1979 85 johnson seahorse no power at full throttle.

[opetous]

on lake starts great and idles great. take off seems alright until about 1/4 throttle then i have nothing after that. just puts along fast enough to create a tiny wake behind us 1500-1550 rpm. took it home and changed spark plugs and tested them all. they all have blue spark. compression tests resulted 122- 125 all the way around. brand new gas with synthetic 2 stroke oil mixed at 50:1. started it in garage with ear muffs on and at 4600 rpm almost wot it sounds like an indy car with tonnes of power with no load on prop(17"). again went back to the lake and same results of great start and idle but alright take off then no power after 1600 rpm. can anyone please help.

[Bob_VT]

Welcome to iboats

You need to verify the spark at ALL cylinders. It sounds like it is only running on two of the four. A motor will freely rev up without all cylinder's firing.

You may have a bad power pack on one side. Use an old fashioned timing light to establish if you have spark.

It is NEVER a good practice to rev the motor in neutral or it may do permanent damage

[opetous]

thanks for the reply. I did check that there is spark on all four cylinders, and they are all blue. And when i had the muffs on in the garage i rev'd it up only for a second in gear to see if it would have any power with no load on the prop, and she had endless power with no load? so i thought i had fixed the problem. went back out and same results. great start and idle but ok take off and no power after 1/4 to 1/3 throttle?.so is it then possible that in my garage i am getting good spark but when i load the prop (on the lake) one or more of the cylinders is dying?

[emdsapmgr]

Check the plugs after you run it. Are they all the same color? Do they all look like they are getting fuel? That engine will run fine on the garden hose on 2 cyls. Best to check for spark when the engine is under load in the water.

[opetous]

yes thanks for replys.. i tried all the above including spark tests and timing check.. all seems well compression again is 120 across the board but still i have a dead spot in the throttle from 3/4 to full even after she plains out at 3/4 throttle it wont give any more speed but i can move the throttle from 3/4 to full and nothing..i ripped the carbs out a bit back and cleaned them although they were just done. reset the floats and it seemed to have a bit more power..any ideas would be great..

[emdsapmgr]

You might have a look at the high speed jets in the carbs. Inspect those jets for any debris.