CAN A BAD CARB REBUILD CAUSE OVERHEATING AND EVENTUALLY ENGINE FAILURE???

[mrecho76]

Hello All,

So I have a 1996 Johnson 115 Bubbleback and the motor ran great with the exception of the difficult cold starts. From all the research I did on this forum (and others), it seems that these motors are known to be somewhat difficult when starting cold. Once warmed up, the motor would start fine the rest of the day (as long as I advanced the throttle, and if I primed it a little if it was off for a while).

But somewhere I read that rebuilding the carbs may help with the difficulty starting issue so I ordered a rebuild kit and decided to have a local shop rebuild them (I mean it couldn't hurt right?) I drop off the boat and rebuild kit at the shop and days later received a call stating that the rebuild was done but that the overheating alarm and light was coming on. Now I NEVER had any issues with overheating and my boat doesn't have any temp gauges, just a buzzer with a warning light. The shop recommends changing the thermostat to start and so I agreed.

After several more days, the shop states that the light wasn't turning on anymore. I pick up the boat and hit the water and the light came on after a short warm up. I turned off the motor for a while and started her up again and the light never came back on. Then all of a sudden mid-day, the motor started running REALLY rough and kept shutting off at idle speed. If I got her started and going, she'd run ok at higher rpms, but as soon as I let off the throttle, she'd die.

I take it right back to the shop and the next day I'm told that the compression is low on one side (like 40 and 60 psi). I'm told that best case scenario it may just be a head gasket, or worst case, the cylinder ends up being scored which would require a whole lot of money spent (either for a powerhead or a re-power).

The question that keeps floating around in my head is why did things go so south all of a sudden? Everything was fine until I took the boat in to rebuild my carbs. Is everything really just bad luck and coincidence? Or could a mistake during the carb rebuild cause overheating issues? I'm no mechanic, but I thought the carb was for fuel/air delivery and the cooling system was different.

Oh, one thing I do wanna mention, within the past year I had the lower unit rebuilt with all new gaskets, new impellor, new VRO pump, new bulb, new fuel filter, new fuel connectors, new plugs, new starter, new ignition coils, and probably more that I can't think of right now. And also, when he showed me the 2 old thermostats, one was closed (which is normal until it heats up) and one was corroded and stuck in the open position. Now wouldn't that mean water is flowing too much instead of restricting it? How would that have caused overheating issues?

Anywho, chime in with thoughts, it'll be much appreciated! =)

 

[Bosunsmate]

Yes a carb problem can cause overheating and ka-pow as if the motor runs leans( reduced amount of gas) that cylinder burns hotter actually even though it has less fuel. It may just be a coincidence that you just had them rebuilt or it may be what caused it, impossible to know unless you forensically unpick the carbs and find an error they did. It may of just being a part of the fuel line randomly coming off and blocking in a jet.
Normally you will notice it running a bit rough, a miss or spluttering at idle and that can indicate a blockage so whenever that happens i always start looking for the reason in case its a blocked carb.
The stuck open thermostat might not of being open at its maximum and i think on some engines you get air bubbles forming in the water passages with a stuck open thermostat as there isnt enough back pressure at the beginning to force air out.

Hopefully it is just a headgasket, if the headgasket was leaking you can get combustion gases pressurising the water jacket and overheating the engine.

 

[emdsapmgr]

It may have suffered an overheat. Couple of scenarios: 1. a thermostat stuck closed on the low compression side of the block. The two stats control cyl head temp on each side of the block. When one sticks closed-no/little cooling water circulates thru that side of the block at idle. Once you get the boat up on plane, the pressure relief valves in the thermostat housing open, flooding the powerhead with extra cooling water to keep the engine cool-whether the stat is stuck shut or not. Your initial overhead warning may have come as the engine idles. Usually you will get a overheat warning horn with this scenario. I would have thought the repair shop's thermostat work would have prevented this type of failure. 2. If a rubber water diverter inside the block has moved or has accumulated debris around it-the engine can overheat on one side. At idle or WOT. Since the water pump is still pumping water to the powerhead-an overheat warning may not sound. Once an overheat occurs the pistons swell inside the cyl liner and the reduced piston-to-cyl-liner clearance makes it hard for the engine to keep running-and may cause ring failure. (low compression) Agree with Bosun, the best case would be if the overheat was minor and a head gasket failed. A cheap fix that will require the head to come off. That would give you the opportunity to inspect the rubber water diverters and cyls/pistons. You'll want to visually check the top rings of both pistons to see that they are still intact.

 

[gm280]

Forensically guessing as what happened or what came first, is at best only guessing. Unless you have verifiable proof, there is no honest or fair way to pinpoint what occurred. Check the head gasket and see if that is your problem. But there are too many other things that can have similar outcomes to create theories and point blame... The fact that one thermostat was stuck open and the other corroded says a lot about the yearly maintenance that goes with ownership of any boat. The sad fact that boats (or their engines) are certainly not like automobile engines in the fact that autos usually get started and run near daily, boat engines sit a lot. And that IS just as bad for an engine then most anything else. I'd say more investigation is needed and repairs as well... JMHO!

 

[F_R]

If I am not mistaken, you have two carburetors on that engine. One feeds the top two cylinders, other feeds the bottom two. But your post says you lost compression in one side. A lean condition should affect either the top two or bottom two, if one carburetor was the cause. For that reason, I doubt the carb job was faulty. OK, a general lack of fuel could cause any or all of the four to have problems, depending on several factors. But still, don't be too quick to judge the guy for the carburetor job. Hey, it was your idea in the first place to work on the carbs, right?

What I do wonder is why everything was suspected for the overheating except the water pump. The water pump would be the FIRST place I would look for an overheating condition, I don't care if it is fairly new. It could have shed a vane or spun a hub, who knows without an inspection?

 

[mrecho76]

Thanks everyone for the input! [F_R], yes there are 2 carbs and your logic makes total sense and puts my mind at ease! The lake did have some debris that day and I'm leaning toward something got sucked up into the lower unit and clogged somewhere.

So now here's the million dollar question. Again it's a 1996 Johnson and I know it's seen saltwater with owners before me. So far it seems that the motor wasn't taken care of as it should have since I'm always having to repair things and replace components. I have 3 options the way I see it:

1. Purchase a re-manufactured powerhead and repair this motor.
2. Re-power with another used motor
3. Re-power with a new motor.

I'd like to avoid option 3 since it'll cost way too much and I most likely won't see much of that back when I sell the boat eventually. Option 2 is a gamble for I might buy a used motor that's crap again. Option 1 would ensure I have a solid powerhead, but then the rest of my motor is still old and have been put through years of saltwater use.

Which option would be best? Or I guess what I'd really like to know is if changing the powerhead will provide me a solid reliable motor? I have done a lot to this motor thus far and would hate for it to have been for nothing. My fear is that I change the powerhead and something else go wrong again and again (can you say moneypit?).

What do you all recommend? Thoughts? =)

 

[Bosunsmate]

Id wait to hear back as it might just need a new head gasket.
If it has damaged the rings you might get a good price on a rebuild of the powerhead from them.
It doesnt take long to undo the head gasket so i would be wondering why they havent given you an answer about that yet

 

[emdsapmgr]

I'd think if it were the water pump, that all 4 cyls might have suffered the same problem, not just one side. Take the head off and have a look.

 

[gm280]

Even if the rings are the issue, If the bores are still sound, new rings could be the only needed parts (other then the usual seals and gaskets) to fix her up again. Even if you have to bore the block, new pistons and a good inspection of everything else will make it like new once finished and at a fraction of the new engine cost. And if you do the work yourself, being tear down and reassembling again, the cost drops significantly as well... So you have a lot of options. But wait to see what is the problem before going to the extreme with possibilities... If the exhaust and lower foot sections are good, then a real good cleanup of any corroded saltwater effects can be taken care of and no further issues again. JMHO!