Need advice: 496s running poorly
09-18-2017, 07:13 AM
#1
Need advice: 496s running poorly
Hi,
I have a mid 90's 38 Scarab with twin 496 HO engines. Bought the boat in 2014 and had some trouble the first season with the engines stalling after getting on plane. The guy I bought it from thought that it was just some "magnetic pickup valves" in the fuel tanks that were hung up, and he suggested going out and trying until the boat straightened up... which it actually did!
After running the boat with no issues in 2015 and 2016 the issue came back this summer:
When started, the boat runs great and takes off planing for about a mile or so, then one of the engines starts losing power. If I'm not fast enough to cut back on the throttles the engine stalls and dies. It acts the same right after getting on plane again. Sometimes the other engine acts the same before the first one gets a chance... Last time out I tried to idle back, since one of the engines sounded like it was misfiring when trying to accelerate. When idling back one of the engines eventually died - even during idle speed. The other engine started doing the same, only running for five minutes at a time, then stalling and dying.
I thought this might be something in the fuel, but the engines act the same, regardless of which tank is connected (have one main tank and two smaller auxiliary tanks, feeding one engine each). I have also disconnected the fuel line connections that are threaded into the tanks... It seems like the pick up pipes are built into the tanks and non-removable. It also seems like there are no fuel filters in the bottom of the tanks where the pipes pick up the fuel. The tanks looked clean on the inside.
The fuel filters were relatively clean. The nets in the inline feeder fuel pumps were relatively clean too...
What should be the next step in trying to locate what's causing the engines to act this way?
Any suggestions as to what it might be?
Engines are Mercury HO 496 Magnums from 2003, with less than 100 running hours on them.
If you're still reading... Thanks!
Any input is greatly appreciated!
I have a mid 90's 38 Scarab with twin 496 HO engines. Bought the boat in 2014 and had some trouble the first season with the engines stalling after getting on plane. The guy I bought it from thought that it was just some "magnetic pickup valves" in the fuel tanks that were hung up, and he suggested going out and trying until the boat straightened up... which it actually did!
After running the boat with no issues in 2015 and 2016 the issue came back this summer:
When started, the boat runs great and takes off planing for about a mile or so, then one of the engines starts losing power. If I'm not fast enough to cut back on the throttles the engine stalls and dies. It acts the same right after getting on plane again. Sometimes the other engine acts the same before the first one gets a chance... Last time out I tried to idle back, since one of the engines sounded like it was misfiring when trying to accelerate. When idling back one of the engines eventually died - even during idle speed. The other engine started doing the same, only running for five minutes at a time, then stalling and dying.
I thought this might be something in the fuel, but the engines act the same, regardless of which tank is connected (have one main tank and two smaller auxiliary tanks, feeding one engine each). I have also disconnected the fuel line connections that are threaded into the tanks... It seems like the pick up pipes are built into the tanks and non-removable. It also seems like there are no fuel filters in the bottom of the tanks where the pipes pick up the fuel. The tanks looked clean on the inside.
The fuel filters were relatively clean. The nets in the inline feeder fuel pumps were relatively clean too...
What should be the next step in trying to locate what's causing the engines to act this way?
Any suggestions as to what it might be?
Engines are Mercury HO 496 Magnums from 2003, with less than 100 running hours on them.
If you're still reading... Thanks!
Any input is greatly appreciated!
