No full throttle, coughs, sputters, backfires

« **on:** July 24, 2015, 09:27:38 PM »

Have a new/used boat, 21' ultra lx, 502, dominator jet, according to previous owner it had been sitting without use for a couple of years but carb had been rebuilt recently (Holley 750)

Took it out for first time today, if I give full throttle it just bogs down and almost dies and backfires, if I ease the throttle up I can get it to cruise at a max of about 4000 rpm (30-33 mph). If I continue giving more throttle it bogs down to 3000 or less, misses and backfires.

I checked secondaries and they seem to be smooth to open, checked the accelerator pump and it squirts gas when manually operated.

I seem to hear the secondaries open and close via vacuum but not completely sure, however when I think I hear them close that's when power come back.

Any ideas??

Does 32mph at 4000rpm sound right?

Thx for any input/suggestions.

Sent from my iPhone using SoCal Jet Boats

« **Reply #1 on:** July 24, 2015, 10:46:54 PM »

Change the Water fuel seperator. And fuel filters. Try that out. Hope it helps

« **Reply #2 on:** July 24, 2015, 10:55:55 PM »

I coukd be wrong, but 32mp at 4k sounds a little on the slow side. I have a 21' Bahner that's is heavy. At 4k, I'm pushing the 50mph mark. How is it in launch?(out of the hole)

« **Reply #3 on:** July 24, 2015, 11:09:14 PM »

Quote from: jim99 on July 24, 2015, 09:27:38 PM

Have a new/used boat, 21' ultra lx, 502, dominator jet, according to previous owner it had been sitting without use for a couple of years but carb had been rebuilt recently (Holley 750)

Took it out for first time today, if I give full throttle it just bogs down and almost dies and backfires, if I ease the throttle up I can get it to cruise at a max of about 4000 rpm (30-33 mph). If I continue giving more throttle it bogs down to 3000 or less, misses and backfires.

I checked secondaries and they seem to be smooth to open, checked the accelerator pump and it squirts gas when manually operated.

I seem to hear the secondaries open and close via vacuum but not completely sure, however when I think I hear them close that's when power come back.

Any ideas??

Does 32mph at 4000rpm sound right?

Thx for any input/suggestions.

Sent from my iPhone using SoCal Jet Boats

Boat speedo or GPS?

My heavy azz cruizer is at 29-30 @ 3200

Impeller might be cavatating or just warn wear ring/skirt.

Also sounds like a lean sneeze, too

Dan'l

« **Reply #4 on:** July 25, 2015, 05:58:36 AM »

I did fuel filters and water separator before putting in water. Fuel pump is new also. Hole shot is hard to say because you can't mash throttle, it hat sputters and backfires, you have to ease it up to plane.

Ideas/suggestions?

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« **Reply #5 on:** July 25, 2015, 08:28:07 AM »

Sucks to be on the water and to have all of these problems. I would trailer it, and line by line, start checking off all of the fundamental stuff. Pull the spark plugs, are any fouled or super lean? Is your distributor set right and firing order correct? Points or electronic distributor? Are there any vacuum leaks? Could the carb base gasket be sucking air? Are your fuel floats correctly adjusted? What kind of cam is in it? Solid or hydraulic? Does the valve adjustment seem right? Is the oil milky? These are just some suggestions. Good luck!

SCJB iPhone

« **Reply #6 on:** July 25, 2015, 08:36:44 AM »

Have you adjusted the float levels? They should be set with boat floating in the water. Sounds like it's definitely running out of fuel. Could be sucking air somewhere.. Double check pressure and volume.

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« **Reply #7 on:** July 29, 2015, 08:15:31 PM »

I had the same problem once, it was the accelerater pump and squitters. Check to see when you hit the throttle you get the squirt of fuel. Good luck....

jim99

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