Evinrude surge problem

I have a 1984 15hp Evinrude, it idles fine, runs great at top speed, but at about 1/3 throttle it surges. When I drop back from full throttle to slow speed it dies. checked compression and both cylinders are with in 3 lbs of each other. I use fresh gas. I put a new carb kit in it.

Try running with another tank and hose.

Try pumping the fuel primer bulb (acting as a manual fuel pump). What difference does this make if any at the problem settings?

Does any fuel/air leaks exist in the fuel connectors or elsewhere (pump would draw air)?

If you have proper spark that jumps a 7/16" gap at cranking rpms and proper compression (3 lbs difference tells us nothing, what are the psi readings?), and everthing check out, the problem is usually carburetion.

Did you manually clean the high speed jet located in the bottom center portion of the upper body?

(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)

Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

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racerone said:

Try running with another tank and hose.

Click to expand...

I inspected the old hose, tank and connectors and found no problems. I hooked up a new tank and hose from another motor I have and it didn't solve the problem.
I checked the spark and it jumps 7/16" gap. The compression is 60 in the top cylinder and 62 in the lower cylinder. I readjusted the carburetor low speed setting per the form suggestion.
The problem still persist, so I am going to take the carburetor apart again and manually clean the high speed jet and retest.
thanks for all of your help guys.

I checked the spark and it jumps 7/16" gap. The compression is 60 in the top cylinder and 62 in the lower cylinder. I readjusted the carburetor low speed setting per the form suggestion.
The problem still persist, so I am going to take the carburetor apart again and manually clean the high speed jet and retest.
thanks for all of your help guys.

I tried pumping the fuel primer bulb and the engine still surged and died when I reduced throttle. I checked the spark and it jumps 7/16" gap. The compression is 60 in the top cylinder and 62 in the lower cylinder. I readjusted the carburetor low speed setting per your suggestion.
The problem still persist, so I am going to take the carburetor apart again and manually clean the high speed jet and check out all of the passages and retest.
thanks for all of your help.