1999 Johnson 150 sputters and stalls at low throttle

Hi, I hope you can help. I’m a new boater, bought it as my kids love to fish. I have some mechanical capabilities related to automotive, but first time working with 2 stroke.

I Bought the boat used last summer (2019); it had bad fuel leaks (fuel filler and vent hoses, fuel sending unit gaskets) and wiring issues. Replaced parts and wiring issues with proper marine grade products.
It was running but still had some idling and stalling issues. Put it away for the winter and this year in April 2020 started working on it. I Found the carburetor were leaking and 4 of the 6 bowls were cracked. I rebuilt all six carburetors (with Johnson (BRP) kits) including replacing the bowl and float assemblies; the VRO was leaking so I rebuilt the VRO (with Johnson VRO Kit), replaced fuel hoses and clamps. Success as there were no more leaks, no fuel smell.

Did additional preventive maintenance; Replaced spark plugs, primer solenoid kit (leaking at the top), fuel filter, primer ball, fuel water separator, thermostats, lower gear oil. It seemed to be running better except the idle is higher than it was, and I am unsure how to adjust that.

I have had it out on the water and it runs well when moving, had it up over 35MPH with more throttle left, so I think it is close to being right. But I don't like the high idle and the last couple of times out on the water it was coughing and running rough under 8 MPH.

I have read online, and it was suggested to do a decarbonization and since I had never done it and do not know when it was done seemed like the right thing at that point. I ran two cans of Johnson Engine Tuner through it following the directions and let the second can sit 12 hours in the engine before running it. It smoked and when it cleared seemed to be running a little better but would still sputter and stall when running slow.
I rechecked and cleaned the spark plugs also performed a compression test.

My plans at this point are to change all of the remaining fuel hoses around the engine and to check the vapor separator.

Any suggestions??????

1999 Hydra Sport 201DC with Johnson 150

What is your Compression? Did you clean the carbs thoroughly? Do you have the factory manual? What are the low speed screws set at? Do you have the OIS ignition?

flyingscott said:

What is your Compression? Did you clean the carbs thoroughly? Do you have the factory manual? What are the low speed screws set at? Do you have the OIS ignition?

Click to expand...

A '99 carbureted 150 should be OIS ignition. In addition to the compression test you need to also make sure you have good spark on all 6 cylinders using an air gap (3/8" gap) spark tester. Also, be sure you're using Champion QL78YC spark plugs only. The OIS ignition system is a bit finicky and does not work well with other cross-referenced plugs.

Definitely check for all 6 carbs being fully clean and well sealed as an air leak can cause a high idle. These engines have Fast Start, which keeps a higher idle until the engine reaches operating temp. Have you replaced the thermostats? If the thermostats are stuck open (or missing) the engine can run too cold. It may be possible that would trick the ignition into constantly running in the Fast Start mode and keep the idle high. You could also have a bad temp sensor in one or both heads that could be reporting bad signal.

With a 150 that boat should be able to do much better than 35MPH so I'd say you still have some significant issues to solve. My Ranger bass boat is 19'6" and a bit heavy. With an Evinrude 150 I can run about 50MPH so your hull should go much faster than 35MPH.

KJ

Hi,

The compression is from top to bottom Port: 99, 97, 95, Stbd: 99, 102, 102
All of the carburetors were removed cleaned and rebuilt with OEM BRP kits including replacing the bowls.
No factory manual using a seloc manual (not that good)
The low speed screw sitting at the top of the motor is about 3/4 to the + side.
It has 2000 OIS ignition system.

The fast start does work as it will run high for a few minutes than drop down, but still high to where it bumps hard when going into gear.
Thermostats are new, replaced in May with OEM parts.
The boat will do much more than 35 MPH, I just have not taken it higher as I always have my kids in the boat and never had the reason to go faster.

Thanks

Hi,

Today I wanted to check the compression again to see if it changed after running Engine tuner, but when I went to start the engine, it clicked and sounded like the battery, starter or solenoid died. I did not think it was the batteries as both are just a couple of months old. Check the voltage gauge on the dashboard and one was showing 12.8 the other 12.3. I checked the voltage at the starter and it showed 12.8, so I thought the solenoid or starter. Don't ask me why but I decided to connect a battery directly to the solenoid and ground than jumped the solenoid and it tried to start. Long story short, the battery selector switch (Perko) failed.

I replace the switch and two cables started her up and she seemed to be running better??? It was on the muffs, but sounded better, no misses and the idle was not as high????

My question is could the failing battery switch cause reduced amperage to the engine to the point that the engine and effect the spark and make it appear like it was a fuel delivery issue?

Tomorrow I will try to get it out to the water and test further. Maybe I'm reaching but it did sound like the engine was running better. I appreciate any assistance

Thank You