1992 johnson fast strike 150

[straitstack]

i have a 92 johnson 150 fast strike on a 24 ft pontoon... i have had it in the shop twice in a month and 1300$ later still no fix... starts easy idles out of the cove and up to about 3/4 throttle (23mph) all is good... give it a little.more throttle and the motor runs rough and missing/losing power... i back off the throttle a bit to where its runnin smooth then in just a short time starts missing and losing pwer again... over and over till im down to about 7mph.... the shop had put on new power pack spark plugs and spark plug wires. cleaned all 6 carbs new fuel lines. new fuel water seperator. still no change . i have new water pump and a good stream of water comming out.... any ideas??

 

[racerone]

I am surprised that the new powerpack did not fix it.-----It usually does fix everything.-------Did they check float bowls for warpage ?-------Run with a timing light and see how spark behaves.----Have an assistant operate the manual fuel pump when motor falters.------Have you checked operation of VRO mixing pump ?----Running at 50:1 premix ?---Try running off another portable fuel tank and hose as a test.-----What elevation are you running at ?

 

[oldboat1]

^^another portable tank with fresh fuel. Or test current tank for water -- draw from the bottom of the tank, and let it settle out in a glass jar. Water will settle at the bottom, fuel on top. Shops typically used their own tanks/fuel.

 

[straitstack]

i emptied and cleaned both fuel tanks and refilled on way to check it out on the lake... i.mix the oil/gas 50:1 manually... they rekitted all carbs and set timing with timing light... we have checked the bulb while running and it is hard.. .. elevation is about 740

 

[straitstack]

i have 2 tanks on the boat.. as i said emptied and cleaned both. new fuel lines from tank through the switch. and switch to the motor

 

[straitstack]

something i forgot to add is it runs great full throttle on the muffs.. but under a load is when it acts up.. the further you go the worse it gets

 

[oldboat1]

By switch, do you mean a selector switch/valve for selecting one tank or the other? If so, perhaps the valve is clogged or defective. Bypass the valve and go directly from tank to motor.

 

[oldboat1]

Never, ever run full throttle on muffs. Idle to fast idle only!

 

[straitstack]

i will try bypassing the selector.... when i said full throttle i just reved it and back down i do not leave it there.. any other ideas.. my fear is the head gasket... is thos a possibility?

 

[straitstack]

also it seems to use an astronomical ammount of fuel.... went 6 miles and burned about 9 or 10 gallon of fuel

 

[racerone]

They all run / sound great on muffs !!-----It would do that on 3 of 6 cylinders.-----That test means nothing

 

[oldboat1]

Think I would go back to the shop with it, or at least discuss it with them. Absent that, measure spark at each boot using an adjustable open air tester.

 

[oldboat1]

A blown head gasket is a possibility. Showing white smoke, engine running hot, loss of compression? If doing it yourself, need to check compression, and monitor operating temp.

 

[straitstack]

ive checked compression 3 times and im 95-105 all the way around.. no over heating horn when running and just the normal oil smoke when running

 

[oldboat1]

Whether the horn sounds or not, surface temp at the top of the heads should be around 120-140F. Over 160F is too hot (and too hot to touch). Bypass that valve, and measure spark on each lead:

 

[straitstack]

i have an infrared thermo... ill check it thank you..

 

[Faztbullet]

This motor don't have head gaskets..it has o-rings

 

[oldboat1]

i my fear is the head gasket... is thos a possibility?

See #17 -- don't know if a defective o-ring would have the same effect(s) of a blown head gasket.