87 Johnson 40 HP Dies on Throttle Up and Full Throttle

[87Johnson]

Have a 87 Johnson 40hp that starts great, idles good but dies on throttle up and at full throttle. I can press the choke right before throttle up and get it going. Once running it runs great until you push it to full throttle then it dies back. VRO Defeated long ago.

Done: Cleaned carb (three times). New carb gaskets and float valves. New fuel lines. New fuel pump. New coils and plugs. Compression test 125 both cylinders.

Run great on water hose at the house. On the hose I can throttle up in gear and cold start. Dies in the water at the lake unless you choke it. Water leaks around lower unit. Good water out of pump.

Any help? Thank you!!!

 

[racerone]

Flywheel key checked ?-----It does not have a choke flapper.-----The electric primer valve opens when you push in the key.----That action puts fuel directly into the air flow.------This fuel bypasses the metering circuits in the carburetors.-----This would suggest a carburetor issue.------Or throttle is opening too soon.-----Test run with another tank ?-----Any material missing on carburetor rollers ?----And on a hose " in gear " is still neutral.----There is no load on the prop.

 

[87Johnson]

Flywheel key checked ?-----It does not have a choke flapper.-----The electric primer valve opens when you push in the key.----That action puts fuel directly into the air flow.------This fuel bypasses the metering circuits in the carburetors.-----This would suggest a carburetor issue.------Or throttle is opening too soon.-----Test run with another tank ?-----Any material missing on carburetor rollers ?----And on a hose " in gear " is still neutral.----There is no load on the prop.

Thank you for the reply. I will check the flywheel key tomorrow. Throttle could be opening too soon... If throttle opens to soon I guess I would need to adjust/sync linkage? I have tested with different tank and no difference. Carburetor roller is good. I understand on hose is no load. I just wanted to be clear that their was not a lower unit issue resulting in excessive loading/stall.

Any suggestions for inspection of the flywheel key?

Any instruction on checking the throttle linkage adjustment?

Thank you!

 

[oldboat1]

Would want to check cylinder compression (post the numbers). If a carb issue, likely a partially blocked high speed jet

 

[racerone]

Compression values were posted in post #1-----A little low in my opinion.

 

[oldboat1]

^^Thx.

 

[87Johnson]

Thank you for the replies. I rechecked the compression. I looked back and I posted wrong in first post. Both cylinders are at 132-134.

The carbs have two orifices, no needles. All are clean. I have pulled them out and cleaned more than three times. I have soaked them overnight and have used two cans of cleaner and compressed air. I ordered two new high speed (bottom) orifice plugs. I replaced only one in the top carb. I will need to remove the bottom carb to replace that one.

I took it out on the lake today and tried to adjust the throttle linkage. It starts to dies as soon as the butterflies start to open, unless I flood with gas using the choke. It will start right back up and idles great. It must be starving for fuel. The bowls are full of gas. The tank is vented. The fuel pump appears to be good. Manually pumping fuel bubble does not help. It all points to the carb but I can't figure out what. How far should the timing be advanced before the throttle cam touches the linkage to open up the air (butterfly valves)?

 

[juno pierrat]

I'v got a 87' 48 and 50hp, haven't had your problems, heres a link to an online manual, PDFforless.com

1987 Johnson/Evinrude CU Outboards 35A thru 55 Service Repair Manual P/N: 507616​