Bogging down, popping, under load

[SHINTON]

This is a new to me boat, 1992 Celebrity 21', with the 5.7L Alpha Mercruiser.

Prev Owner had the carb rebuilt, engine was tuned up, EARLY last year and then only run maybe 45 minutes last season, he was not a boat guy.

I traded for it, and when we put on the earmuffs and start the engine in neutral, runs good, will go to 5-6000 rpm smoothly!!

But Day 1, on the water, I would get to 2000ish rpm and it would bog down, act like it was gonna stall (like possibly starving for fuel, etc)

In Neutral...no problems, can run 5-6k rpm smoothly, so this is only under load.

So I am thinking the gas is pretty old at this point, and mostly the boat just needs running. I added 20 gallons to fill it up at the Marina, and kept driving it alot that day!! Probably burned through 10 gallons all told and by the end of the day, the sputtering and popping, bucking etc was only at 3000-3500ish rpm range so it got better as the day went on.

Guy at the marina said the up/down floats was his guess, to have them replaced/rebuild kit. But not sure I told him that it would run fine when not under load.

Another guy (brother in law) wondered if it was a coil pack breaking down?


SO I have driven it 2 more times, it now gets to 3500-3600ish rpm before any issues, planes out nicely, 30ish mph, but if I go full out it still sputtering a bit in the high 3000s rpm.

I am down to maybe 1/3rd of a tank now, I am hearing to add SeaFoam when I fill it up this time, to clean up everything good.

Wanted to get any other thoughts as well?

I "thought" with a 5.7L, 21' boat, this boat would be faster than it is, but I am guessing mid to low 30s is where it will top out at speedwise? Does that sound low? Could be if I get it running cleanly at the top end of the range it will keep getting a bit faster?

Right now it is "fun" as is, we are going plenty fast enough, just would like for it to run "GOOD"...

Thx in Advance for any and all thoughts!
Sam

 

[Bondo]

Re: Bogging down, popping, under load

Guy at the marina said the up/down floats was his guess, to have them replaced/rebuild kit. But not sure I told him that it would run fine when not under load.

Another guy (brother in law) wondered if it was a coil pack breaking down?

Ayuh,.... Welcome Aboard,... I'd start by pullin' the fuel filter, 'n inspectin' it's contents,...

Then put on a New fuel filter, 'n Try it...

Ya might also try usin' a remote fuel tank, by-passin' the boat's tank, 'n the rotten gas in it...

In Neutral...no problems, can run 5-6k rpm smoothly, so this is only under load.

Btw,.... Don't do that,.... It proves absolutely Nothin', 'n can lead to a blown motor...

 

[littlebookworm]

Re: Bogging down, popping, under load

Welcome to the forum. Definitely follow Bond-o's advice. I would also suggest you check the distributor cap and rotor. mercruiser had a recall on some problem V* distributor caps. There was some arcing between contact points, causing all kinds of ignition problems, including backfiring and missing. Hy

 

[capecodder116]

Re: Bogging down, popping, under load

I'd do the same...remove, inspect, and replace all fuel filters, and check to see that the vent is clear. Then run again with a remote fuel supply.

 

[NHGuy]

Re: Bogging down, popping, under load

Not to say that this is your problem, but I had a popping under higher rpms. It was the first year I had my boat, which was 20 years old at the time. The popping got worse as time went on and moved down to lower rpms. I had already done fuel filters, fuel lines, cap, rotor and plugs.
The solution for my motor was some new stainless core plug wires. After that it was like I had turned a switch. The boat absolutely leaped onto plane. I ended up getting a prop with 4" more pitch, and got a lot better fuel economy as well as top speed.
Hope your solution is just as easy as that.

 

[Volphin]

Re: Bogging down, popping, under load

Welcome to the forum. Definitely follow Bond-o's advice. I would also suggest you check the distributor cap and rotor. mercruiser had a recall on some problem V* distributor caps. There was some arcing between contact points, causing all kinds of ignition problems, including backfiring and missing. Hy

I agree with littlebookworm, and would encourage you to double check: the firing order (verify it), spark plug condition, spark plug wire condition, base ignition timing and the timing advance curve.

V

 

[Black as]

Re: Bogging down, popping, under load

I agree with littlebookworm, and would encourage you to double check: the firing order (verify it), spark plug condition, spark plug wire condition, base ignition timing and the timing advance curve.

V

Check your fuel pump as well as a worn or tired fuel pump will give you the same symptons.

 

[Lennyd123]

Re: Bogging down, popping, under load

Check your fuel pump as well as a worn or tired fuel pump will give you the same symptons.

Have to agree with most everything suggested above, and IMHO inspect of replace all of the simple things involving fuel, fuel supply, spark and timing as the popping described it most often a result of a misfire or some result of the engine pushing up the intake instead of out the exhaust.

This would include plugs, wires (dbl chk firing order), cap, rotor, distributor (and position or advance etc), coil, ignition, fuel, filter, filter in the carb,carb floats and jets, and if all this fails in extreme cases move on to compression, timing chain, valves and cam etc.

All but my last experience it was one or a combination of the "small stuff", and the last one sadly was the extreme from a improper set up of a new rebuild that had the valves making contact with the pistons and causing just enough damage to cause the vales not to properly seal.

I doubt your problem is on the extreme level based on your getting fully onto plane and to nearly 4000 rpm before it starts (or is that were it gets so bad you got to throttle down?).

Also since most of the parts are not too overly expensive and many part of a normal tune up I would say just do them all, but be cautious of solid core SS wires if you have any sensitive electronics on board as they can create lots of interference etc.

Good luck, and hope you find the source of your problems sooner rather than later