87 nodel 350 magnum bogging at WOT

[Boo_Daddy]

hey guys, I am new with mercruisers, I have an old 1987 model 350 magnum that is bogging down at wot. The engine runs fine at every other throttle and speeds. It even fires up perfectly with no trouble at any time (hot or cold) its just that when you go past 3/4 throttle, the engine losses power and the tone changes to a bog and kindof sounds like a miss. IT usually happens around 3800rpm. The engine has arounf 400 hours on it.<br /><br />can you give me some things to check?

 

[hoot]

Re: 87 nodel 350 magnum bogging at WOT

just start with the basics. when was the last tune up? need to inspect fuel components and ignition parts. filters, spark arrestor clean, float level, point gap, plug gap, plugged carb jets, timing, advance, ignition coil breaking down, condensor, plug wires, alternator charging,... read over the other post on this subject. one of the most extreme post i saw with similar symptoms was cracked block and heads. hope it isn't this.

 

[JustMrWill]

Re: 87 nodel 350 magnum bogging at WOT

On my 87 OMC 4.3L I had the same thing...got worse as the day went on...found that my Distributor retaining bolt had lossened and my timing was all ove the place...I would look at timing first...then carb...

 

[Boo_Daddy]

Re: 87 nodel 350 magnum bogging at WOT

Thanks guys. I replaced the plugs this weekend, but still doing it. I am going to totally condition the ignition system (cap, rotor (points if need be) and put a new set if wires on her. I will give the timing a check also. Is there a good advance to run on these engines? <br /><br />If this doesnt help, my next target will be getting the carb rebuilt. There is a guy here locally whom is supposed to be awesome on any carb at rebuilding, and he is gonna charge 25 bucks plus parts.<br /><br />I will post and let you guys know what remedied it.

 

[Wart T]

Re: 87 nodel 350 magnum bogging at WOT

If he were awesome he'd get a lot more than 25 bucks. Be careful, you get what you pay for.<br />Is it a Rochester 4 bbl? If so I'd try a simple restrictor plate adjustment first.

 

[ahein]

Re: 87 nodel 350 magnum bogging at WOT

I had exactly the same symptoms you've described with my engine. It's a Volvo Penta AQ-260 (GM 350 with a Rochester QuadraJet carb). It was converted to HEI by the previous owner. The carb was recently rebuilt and all new filters were installed. I gave a complete tune-up including new cap, rotor, coil, wires, and plugs yet it would still breakdown at high rpm's. Turns out the mechanical advance in the distributor was sticking and the timing was off when I got up to 3/4 throttle.<br />See if you can check the timing at WOT (or when it begins to break down). I'm not sure what the Mercruiser timing is, but my Volvo is supposed to advance to 30 degrees at 4200 rpm (8 degrees btdc at idle). Once I freed up the advance so the weights would swing out easily the boat ran great from idle to WOT. <br />Good luck.

 

[Blk-n-Blu]

Re: 87 nodel 350 magnum bogging at WOT

Lynn,Check for water in the fuel. When at WOT any water in the fuel will be in the most likely spot to be picked up by the pump,also any water in the carb bowl will be pushed through at WOT