1986 Evinrude 90 V4 Doesn't Like Wide Open Throttle

[TheFishAreLaughing]

First, some background: A few months ago when my motor started running on 3 cylinders I diagnosed a fuel issue and rebuilt the carbs. During the rebuild I found pieces of deteriorated fuel line stuck in the jets. I replaced all interior fuel lines and added an inline fuel filter. Engine started running on all cylinders again, but a new issue popped up. The motor will run all day long on anything under 3/4 throttle, but above that it will start surging like it is not getting enough fuel. Deciding that the small, cheap fuel filter may be the issue, I changed out the external fuel line and squeeze bulb, installed a new, high flow fuel filter and installed a brand new 12 gal fuel tank. The problem persists. One thing I noticed is that the vent on the new fuel tank seems tight and the tank appears to be pressurized even with the vent open. Is it possible that the problem was too small of a fuel filter but now there is not enough vent so that at WOT it prevents proper fuel flow? Next time out I am going to crack the fill cap loose a little to test that theory. One other issue, maybe related, maybe not, that has existed both before and after the carb rebuilds is that if I throttle up too quickly from idle the engine will throttle up for a few seconds and then die. After that the engine will restart easily. If I throttle up slowly, the engine does fine until it has been running for a few minutes above 3/4 throttle, then it starts surging.

 

[ondarvr]

If it is a fuel delivery issue you will destroy the engine very quickly running it like that, so don't. It could be fuel, it could be electrical, I would clean the carbs thoroughly and make sure the link and sync is correct. If the carb cleaning doesn't help try to check the spark with a timing light at WOT. Also try squeezing the primer bulb, if this helps it could be a fuel pump or air leak.

You should probably check compression while you're at it.

 

[SparkieBoat]

what about the possibility that the fuel connector to the engine is sucking air? if your fuel line is sucking air anywhere before the fuel pump it can be a problem, also link and sync and check your timing. lost of post in here on how.

 

[TheFishAreLaughing]

It is a fresh rebuild on the carbs and all cylinders are firing. I have been keeping the throttle setting where the engine is happy. I'll check the timing.

 

[TheFishAreLaughing]

I think all the connectors are tight, but I will double check. All the fuel lines are brand new at this point.

 

[TheFishAreLaughing]

I probably should mention that before it started running on 3 cylinders and I had to do the carb rebuild it was happy at WOT as long as I didn't throttle up too suddenly.

 

[ondarvr]

Having clean carbs yesterday does not mean they are clean today, and you continued to have have issues.

 

[SparkieBoat]

also you could have messed with something or just not did the carb job right. new fuel lines and connectors? I usually bypass the motor fuel line connector and run the hose directly to the fuel pump. those connectors give a lot of problems, the one at the tank also, I just replace it with a barbed fitting.

 

[SparkieBoat]

try pumping your buld when you are experincing the loss of power and see if that makes a difference.

 

[James R]

A simple way to isolate the tank. Mix a jug of fuel and stick the end of the bulb hose in and run. If you have used anything but an OEM fuel connector you are asking for trouble. The Atwood and other fittings dont fit properly. The Atwood wally world tanks dont vent properly and the bulbs are questionable. Of course I am assuming that you may have fallen into the cheap trap. Certainly sounds like a fuel shortage problem.

 

[TheFishAreLaughing]

I doubt this boat has ever had the Evinrude OEM fuel connector on it. It is a 1986 Sea Nymph Fish N Ski 19' side console walk thru. From the factory it had an under deck built in tank, but a previous owner took it out, along with the VRO system. When I bought the boat just about a year ago, it came with a tiny 6 gal portable tank. I replaced all of the fuel lines between the tank and the fuel pump with new 3/8" fuel line, a new Sierra squeeze bulb, a new high flow Moeller fuel filter and a new 12 gal Moeller fuel tank. (pics below) All connections are 3/8" barb fittings with hose clamps, and are tight. Saturday I will have the boat back in the water. I will try running it with the fuel tank cap cracked open to ensure adequate venting and see what happens. If that doesn't work, I will try squeezing the bulb. To me, it seems like it is needing more fuel flow at WOT than the fuel system can provide. Weak fuel pump maybe?

 

[TheFishAreLaughing]

Looks like the mystery is solved. I cracked the fill cap open on the fuel tank and ran at wide open throttle for about 40 minutes this morning. The motor never hiccupped. I think the original problem was too small of a fuel filter restricting fuel flow at WOT and I exchanged that for an improperly vented fuel tank, which caused the same symptoms.

 

[SparkieBoat]

glad you got it figured out.