351W won't rev past 1400 under load - Hot Rod Forum : Hotrodders Bulletin Board
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Old 07-07-2008, 06:02 PM
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You got a leaky spark tube...
 
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351W won't rev past 1400 under load

The engine in my boat doesn't want to run to WOT like it should. It gets to 1400 and cuts out when the drive is in gear. It doesn't matter how gently I ease into the throttle it starts cutting out badly at 1400 and just falls on its face. It had been running fine for almost three hours on the lake then it started cutting out at cruising speed (about 3000 rpm) and quickly got worse. By the time I got back to the boat launch I couldn't get over 1400. In neutral with the throttle lever up against the stop the engine will rev to 2800-3000 rpm just like it should.

I just checked the timing and it was rock solid at 10 deg before at 600 rpm idle, 15 before at 1400 rpm and 24 before at 2800 rpm. The timing was steady without jumping around and the engine ran fairly smooth, especially at idle. In order to run the engine any higher than that I have to put the drive in gear and I don't want a prop spinning under the boat with my water hose nearby without a second person handy.

I thought maybe I had water in the gas but I filled my truck up from the same pump right after filling the boat and I've gone 250 miles on it without issue. I checked the gas cap on the back of the boat and it was on tight and the o-ring on the cap is in good shape.

I did pull the primary bowl off the carburetor (single feed, vacuum secondary four barrel Holley) the day before I went out because I suspected it needed a new power valve, which it did. It wasn't completely blown but it did have a pin hole in the diaphragm. It was very old, possibly the original. I replaced the power valve with a new one of the same rating. When I originally put the carb back together I accidentally cut an o-ring on the tube that feeds fuel to the secondaries and I'm wondering if a piece of that is stuck somewhere in the carb.

I haven't gone any farther yet but is there ANYTHING ELSE I should look for that could cause my problem?

The engine is a completely stock 250hp Indmar marine 351W.

Last edited by Blazin72; 07-07-2008 at 06:07 PM.
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Old 07-07-2008, 07:29 PM
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Fuel filter, fuel pump. Those two would be my first look.
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Old 07-07-2008, 07:40 PM
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You got a leaky spark tube...
 
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Thanks for the response Jmark. I think I found the culprit. I just got the carb pulled apart and it did turn out to be a piece of that shredded o-ring I mentioned. It's completely blocking one of the jets. I do have a new fuel filter/water separator I'm installing for good measure though.
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Old 07-07-2008, 08:12 PM
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Glad you found it!

A short story. Years ago, a friend had an import that would run, then crap out for no reason. I knew it was fuel related but the pump and filter were fine. It had some goofy dork import carb but I managed to get the top off. Sitting on THE ONLY main jet was the wing of a small bug!! It would slosh around and every once in a while get sucked onto the jet. I got some tweezers and got it out and put it in a little bag to show her. She did not believe me so I told her to go drive it! She called about a week later and thanked me for fixing her car!! LOL
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Old 07-07-2008, 08:18 PM
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You got a leaky spark tube...
 
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LOL, that's pretty funny. I drove a Subaru STI one time and somehow scooped a bird up with the large hood scoop those cars have. When we opened the hood up the bird was laid out (dead) across the intercooler. Didn't affect the car at all but still an odd thing to happen...
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