1961 40hp johnson losing power at wot.

[Nasbinator]

Hello everyone. I just got back from the lake today and experienced a problem. My 1961 40hp johnson starts and idles great. I can run it wide open fine for about 5 to 10 minutes then I lose power like its running on one cylinder. After I idle the motor for a few I get my power back but does it all over again. Kind of seems like the motor is overheating but I'm pumping water fine. And I dont know if this is what happens when one overheats? I dont have a temp guage. I recently rebuilt carb and just put new spark plugs in. Thanks for any help.

 

[Bifflefan]

Re: 1961 40hp johnson losing power at wot.

Is the tank vent open? or is the bulb colapseing? The fuel filter?

 

[Nasbinator]

Re: 1961 40hp johnson losing power at wot.

Yes, I checked the vent. I have 2 tanks and acted the same way with both. Bulb is new. Also new fuel filter.

 

[kenmyfam]

Re: 1961 40hp johnson losing power at wot.

Yes, I checked the vent. I have 2 tanks and acted the same way with both. Bulb is new. Also new fuel filter.

Bulb is new ????
Have you only experienced this with the new bulb ????
Have you tried the old one ???

 

[Nasbinator]

Re: 1961 40hp johnson losing power at wot.

Yes I run with 2 tanks. 1 has a new bulb and in line filter, the other has a bulb that is a few yrs old and new inline filter. I ran it with both to make sure. I havent rebuilt the fuel pump so I just ordered one online. I will also replace the fuel lines wich I havent done.

 

[Nasbinator]

Re: 1961 40hp johnson losing power at wot.

I was checking my thermostat today to find there wasnt one.. I ordered one online. Do you guys think this could of been giving me problems. I know they say it takes longer for a engine to warm up, but also heard that it can cause a engine to overheat. What do you guys think?

 

[Doug N.]

Re: 1961 40hp johnson losing power at wot.

I wouldn't think it's temperature related. Sounds like a fuel problem. Since the supply is good, I would start looking at the carburateur (or however you spell it). You might be getting a trickle to the bowl, but not enough to keep up with high speed operation.

 

[Nasbinator]

Re: 1961 40hp johnson losing power at wot.

Thats what I'm starting to think. I'll check the carb too.

 

[Rubixone]

Re: 1961 40hp johnson losing power at wot.

I would like to know if you found a solution to this cause my 1960 and my 1961 do the same exact thing really frustrating!!!! and I rebuilt carbs and good every thing strong flow of fuel.

 

[Griff805]

Re: 1961 40hp johnson losing power at wot.

I had the same issue on my 61' 40HP Johnson. I believe mine was caused by the fuel pump, but I rebuilt the carb and fuel pump at the same time- so I can't say for sure. I also replaced all the fuel lines and put hose clamps with screws on instead of the stock ones.

 

[Nasbinator]

Re: 1961 40hp johnson losing power at wot.

I got my fuel pump kit in the mail today. I also got new fuel lines and correct sparkplugs. I wont be able to test it out on the lake until next weekend Thats frustrating! I'm going to go through everything the best i can.

 

[tmcalavy]

Re: 1961 40hp johnson losing power at wot.

Could also be a weak coil getting weak enough to drop out once the operating temp comes up...leaves you running on one cylinder. If the fuel system recommendations don't work, pull the flywheel and inspect your coils...if they're cracked they're probably original equipment...might be time for an ignition tune up.

 

[Nasbinator]

Re: 1961 40hp johnson losing power at wot.

I finally was able to get out on the water today and it ran like a champ! So the problem had to be one of these things.. I replaced a missing thermostat, new fuel lines and pressure line going to fuel pump, rebuilt fuel pump, new spark plugs, cleaned carb again. I figure it was propably the fuel pump. The manual says it should pump a minimim of 2psi. So even though I was getting fuel it might not of been enough at wot.