1993 Johnson 150 Engine Repair

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1993 Johnson

Silver Star Series 150

Engine Repair

My 1993 Johnson 150 Silver Star Series engine started smoking badly at idle and having loss of power trying to get up on plane. It was intermittent at first, but got steadily worse until it would not hardly idle. The smoking at idle was so bad that I could barely see out of the cloud that surrounded the boat.

I figured out by reading on http://www.bbcboards.net/ that it was likely a fuel delivery issue and possibly a leak in the diaphragm in the VRO pump. I had disconnected the oil pump line and removed the oil reservoir to begin mixing the oil and gas when I purchased the boat six years ago. But I was still using the VRO for a fuel pump.

I also posted the whole process on BBC in this thread.


One thread on http://www.bbcboards.net/ pointed me to a standard pulse driven replacement pump assembly sold by Offshore Marine in Sarasota Florida. It uses two pumps mounted back to back on an aluminum bracket. Once the VRO pump is removed, It mounts in the same spot. I ordered one and it was here in about four days.

The instructions were pretty straight forward, but the pictures were just black blobs of black ink. Better pictures would help identify the small section of the VRO bracket that must be removed so the pump will fit flush. I used some small wire cutters to snip out the section to be removed.

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Two of the original mounting screws are used to mount the aluminum bracket. I reused the OEM 3/8" "U" shaped fuel delivery line and used a short section of the smaller fuel line they supplied for the pulse feed. The fuel outlet comes with an OEM style fitting that just plugs in and is held in place by the aluminum bracket. It was a fairly easy install.

I also replaced the fuel bulb with a new Yamaha fuel bulb to be sure it was working correctly.

I tested it out on nearby Jackson Lake. It idled better, but the cloud of smoke was still there. I tried WOT to get up on plane and could only get to 3000 rpm and it took forever to get on plane. Something was still wrong!

I went home and checked compression. All good. So, it still must be fuel delivery. Then I pumped the bulb while watching the pump and found fuel squirting out of the vent hole on the back of the rear fuel pump. AH HA! That won't work. I called Offshore Marine and talked to Ron. He agreed to send me a new one but wanted the leaking one to see what was wrong. That was great customer service!

I got the new one two days later and put it on quickly since everything was ready for it.

A quick trip to the lake confirmed that was it. It now runs like it is supposed to run. Now I can do some fishing!

Well, I went to Lake Oconee to do some fishing since I was sure the boat was fixed. NOT! I got a lot of smoke while launching it. It ran OK for the trip across the lake to my first fishing spot. When I got to the spot, the engine would not idle without dying and the thick cloud of white smoke was present again. I took the cowl off and started the engine. Now I could see fuel leaking from the red adjuster in the top of the electric primer assembly. Further inspection revealed that the red plastic was cracked going into the housing and letting fuel leak out. I guess that when the fuel pressure increased, it found a new way to leak out.

Back at home, I took the primer assembly off and dismantled it.

The red plastic adjuster is used to set the amount of travel for the plunger inside the solenoid. It also has a valve on the end of it like a tire valve. I guess over time the brass valve caused the plastic to crack. I thought that maybe the O-ring was bad, but it was not cut or severely worn. I found a small hole in the end of the plastic part that allows fuel into the valve. When I blew into the end of the plastic piece, I could hear air escaping from the crack.

I figured that since I never use the valve, I could just plug the hole and get the boat running. I did order new parts to fix it properly, but wanted to get the boat back in the water this today. I have used JBWeld successfully in the past to fix carburetors, so I knew it would hold up to fuel. So, I cleaned the oil from the plastic, kneaded a small ball of JBWeld and plugged the hole. I will take the boat to the lake later today and see if it works for a temporary fix.

I will update later on how this worked out. Now I am off to the lake for a test run! It still was not running correctly.

One of the forum engine mechanics suggested that I check the vapor separator bowl. I took the vapor separator bowl apart today.

It seems to be working since the float seals off the needle valve and there are no leaks. So, I reinstalled it on the engine.

I did the check another engine mechanic's suggestion to be sure the primer system has no voltage on it with the key in the run position. I also got the new Schrader valve assembly and installed it on the primer solenoid. It does not leak now.

Then I removed the vapor pump and made sure I installed the new gaskets and diaphragm correctly and reinstalled it.

After getting it all back together, the engine still smoked excessively and does not want to run at idle. I pulled the new spark plugs to check if it is a problem with only one cylinder, but all the plugs are getting black and are wet when pulled. So, it is still getting too much fuel.

I then tried a forum member's suggestion to eliminate the vapor separator bowl and vapor pump. I connected the fuel line from the tank directly to the inlet on the new pump. But I left the output of the new pump plugged into the vapor bowl assembly. The bowl section is separated from the pressure side that feeds the fuel tee to the fuel rails and primer system which I verified by inserting a piece of the 3/8" fuel line into the hole and blowing on it. It held pressure without letting anything escape. The pressure side of the tank uses the slot in the side of the tank and the lid shown by the yellow arrows on the picture below.

I also primed the lines with the fuel bulb, but opened the test valve arm upward to see if fuel would come out the two small 1/16" lines from the primer to the crankcase. Fuel did come squirting out. With the valve arm down, no fuel came out. Now I started the engine again. STILL excessive smoke! To be sure the primer system was not causing this, I pulled one of the small 1/16" lines and cranked the engine. No fuel came out the line, but the engine was still smoking badly. Unless the new pump system is over-pressurizing the floats in the carbs causing them to flood, I cannot figure out how the extra fuel is getting into the engine.

More suggestions were offered on the forum so I began testing them.

I am mixing the fuel at 50:1 and have been since I have owned the boat about six years. I could not find my temperature gauge, but will try to get and verify engine temperature while running. The vacuum switch has not been connected for six years either. I believe I disconnected it when I disconnected the oiler side of the VRO.

Today, my brother and I tried many different things to see if we could identify the issue.

I inspected the diaphragms in the VRO and found them good so I reinstalled the VRO to pump fuel.

The engine ran, but still smoking badly and running a little rough at idle.

We found that we were not getting a firm fuel bulb, so I pulled it up and pointed the tank side end toward the ground and started pumping. It did start to get firm quickly, but then we had a fuel leak at the primer lid gasket. We tightened the screws and the leak ceased. The engine still was smoking badly and running a little rough at idle.

We checked and made sure that the primer was not putting fuel into the two small 1/16" lines while the engine was running. It checked good.

We pulled the plugs and all were getting black and were very wet with fuel. Somewhere fuel was still getting into the engine excessively.

We tried using the second tank to be sure the fuel was not improperly mixed. The engine still was smoking badly and running a little rough at idle.

We filled a six gallon portable fuel tank with new gas and mixed oil in it at 50:1 and ran the engine with the new gas. The engine still was smoking badly and running a little rough at idle but after a few minutes the smoke reduced to the expected level and the engine smoothed out. So, we switched back to the on-board fuel tank and after a couple of minutes the engine started running rough and smoking badly again. We thought we had found the problem. We switched back to the six gallon tank and the engine started running correctly again. Then this happened:

The air silencer was off, so the tube from the vapor pump was not attached to anything and while the engine was running badly, fuel suddenly squirted from the tube. We found that the small vacuum line attached to the other nipple on the pump also had fuel going in it. So, we took an extra rubber gasket that came in the gasket kit and used it to close off the fuel at the O-ring.

Now no fuel could get into the engine via the vapor pump. The engine started to run much better now and the smoke level was correct.

I took the boat to the lake to test run it at speed. It started well and ran smooth at launching. I ran it to top speed several times on the starboard tank. Then to top speed on the port tank and everything seemed good. While idling back in to the dock it started running rough and making excessive smoke again.

I took the cowl off to look for fuel leaks, but found none.

I gave up for the day, loaded the boat and headed home. Boy am I getting frustrated! I really feel like I am overlooking something simple that is common to the fueling system. I feel like the carburetors are good since it will run OK sometimes. Likewise, the fuel is mixed correctly and is good fuel. How can that much extra fuel be getting into the engine?

The forum members came through again with new suggestions. They included checking the recirculation system including the recirculation valves and hoses.

Also, that running with the vacuum switch disconnected could lead to major problems if the motor runs lean at WOT.

I had also noticed that the carburetor bowls appeared to be warped. So I took the carburetors to replace the bowls. I also took the intake manifolds off to inspect the valves and reeds.

The check valves appear to be bad. There is a small fiber disc that has come out of several of them.

So, I ordered new check valves and gaskets. The reeds look good from the outside and do not appear to be worn or bent. The carburetor bowls were starting to warp, so I ordered new bowls and carburetor kits.

Not sure if these parts will fix the problem, but I sure hope they do. I will post results when I get the motor back together and test it.

Thanks again for the help everyone.

Today I took all the carburetors apart and cleaned them to be ready for the new parts. I did remove the high speed jets from the bowls since I have new bowls coming.

Then I started taking the check valves out of the intake manifold. They would not come out with pliers. So, I ground the tip off of a drywall screw and used it to pull them with a claw hammer. I was careful not to seat the screw too deep so I did not damage any of the tiny screens below them.

Most of the check valves were missing the inserts. It appears the small brass tabs break off and allow the inserts to come out.

There were some where the tabs were still all intact, but I removed all the valves and will install new ones.

I cleaned the screens. This one needed it badly but it was the worst one of the bunch.

Here is a picture of some of the reeds. They all look good on both sides like the ones in the picture.

Parts are supposed to be here tomorrow per the shipping tracker.

I noticed that the three bolts holding on the inside edges of the intake manifolds had a sealer on them. One of the forum mechanics said it OK to use Permatex Ultra Gray silicone for reinstalling them. Also, the screws that hold the reed assemblies onto the intake manifolds need some type locker per the OEM manual. He also said blue Loctite would work for that.

Another member said someone had some new reed assemblies for sale recently. I checked and was able to purchase all six reed assemblies new for very little cost. So. I could not pass them up.

Most of my parts arrived yesterday. I got to installing them today. First I put the carburetors back together. I took my time and made sure to check the float adjustments and install all the parts. On one I almost forgot was the gasket for the stem.

That stem gasket is very important. I once bought a 25 hp engine for about half price because the owner could not get it to run right. A friend of his had "rebuilt" the carburetor for him. The engine would run but not at speed. I found the center gasket missing when I removed the carburetor. That fixed it.

Then I installed the top two carburetors on each throttle body and carefully torqued the bolts. The bottom one will be put on once all the bolts are installed when the throttle body is installed on the engine.

I also installed the high speed orifice into the new bowls. That would not be good to leave out! I ground the edges off a good screwdriver so it would fit in the hole.

As I mentioned above, I bought new reed assemblies from one of the forum members. Not that I needed them, but they were available and would eliminate possibility of a cracked reed.

All six assemblies are brand new. So, I installed them on my intake with new gaskets. I used blue Loctite on the screws and torqued them carefully.

I also installed the new re-circulation check valves and used the old screens I had cleaned. I used a flat round punch to tap them into place.

Then I installed the intakes onto the engine. Again, I was careful to torque the bolts.

Next I installed the throttle plates with the carburetors.

Then I reinstalled the fuel system and connected all the hoses.

Notice that I reinstalled the VRO pump and unblocked the vapor pump.

I pumped fuel into the system with the fuel bulb. It took a little pumping, but I now have a very firm bulb and could see no leaks. I plan to test run it and make any needed adjustments tomorrow morning. If everything checks out, I am going to test it at Lake Jackson tomorrow too.

I will post the results tomorrow evening. Boy I hope this works!

Maybe I will even get to fish for a few minutes!

I find it funny how I can wake up at 3:00 am and remember stuff. Last night, I remembered that I may not have attached the pulse feed to the vapor pump. Sure enough, looking at the last picture, I can see it is not connected. I will do that before the test run this morning. I hope nobody yells SQUIRREL while I am attaching it, or I may forget again.

Thanks to the BBC forum members for all the help. I had little experience with this engine. Now, I have much more knowledge if I can just remember it. One of the reasons I take pictures often when doing something like this is to help me remember how I did it in the future and to help me do it right the first or second time.

Again, thanks for all the help. I could not have gotten this far without it.

Before taking the boat to the lake, we adjusted the throttle plates to the timing arm. I have no special timing tool, so we did not mess with the timing itself. Only made sure the throttles begin to open as the timing arm starts to move.

The test runs we made today are on the hose. We could not get the engine to run properly, so we did not risk taking it to the lake yet. I may tomorrow if that is the only test left we can try.

Here is a link to a video I made while it was running at temperature. About 2000 rpm then moved to idle.

1993 150 hp Johnson Silver Series smoking badly

We did a compression check again. The compression was 89 psi on the port bank and 91 psi on the starboard bank. Very consistent. All the plugs are extremely wet.

My digital temperature gauge on the top of the cylinder heads showed 135 deg. F as the highest temperature after running the motor for over 10 minutes to warm it up. Never ran above 2500 rpm during the entire time. The thermostats were replaced last season.

Tilting the engine seemed to have no effect. Total run time is probably close to 30 minutes in 5 to 10 minute runs. We pulled the pulse limiter and it looks new. It allows air in and out. Not sure if it should but you can blow both ways through it.

The engine is still smoking badly and is getting too much fuel. Tomorrow will be a better day for me to take it to the lake. I think I will install the kicker before going...just in case.

FYI, I will be keeping the new fuel pump in the boat until it is needed. It will be good insurance for the future.

I took the boat to the lake. It barely would run to get it launched. This is it just after launching.

1993 150 hp Johnson Silver Series First Lake Run

One of the mechanics suggested that I run the "snot" out of the engine to clear it out. So, I did. The first run it would get out of the hole OK, but would only get to 3500 rpm at WOT. I ran it for a few minutes at WOT then stopped to see if the smoke had cleared up. It looked better, so I made another run. This time it reached close to 4000 rpm and just under 40 mph. After a few more runs it finally got up to about 5000 rpm and 53 mph. I ran it for about 45 minutes at WOT total.

I tried taking temps while on the water, but would have to stop to do it. Then my cheap infrared temperature gauge quit working correctly. The closest I got for a temperature was 126 degrees F before it flaked out. I will have to buy a new gauge.

I guess I got the snot out of it. Now it idles correctly with the correct smoke level. At LAST! I am so glad. Now I may be able to fish in our yearly big fish tournament Thursday, Friday and Saturday. I sure hope the engine stays fixed.

This is it just after it started running correctly.

1993 150 hp Johnson Silver Series after snot is run out of it

I really appreciate the help from all the guys who helped me on the BBC forum. There really is no substitute for good experience. Thanks for sharing yours!

A few days later I took my brother over to Lake Oconee to further check out the boat and let him fish since he helped me fix the boat. I did catch several fish. This one was the best at 3-3.


As of 12/31/2018 the engine is still running great! Success!