Ryobi Lawn Scorpion runs for only a few seconds

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  #1  
Old 07-13-13, 02:26 AM
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Ryobi Lawn Scorpion runs for only a few seconds

I have a very frustrating problem, and look for advice.

The unit has been ultra reliable and ran perfectly. Noticed that any fuel left in tank would leak out between uses. Machine is over 10 years old. Fuel leaked out through carby. (Walbro). Unit still started and ran perfectly.

Purchased and fitted a carby kit. Needle valve not leaking. Replaced all fuel lines with proper replacement - confirmed no air or fuel leaks. Replaced in-tank fuel filter. Have confirmed all passages in carby are free and clean. Confirmed that the needle valve is working and seals properly. Cleaned the mesh filter in the carby. Confirmed (old fashioned way - blow/suck that the flapper valves are working. Even replaced the spark plug!

I can prime the unit with the bulb, and the unit starts on the 2nd or 3rd pull - every time, but only runs for a few seconds - unless I give the primer bulb a little push every so often.

All parts fitted are genuine replacement parts purchased from the dealer.

Needle valve lever height set set using proper tool.

Tried starting unit with fuel cap off in case vent blocked - no joy!

I can nor think of what I can do, and really look for some advice. The unit was fantastic right out to when I 'serviced' it, with loads of torque.

Last thing tried was to put the old parts back in carby - but no change.

Appreciate any help.
 
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  #2  
Old 07-13-13, 05:32 AM
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It is something in the fuel circuit. Probably the carburetor and sounds like a passage in the carb is still blocked since it will run off the primer. If it was a piece of dirt (rock) or metal that clogged the passage/orifice than soaking and solvents can not dissolve it like varnish and must be mechanically removed. I would remove the carburetor and go through it again.
 
  #3  
Old 07-13-13, 05:40 AM
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Just checking to make sure of what you have. I was thinking that was a string trimmer - guess it is.

'The problem would likely be in either the pump diaphragm, the lines going to the carb, or in the pulse port coming from the crankcase. There could be some type of blockage, but a line leaking fuel would be the source of air leaking into the system.
 
  #4  
Old 07-13-13, 06:34 AM
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Ryobi String Trimmer

Thanks Marbobj - appreciate the quick response.
Yes - my apology, it is a string trimmer. The pump diaphragm and lines are new. I even tried the old diaphragm, which was working until I replaced it, but still no joy. I have visually inspected the ports, and blown through them, so reasonably confident they are not the problem.

I have visually checked the pulse port at the crankcase, but not sure how to test if it is working or not. Any suggestions?
Cheers
 
  #5  
Old 07-13-13, 06:40 AM
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Ryobi line trimmer

Hi Pilot Dane. Have done as you suggested - but still no Joy. Agree with your thinking, but don't know where to turn next. Cheers
 
  #6  
Old 07-13-13, 06:44 AM
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If it's clear it would be working. You can just pull the cord and you should feel a pulse of air come out of the crankcase port. It's driven by the piston coming down.
 
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Old 07-13-13, 12:49 PM
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I'm just thinking that ports clear and good diaphragms are easy to check or test but the passages, jets and orifices in the carb are really tiny and can be a bugger to get clean or even test to know you've gotten them clean. I've tried spraying carb cleaner in them and so much more comes out of the can that most sprays in my face making it difficult to tell if the carb is clear or not.
 
  #8  
Old 07-14-13, 09:48 PM
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Hi marbobj. Felt the pulse - went one step further and removed the assembly. Unfortunately still no joy. Don't know what I have done - but I have done it well!
 
  #9  
Old 07-14-13, 09:53 PM
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Hi Pilot Dane. Yep, you are right, and the thing is frustrating. I keep coming back to the thought that it must be something I have done. The machine worked so well before I 'fixed' it - just leaked fuel. I have gone over everything again, and even checked the placement and orientation of the fuel lines and primer bulb. I took the opportunity to take a look at the piston - not scored or discoloured. I have visually followed the path from the pulse port to the membrane. Yes, I have even stripped the carby again and cleaned it. I can blow through all galleries that I can see. I am not going to let this thing beat me!
 
  #10  
Old 07-15-13, 01:23 PM
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Carb issue

I had this happen on the same type of trimmer and you mentioned that you cleaned the little screen.It should have come with a new screen in the carb kit.Also you may have to open the welch plug and make sure those little idle holes are clean and blow thru them.I had to do both on the one I fixed.
Usually a walbro will take a kit with no issues but I have also had to replace the whole carb,too.
 
  #11  
Old 07-15-13, 07:14 PM
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Is it possible with all the activity you may have moved the carb to insulator gaskets to block the pulse port, usually upside down. Have a good one. Geo
 
  #12  
Old 07-17-13, 06:28 AM
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Hi Geogrubb. Thanks for a great tip. I went and had a good look at the gasket, and found that it is completely symmetrical. Either side up, or upside down will not make a difference. There are two 'pulse' holes in the gasket, and which ever way I mounted it the actual pulse hole was exactly lined up with a hole in the gasket. As there is only 1 actual pulse hole, the hole in the other side of the gasket is blind and goes nowhere.
That wash a great thought Geo, but unfortunately in this case not the problem. Thanks for the thought
 
  #13  
Old 07-17-13, 06:34 AM
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Hi Butcho. Interestingly I did not get a replacement screen with my carby kit! I went back to the dealer who checked some others in stock, and no screens in them either. I was able to get a replacement screen from him - will have to wait for the weekend to fit it. I am reluctant to doctor the welch plug, but will wait and see what happens with the near screen. I very much appreciate you help on this, and will post the results.
 
  #14  
Old 07-17-13, 10:49 AM
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Metering side of Carb

oldbloke,one other thing.The metering side of the carb where the needle valve sits,make sure the gasket goes to the carb side and the diaphragm sits on top of gasket.I've made this mistake for sure myself.
 
  #15  
Old 07-29-13, 05:15 AM
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Update

I am running out of ideas and would welcome some direction here. I have replaced the carby kit again, including the needle valve and fuel lines. I have blown air through all the galleries I can access? There was no buildup of varnish in the carby. Any ideas?
 
  #16  
Old 04-27-14, 06:52 AM
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Fixed it!

After what seemed like a lifetime I have finally fixed the beast! Thanks to those who contributed. The problem turned out to be a skin like deposit on the inside of the passage that linked the second 'flapper valve' to the main filter screen feeding the needle valve. Seems that blowing air through the passage was no issue - I used a piece of fuel tubing. I did however blow in the reverse direction to fuel flow. I have now discovered that a skin like deposit in the passage would fold down and block the passage, starving the engine for fuel. The skin like deposit took a LOT of removing, but now the engine stares and runs to perfection. See - persistence does pay off. Thanks to all.
 
  #17  
Old 05-03-14, 08:20 PM
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Yes, persistence does pay off. Don't it feel good to finally find the problem source after so many hours of fiddling around...
 
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