View Full Version : New prop and running rough
09-04-2007, 10:59 AM
Well I didn't have a real good Labor Day, or at least the boat didn't. The kids were skiing and my wife was driving, when we hit the rock bar. It snubbed the engine. The prop was curled around pretty good but I had a spare prop. The next morning I swapped the 13X14 that was on the boat with the 13x13 that I had as a spare since my '88 PS190. (My current boat is a '01 19Skier with the Predator 310hp) Put it back in and it accelerated smooth, no vibrations, and the speed was down and rpm was up as I suspected with the 13 pitch prop. At the top end, as the RPM reached 4800, the engine started to miss. Almost felt like it was running out of gas. If I backed off at all it ran fine.
Is there a governer, or something to keep the motor from over reving? I am going to check the fuel filter also.
The next day when I was running, I could smell burnt plastic. I checked the water pump and it was cool, and the hoses going to both manifolds were cool so I assume water was flowing.
09-05-2007, 03:33 PM
I guess I never really stated a question to be answered..
Why would my boat, that never missed before, start to when the only thing changed is the prop, from a 13x14 to 13x14?
Is there a reason my motor would start to miss at 4800 RPM?
Could hitting a rock bar effect the engine?:confused:
09-05-2007, 04:20 PM
Is it possible that something slipped, causing the timing to be off? Maybe the Distributor rotated a little when the engine stopped abruptly, causing it to miss at top end???
Have you checked the timing?
09-05-2007, 04:56 PM
No...Not sure how to check the timing. Is there an easy way to do at home or do I have to bring in to a dealer? Would I be able to see if the distributor moved? I will look tonight.
It sounds like you hit the rev limiter. I only mention this since it was the advice given to me by Jim Thelen at Acme props. I was propping my 2002 PS 209 with the 310 hp TBI engine. I was all set to go with an Acme 13x12 prop. I made one last call to Jim and he said this engine made gobs of low end torque and could spin the Acme 13x13. By the way, my stock prop was a 13x14. Jim said if I went with the lower pitched prop on the older TBI motor that I would likely hit the rev limiter.
Based on my experience the rev limiter basically cuts the spark once the limit is reached. That would explain why the engine started cutting out and also explains why it smoothed right back out when you let out of the throttle. I only mention this since it sounds like you have the same engine I had. The top end on that motor was right around 4800 which might explain things.
What follows is info from a racing site explaining rev limiters.
At a pre-set rpm - say 7,000 rpm - the rev-limiter engages sometimes scaring the very cool driver half to death!! : Once the engine reaches 7,000 rpm, it interrupts the signal to the coil, alternating on/off, slowing the firing sequence and/or fuel flow, preventing the engine from continuing to shoot up in rpm's.
Hope this helps.
09-05-2007, 06:23 PM
I hadn't thought about the rev limiter...both my cars have one, and I use them once in a while :rolleyes: I changed one of them and added 500 RPM when I re-mapped the air/fuel mixtures...
Do new MC's have a rev limiter? I guess they should...
09-06-2007, 10:22 AM
It does act like a rev limiter. Can these be removed or adjusted?
I still do not understand the burnt plastic smell?:confused:
09-06-2007, 10:34 AM
Does sound like rev limiter (if it has a rev limiter), although WOT for the Predator is spec'd at 4800-5200 RPM.