuel, so no obvious obstructions in tube or fuel-filter
• Cleaned some carbon buildup from exhaust port
• Pressure tested crankcase: holds steady at 10 psi
• Vacuum tested crankcase: holds steady at 15 in Hg, returns to 15 when I rotate engine

Only adjustment on carb is throttle idle screw. Might be possible to adjust the needle on the barrel-valve of the carb, but looks like a special tool may be needed.

Would appreciate any ideas of what to try next.

 

[Auto Doc's]

Use a spark tester to make sure it is not the coil failing or the off switch. To confirm which it is remove the cover and pull the coil kill wire off temporarily and retry.

 

[ttimtucker]

Have not tried spark tester yet, but did disconnect the kill wire and no change to symptoms.

 

[Auto Doc's]

The next suspect would be the fuel filter located on the end of the fuel supply line down inside the tank, or possibly the supply line has a crack or pinhole in it. These flexible fuel lines don't last but so long. This unit has been around for quite some time.

 

[Scrubcadet10]

Have not tried spark tester yet, but did disconnect the kill wire and no change to symptoms.

When you get a spark tester, get the Briggs and Stratton or Oregon tester that has a gap for the spark to jump.

 

[ttimtucker]

Tried with 2 different spark testers. One was the light-up type, one was a gap-type (although not B&S or Oregon). Both showed spark until the engine died. in other words I could not see any diminished spark prior to the engine dying. I will try replacing the fuel supply line and fuel filter tomorrow (although I did run an earlier test to with my vacuum pump to show that I could pull fuel up through the filter/line by applying a mild vacuum). One other test I ran was to pump the primer bulb as the engine began to sputter in the hope that if engine were fuel starved that this would keep it running, but that was not the case.

 

[Auto Doc's]

Tried with 2 different spark testers. One was the light-up type, one was a gap-type (although not B&S or Oregon). Both showed spark until the engine died. in other words I could not see any diminished spark prior to the engine dying. I will try replacing the fuel supply line and fuel filter tomorrow (although I did run an earlier test to with my vacuum pump to show that I could pull fuel up through the filter/line by applying a mild vacuum). One other test I ran was to pump the primer bulb as the engine began to sputter in the hope that if engine were fuel starved that this would keep it running, but that was not the case.

Another thought came to mind... loosen the muffler slightly and see it will try to keep running. Why?

Last year, I had a Stihl FS45 that a guy was going to throw away after the Stihl tech said it needed a motor. I told him to let me give it a try and he agreed.

To cut to the chase, I removed the muffler and heated it up red hot with an acetylene torch. once good and hot it burned all the carbon for a solid 2-3 minutes. After it cooled, I shook out the carbon flakes and bolted it back on the motor and fired it up like a new unit.

The theory is simple: On a two stroke, especially, if air cannot get out of the exhaust, fresh air cannot be drawn into the intake for the engine to run.

This also might explain why the compression seems a little low.

This problem is often created by customer self-mixing their fuel and using a little too much oil (for extra protection). The wrong can ready premix can also cause the same problem.

 

[Tiger Small Engine]

Trying to repair a Ryobi RY253SS 2-cycle trimmer. Starts up fine, runs for ~10 seconds and dies. It dies regardless of whether full/no-choke, full/no-throttle. Restarts right away, but exhibits same behavior (which leads me to think not an electrical issue). Here is what I've done:

• New 50:1 fuel in tank
• Dry compression: 80 psi
• Wet compression after dripping some oil into cylinder: 120 psi (so some leakage around rings? would this explain symptoms?)
• Cleaned passages in carb, gaskets/diaphragms seem in reasonable shape
• Intake and exhaust gaskets look fine
• Applied 10 psi pressure to carburetor fuel intake pipe and it holds steady
• Applied vacuum to fuel inlet tube going to tank, and it sucks up fuel, so no obvious obstructions in tube or fuel-filter
• Cleaned some carbon buildup from exhaust port
• Pressure tested crankcase: holds steady at 10 psi
• Vacuum tested crankcase: holds steady at 15 in Hg, returns to 15 when I rotate engine

Only adjustment on carb is throttle idle screw. Might be possible to adjust the needle on the barrel-valve of the carb, but looks like a special tool may be needed.

Would appreciate any ideas of what to try next.

Compression is low for a 2-stroke if you are using a proper compression tester for small engines (Schraeder valve). You have spent a lot of time on this Ryobi turd trimmer. If you can’t get it running, move on to real equipment.

 

[ttimtucker]

Tried with 2 different spark testers. One was the light-up type, one was a gap-type (although not B&S or Oregon). Both showed spark until the engine died. in other words I could not see any diminished spark prior to the engine dying. I will try replacing the fuel supply line and fuel filter tomorrow (although I did run an earlier test to with my vacuum pump to show that I could pull fuel up through the filter/line by applying a mild vacuum). One other test I ran was to pump the primer bulb when the engine began to sputter in the hope that if it were fuel starved that this would keep it running, but that was not the case.

Compression is low for a 2-stroke if you are using a proper compression tester for small engines (Schraeder valve). You have spent a lot of time on this Ryobi turd trimmer. If you can’t get it running, move on to real equipment.

I agree. This is now mainly turning into a learning exercise as I try to figure out what's wrong.

 

[Tiger Small Engine]

Tried with 2 different spark testers. One was the light-up type, one was a gap-type (although not B&S or Oregon). Both showed spark until the engine died. in other words I could not see any diminished spark prior to the engine dying. I will try replacing the fuel supply line and fuel filter tomorrow (although I did run an earlier test to with my vacuum pump to show that I could pull fuel up through the filter/line by applying a mild vacuum). One other test I ran was to pump the primer bulb when the engine began to sputter in the hope that if it were fuel starved that this would keep it running, but that was not the case.

I agree. This is now mainly turning into a learning exercise as I try to figure out what's wrong.

You need to be able to adjust the carburetor. If it will start and idle for about 10 seconds, it could be as simple as a carburetor adjustment. Increase idle screw temporarily and try to adjust high and low screws. Sometimes you can take an electrical crimp connector with hard plastic cover and heat it up and hold it on the screw until it cools to form the threads.