evinrude 4 hp worktwin fuel problem

berrynghtwl

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May 1, 2007
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I recently acquired this motor (model#4R79D). It had fuel in it that had seperated down to varnish and water. I have a mechanical background so i disassibled the carberator and cleaned it,but i cant get it to fire back up. Searching miles of forums,i found some carb settings but all spoke of two brass adjusting screws, mine only has one, can some one give me somewhere to start?
 

Xcusme

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Apr 21, 2003
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Re: evinrude 4 hp worktwin fuel problem

Welcome to iboats!

Carbs should be soaked in carb cleaner followed with compressed air to be sure all traces of varnish are removed from the jets and passageways. Install a carb rebuild kit. It containes all gaskets and seals including a new float.
Try sprayiing fuel mix (gas and oil) into the carb throat and pulling the rope to see if it runs for a few seconds. If it does, you have a fuel delivery problem at the carb. If it doesn't check the spark at the plugs. If no spark, you'll have to pull the flywheel with a harmonic balancer type puller only. Inspect the coils and replace if cracked. Clean and set points for a .020 gap on the high side of points cam.
The single needle valve on the carb is the slow idle mixture screw. Screw neeedle valve in until lightly seated and then back out (open) 1.5 turns for an initial setting. Your carb has only one mixture screw, the high speed jet is fixed.
Most folks here will tell you to find an OMC service manual for your motor and is good advice. All of these procedures are covered in the manual. Since this is a new to you motor, replacing the water pump and lower unit lube would be a good idea too.
 

berrynghtwl

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Re: evinrude 4 hp worktwin fuel problem

thank you for your quick response, i did all that you suggested, it will run as long as i feed gas though front of carb.Is this carb gravity fed or will it suck out of a fuel sell?
 

Xcusme

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Re: evinrude 4 hp worktwin fuel problem

You're describing the classic symptom of a blocked carb. Spraying and soaking the internal passages with carb cleaner, followed with compressed air is the fix. Replace all seals to include the low speed needle packing, gaskets and float needle. All these parts are included in a carb rebuild kit. To check for fuel delivery from fuel pump, disconnect fuel line at carb, coming from the fuel pump. Place this fuel line in a can and pull starter rope. You should see fuel being pumped into the can. When you squeeze the primer bulb, you should see fuel being pumped through the fuel line too. It's the fuel pump that pulls fuel from the tank, not the carb itself. Needless to say, never run the motor out of water. Run in a test tank with enough water to fully cover the lower unit and high enough to cover the water pump. When running, water will spritz from the little holes on the rear of the midsection, you won't see a steady stream of water, just the misting....
 

berrynghtwl

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Re: evinrude 4 hp worktwin fuel problem

this particular motor there is no fuel pump, fuel line comes directly out of tank (under hood), to the carb intake port
 

Xcusme

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Apr 21, 2003
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Re: evinrude 4 hp worktwin fuel problem

Sorry, duuh, I assumed you had a remote tank. Yes, you have a gravity tank. Fuel is supplied directly to the carb bowl. You should have a fuel shut-off too. Again, disconnect fuel line at carb and open fuel shut-off. You should se fuel flowing from fuel line. If no flow, check fuel lines, shut-off valve, fuel line filter screen and be sure tank vent is open.
 

berrynghtwl

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Re: evinrude 4 hp worktwin fuel problem

ok, I have ordered the repair kit and i am going fishin. will try the settings and information that you gave me and i will let you know what happened when i return, thank you again for you time and info
 

Xcusme

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Re: evinrude 4 hp worktwin fuel problem

I seem to be jumping the gun today. I just looked at the print for your motor and you should have electronic ingition , not the older magnito ignition. Disregard the info I posted about points and adjustments. If you have ignition problems, post back, I'll have my head in gear.
 

F_R

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Jul 7, 2006
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Re: evinrude 4 hp worktwin fuel problem

This question is asked over and over, with the same symptoms. Did you pay particular attention to the high speed orfice? It is in the center of the carburetor sticking down into the bowl. It has to be absolutely, positively, shiny CLEAN. If there is any coating at all in the tiny orfice, the motor will run as you describe.
 

berrynghtwl

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May 1, 2007
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Re: evinrude 4 hp worktwin fuel problem

thank you for all that answered this post, you all were right, a carb kit,and a good cleaning,and some very good avice does wonders. thank you all again
 
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