90 hp johnson losing power at WOT

[Concepra]

1998 90hp johnson v4...Ran my boat yesterday all day with no problems. today i got back in the water and 1/2 hour in I notice at WOT it started to lose power. while trolling after that engine shut off. I turned it back on and head to shore at full throttle and it started to lose power again , this time it would do it on and off. I would go slow then fast then slow again with out touching throttle. Finally I just headed to ramp at really low speed. I got no signs of misfire, spark is good and so is compression. I changed plugs while on the water today. When I got home I ran it on hose and when engine started to shut off I pumped bulb and it idle right back up so staring to think its a fuel feed issue and hope it's something not very expensive. I will be changing fuel lines and bulb in the morning but wanted to hear some other thoughts.

 

[jakedaawg]

Fuel restriction or weak fuel pump. New bulb and hose is fine place to start. It's probably old right? If newer save the 60 bucks and try to get your bulb to lay in an upright fashion in the well.

Has the vro been disconnected? If so fuel pump repair kits shouldn't cost to much and are easy. If your still using the vro or the fuel side of it you have some choices to make.

Make sure you were not overheating. Pee stream tells you little. You should be able to hold your hand on the top of the cylinders.

What were the compression values?
What length spark did it jump?
Take a fuel sample into a clear container to check for phase separation.

But the squeezing the bulb pretty much tells the tale.

 

[Concepra]

Fuel restriction or weak fuel pump. New bulb and hose is fine place to start. It's probably old right? If newer save the 60 bucks and try to get your bulb to lay in an upright fashion in the well. Not sure how old but have owned boat 1 year and still the one it came with.

Has the vro been disconnected? If so fuel pump repair kits shouldn't cost to much and are easy. If your still using the vro or the fuel side of it you have some choices to make. VRO is disconnected.

Make sure you were not overheating. Pee stream tells you little. You should be able to hold your hand on the top of the cylinders. Have not checked this

What were the compression values? 130-135
What length spark did it jump? .030
Take a fuel sample into a clear container to check for phase separation. Fuel in tank is new, filled last friday, used Johnson 2 stroke oil and fuel additive

But the squeezing the bulb pretty much tells the tale.

 

[oldboat1]

premix at 50:1, I assume.

It sounds offhand like a fuel pump issue (diaphragm). Replacing lines and primer pump (hand pump) probably won't help, but won't hurt. If the old assembly is still decent, keep it for a spare.

You need to measure spark with an adjustable tester. Look for about a half inch to establish the ignition is strong.

Adding fresh gas to contaminated fuel doesn't solve a fuel problem. Water will be at the bottom, where the engine sucks it in. Permanent tanks can be a problem.

Motor could be overheating due to lack of water. (Typically, change the impeller. Make sure there is no blockage around the intakes.)

Motor could be overheating due to lean burning (fuel mix or delivery issues).

(edit. Think jackdaawg pretty much covered it for you. In addition, might consider a prop issue -- hub could be slipping.)

 

[Concepra]

premix at 50:1, I assume. Yes I do premix 50:1 VRO has been disconnected.

It sounds offhand like a fuel pump issue (diaphragm). Replacing lines and primer pump (hand pump) probably won't help.

You need to measure spark with an adjustable tester. Look for about a half inch to establish the ignition is strong.

Adding fresh gas to contaminated fuel doesn't solve a fuel problem. Water will be at the bottom, where the engine sucks it in. Permanent tanks can be a problem. I emptied gas tank a few weeks ago and been using fresh new fuel with additives since then.

Motor could be overheating due to lack of water. (Typically, change the impeller. Make sure there is no blockage around the intakes.) I thought about over heating. Motor seems to be peeing well, stats are about a month old. Not getting any alarm. Is the losing power a symptom of over heating?

Motor could be overheating due to lean burning (fuel mix or delivery issues). if this is the case do is 40:1 recommended

 

[Fed]

Make sure the fuel tank is breathing, test the motor running with the fuel cap off.

 

[oldboat1]

and check the temp (shouldn't be too hot to touch on top of the heads). 50:1 is good.

 

[jakedaawg]

Just put a fuel pump kit in it. The pumping of the bulb pretty much is the most important clue. If that doesn't solve it your only out $18 and 25 minutes