65 hp evinrude losing fuel prime? or bad carbs?

Well the motor is a 1973 65hp evinrude. Have had the boat back in the water for about 2 months now and she has run top notch, never even a hiccup. But yesterday I was out at the lake doing some kneeboarding and it started acting up. The symptoms are that it slowly runs out of steam almost like its losing the prime on the fuel system. All of the fittings and the tank are less than a year old so I don't think I have an air leak anywhere, but it has done this before and an air leak was the problem (hence the new tank and fittings/hose). The only other thing I can think of would be junked up carbs but it hasn't been sitting as I run it almost every weekend. Any ideas/comments are greatly appreciated. Thanks in advance. John.

Re: 65 hp evinrude losing fuel prime? or bad carbs?

My first thought would be; Are you still using gas from last year? I'm not a expert by any means but just giving my 2 cents from my experiance. It does sound like it starving for fuel from what you explained. I also think you might be on the right track thinking the carbs are gummed up. Pull em off clean them up real good and try it again

Re: 65 hp evinrude losing fuel prime? or bad carbs?

vent open on fuel tank? the bulb is suppose to soften when the fuel pump starts pick up fuel. did you check spoark and compression?

Re: 65 hp evinrude losing fuel prime? or bad carbs?

tevans720 said:

My first thought would be; Are you still using gas from last year? I'm not a expert by any means but just giving my 2 cents from my experiance. It does sound like it starving for fuel from what you explained. I also think you might be on the right track thinking the carbs are gummed up. Pull em off clean them up real good and try it again

Click to expand...

Yeah I think I'll pull the carbs and give a good cleaning, I've done them a couple of times before.

tashasdaddy said:

vent open on fuel tank? the bulb is suppose to soften when the fuel pump starts pick up fuel. did you check spoark and compression?

Click to expand...

Um.. I leave the vent open all the time on the tank and it has never affected it before. The reason being that the buildup of fumes causes the tank to bulge out significantly. I have always done this and thought that is what it was for ??? As for spark and compression, wouldn't they affect the performance all the time? To clarify the problem, I can pump the ball and the motor runs normally for a few minutes and then it starts acting up doing the bogging down thing.

Re: 65 hp evinrude losing fuel prime? or bad carbs?

Bump... any ideas on the tank vent issue or any other possible causes?

Re: 65 hp evinrude losing fuel prime? or bad carbs?

Another thought what about your fuel pump. Cuz if your pumping it and it runs fine then boggs down till you pump it again sounds like it isnt suckin up the gas right.


BTW with the vent its is a vent for hot summer days so where it dont expand but again your tank and lines run like a vacuum and with that vent open while running its like poking a big hole through the bag in your vacuum cleaner

Re: 65 hp evinrude losing fuel prime? or bad carbs?

tevans720, you are 99% wrong. the fuel tank vent has to be open when ever the motor is running. the air has to enter the tank for the fuel pump to be able to pull fuel from the tank. the pump cannot pull fuel out of a vacuum. thru the vent prevent the expansion on hot days. if it were not open, the excess pressure will force the needle open and flood the motor.

Re: 65 hp evinrude losing fuel prime? or bad carbs?

tashasdaddy said:

tevans720, you are 99% wrong. the fuel tank vent has to be open when ever the motor is running. the air has to enter the tank for the fuel pump to be able to pull fuel from the tank. the pump cannot pull fuel out of a vacuum. thru the vent prevent the expansion on hot days. if it were not open, the excess pressure will force the needle open and flood the motor.

Click to expand...

I agree 100%. My 1989, 60HP Evinrude has been freshly rebuilt and runs AWESOME! If you are in South MS or LA and need a good mechanic, shoot me a message, I have a recommendation! However, the tanks MUST be vented. Your motor may function at idle or low speeds just fine, but to operate at WOT or even more than half throttle the tank has to be vented. In fact, it has to be WELL vented. I have a cheaper grade fuel tank that has a not so well constructed vent on the cap and my motor runs VERY poorly on that tank. At WOT, it will stall. In fact, I plan to demote that tank to storage only for extra fuel for weekends at the lake and such. I plan to replace it with a better made tank. The point is, check your ventilation before tinkering with your carbs especially since you have been running the boat regularly with no other problems.

Re: 65 hp evinrude losing fuel prime? or bad carbs?

Thanks for all the help guys. I leave the vent open all the time when I'm running the boat so I don't think that's my issue. I did clean the carbs yesterday but I have yet to do a test run. The only other thing I could think of would be a leak somewhere in the fuel hose, guess I take a look at that too.

Re: 65 hp evinrude losing fuel prime? or bad carbs?

Just a thought, perhaps you should take a look at your coils. If they are cracked they can loose spark, especially when they heat up.

Re: 65 hp evinrude losing fuel prime? or bad carbs?

Well the carbs were cleaned and I took it out for a test run, only to find that im still having the same problem, only less severe. Idk what the problem is, unless I just didn't get the carbs cleaned good enough. Also checked for leaks in fuel system and found nothing. Any further ideas?

Re: 65 hp evinrude losing fuel prime? or bad carbs?

HI Big-
DOn't know if your still working on this motor. I Have the identical motor, And I jsut paid the big $$ to the mechnic to take a look (I have simular issues with mine)
He took the carbs off for a modest departure of $200 from my pocket. He told me the needle vlavle on my carbs were stuck shut, he said the center carb bowl needs to be working to let fuel into the other carbs, sounds a little iffy but hey, he's the expert...
Anyway, he found that the needle valves in my carbs were missing those little spring clips that pull the needle down when the floats start to drop, basically, if there was not enough down pressuer+gravity, I wouldn't get that needle to open up. Do you see those spring clips on your floats/needle valves.
Also, when he rebuild the carbs he obviously replaced the gaskets, he said that if the gaskets were shot, peices of it will find there way into the rest of the carb/combustion chamber (no good)

Re: 65 hp evinrude losing fuel prime? or bad carbs?

Rebuild the fuel pump before the carbs and verify that the pickup in the fuel tank is not clogged. I've seen brand new plastic tanks with debris from the manufacturing process plugging up the pickup.