1993 115HP TLETS bogging down

[johnny be]

Over the past year and a half when I leave the launch ramp area and begin to accelerate, the engine would sound fine but then bog down for a couple seconds and then go back to being normal and I could go wide open throttle no problem. When I stopped, turned off the engine and fished, and went to start it up again it would do the same problem. It's gotten to the point now that it's permanently bogged down and I can only reach max 2700 rpms. This weekend I changed the water pump because my overheat alarm kept going off over the last couple trips.
I bought this engine five years ago. I use it for saltwater fishing.
Thanks for all of your help. Any response is greatly appreciated.

 

[Bosunsmate]

Check spark jumps a 7/16 gap on every cylinder- might be an ignition fault.
If they are all ok check compression next

 

[emdsapmgr]

That 93 115 did not have the SLOW system in the ignition module. So the rpm limiting is not related to the overheat. Based on that, I'd agree with Bosun, check your spark when the engine seems to be bogging. You can check it with an inductive timing light-clip it on each plugwire when under load. The flashes from the gun will show good spark, intermittents, weak, misfires, etc. Weak ignition components tend to fail once the engine warms up to normal operating temps. (may run fine when it's cold, crappy when warmed up.)

 

[johnny be]

Thanks guys for your help.
Do you think the carb needs to be cleaned out too?

 

[Bosunsmate]

Thanks guys for your help.
Do you think the carb needs to be cleaned out too?

Not at this stage, sounds more like ignition but if that checks out ok move on to the carbs

 

[johnny be]

Thanks fellas.

What Ive noticed is that this has progressed to this point. It started with the engine sputtering, bogging down, then it would go back to higher rpms and be good. Then stop and fish, and then start it up again and do the same thing eventually bogging down for a a few seconds here and there, kick in good rpm's then go back down to low rpm's up and down up and down.
Frustrating.

 

[racerone]

What are the numbers from a compression test ?

 

[johnny be]

Gonna buy a compression test tool soon as I don't have one. Also, just started it up on the hose in the driveway and it started right up and the rpm's went to 6000. Now I'm really confused. Works great in driveway but in the water it gets max rpm's at 2500.
Maybe this new information will help someone give me their diagnosis?
I will still check compression, spark, fuel filter and lines

 

[racerone]

They all wind up in the driveway !!----The motor does not have to do any work !

 

[rothfm]

6000 rpm on muff is soooo not a good idea! There are ways methods to test rpm's using a test prop in the water or a test barrel. Dont run it much over idle on muff's. Even then not long, short bursts.

 

[johnny be]

That's what I meant. Short couple of bursts then turned off. If I get the lower unit in a trashcan will that be the same as putting it in the lake(bay)? The drive to the bay is killing me just to be disappointed.

 

[Bosunsmate]

a big trash can would do, so long as its submerged and wont suck in air. The water needs to be like 7 or 8 inches above the LU (anti cavitation plate) when submerged

 

[Bosunsmate]

Check your fuel bulb holds firm with engine off, that checks that the carb floats arent flooding out.
IF thats ok, run it in the trash can and prime the fuel bulb with your hand to act as a manual fuel pump to check its not starving for fuel

 

[emdsapmgr]

That engine could be running on 2 cyls and still make 6000 rpm's sitting on the trailer. As the guys have said, the real test is when the prop is in gear and under load. Unlikely a fuel problem. Fuel pumps typically don't "work" sometimes and "not work" other times. Check the spark when warmed up and under load.