View Full Version : 1987 Johnson 150 GT runs rich and smokes

07-02-2008, 09:33 AM
"I was having problems with WOT misses and miss-firing at all RPM ranges. Found the stator to be the problem and replaced it with a new CDI model. That corrected all the problems I am having, well almost. Before I begin, I purchased the boat and motor new in 1987 and it has provided 21 years of outstanding service. Itís a Johnson 150 GT. The stator and a rectifier\regulator are the only major items I have had to replaced, other than regular maintenance.

The engine is running very very rich, but, not fouling any plugs, and smokes very bad with the flusher attached at idle and at the lake, trolling and at idle. This year it has began to smoke more and more. I am running Pennzoil 100% synthetic. All the plugs are wet but not black or carbon. New QL77JC4ís as I have ran for many years. In years past, after switching to synthetic oil, the plugs were dry and clean. Itís firing on all cylinders, 100 to 105 compression, and was decarbed last week. It seems to run ok but is not quite as good as I am use to. It gets to about 4600 RPMís @ WOT ; 5200 is about normal.

Of course, the VRO comes to mind but I tend to think there may be an air leak in the fuel line or, the likely problem is at the carburetors. I removed the silencer cover and noted gas in the two brass tubes that point towards me. It also looks like a small amount gas is at the bottom of the silencer. I read where this points to needle and seat problems? The carbs have never been rebuilt. I am considering rebuilding the carbs; should the floats be replaced? Are the kits and floats available together or separate?
I like the VRO and my guess it is working ok but that may be wishful thinking. Should my approach be to rebuild the carburetors first, then if the rich condition still prevails, look to the VRO, maybe disconnecting the VRO and going with 50:1 premix?

Iíve read many posts and need some expert direction. Thanks for any assistance.

Sid Helms"

07-02-2008, 10:13 AM
"(Compression & Spark Test)
(J. Reeves)

1st - Regardless of what problem one might encounter, always start with the basic troubleshooting procedure. Check the compression which should be in the range of 100+ psi (somewhat less on the smaller hp engines) and even on all cylinders.

NOTE #1 - You've already covered the compression area so ignore the above mention of compression.

2nd - With the spark plugs removed, rig up some type of spark tester whereas you can set a gap to be jumped. On the solid state OMC ignition systems from 1973 to the present (yours), set the gap to 7/16". The spark should jump the gap with a strong blue lightning like flame..... a real strong blue snap!

NOTE #2 - You say it's firing on all cylinders BUT is the spark as described above? Checking the spark via using the spark plugs is a waste of time and proves nothing. The above stated gaps must be used for a proper test.

The VRO.... If the VRO fails on the oil side, an alarm will sound (beep every other second) BUT if the fuel side starts to fail, there is no warning and the "fuel pump" delivery drops off, and at the same time this causes the oil side to load the carburetors with a extremely rich (too much oil) mixture.

A VRO repair kit may be available for your VRO, check with your dealership. From what you've said, it appears to me to be a case of rebuilding or replacing the VRO or going the premix route.

You mention that the carburetors have never been rebuilt. They are overdue. Remove, clean, and rebuild them with complete carburetor kits. The factory kits come with floats, the 3rd party kits may not, however I have never seen one of those floats go bad. Be sure to manually clean and inspect the fixed high speed jets that are located in the bottom center portion of the float chambers..... don't count on the cleaning solution to do that for you.

When time permits, visit my store at: http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store ("")"

07-02-2008, 10:40 AM
"Joe, thanks so much for responding. I apoligize; I did check the spark with a home-made tester that you designed. The spark was strong, not like it was with the bad stator-left bank was weak before. You can almost weld with the spark, almost.

I have a factory service manual for that year. Are the high speed jets located on the side of the carb? Mine have #38 stamped on all three carbs. Also, is there a post that explains the rebuild steps and special tools? Any special steps?

I think I will go with the carbs and see what happens. I saw a rebuild kit for the VRO on EBay for the fuel side. I am also replacing all the VRO and fuel hoses and clamps.

Lastly, are there rebuilt VRO pumps available, should I go that route?

Thanks for all you advice!! I agree, the carbs are about 10 years over due for a rebuild."