3.0 130 choking at high RPMs???

[cvbdrew]

Here's the problem... The boat (1990 Searay 160 I/O) starts and runs normal. It has power and will get up on plane. It will even run at 4500 RPMs without a hick-up for about 10min. However, after 10 min or so, it starts to choke out. If I back off the throttle a little bit, it'll stay running, but gradually get worse. I have recently rebuilt the carb, replaced fuel lines and filter and just put a new pump in this morning. With each step, it got better and better. This morning after the new pump, it was running the best, but still choked out after running it for 10-15min at high RPMs. Obviously, I suspected a fuel delivery issue. But with all that cleaned or replaced, it's still doing it. Putting the boat into a sharp turn while on plane or pulling a wake boarder seems to cause it to choke more than just running it at 4500 in a straight line on calm water.

Could this be something un-related to fuel? Why would it run so well at first, but get worse after 10 min? Can a bad outdrive cause enough load on the engine to choke it out? Could the spark be an issue, but if so... why not do it all the time? Would running too much engine oil cause this problem?(I'm at the full line while hot)

The only other clue that may help is... I've noticed the temp reads higher than it did last summer. When under way it's just higher than the middle... say 160. When idling at the dock, it goes up to around 220. It didn't do that last summer. Why would it run hotter at idle vs under way? Could I have a clog in my cooling system? Could this be a related issue to the engine choking out at high RPM's?

I know... lots of questions. I appreciate the help as always!

-Drew

 

[Lodgepole]

Re: 3.0 130 choking at high RPMs???

I would check for a pluged fuel tank vent. and yes, your water pump line may have a restriction or worn or damaged impeller.

 

[Maclin]

Re: 3.0 130 choking at high RPMs???

As mentioned, a plugged fuel tank vent or less-than-adequate venting can cause that symptom. When the fuel is drawn out of the tank then air has to replace it. If air cannot get in fast enough then the fuel pump eventully cannot draw against the higher and higher vacuum. Try loosening the gas cap right after this happens, and listen for a hissing as air rushes in. That would indicate a venting problem. You can try running with the gas cap loose or even off to see if it acts any different.

Also, if there is junk in the tank the pickup tube can clog with a log-jam after a while as more and more of the larger junk is drawn to it.

In both of these cases the problem alleviates once the engine is shut off and the fuel pump draw goes away. The venting finally catches up, or the junk drawn to the pickup tube backs off.

The problem could also be the the check valve at the top of the tank. Those are usually in the 90 degree fitting that the fuel pump hose connects to. They can cause a restriction and I suppose it could act like that, let enough fuel by to run for a while then begin restricting if some junk shows up.

The reason in my opinion that it is better when running flat is the carb bowl is low on fuel and when you tilt it the main jet or jets uncover and lean out the mixture.

Another diagnostic test for this is to run the boat on a separate fuel tank, like from an outboard but plumb it to your fuel pump. Make sure THAT vent is open! then try the boat out. If the problem persists then I would bet that there is an old filter in the carb or the fuel pump hat you missed.

About the overheating at idle, GENERALLY overheat at low speeds indicates impeller/pump issues. Conversel and again GENERALLY when the boat does not overheat at idle and slower speeds but overheats at higher speeds that indicates a restriction in the exhaust mainfolds.

 

[newcdnboater]

Re: 3.0 130 choking at high RPMs???

I have the same engine and had the same problem last year. Turned out to be my condenser beleive it or not. After about 10-20 min the engine compartment got up to temp and the coil was getting VERY hot. Put a new coil with no resolve. Put the old condenser back in (this was right after new points/cond) and voila. Problem solved. Everything I had read said it was very rare for a condenser to fail so I never gave it much thought. The only reason I even tried it was on the advice of an old fella I met at the dock after spuuttering home late that night.

 

[cvbdrew]

Re: 3.0 130 choking at high RPMs???

Figured it out. The over heating was the impeller. Quick fix. Rebuilt the water pump and it's running at normal operating temps. However the choking at higher RPMs is caused by a bad head gasket. I can see the leak and the oil gauge drops when it's choking. Gonna let a mechanic handle this one. Any idea how much time it'll take to replace? The gaskets are only $20 for the head, and $10 for the valve cover. Gonna pay a lot more in labor though.