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Ryobi trimmer 725R 31CC 17" won't stay running


kfcm78660's Avatar
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06-03-06, 11:03 PM   #1  
Ryobi trimmer 725R 31CC 17" won't stay running

This trimmer will start fine in choke or half-choke and will stay running only in half-choke. It will not start in RUN or if I start it in half-choke and switch to RUN, the engine will die. I took apart the carb and blew air in all the holes, put it back together, but the problem persists.

Any help trouble-shooting this problem is greatly appreciated.

Thanks in advance.

 
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06-04-06, 01:49 AM   #2  
Remove the carb take it apart and Soak it over night in carb cleaner remove the rubber parts before giving the carb a bath. If that don't help then you need to rebuild.

 
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06-06-06, 01:56 AM   #3  
Check all fuel lines from the tank to the carb for cracks or pinholes. If they are fine, you may need to do more extensive carb cleaning/rebuild.


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06-06-06, 09:17 PM   #4  
I got the carb cleaner from an autopart store, but the instrutions say to soak for 20min, instead of overnight as you suggested. I'll soak it overnight then.

Fuel line from primer bulb to carb seems loose (the end connected to bulb) and I can see air bubbles in this fuel line as I press on the bulb. Could this be a problem?

Thanks for your suggestions.

 
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06-06-06, 09:47 PM   #5  
Some air bubbles may be normal.... if you have hard and stiff fuel lines, and cracks..... well then replace the lines and filter while your there.

DID you get a carb rebuild kit for the carb? I'd get one, just soaking the carb and using the old parts is like waxing the car without washing it.
I'd blow the carb out (through any and all holes you see) with compressed air after the soaking.

 
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06-06-06, 10:03 PM   #6  
Could you tell me where the filter is? Thanks.

 
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06-06-06, 11:17 PM   #7  
In the tank, on the end of the fuel supply line.


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06-07-06, 11:04 PM   #8  
I just ordered a rebuild kit for the trimmer so I'm waiting for it in the mail.

Meanwhile, I'm trying to figure out why it will run in half-choke and not in run (no choke). It tells me that the carb gets gas from the tank ok, so the fuel line should be ok. For some reason, it likes high gas to air ratio, and not vice versa. Someone who understands how this carb works can probably explain this behavior. Please explain if you can, because I'm just as interested in knowing how it works as much as getting my trimmer fixed.

Thanks in advance!

 
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06-07-06, 11:28 PM   #9  
It's not that it likes a high fuel/air ratio. It likes a normal fuel/air ratio. The problem is that the carb is not delivering enough fuel to create the ratio needed to match the amount of air it is delivering. When you close the choke, it decreases the amount of air taken in, so the fuel delivered has less air to mix with...thus, a closer to normal fuel/air ratio. Cracked fuel lines, primer bulb, restricted filter, restricted carb, or faulty carb parts can cause this.


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06-10-06, 09:10 PM   #10  
I cleaned and rebuilt the carb. There seems to be some improvement. I can run it in full throttle now, but I have to squeeze hard on the trigger, otherwise, it will die. I'm thinking about taking it apart and clean the carb again. What do you think?

 
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06-10-06, 10:56 PM   #11  
trimmer

i had a trimmer do that once,after awhile,i knowticed that the little clear fuel line tube,had weakened and closed up..collasped..cutting the fuel off to the carb.i guess that oil and gas blend,ate it up,from the inside out..

 
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06-11-06, 07:06 PM   #12  
The fuel lines are all in good shape, no cracks that I can see. I blew compressed air into all the holes in the carb, but it didn't help. I noticed 3 tiny holes in the carb near the throttle plate and I bet those are clogged up but I'm not sure how to clean them.

 
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06-12-06, 11:02 PM   #13  
Disassemble the carb and soak it in a bath type carb cleaner while following the directions on the can. This will usually get the crud out of the small passages.


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06-17-06, 08:05 AM   #14  
DCLittlejohn
In regards to this carb, what about the red and white plastic adjustment screws? My 725r has this exact same problem, and I have already cleaned everything. I am able to get it running by making some adjustments on the red and white, but I really don't know where they are supposed to be set, or the procedure for doing so.

I have been searching several websites, and this information never seems to get addressed. Also, the Ryobi website doesn't even list the 705r or 725r on their manuals search pages. I have the printed manual that came with the unit, but it just says to take it to a service center to have the carb adjusted.

 
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06-17-06, 12:23 PM   #15  
The screws are set at the factory and if all else is in proper working order, tthey shouldn't need adjusting. Granted, that's a big "IF". Things like air leaks, worn parts and even normal wear in the engine can cause the need for minor adjustment. I usually set the screws 1 1/2 turn from lightly seated, start it, and adjust from there. I like to set the high speed screw first. Run the engine at full throttle and turn the high speed (red) screw in until the engine races like a banshee, then back it out until the engine just begins to flutter. Then set the low speed screw with engine idling until you get a rather choppy but consistent idle with good throttle response. If you get good idle, but throttle response is lacking, back out the high speed screw just a tad.


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06-19-06, 11:32 PM   #16  
Some times when a 2 cycle has to be choked to keep running, it could mean that it`s getting the proper air-fuel mixture through the carb, but an air leak has occurred either at the intake gasket or the insulator gasket (the black fiber block behind the carb,) causing a lean mixture. So by closing the choke full or half way your pulling in more gas creating the proper air-fuel mixture ratio that the engine was made to run on.
Check for gasket leaks, check behind the insulator, but be careful because the insulator gaskets on those particular Homelite w/e (st & stx)tear very easily when separated. Also, on the front of the insulator you`ll see a curved channel, at the end of that is a hole. That is an impulse hole. that hole must be clear in order for the crank case vacuum to pump the the carburetor.
The engine, the Carburetor and the gas tank are all pressurized.


Last edited by mikesmalleng; 06-22-06 at 09:55 PM.
 
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05-24-07, 09:29 PM   #17  
near-miss fix for this kind of carb problem

My RB-30 trimmer would run up to high RPM with no problem-- as long as it was in 'full choke'-- but even a slight opening of the choke killed it.

Fixated from the outset on the idea of plugged jets, it nevertheless took about six carb disassemblies/reassemblies to get anywhere good. Compressed air alone did nothing, nor with brakleen (nasty solvent spray). The running jets (just silly little holes in the aluminum casting in the bore of the carb, three of them, which are progressively uncovered as the throttle plate opens) apparently widen out to a hidden/plugged drilling beneath them, but there ain't NO way for a casual repairman to get in there to clean it out properly without destroying the carb. I finally figured out (via brute force) that the big nylon idiot-proofing guards (meant to limit screw adjustment) on the mixture screws could be removed, allowing the screws themselves to be backed off and extracted, this allowing SLIGHTLY better access to that gunky gallery. I used some fine wire spray-gun tip cleaners to poke around (errr...the third such attempt) and was, this time, rewarded with a bubbling of brakleen from the idle jets when I sprayed it into the hole where the idle adjuster screw had been...that was my thrill for the afternoon. I suspect the closed-off passages were plugged by aluminum oxide that resulted from condensation in the fuel...probably some still in there, too. Yuck.

I was rewarded for those long hours by a trimmer that ran, at least, this time without having to be in choke, but the idle adjustment seemed VERY flaky. To keep it going, a too-high idle was necessary, but any time I tried to adjust down to a lower idle, it would die. This would leave me to wonder whether it was too little throttle causing this, or too much/little idle mixture. And maybe there's still some crap in the tiny jet openings...who knows?

The capper to this maybe-near-fix was noticing that the plastic pull-handle had a crack in it. On very the next pull, it fell in two in my hand, and the pull-cord snapped home, leaving the knot just barely clinging to the hole in the case for the pull-cord. I watched in disgust, as before I could stop the machine and grab the knot, it disappeared into the hole and spun to a stop, after releasing all the spring tension. Getting to the pull-cord on these is an absurdly-difficult exercise, requiring nearly complete disassembly of engine shroud, separation of motor from stem, and even removal of the clutch. And THAT will only get me back to the point where I can resume wondering if the carb is really operable at idle.

I think I might instead take it for a scrape on the freeway...more satisfying. This might teach me to try to rescue any more Ryobis from my neighbors' trash.

 
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05-25-07, 02:01 AM   #18  
Thanks for the story, I'm sure someone will find it useful. But, this thread is nearly a year old.

 
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01-21-09, 02:08 AM   #19  
this is a really good thread, some great info-

 
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