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1995 Mercruiser 350 Magnum Tournament Ski Stumbling

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pwskicat

Regular Contributor
Throttle Body EFI, Ser. OF562552

This engine powers a 1995 Ski Sanger DLX20 that I bought end of 2016. After a lot of work chasing down a fuel delivery problem, the boat has been running great for the last few years. Today it was stumbling off idle when trying to pull up a slalom skier. Usually it jumps right up to 3,500 rpm and has no trouble pulling anybody up. I also tested acceleration with no load behind the boat and it did the same thing. WOT is usually 40mph, but today it was only 36 on a windless lake. I last changed the fuel lines in 2017. Time for replacement? I put in a new fuel filter at the beginning of the season. Today I'll try injector cleaner and check all the unions in the fuel system. Any other troubleshooting tips are most appreciated. Thanks!
 
pwskicat said:
Throttle Body EFI, Ser. OF562552

This engine powers a 1995 Ski Sanger DLX20 that I bought end of 2016. After a lot of work chasing down a fuel delivery problem, the boat has been running great for the last few years. Today it was stumbling off idle when trying to pull up a slalom skier. Usually it jumps right up to 3,500 rpm and has no trouble pulling anybody up. I also tested acceleration with no load behind the boat and it did the same thing. WOT is usually 40mph, but today it was only 36 on a windless lake. I last changed the fuel lines in 2017. Time for replacement? I put in a new fuel filter at the beginning of the season. Today I'll try injector cleaner and check all the unions in the fuel system. Any other troubleshooting tips are most appreciated. Thanks!
Click to expand...
Is the ignition system in good shape and advancing timing as rpm increases
 
Yesterday, I had to pull the boat out of the water for the season, and I hadn't had time to work on this problem. I did a few test runs, and the problem seemed to have gotten worse, with a lumpy idle and the occasional backfire being added to the stumble. While I waited on the water for my boat hauler to drop in my trailer at the city ramp, I opened the engine cover and checked all the plug wires at the coil, distributor and plugs. One had popped off a plug. Hooked it back up, made another test run, problem solved! I was not looking forward to a long process of elimination trying to solve this come spring. Thanks again for your helpful suggestions!
 
350 Mag - tune up every three year with OEM parts and NGK plugs. Consider replacing the $300 coil. May have to shave socket for some plugs, Oh, you have the crab style cap which is a known problem, 3 years
 
pwskicat said:
Yesterday, I had to pull the boat out of the water for the season, and I hadn't had time to work on this problem. I did a few test runs, and the problem seemed to have gotten worse, with a lumpy idle and the occasional backfire being added to the stumble. While I waited on the water for my boat hauler to drop in my trailer at the city ramp, I opened the engine cover and checked all the plug wires at the coil, distributor and plugs. One had popped off a plug. Hooked it back up, made another test run, problem solved! I was not looking forward to a long process of elimination trying to solve this come spring. Thanks again for your helpful suggestions!
Click to expand...
I love it when it is the simple stuff... I had the same thing a with a VW fox I had years ago. Started bucking under acceleration. Was driving out of town the next day due to grandparent being in hospital so I rented a car ... When I get back in town and look into it had a dead cylinder due to plug wire...
 
Dieter said:
I love it when it is the simple stuff... I had the same thing a with a VW fox I had years ago. Started bucking under acceleration. Was driving out of town the next day due to grandparent being in hospital so I rented a car ... When I get back in town and look into it had a dead cylinder due to plug wire...
Click to expand...
(y)
 
sab said:
350 Mag - tune up every three year with OEM parts and NGK plugs. Consider replacing the $300 coil. May have to shave socket for some plugs, Oh, you have the crab style cap which is a known problem, 3 years
Click to expand...
I tuned it 2 years ago. See above for what the real problem was.
 
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