V4 120hp evinrude drops power for a second, then back up again

[rfeiler007]

Hey everyone. I have an '85 or '86 120hp v4 evinrude. When i first get out on the water and give it some throttle, she will run fine for a while, then all power just stops and the engine loses all momentum briefly, a few seconds later shes back up again. I have replaced the fuel tank with a brand new one, new fuel filter in the line, and she still does it. Mind you, after about 30 minutes of running, it will run fine with no issues. What could be the problem? This is more annoying than anything... Thanks for any help..

 

[Joe Reeves]

'85 or '86 120hp v4 evinrude. When first out on the water, giving throttle, she'll run fine for awhile, then power stops and loses momentum, a few seconds later it's up again. Fuel tank replaced with new one, new fuel filter inline, after about 30 minutes running, it will run fine.

6 gallon portable tanks, or larger?

New hose & primer bulb or same one on the new tank?

Do you pump the fuel primer bulb up hard before starting the engine?

Does it make any difference if you or someone else punps the fuel primer bulb constantly, acting as a manual fuel pump? Does this eliminate the problem?

 

[rfeiler007]

12 gallon permanent tank, I prime the bulb as much as i can before starting..

 

[rfeiler007]

same hose n bulb on new tank..

 

[Joe Reeves]

85 or 86 120hp V4 evinrude. (1) -When i first give it some throttle, it will run fine, then all power stops, the engine loses all momentum briefly, a few seconds later shes back up again....... (2) - I have replaced the fuel tank with a brand new one, new fuel filter in the line and it still does it..... (3) - After about 30 minutes of running, it runs fine with no issues

1 - I assume you're saying that the engine slows down BUT does not die out and stop running... rather that it catches and continues to run. Sounds like you're not getting the proper amount of fuel to the engine to start with and the fuel pump has to play catch up.

2 - You indicate in post #4 that you're using the same hose and primer bulb on that new tank. In post #3 you state that you pump the bulb as much as you can before starting... I have no idea what this means. The fuel primer bulb MUST be pumped up until it become hard and cannot be pumped any further which indicates that the fuel system of the engine's carburetors, pump, fuel lines, etc are full as they should be.

If the fuel primer bulb does not become hard, replace the bulb assembly or the entire hose assembly as this is most likely your problem.

3 - This portion of your quote is where the fuel pump of the engine finally catches up and the engine runs normally.

 

[rfeiler007]

1. Correct, I am saying that the engine will be running fine at 3/4 throttle, then it will lose all momentum and power (while not shutting down) and then after a couple seconds, catch itself and be back up to 3/4 throttle speeds..
2. I am stating that I prime the bulb to its MAX capacity-meaning that i pump it until it is hard and it cannot be pumped further. I have not had a chance to have another person in the boat to check the bulb pressure when this happens yet.

 

[boobie]

Put a timing light on each cylinder when it's acting up and look for black spots. If you have them you have an ignition problem. Not fuel.

 

[ob]

Don't overlook the safety lanyard kill switch. Especially if yours is the rubber cap style.

 

[rfeiler007]

No Title

would having the below style fuel filter have ANYTHING to do with the issue?

 

[rfeiler007]

Don't overlook the safety lanyard kill switch. Especially if yours is the rubber cap style.

It doesn't actually die though, it just loses all power/rpms for a few seconds. Would the kill switch still be something to look into?

 

[ob]

It doesn't actually die though, it just loses all power/rpms for a few seconds. Would the kill switch still be something to look into?

Yes. The rubber cap on the safety kill switch tends to stretch out over time and can cause intermittent loss of ignition before finally failing.

 

[CaptnKingfisher]

Recently fixed the same issue on one of my V4s. I was thinking one of my coils might have been intermittently failing since I observed cracking on the ceramics. Well, I brought the new coil on the water with me and before replacing the part I started the motor and observed the engine running at idle during a miss and was lucky enough to hear some 'snapping' like a spark arcing out to the block. Found one of my plug boots had a crack in it that I hadnt noticed and it seemed to only act up when engine was warm.

Long story short, intermittent power loss - - check the condition of your coils and plug wires.

 

[rfeiler007]

Yes. The rubber cap on the safety kill switch tends to stretch out over time and can cause intermittent loss of ignition before finally failing.

Over the weekend I believe I ruled out the kill switch and fuel being the issue. I noticed it had been jumping out of gear when the "loss of power" while at higher speeds occurred. When the motor would wind down to a slower rpm, i could feel it catch again and be able to plane back up again. I marked the propeller exactly below the round end of the cotter pin to detect any movement. (i was told that if it slipped it was more than likely a clutch dog issue then) On my last trip out, The motor ran flawlessly with no issues at all, as if it were brand new. Upon pulling the boat out of the water, I DID notice however, the location of the mark to the round end of the cotter pin, had moved a quarter turn. Does this mean that it is in fact a gear/clutch issue? Or should I try adjusting the cable linkage first?

 

[ob]

What it would indicate to me is that you have what if referred to as a spun prop hub. Meaning that the rubber fit between the barrel of the prop between it and the center splined hub has broke free from its fit. You'll need to a new one pressed in to fix it. Unless you happen to have both worn gear lobes and or a worn out clutch dawg , the two are unrelated issues.

 

[rfeiler007]

So I understand correctly, are you stating I need a new prop hub?

 

[ob]

Yes. If I understand you correctly with respect to the mark you made on the prop hub that had moved from its original position. Of course if you could post a pic or diagram of the mark you placed , it would shine some clarity.

 

[rfeiler007]

would this prop hub cause the boats speed to just suddenly drop out?(see issue above) Then after the rpms drop down to more of an idle, the motor seems ready to go back to a higher rpm and a faster speed?

 

[ob]

Usually a spun prop hub would allow the engine rpms to increase under harder/faster throttle application while the boats forward progress slows. "Slippage". At slower speeds it may well catch again allowing for more normal operation. Eventually it will slip at moderate throttle application rendering your vessel inoperable.

 

[rfeiler007]

so, yes?

 

[ob]

If your prop hub has slipped from its original position....... a resounding Yes.... A pic of course clears the air for us folks who can't see it.