GT150 Will only troll in water.

Hello everyone first time poster and here is my problem with a 1989 150 gt on a 89 basscat sabre.Out of the water it appears fine but when put in water it will max out at around 1200 rpm.So far i have replaced spark plugs 0.30 gap new timing base,tried a remote fuel tank to eliminate inboard tank problems and replaced all fuel lines.Spark jumped a 7/16" gap but not sure how much of a snap it should be.Did a compression test and cylinders were starting with top one 105/103/90/100/100/100.Carbs were cleaned and fuel pump rebuilt by a friend as i am a little nervous about playing with the carbs as you can do more damage than good if you have not done it before.I am a little skeptical of the work he did but he does a lot of small engine work as he used to be in the trade.I have not had it working since i got it,previous owner stated it started to only take off when it wanted to and then it would just go at trolling speeds.After the last time out i noticed something that may mean something to knowledgable members of this board.When it was in the water under load tilt and trim did not work and i would have to pull back on the throttle to get it to work.
Thanks in advance Jim
Waiting to fish a little further than the boat launch but it is good on GAS!

Re: GT150 Will only troll in water.

That engine came with a combination oil/fuel pump. I am not aware you can overhaul them. You may have a fuel delivery problem. When on the water, try squeezing the primer bulb. It forces fuel around the pump into the carb bowls. If it runs ok when squeezing the bulb, you may have a weak fuel pump.

Re: GT150 Will only troll in water.

Sounds like an intermittent electrical problem to me. Powerpack etc.
Had an old 60hp twin cylinder that did the same thing some years back.
Just my thoughts at this point. There will be many folk along shortly with all kinds of experience.

Re: GT150 Will only troll in water.

Repeat the spark test. This time pay close attention to the spark, is it a bright blue hot snap or a lazy orange/yellow arc?

This is very important as spark intensity is critical to performance, if it is not a bright hot blue snap then you have an ignition limited motor that will never perform and needs further testing to determine which component is failing.

DO NOT BUY ANY PARTS until you have reposted and tested to determine the fault as there is NO RETURN oon electrical parts.

Re: GT150 Will only troll in water.

if the guy who did the carbs, did not remove and clean the high speed jets, it will not take off, due to lack of fuel. also if the motor in not in sinc, the timing and the carbs are not working together, causing your problems. i suggest asking if the jets were removed and cleaned. if so, i would try a link n sinc.

Re: GT150 Will only troll in water.

Yes i should have stated pump was changed to a used rebuildable and rebuilt i also tried pumping the bulb when in water with no change in performance.
When i did the spark test it was done out of the water one plug at a time but was a little to here a snap,but would say only the top cylinders had a good and appeared blue and lower ones had less sound and color.I will repeat test when i get home from work.
Am i using the correct process to test the spark?

Re: GT150 Will only troll in water.

If you have a timing light, use it to check the flashes on each cylinder's plug wire. You are looking for constant, bright rhythmic flashes. All cylinders. If you can do it while idling in gear at the dock it will help by putting load on the ignition system.

Re: GT150 Will only troll in water.

Update have been very busy to busy actually so brought boat to johnson dealer that a friend referred me to for expeinced opinion for preliminary diagnostics.He did compression 5 cyl at 90-100 psi and left hand middle cylinder 80 psi.Spark checked out ok but 2 of the new or 2 trolling rides on them were no good plugs?So he changed them before putting motor on dyno and said it pulled 2300 psi and once surged to 3000psi but should pull 3800.At that point he called me and asked what to do next as it perform like a 115 hp and i told him in the water it was more like a 15 hp!He suggested it was the 2 plugs and may actually work now.But no time today to do that but dont believe it will make a difference.Over the phone his thoughts were that it did not sound right or not like a v6 and possible fluttering ignition problem and the 80 psi need to be addressed first and mentioned that he wondered if the bottom end had ever been apart as he mentioned that there are 2 piece plates on the crank ceiling off the cylinder chamber and maybe cracked.
When i picked it up i talked to them and told them the compression spread was a little more than i tested but it should still outperform my trolling motor.So pushed the question what was the diffrence between the dyno and water and that is when pitch came up,and after checking it is a14.5 x 24 pitch possibly a little much?
Dazed and Confused now but slowly learning, what would the next course of action be? Oh yea what symptom would a exhaust blockage do is it even possible and mechanic did not think it was fuel problem and friend from early post said high speed jets were cleaned.
Must get tylenol head starting to pound thanks in advance Jim