backfires under load

I have what been been said to be a 350 4 bolt main engine (serial number14093638)with a quadrojet carb (01761N) We have replaced the plugs, wires, rotor, cap, and checked the timing which appears to be right on. When on the trailer the engine runs perfect. No problem shifting in and out of gears without stalling and with the rpm's 6000+ in and out of gear.<br />When it is in the water it will stall out when putting in and out of forward, reverse, and nuetral. The max rpm's is 2500 before it starts backfiring out of the carb. Any ideas for a new boater? This is a "74" Stamos 240 Clearwater. Thanks

Re: backfires under load

Welcome to iboats Did you change your water separating fuel filter?<br />Water in fuel can result in loss of power & backfire...<br />A lean condition can also cause a backfire...<br />I doubt if it is a timing problem...<br />However, since I don't have acess to serial # ID, I have no idea what year the engine is....<br />There are those here who will know exactly what you have....Posting the year would be helpful...<br /><br />I also think that you have a separate issue regarding your shift problem.....I think that your lower shift cable is bad- How old is it?....JK

Re: backfires under load

The number at the back of the block is 14093638. I was told it was an 1995 engine. I don't have a clue how old the shift cable is and don't have a way to contact the previous owner. I'm green at this and wouldn't now how to check the condition. I'll check the fuel separating fuel filter. It looks relatively new? Should I try replacing it? Thanks for your help

Re: backfires under load

Yes, replace it (the separator) ....<br />Dump the contents into a clear container & look for signs of water.....<br />Does it shift hard at the helm? (resistance)<br />How long have you owned the boat?<br />Look on Mercstuff.com while waiting for more feedback...Lot of info there, as well as the red "search' button at the top of this page....JK

Re: backfires under load

the alpha type drives use a shift cut switc, this allows for a momentary ignition kill while the clucth is trying to move away from the gear its engaged with. in a perfect set up you will notice a momentary blip on the tach, on an old one with binding cables,binding acuator or a sticking shift slide it may try to acuate with any cable motion and stall the engine, its more noticable with the prop loaded than on a trailer.<br /> only a few things make it backfire from the carb, a flat cam lobe, a stuck or damaged intake valve and a lean air/fuel mix in the intake manifold. the valvetrain can be spotted when performing the compression test, the timing can be checked with a timing light but its rare its that far off.<br /> most the q-jets left the factory with a filter inside the fuel inlet, check that as well.<br /> the last thing that creates a backfire is a leaking riser or manifold that is creating a water in the cyl issue. usually it will show up on the spark plug electrodes, check them carefully.