460 idles fine, backfires and dies when trying to plane out

[H20MOFO]

You may want to try a compresion test,and or a leakdown. Poping through the exaust could be a burnt valve. or head gasket. Hopefuly not.

[justfloatn]

You could be chasing the wrong problem. Backfires in the exhaust are useualy a secondary ignition problem. Unless you have raw fuel dumping down the carb when ideling or accelerating. That you would see. If it were somthing plugged it would probably backfire through the intake. When was the last set of cap & rotor, plugs or wires installed?
It sounds like you are loosing more than one cylinder so the cap and rotor are where I would start. Plugs are a must if your carb was the problem. If you have an ohms meter check the wires. If you have one or more with excessive resistance that could be the problem. Or if they are five or more seasons old change them. I would check the timming too.
Back to basics..

[DK_Hallet]

Try another Carb . That should eliminate any ? about whether that is your problem. Its always the simple stuff that kills you. Thought of one more thing . What Distributor do yo have. Check the hold down and check the advance also . Trying to give the easy checks first .. hope that helps

[BrotherWolf]

You could be chasing the wrong problem. Backfires in the exhaust are useualy a secondary ignition problem. Unless you have raw fuel dumping down the carb when ideling or accelerating. That you would see. If it were somthing plugged it would probably backfire through the intake. When was the last set of cap & rotor, plugs or wires installed?
It sounds like you are loosing more than one cylinder so the cap and rotor are where I would start. Plugs are a must if your carb was the problem. If you have an ohms meter check the wires. If you have one or more with excessive resistance that could be the problem. Or if they are five or more seasons old change them. I would check the timming too.
Back to basics..
this is were Im starting, I had a simular thing happen to me yesterday while at the lake.....after about 5 min at full throttle it sounded like it was starving it self and was making a loud noise, if I let of the pedal it ran fine but every time I got on the gas 5 min was top and it would start running like crap then the last time it did that it started backfiring out of the carb...and now when you try to start it it just pops..ugh...Im hoping its not a sucked valve or the timming chain slip a few teeth

[Legal Chemistry]

I had the EXACT symptoms, unfortunately it was burned up valves. If you think about it, to me it makes sense with the water in the fuel. A leakdown should tell you if it's the valves. Good luck.

[justfloatn]

this is were Im starting, I had a simular thing happen to me yesterday while at the lake.....after about 5 min at full throttle it sounded like it was starving it self and was making a loud noise, if I let of the pedal it ran fine but every time I got on the gas 5 min was top and it would start running like crap then the last time it did that it started backfiring out of the carb...and now when you try to start it it just pops..ugh...Im hoping its not a sucked valve or the timming chain slip a few teeth
Do you have a fuel pressure gauge. This sounds more like fuel starvation. Possibly a plugging fuel filter. It allows the fuel flow to keep up at low rpm then slowly falls off under half or full throttle untill the engine leans out and backfires out the intake. I have also seen electric fuel pumps do this when they start to quit. They work good when cold and as they get hot they get weak and fuel pressure drops off. I just hope you didn't run it too lean for too long and burn a valve or piston.

[bp]

after reading all this, it's an ignition issue period. if there were something wrong with valves/valve train, it would not run even close to well up to 4000 rpm, and after all the attention to the fuel system, it's not fuel.
i've had problems similar to the symptoms you describe in the past; it's always electrical or ignition related.
someone suggested cap/rotor, great suggestion. cap/rotor can cause the problem you're describing. but, a better description of your ignition system would be helpful. check every ground connection on the boat, make sure no ground wires are scrunched or hitting anything, make sure all ground connections are clean and tight. check other electrical connections to make sure they are clean and tight.

[SBC Jetboat]

Well, I can tell you that that Holley fuel pump is garbage. They NEVER flow the fuel they are supposed to. N E V E R and Ive got friends who have had the same experiences. Wouldnt you think a pump supposed to flow 69 gph would keep up with a mild small block that is pulling 23 gph on a flow scan fuel flow meter??? Well it wasnt keeping up. I just run the high flow mechanical pumps now. You do need more than 4.5 psi. Should be more like 6 or 7 but you need a fuel pressure gauge on the dash to make sure you are MAINTAINING proper fuel pressure. Good luck

[VAMI]

That 25 your talking about is the heat range number not gap thats way to small should be .035/.040,I think thats a autolite number.If you had burnt valves it would pop at idle too and head gaskets would show milky oil.For sure try another carb to eliminate that then check out your ignition its one of the 2.

[BrotherWolf]

Well i got into my boat today and thought I would start with cap, plugs, and wires. Well to my suprise 5 of the 8 spark plugs had busted electrodes and no gap??????.....my first thought was W.T.F?????......So I threw in some new plugs and hooked up the hose and fired it up and sounded great and no pop.
I was so pumped up and was going to head to the lake to run the boat and thought I better check the oil.....now I got milky freaking oil...UGH!!!!!!..,,,Off to the store for some head gaskets.....what brand do you guys recommend??
for a 460??