Engine cuts out as RPM's increase above 3K, runs almost perfect below 3K RPM's

[orangutangsurfer]

so.. I just finished writing everything below, it was pretty long but I wanted to give as much detail to try and avoid Q&A to solve the problem, however if I left something out please ask!

I've seen lots of posts regarding sputtering/dying/bogging boat motors at high RPM's but none describe my problem exactly.

I have a volvo penta 4.3GL V6 with an SX outboard (I hope that's the "needed" info) i know it has a holly carb as well. I've been running it most of the summer with out any issues (until now), it starts well needs to warm up a little but otherwise runs great. I keep the RMP's at the recommended range when WOT and boat maintains a good 40 knots + on some smooth water. the steering is a little sloppy but lower on my to-do list.

So here is what I KNOW happened. my ignition switch broke, the key would spin a full 360 but it would hit all the "right" spots with out issues, the start spring broke so you would have to manually switch the key back from start to on. I tested the boat in the drive way to make sure it starts and runs for several minutes before heading to the lake (I do this every time). No problems! started fine ran fine. we got to the lake and I couldn't find the "ON" position so the starter would turn but there was no ignition. after about 10 minutes foolin' with it I finally got it working and we took off (against better judgement of course) we tubed and played for 2-3 hours with out any problems for the most part. before the ignition switch broke the boat ran smooth as butter. I'm hoping that maybe i burned something (cheap and easy to fix) out when searching for the "on" position.

There was an occasional sputter, almost like a misfire but more like a short, or at least that's what I thought. Since I had the bad ignition switch and all i figured it was the rough spots on the water banging on the boat and rattling the ignition switch causing a quick short and a "sputter" in the motor. It didn't seem to happen in the lower RPM's but but when pulling the tube and getting up a little speed I would notice it more but it still felt in sync with rougher water. I never opened it up fully with a tube behind me of course but the problem was very minimal, didn't causes us any greif so I continued to attribute it to the faulty ignition switch....

A week later I replaced the switch I didn't use anything fancy just a basic switch with accessory, off, on and start. tested the boat in the driveway everything checked out so we headed back to the lake. This time out the sputtering was much worse, the boat would idle great start great run great up to about 2800-3000 rpm's above that the sputtering would get worse the engine would bog some times only a split second others a second or more I would occasional give more throttle to see if I could reproduce the problem and it just got worse, however I could go full throttle from a dead stop and not have a sputter or anything until I was up on a plane and starting to gain speed and increase RPMs.

I noticed the second time out that the issue, though would still seem to occasionally be in sync with the rougher water, it was more related to speed/rpm's. we found some smooth water and I messed around speeding up and down and watching the RPM's and the speed and it definitely was more of a problem as speed and rpm's increased.

I'm not a mechanic, but I have some skills, my brother is the motor head together we built a couple old harley's from basket cases I spent time tuning, jetting carbs, timing etc. I'm not great at it (he is) but I get the concept, one day my bike started crapping out at higher rpms (similar to the boat) it was something as simple as replacing the condenser.

could the condenser be the culprit? any mechanic out there think that this fits the bill? I've read lots about fuel system being involved but we ran back from our little swimming cove to the marina at 2800 rpm, 20-25 knots or so with out any sputtering for the most part only an occasional "misfire" (or so it felt) but hardly noticeable. I would think smooth operation at this speed would make fuel delivery problems unlikely. OH and if I pulled back on the throttle when it seemed to be stuck in a sputter it would correct and run smooth for a few seconds then sputter until I got it back below 3k rpms, then pretty much smooth again...

any suggestions before I tear it apart? anything to check/test? can I test a condenser? (I suppose I could google that). anyway thanks in advance for ANY help/suggestions.

Jes
2002 Crownline 180br
volvo penta 4.3GL V6 with SX drive.

 

[insttech1]

Re: Engine cuts out as RPM's increase above 3K, runs almost perfect below 3K RPM's

Sounds like you should first replace the ignition switch with the exact, correct switch.
Try and search for the electrical diagram of your switch, and see if the one you installed has some circuit (resistor, etc...) that is somehow lowering the voltage levels. This may sound weird, but from a basic electrical standpoint, if you installed a new component and things got much worse, then that is the logical place to start troubleshooting.

Second, when is the last time the carb was rebuilt/tuned up, and had float level checked.

Try and pull up the exact engine model number from the id plate on the engine. That'll give people more to go on.
Welcome to iboats!

 

[Fleetwin]

Re: Engine cuts out as RPM's increase above 3K, runs almost perfect below 3K RPM's

Does this engine have points?

If so, your faulty ignition switch may have left power to the points with the engine not running and burned/pitted them, especially if they happened to be in the closed position.

That was not uncommon with old cars/trucks.

The condenser can cause ignition misfires also. If it has points, I would replace both.

The next step would be fuel delivery.

 

[Walt T]

Re: Engine cuts out as RPM's increase above 3K, runs almost perfect below 3K RPM's

I think this is electronic ignition. The problem he is describing reminds me of the prestolite distributors needing ignition modules. I fixed them just by buying a replacement distributor. However you're here because you don't want to throw parts at it. I'm assuming it runs fine in neutral on the driveway and on the lake? Have you checked the distributor cap for water inside? Try running a jumper wire to the coil and see if that stops the problem. If it does then ignition switch or wire is suspect. A simple timing light on the coil wire or on a plug wire can tell you if it is misfiring, but you need a helper on the lake.
If it revs up fine in neutral always that would suggest fuel delivery.