40HP Johnson cannot keep running without Primer

[oldjeff]

Hello, Any help would greatly be appreciated. I have a 1991 Johnson 40hp that I just purchased for my retirement fishing boat. I eliminated the VRO and replaced with new Vacuum pump. Replaced all fuel lines. Rebuilt Carburetors. New water pump. New plugs. New filter. Carburetors looked very clean inside with no corrosion. Cleaned them very well and all passages were cleaned and kit installed. New Primer kit installed. Engine will start and Idle for 5 to 10 seconds and die. Can keep running if bump the Primer. Has 145 and 150 compression. Primer ball pumps up and gets hard. Does not help to use primer ball to keep running. I have went back thru all my work and cannot find what is wrong. Any ideas? I am ready to go fishing and start my retirement finally.

Thanks Jeff

 

[racerone]

Did you replace VRO with a conventional pump on the side of the top cylinder ?-----Actually the fuel pumps run on a pressure pulse.----The electric primer puts fuel into the motor.---This fuel bypasses the carburetor metering circuits.----This would suggest that you have fuel delivery issues.

 

[oldjeff]

Thanks for the reply. Yes it was replaced with a conventional fuel pump. I agree it is defiantly a fuel problem but where. I can also keep running if i feather the throttles when tries to die.
Thanks Jeff

 

[jimmbo]

Dirty Carbs, air leak in fuel line prior to fuel pump. Are you using the fast idle lever during startup?

 

[Crosbyman]

with the carb bowl full it should run a while
how did you clean the carb . was the upper idle circuit chamber under the core plug cleaned out ??

see picture

your carb js similar to this one with a HS needles ....

more modern t your's has a non adjustable fixed HS - a LS jet orifice and side needle

the top chamber feeds gas during idle by sucking gas up the idle channel then "down" 3 very small orifices

 

[Crosbyman]

modern version

 

[oldboat1]

high speed jet in the front of the bowl needs to be squeaky clean, and the nozzle gasket has to be in place.

 

[oldjeff]

Morning, I did remove the core plug and clean and replace. I will remove the Carbs again today and check. I apparently missed something in the Carbs. Fuel lines are all good and no leaks. Thanks for all the reply's and will let you know how it goes.

Thanks Jeff

 

[kbait]

Partially clogged main jets will cause your exact problem.. along with stale/watery fuel..
Good luck!

 

[oldjeff]

Crosbyman and kbait you were both right. Problem is fixed and I am going fishing. Thank you very much for the help.
Be well

 

[Kato K]

I have a 40 vro with pump conversion like yours. It was running fine...then later in the year became hard starting. Next it began stalling under low rpm and was difficult to restart. My carbs are clean and fine but I had a mechanic check it to shed light. It would start but die off. You could keep it running by putting your hand over lower carb. Mechanic said there was a very good chance that the crank seals were bad causing engine to not have proper vacume to suck the proper amount of air and gas through carb.