Thread: Compression info on my 1989 Johnson GT 150 (model #J150STLCEM)

Gauges will vary, as long as the 6 cylinders are within 10-15% of each other you should be fine in the 80-90 range.

punt66 and bassmeister,

THANKS for the info. Going to do compression check now. You two are fast!!!!Thanks!!

The compression on my 1985 is in the 85 - 90 Range and it runs just fine although, you can expect it to be a gas hog because it loves the stuff. One other thing you might consider is a leak-down test to see if all cylinders are less than 10% leak-down

Regards,

OK......compression check results. I'll list the 6 cylinders from top left to bottom right.

1. 98 4. 95
2. 98 5. 91
3. 95 6. 88

Here's some info on how it's running. Idles very high when in neutral; when I backed it off the trailer and started forward, absolutely no power when increasing throttle. It started to bog and run very rough immediately. Guessing at speed, but runs 10-15 MPH at full throttle, and rough.

Thankfully, compression seems good, so what should I go after next? Last week, I took the 3 carbs off, cleaned the jets with a tiny piece of wire and carb cleaner, and re-installed. Needle valves all looked good. Should I have done anything more to the carbs? Is a carb repair kit or rebuil much more than what I did?

Thanks,

Jason

Changed both. Owners manual called for a Champion plug QUL77......all I could find at the auto parts was a QL77. Checking with my local marine store to verify correct plug.

Verified QL77J4C is the correct plug.

Very good questions Punt. All the info we can get the more we can help.

If you've gone through all that on your GT-150 and it won't get going, I'd suggest that after the carb going through that you check your carb linkage and make sure the plates are all opening up together. The cross flow carbs have a linkage that runs between the upper,mid,lower with a half moon linkage on the center carb. The Center carb's cam follower controlls the throttle plates opening and closing provided the linkage is correct.
On the middle carb there is a roller on the cam that has a phillips head screw on it with a black plastic roller that should have a clear roller over it. The clear part of the roller should be touching the short embossed (raised) mark on the Cam. If the clear cover is missing order a new roller assembly or take a 3/8" id piece of clear hose and install it over the black roller. Adjust it so the center roller touches the cam and make sure the plates open a WFO.

Thanks.........I know what you're describing and will verify in the morning. The carb linkages on this motor were very easy and uncomplicated, compared to some of the "war" stories from other members. If the power pack were bad, how would the motor operate?

Usually no fire on one side, could be one or all cylinders on that bank.

So if cylinder compression is good, cylinder is firing.........correct?

Not all the time, at timing light would verify that. Move the lead to each cylinder and shine it at the block.

OKAY......here's the latest. Carbs cleaned and linkages are synchronized. Compression test was good. Just did a spark test to see if I was getting fire to all the cylinders. The right bank of 3 cylinders all have good spark. On the left bank, the middle cylinder (I'll call it the #2 cylinder) has NO spark at all, the top and bottom cylinders have good spark.

What should I troubleshoot next, the spark plug wire, the power pack, etc......?

Swap coils with that cylinder and see if it follows the coil.

It didn't follow the coil, so I took it that the power pack was bad. New power pack ordered and on the way. I'll let you know the final outcome. I, along with everyone else I'm sure, really appreciate the help and direction that guys like you provide. THANKS!