2 Cycle Carb Problem

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  #1  
Old 04-14-03, 08:10 AM
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Ryobi string trimmer carb

I have a three year old Ryobi 2 cycle 31 cc trimmer (actually it a Craftsman) that's driving me crazy. Last summer I began to have problems with fuel leaking into the cylinder when not in use.

Here's what happened. When I would remove the trimmer from its storage hook (it's stored in a vertical position) it would drip fuel and I could definately feel a hydraulic lock in the engine when attemping to pull the starter cord. To temporarly correct the problem, I could remove the plug and use compressed air to dry out the cylinder and the plug; the machine would start right up and run well -- until the next time it sat unused for a week or two.

I figured that there must be either torn diaphram or a bit of dirt under the needle valve in the carb. So I purchased a Walbro gasket kit and carefully disassembled the carb but found no dirt, bad diaphrams, or other obvious problems. Not knowing any more about the source of the problem, I then installed the new gaskets and diaphrams.

As you might guess, I still had the same problem. So, I next purchased a new needle valve spring and installed it. Again, no change, I still had leaking fuel when shutdown.

By this time I'm figuring that something was going on with the carb that I was not skilled enough to identify so I purchased a new Walbro carb and installed it.

Well, no luck. It's still leaking fuel into the cylinder when not in operation.

My question is: How can fuel leak into the cylinder without going through the carb? Or am I missing something here?

I could simply trash the Roybi and buy a new trimmer but I've got to know what causing this to happen. As I said, It's driving me crazy.

thanks,

barry
 
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  #2  
Old 04-14-03, 09:49 PM
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Hello zoomzoom!

A new carb and still doing it....hmmm. The only thing i can think of would be excessive pressure developing in the fuel tank, forcing the fuel past the needle valve. Check your fuel cap vent.
 
  #3  
Old 04-15-03, 01:32 PM
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Hi cheese,

Excessive tank pressure? A possibility? I never heard a "hiss" when releasing the fuel cap. Also, wouldn't a running engine starve as vacuum increased as fuel was used?

As you said it's easy to check, leaving the fuel cap loose when it's not running should tell if the vent is blocked. I'll let you know.

Now that you got me thinking about pressure, how about the push bulb primer? Any way that could cause the flooding?

thanks,

barry
 
  #4  
Old 04-15-03, 08:40 PM
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No, the primer shouldn't cause it.

The tank vents on many of these trimmers have a 1 way valve. They allow air to enter the tank to avoid developing a vacuum, but they do not allow air to exit the tank. If the tank is getting warm, ie: sitting in sunlight, it would develop pressure, possibly forcing fuel into the chamber. Then when the sun goes down and it cools off overnight, the tank draws more air in through the check-valve vent, and the process repeats itself the next morning.
 
  #5  
Old 04-21-03, 05:01 PM
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roybi carb gas cap

Hi Cheese,

I think you hit the bulls eye when you suggested a bad valve in the gas cap. While I haven't had time to buy a new cap yet, I have unscrewed the cap after running the trimmer. Because the fuel would leak if I hung the trimmer on my vertical hook, I had to layed the trimmer horizontally on the floor for the experiment but I always make sure that there is sufficient fuel to cover the fuel inlets. So far its sat for three days without any signs of leakage.
When I buy a new cap and test it I'll let you know the result.

thanks,

barry
 
  #6  
Old 04-24-03, 09:01 AM
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Back to square one

Hi Cheese,

I installed a new replacement fuel cap yesterday and hung the trimmer vertically on its storage hook. When I checked it this moring it was seriously flooded again.

Leaving it stored on the floor with the cap loose seems to be the only way to keep it from filling the cylinder with fuel. What are the odds of buying a bad fuel cap? I still think you're right about abnormal pressure in the tank.

Any addition suggestions would be greatly appreciated.

thanks,

barry
 
  #7  
Old 04-24-03, 08:15 PM
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With a new carb and fuel cap, I cant think of any reason for it to be doing this. I doubt very seriously that the new cap is bad. I doubt that the old cap is bad too, because they are usually designed to keep air from escaping. It's just doing it's job. If there is some trash/debris in your fuel system, there may be some in the carb, keeping the needle from seating well, and if this carb has 2 fuel lines, it could be back-feeding through a check valve in the carb on the return side if trash were hung in it.

It could also just be poor design...Ryobi has never really been the leader in engineering quality you know, lol.
 
  #8  
Old 05-02-03, 03:03 PM
deancj
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Hi All
I just thought I would put my two cents in. I have the same problem with the same little engine! I am on my second carb. also. I would love to know the fix. This will be my third year with this problem child. I finaly give up and just run it out of gas or drain it when finished. So, now I know I don't have the only one.
 
  #9  
Old 05-03-03, 12:08 AM
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I think there is no cure, using original parts anyway. There may be a fix, like bending the needle tab down a couple thousandths of an inch or so, or doing an alteration, but the carb is about the only thing that will let the fuel into the engine. With new carbs on these machines, It shouldn't be doing this. That's Ryobi for ya.
 
  #10  
Old 05-03-03, 04:44 AM
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Well, I too am glad to find out that I'm not the only one having a Ryobi flooding problem that can't be repaired --- I thought I'd never say that about any machine!!

Since I last posted a note to the list, I put my old rebuilt carb back on just to satisify myself that I didn't rebuilt it incorrectly (runs fine), and instead of running it dry or draining the fuel, I loosen the fuel cap and lay it flat on the floor instead of hanging it.

It'll be a long, long time before I buy a second Ryobi product.

barry
 
  #11  
Old 05-03-03, 05:35 AM
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Hello: Guys

The design flaw, if there is one, is most likely within the carb itself. That factor was not considered correctly when the carb was designed, engineered or manufactured. Chalk those factors up to cost cutting considerations.

The weight of the fuel and the pressure it causes within the carb must be taken into account when the machine is hung in the vertical position.

Althought there isn't much fuel weight inside the carb, the weight of the fuel in the tank increases the pressure on the needle and seat. This is most likely allowing fuel to pass by the needle and causing flooding.

That being the case, there is nothing that can be done to resolve the problem except store the machine in it's horizontal position, as it was intended to be used in. That is really a minor problem.

This type of problem is not exclusive to any brand or diaphram carb. Can happen with small 2 cycle garden tillers hung by the handbars, hedge trimmers, same applies to 2 cycle lawn mowers, hand carried generators and other assorted power equipment.

One would not or at least should not lay a boats out board motor in the horizontal position either. These engines are designed to be vertical and should be stored likewise, in the vertical position.

Regards & Good Luck. Tom_B. Web Site Host & Small Engine Forum Moderator. "Accurate Power Equipment Company"
Small Engine Diagnostics Services and Repair.
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