4.3L OMC Cobra lacking power

[89 VIP Valiant]

Hello all, owner of a 1989 OMC cobra, pretty much gone completely thru this boat, have got around 10 hours on the new engine. Has run great so far, had it on the water this weeked, and it had been sitting in a cove for a couple of hours, occassionally starting up to move a little and stay away from the shore (not operated by me, was one of several people). I hopped in to go back to the dock, and shortly after take off, the motor seemed to bog down, and eventually died. Would not fire up at without some throttle (in neutral), and without a load, would wind up seemingly fine. With the drive lowered completely, would bog down and die, like it was missing at least one cylinder. Eventually, i got it up and running by trimming up some, and with a 19 pitch prop, and about 750 pounds of people in the boat, would only get up to about 25 at 3500-4000 rpm with it trimmed up about 1/4 way. After a bit, it got up to about 30 when the water calmed a bit. After dropping off some people, I headed back to my dock, and it took right off with the trim down completely. The points are one thing i never changed, looked fine at time of engine install. My coil wire on the cap was a little loose, but not terribly, i snapped it down completely, but not like it was just way off. I do run an electric fuel pump (properly installed near the tank). My thought is that it is points, coil, or fuel pump. I just don't want to go on the water this weekend an it not be fixed. I am leaning towards the points, but would like other input if anyone has any. Also, the carb is freshly rebuilt, and this thing has been running like a top since i rebuilt the engine. Anyone have ideas?? I do wonder if the ignition was left on when others were moving the boat, but not sure. Love to hear any ideas!!

 

[mkast]

Re: 4.3L OMC Cobra lacking power

What is the wide open throttle RPM with one individual on board?

 

[89 VIP Valiant]

Re: 4.3L OMC Cobra lacking power

Thanks for your reply, to be honest I'm not 100% sure, seems like I never run it at WOT. I would say, in the neighborhood of 4700???

 

[Bondo]

Re: 4.3L OMC Cobra lacking power

Ayuh,... The basic symptoms you explain would lead Me to the Fuel Delivery System....
Including Everything from the tank Vent to the freshly rebuilt Carb as Suspect...
But,..??..??

The points are one thing i never changed, looked fine at time of engine install. My coil wire on the cap was a little loose, but not terribly, i snapped it down completely, but not like it was just way off. I do run an electric fuel pump (properly installed near the tank).

That tells Me that you're runnin' a freshly rebuilt?? motor that hasn't even had a basic Tune Up,..??

Btw,... Electric fuel pumps are usually motor mounted, next to the fuel filter on boat motors...
Never heard of near tank mounting it.....

 

[89 VIP Valiant]

Re: 4.3L OMC Cobra lacking power

Bond O,

Thanks for your input also, let me give you a little more info. Speaking of the tank vent, I will mention that when filling this up wiht fuel, it usually wants to shoot some (when full) out of the filler. So, when filling i have been putting a rag around the nozzle of the pump so it doesn't get on the boat. Well, the last couple of times, it has shot out the tank vent. So....this would leave me to believe the venting system is good?? As far as tune up, no, the cap, rotor, condenser were all new, then the past owner let the block crack. I will say the wires look worn, need replacement. Have not yet looked at my points. I was mainly concerned about that fuel pump, since it is not quite as easy of a fix on the water. I mounted it near the tank, with an inline filter immediately following (removed the fuel/water separator cannister) and mounted it where i did as it is designed as a pusher, not a puller, and from the time i used to sell these things, should be mounted as close to the tank as possible, so it is pushing, not pulling the fuel. As far as the plugs, I put in fresh ones after de-winterizing. Hope this may give you some direction; one other thing, i did have some water in my bilge (i think leaking from the transom gasket) that was enough for my pump to kick on for about a minute or so.

 

[Bondo]

Re: 4.3L OMC Cobra lacking power

As far as tune up, no, the cap, rotor, condenser were all new, then the past owner let the block crack. I will say the wires look worn, need replacement. Have not yet looked at my points.

Ayuh,.. I'm just Baffled that you swapped blocks,+ aren't intimately familiar with the Points...
How did you stab the dist.,..?? Set the Timing,..?? Set the Dwell,..??
Maybe it's Just me, but a New motor always deserves a complete Tune Up to start life,+ for a Baseline...

Btw,.... Time is the Points worst Enemy.... They glaze over...
Read the topic in the Adults Only section...

 

[89 VIP Valiant]

Re: 4.3L OMC Cobra lacking power

Bond-O,

Well, I did have some help doing all of the work; I did not set the dwell, do not own a dwell meter. I used to help my dad with that on his old Ford pickup when i was little, what exactly do I need to set the dwell for? I did set the timing at about 7 degrees, i think the manual called for 8. I was not aware of that with the points, had no idea they glaze over, i would say they are a good 2 years old, maybe more. I am going to change tonight, got them in my car. Couple of other things, the fuel/water separator. First, as i stated above, I removed this (still have it) and replaced it with a simple in-line filter. Is this terrible? Second, my pcv hoses are connected to the spark arrestor. I did clean the arrestor a couple of weeks ago as i noticed it was a little dirty, but I do have an oily film (I'm sure my blow by) inside my freshly rebuilt carb. I know this is how it comes from the factory, but how good is this for my carb? Should I get some aftermarket filters that plug into the tops of the valve covers, or not worry about it gumming up my carb? Thanks for any further help!!