1979 100hp Johnson Javelin Power Issue

[REM 6824]

Hi Fellow Boaters,

I am trying to work some bugs out with my motor. I'll First give you a little history.

I bought this boat last November. I have had the boat out 6 to 7 times this years with no issues at all. She has been running quite well. On our last outing she took off fine (cruising around 32mph) for around 3-5 minutes then dropped to around 11mph and would not go any faster than that. We messed with it for a few hours, checking hoses, plugs, wires, etc and threw in the towel for the day. After getting home I drained the fuel and checked the tank for foriegn objects, the fuel lines and filter for blockage. I did find that the little (water) discharge line had managed it's way into the enigine compartment. I thought maybe the water mist was getting sucked into the inlet of the carb. So I fixed that issue and headedback to the lake. She never got up past 11-12 mph.

I did notice that one of the coils looked original so I ordered 4 new coils, 2 power packs, and a rectifier. I know you are to replace what is broken but I really hate having to continue the trip back to the store for something else. I changed them all this past friday and went to the lake saturday morning. She ran great for about 15-20 minutes. I slowed down and speed back up on the third attempt she only got up to 21mph.

Things I know for certain. I have installed a new starter, coils, power packs, rectifier and plugs.

Any help would be greatly appreciated.

Rob

 

[whalerfreak22]

Re: 1979 100hp Johnson Javelin Power Issue

uve got one hell of a motor there.the next thing i would do is rebuild those carbs and check for any bad connections or semi broken wires.also give us the compression readings on all 4 cyls.

 

[REM 6824]

Re: 1979 100hp Johnson Javelin Power Issue

Okay, I will get the compression reading on all 4 cylinders tomorrow and let you know. I have checked the connections (electrical) and they are all tight. I will also recheck all fuel lines for damage.

I am going to check on carb kit now. thanks for the advice.

Rob

 

[emdsapmgr]

Re: 1979 100hp Johnson Javelin Power Issue

It's possible you are losing spark to one or more cylinders. When the engine starts to run slowly, check each plugwire for spark. An inductive timing light will show the spark condition on each wire. Best to check them when the engine is laboring under load. You will see in the gun flashes if there are any misfires or no fire in the plug wires. Weak ignition components tend to fail after the engine warms up to normal operating temps. There are still two other expensive ignition components, the timer base and the stator-which can cause problems.

 

[REM 6824]

Re: 1979 100hp Johnson Javelin Power Issue

Okay here are the results from the compression test I did today.

While facing the motor

Top Left Cylinder 120 Top Right Cylinder 109
Bottom Left Cyl. 113 Bottom Right Cyl. 120

I have 2 carb kits, fuel pump kit and thermostat kit on the way it should be here thursday.

 

[emdsapmgr]

Re: 1979 100hp Johnson Javelin Power Issue

A 120-125 reading is normal for compression. You have one that is a little low, the 109. When you get the running issues straightened out, you might want to do a decarb on it. A can of Bombardier Engine Tuner run through the powerhead may help bring the compression up a little. It may start and idle better, too.

 

[REM 6824]

Re: 1979 100hp Johnson Javelin Power Issue

Should I replace the head gasket on the side that shows lower compression?

 

[emdsapmgr]

Re: 1979 100hp Johnson Javelin Power Issue

With compression numbers like that, the head gasket is probably ok. .

 

[REM 6824]

Re: 1979 100hp Johnson Javelin Power Issue

Hey Everyone,

Great news. With the multiple problems I was having, she is now back on the water doing what she does best. Giving the family and I a lot of fun.

I installed the new thermostat kit. It was way overdue. I rebuilt both carbs, and the fuel pump was fine.

Took her back out to the lake. She was running fine and when I went to give her a little more throttle she fell flat on her face, I took the engine cover off and had my friend working the controls, I then noticed the the cables were slipping in the hold down when he attempted to give her more throttle. We headed back to the dock, parked her and headed into town for some zip ties.
I zip tied the adjusters to the hold downs and boom she was ready for the day.

I have to say that I can tell a huge difference in power and response especially when pulling a person behind the boat. She jumps out of the hole now and planes out a lot faster.

One more little issue and I believe all the bugs will be worked out. The fuel sending unit. It only goes from Half to Full unless you disconnect power then it will drop to "E", but as soon as power is reapplied it is back to Half. Any ideas besides replacing the sending unit?

Rob