86 Johnson GT 150 Performance Problem

[Costa Plente]

I bought a boat that had this motor on it that had two cylinder that were bad, so I had the powerhead rebuilt by Southwest Marine in Ft Myer, Fl. While the motor was being done I replaced all the fuel and filler hoses in the boat with marine hoses from Wholesale Marine. I removed the fuel tanks and cleaned them and replaced the tank select valve with a new one and put new clamps on everything. When I got the powerhead back I replaced all the fuel hoses on the motor and put a new fuel filter on it. The carbs were rebuilt and a new VRO was installed prior to starting the motor for the first time. I also added 1 pint of oil to 6 gal of gas just incase the VRO didn't work right. The motor started up and runs good with the ears on the lower unit at home with no problems. I took it to the lake and it started right up, backed off the trailer and ran really well until I got it on plane. While running at 3500 rpm everything is running smooth but when I tried to bring the rpm higher to 4000 or more like I was told to do during break in the motor starts to cut out and miss. I don't know what it could be and need help.

[taterjones]

One of the pro's will be here shortly. In the meantime, add your model # so they can better assist you.

[Bassmeister]

Take it back to the builder.......warranty....

[Costa Plente]

The model # is J150STLCDC. From everything that I have found out about this motor it has a different spark plug than most Johnson 150. I takes a QL16V plug where most use a QL77JC4. The builder did an excellent job on the rebuild and had nothing to do with the electrical or fuel part of the motor, all he got sent to him was the long block.

[omcforever]

The model # is J150STLCDC. From everything that I have found out about this motor it has a different spark plug than most Johnson 150. I takes a QL16V plug where most use a QL77JC4. The builder did an excellent job on the rebuild and had nothing to do with the electrical or fuel part of the motor, all he got sent to him was the long block.

Stay with the QL77JC4 gapped at .030.......that's what it takes. Have you done or had done the link and sync? Verify all plugs, plug wires, coils are good?

[omcforever]

You removed and re-installed the powerhead? Where the bad cylinders opposing( 1-2/3-4/5-6)? Where the carbs rebuilt with all new gaskets/seals/needle and seats/cleaned passages with orifices removed? Floats set to OMC specs in your OMC repair and service manual? Also re-torque your head gaskets. I would re-torque the powerhead mountings screws as well. Must be done after a few heat cycles.

Hope your not blaming the VRO,,,,,with only 2 cylinders trashed probably wasn't the culprit. If Opposing cylinders probably a carb/fuel delivery issue that killed the cylinders.

[ChampioNman]

It may be hard to read but here is the break in process.

Break in_20190613_0002.jpg

[Costa Plente]

The carbs were rebuilt by a local marine shop here and from what they charge me I hope that they were rebuilt correctly. I will go by and talk to them and ask but they were highly recommended by others. The old engine block that was sent for rebuild couldn't be rebuilt and had to be replaced with a different one. The coils and power packs have been checked and new plug wires were installed before I ever tried starting the motor. I haven't retorqued the heads yet and am following the break in procedure that the builder sent me which is the same as above. The local guys are saying that it may be the stator.