Force 120 bogging down on take off

[kamboat64]

Have a 1998 Force 120 HP Serial # 0E330402. Took the boat out last week and it ran great. Was pulling it on to the trailer and the over temp alarm sounded. Went ahead and purchased a thermostat, just in case. Changed out the thermostat this week and tell tale looked good running in driveway. Took the boat out yesterday and at WOT, the darn thing acted like it was stuck in mud for about 4 - 5 seconds and then would take off. Did this all day. Not sure what to make of it. I did have three of us in the boat and loaded down, but had three other times without this problem. RPM's seem low also. Only getting a little over 4000. I believe I should be closer to 5000. Carbs rebuilt last fall. Any thoughts?

As always, all input and assistance is appreciated.

 

[Jiggz]

Because it overheated, it's recommended to do the following:
1. Check compression on all cylinders, if good (within 10 psi of each other) continue on next step

- Does it hesitates if you smoothly accelerate all the way to WOT or is it only during a rapid acceleration like slamming it to WOT?

If it only hesitates during rapid acceleration check the timing tower make sure it is not binding. If it hesitates on both situations, check the fuel filter making sure it's at least half full. This could be a problem on fuel delivery or carburetion. Does the primer bulb collapses at high speed? Does it idle smoothly and maintain ~700 RPM in gear at idle?

 

[jerryjerry05]

I believe the top and bottom cyl. will have lower compression.
I think it's about 10# different than the 2 center holes.

You said:

Was pulling it on to the trailer and the over temp alarm sounded.

Sometimes if you leave the key on and the water drains from the motor.
It can make the alarm sound off. Seem the heat stored in the block/head sets it off when the water's drained.

If you change anything you should have started with an impeller.

One handy tool is a temp gun. $16 on eBay.​

 

[kamboat64]

Jiggz, compression tester due in the mail today. My first thought was lack of fuel... either filter clogged or pump. I'll pull the filter and check this week. It wasn't just a hesitation as it was still trying to accelerate and it lasted for about 4-5 seconds. It was like something trying to hold it back and then they just let go. I'll check the primer ball next time out. It was more pronounced when slamming into WOT, but was there when trying to smoothly accelerate also.

Jerryjerry, impeller was new last November. Should be OK. I started looking for a temp gun the other day, but procrastinated on ordering it. Seems I have to read reviews on everything a hundred times before I buy. I'm anal that way.

All good things for me to check next time out. Thanks again and I'll post results afterwards.

 

[Jiggz]

No tools required to check the timing tower for binding. All you need is a second person to move the throttle control while you watch the tower moving. Also check for slops and binding from the control cable. If all is good, check all fuel connections for air leaks. If you have a see through clear fuel filter you should see bubbles if there is air leak. Or a clog in the fuel system if the fuel filter stays low.

 

[kamboat64]

Checked compression. Numbers way high but very close.
170-175-175-175

I won't swear the tester was good. It is brand new, but who knows.
Going to borrow one and check again.
Went to adjust carbs and top one was only 3/4 turn out. Bottom 1-1/4 out. They were rebuilt last fall. Adjusted each. Now about 1-1/4 out for each. Synched up carbs according to sticky at top. Replacing fuel filter tomorrow and hitting the water. Will post results.

 

[Jiggz]

Compression looks good. Keep us posted.