troubleshooting 1985 vro 90 hp johnson outboard

Engine stopped suddenly and I diagnosed a split primer bulb as well as a split oiler line. Replaced both and now engine runs rough in low to mid throttle speeds, runs fine at 2/3rds to full throttle. Also intermittently in neutral it ramps up the rpms so high I can't put it in gear for fear of breaking something. Also Engine wouldn't start unless I raised the throttle advance lever as high as it would go, so I adjusted the throttle screw under the hood up to where I can start it and it will idle so I can put it in gear after the rpms go down. I put in a can of seafoam and it didn't help. I replaced the plugs, checked the spark, and tested the cylinder pressure which came out to 120 psi in one cylinder and 130 in the other three. Took the fuel pump apart to check for any noticeable problems and cleaned out the sediment bowl and filter. Does anyone know if there is a fuel filter I missed cleaning or have any other advice to offer. This motor was bought used in 2005 and has run great up to now. the motor was bought from an estate and the owner had little chance to put hours on it before he passed away, so the most hours on it is around 500. Thanks for any help.

Re: troubleshooting 1985 vro 90 hp johnson outboard

You may want to re-adjust the idle. Best to disconnect the throttle cable at the engine end and set it first-then reconnect the cable. You'll want to set the idle when the boat is floating normally in the water and it's in forward gear. You can't set it on the trailer. If you still have running/idle issues, you may need to overhaul the carbs, paying attention to the idle passages in the upper carb body. Not unusual to have to overhaul carbs if the engine was not run for a long period of time.

Re: troubleshooting 1985 vro 90 hp johnson outboard

Thanks for the reply. This motor was running fine since I bought it and was in the water and running all summer with no issues so it really hasn't been sitting unused. I have purchased a clymer manual for it and it suggested that it may have a small hole or tear in the fuel pump diaphram that may be causing the rough running at lower speeds. I also talked to a marina owner who suggested a carb rebuild as a solution. I also found out that I disassembled the oil pump instead of the fuel pump, so I'm planning on dissasembling the fuel pump(now that I know where it is),cleaning/ replacing the inline filter and pump filter to see if that helps and adding more seafoam as a way of cleaning the carbs. Since the motor suddenly has been rough running I keep thinking it is a fuel delivery problem at lower rpms. Any thoughts?

Re: troubleshooting 1985 vro 90 hp johnson outboard

You'll not get much good info out of the clymer manual. The factory manual will give you better information. Have you checked for spark when running the engine after it's fully warmed up?

Re: troubleshooting 1985 vro 90 hp johnson outboard

emdsapmgr said:

You'll not get much good info out of the clymer manual. The factory manual will give you better information. Have you checked for spark when running the engine after it's fully warmed up?

Click to expand...

The engine was warm when I checked the spark.That was the first thing I did since I thought it was the coil that had gone bad since the problem started suddenly. Any other suggestions? If there isn't a problem with the inline filter or the fuel pump filter or a hole or tear in the fuel pump diaphram then I'll need to take it to the repair shop. Thanks for the suggestion.

Re: troubleshooting 1985 vro 90 hp johnson outboard

Fuel delivery problems usually result in an engine that won't run well at WOT. A normal recommendation is to have someone constantly prime the fuel hose bulb when the engine starts do miss or slow down. That overcomes a weak fuel pump by forcing extra fuel into the carb bowls. You indicate your problem is at idle. Likely this procedure may not help much, but you can try it at idle and see what happens. I suppose it is possible that at low vacuum, the pump has difficulty drawing fuel. Check the anti-siphon valve for debris inside it which may restrict fuel flow.