1988 Alura - engine bogging at 3000 RPM

Hey everyone. I've been searching awhile on this topic and have found a few older threads but nothing recent. Here is my problem:

I have a 1988 Alura with a Chrysler 270 engine. We can't get the boat to plane out. At about 3000 RPM, the engine sputters, bogs down, and dies unless we pull the throttle back. If we do this fast enough, the engine comes back up to speed, and will run. If we try to push it, it just bogs down and dies. We can rev the engine up as high as humanly possible at the dock with no issues. Only at load does this problem occur.

We've rebuilt the engine twice now, played with the carbs numerous times, checked the gas tanks, sucked from a 5 gallon bucket, replaced the distributor. Originally, the engine would get up to only 2500 RPM and then bog out. We rebuilt it, replaced some rings on one dead cylinder, then reinstalled. After rebuilding it, it increased to 3000 RPM before having issues. We noticed oil pressure spikes before the previous rebuild. Now those are gone.

We're currently at a loss. What else could it be? If the prop is wrong, what would cause the engine to slow/bog at different RPM levels (2500 then 3000)? What about the exhaust? Could the mufflers be causing too much backpressure as the engine loads up at 3000 RPM? We're running out of things to look at....and we're getting very discouraged.

Any and all help would be appreciated. We just need a direction at the moment.

 

I'm sure you will get the correct answer to your problem. Just wanted to relate an experience I had with a Chevy pickway, As I speed up it would go so fast then quit until I got to lower speeds. Try it again and the same thing happened. Took to 2 mechanics without any success. Took it to a third and he drove it and said "change your battery cables." I did and the problem was solved.

 

Exhaust and air intake can affect performance. But what you describe sounds like fuel flooding. Could be from carb settings but more likely bad spark.
Mechanical issues are normally more associated with lowered performance than faults.
I don't know or have interest in these engines but you should research a bit about their coils, distributors, plugs and leads.
Also checks on voltages at the higher revs. Weak wiring, alternator cutting out, shorts, these are the things I would make sure about.

 

With an engine that has been worked on several times, all things are possible.

To me the most likely cause is insufficient fuel flow: a clogged filter, fuel line or a bad pump diaphragm. At the dock you can rev up to the red line because there is no load and little fuel is needed; with load the fuel requirement increases 10-fold and more.

 

I appreciate the help guys. I'm looking at the different issues you've touched on. I think we're gonna focus on an electrical issue at the moment, either in the distributor or the wires running to the spark plugs. Those wires have been replaced but upstream they have not. The wiring on this engine is not pleasant to look at so there is a very good possibility something could be wired incorrectly or disconnected that shouldn't be.

 

Aggie,
I had one of the original Datsun 240z' and its fuel filters would clog with what looked like a clear jelly bean. You couldn't see it and the filter looked ok. It did the same thing you described. Try replacing the fuel filter if you haven't already done so. Just a suggestion. Good luck

 

Chuck,

We've replaced the fuel filter twice now. We've removed the old fuel lines and installed new ones. We even took a suction from a clean 5 gallon bucket while trying to get up on plane and had the same exact issue. I think we've cleared the issue of insufficient fuel at load. It still is on my mind but we have to make some progress somewhere.

Issues still ongoing...will update as I can.

Thanks all!

 

Quick question on this particular engine (Chrysler 270): anyone know what the timing/advance should be set at on the distributor when at full load?

We have mixed thoughts on this setting. Right now it's set at 33-35 degrees. Seems high to me. When we replaced the old distributor, the new one was a different design that came with multiple stops.

 

Why did you rebuild the engine twice, how did it fail? The answer may narrow down the troubleshooting.

 

Take the engine back to it's base line and systematically go through it. The "hunt and peck" method of diagnose is for novices and shade tree nut jobs. You'll just be chasing your own tail on this, unless you establish a base line and use practical diagnostic procedures.

Every boat that comes into my yard gets this done, unless the issue is obvious. What does this mean? I call it the "level the playing field" charge. This includes new plugs, new wires, cap, rotor, points and condenser if it has them. Also new fuel filters, cleaned arrestor and fuel line inspection. Then the engine is tuned to spec. Now, is the time you can actually find out what's wrong (if anything) as often this alone fixes it's issues.

I suspect you have too much timing and possably jetting issues. The jets are probably fine, just partially plugged up with varnish or debris. You could have other issues, but all of these things are easy to diagnose if done systematically.

 

My guess is you're running way lean on fuel could be the jets are too small. To check this I would run the engine up to about 2000 RPM under load for a couple of minutes shut the ignition off without closing the throttle and let it coast to a stop. Pull the plugs and see what color they are if they are real light grey or white then the engine is running too lean and if its run this way for too long you will be rebuilding it again. While you have the plugs out I would take a compression check to make sure the engine is still ok. When the engine was rebuilt what did the pistons look like. Did they have to be replaced and were the cylinder walls scored this would be an indication that engine was run lean. Why was the engine rebuilt a second time? When the engine cuts out does the RPM drop off and then pickup again and then drop off again this would indicate a fuel supply problem. If the engine runs up to a certain RPM and then cuts out and then stays about the same RPM but misfires and runs real rough then its most likely an ignition problem.

Good Luck
Dave T

 

It's likely something fairly simple for a skilled tech, as reading the plugs would be one of the first things I'd do naturally, but you have to start with a level playing field, the engine timed and metered where it's supposed to be. The distributor would be suspect, seeing as it's been replaced. A vacuum gauge read by a real, pro could knock most of the guesses off the list in 5 minutes. A WOT pull and shut down would reveal a lot too, but again, these are things we'd do right out of the box as a set of diagnostic procedures.