Please Solve Blower Mystery!

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  #1  
Old 12-08-12, 02:12 PM
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Please Solve Blower Mystery!

Hi all, I have a RBL500 blower (Robin). It's old but I love it. Here's the good first: brand new carburetor (pure gas mix except for 1/4 tank of ethanol gas), exhaust cleaned and ported, both fuel lines are clean, air filter is new.

When the blower gets warm, it tries to die at wide-open throttle, or I have to slowly rev it up to keep it going at WOT. Pulling the trigger quickly will kill it. Again carburetor is NEW. The longer I run at one time it the more power I lose at WOT.

What the heck is causing this? Would worn piston rings cause this? Thnks in advance. I'm stumped.
 
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  #2  
Old 12-08-12, 03:33 PM
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Sounds like and air leak, while the engine is running, spray/dribble carb/brake parts cleaner behind the carb and along all the mating surfaces, if the engine tempo changes you have found your leak. Have a good one. Geo
 
  #3  
Old 12-08-12, 03:35 PM
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Could be a couple of things.

Normally, a loss of power is associated with a shortage of fuel or fuel/air flow (like plugged filter or plugged exhaust). The shortage of fuel before the new carb you have could be in the lines leading to the carb, or the fuel tank plugged, or the vent on the tank is plugged. The vent issue can be checked by loosening the cap and see if that helps.

The ignition module/coil can get hot the longer the engine runs and produce either a very weak spark (yellow) or none at all. Either of the compromised sparks will result in loss of power or a none running engine. The weak spark simply can't cross the resistance of the compressed air in the combustion chamber. An engine that runs with a miss or quits altogether is more common than a low power output, but either is possible.

If you have an engine that is running normally, then produces less power and with it a higher rpm, the engine is running low on fuel = lean air/fuel mixture.
 
  #4  
Old 12-08-12, 04:18 PM
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Like marbobj mentioned......it is running on the lean side.

Does your carb have two adjustment screws on it ? Most older stuff did.

One will be high speed mixture. Probably only need like a 1/4 turn counter-clockwise.
 
  #5  
Old 12-08-12, 05:13 PM
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Thanks, guys. It was doing this before which is why I spent $100 for a new carburetor -- and also why I'm hestitant to adjust it brand-new.

I'll try all of these ideas tomorrow...definitely hadn't thought about the gas cap or a vacuum leak.

I'll let you know how it goes.
 
  #6  
Old 12-08-12, 05:23 PM
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Oh and I also meant to ask...so the ignition coil will always do this when hot or only as it ages? (Should I consider getting one as general upkeep?)
 
  #7  
Old 12-08-12, 05:43 PM
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I don't think it's the coil. A coil normally works or does not work. The unit is getting too much air in the air:fuel ratio. I would suggest opening the high speed mixture screw a bit. A new carb still needs to be fine tuned to the unit. If that doesn't do it, you probably have an air leak.
 
  #8  
Old 12-08-12, 06:44 PM
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If I was to lean one way or the other, it would be in the direction of the fuel air mixture being too lean. With Geo on the air leak, still a possible plugged cap vent, maybe a bad spark plug or the wrong one.

Then if you're working with a two stroke blower engine, there's the crank seals.
 
  #9  
Old 12-09-12, 09:53 AM
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Vacuum leak!!! And sure enough, I checked the gaskets (which I never paid much mind to) and I had doubled-up on one which left the right location without one. When I moved the gasket it went straight up to full throttle.

I also tried to move the hi-speed screw but it seemed locked in place and didn't want to move counter clockwise...only clockwise. I suppose now it doesn't matter anyway.

Thanks for the help! Sad thing is, I already cursed my way through all the leaves so I'll have to find something else to use it on...
 
  #10  
Old 12-09-12, 03:50 PM
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Success is a wonderful sound. Have a good one. Geo
 
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