Mercruiser 5.7 2 barrel A1G2

[Southern Transplant]

Can't get up to speed. Bogs down like weeds on prop.
History... Boat is new to me. I replaced boots, lower shift cable, gimble bearing, rebuilt mercarb, new Fuel level sensor, water separator.
With boat on trailer bow up, pumped gallon of gas, found about an ounce of water. Pumped a second time found couple of drops.
Ran engine, idled an reved fine.
Took for test drive for 3 hours. Ran Great!!
Took on vacation a week later... Put boat in water and ran for couple minutes. All good.
Took friends for ride, didn't want to get up on plane. Repositioned load and got up and running.
Performance deteriorated over next half hour.
Dropped off friends, still couldn't get up on plane.
Checked spark plugs, all clean.
Adjusted choke, not sure why at this point lo
Changed water seperator, Note. No water or contamination in gas from filter.
Test drive... Ran great for about 3 minutes. I stopped to pick up some debris in the water.
Could not get back on plane.
Back at home... New water seprator again. No contamination or water found
Checked fuel tank pick up, all clear no cracks,
Replaced fuel line.. Cut the old line in half to check for desalination. Saw marginal buckling on the inner wall.
Removed fuel pump and lines, all checked clear.
Tested pump for 10 minutes. Ran great, no failure
even when wiggling wires.
Ordered new Fuel pump any way, also new plug wires
Worthy to note... After checking plugs I left a wire off, didn't make any difference when I replaced it.
Also, choke is wide open whan warm.
Any ideas? What am I missing?
Crazy about that 3 minutes of good run time.
Sorry for the Novel

 

[Scott Danforth]

welcome aboard

check the stickies at the top of the forum, I believe line 14 is the causes and testing for low WOT

weeds on prop would allow the motor to spin to 5000 RPM and not go anywhere. is this what you have going on. if so, check your prop hub.

however it sounds more like a bug made a nest in your vent line

 

[garbageguy]

pumped fuel noted - from fuel tank?

it ran OK, then not - taking on extra weight? hopefully no water weight

anti-siphon valve working OK?

what boat?

 

[Southern Transplant]

The boat is a 2000 Caravelle 212 interceptor,
I had checked the vent line early on and it blew clear..However, this boat has a perko 350 gas fill with integral vent/overflow. The gas cap gas a check valve that actually let's the system vent. I Checked mine... Guess what... It was clogged shut. You could blow out the vent line all day long and it won't vent with the gas cap on tight. The valve is clean and free now.
Thanks for the replies. I'll let you know when I get to water test it.

 

[Southern Transplant]

Well... Really thought that the vent issue was my problem. installed a new fuel pump and new spark plug wires anyway.
just got back from test ride. The engine started and idled fine. Was hard to get up on plane. Has to feather throttle, smelled rich. Note, no water in bilge or weeds on prop. Once I got it on plane and over 26 hundred rpm. The engine ran great all the way up to 35 hundred rpm. Great throttle response. Unfortunately, could not get over 35 hundred. With Plenty of throtle left. Flame arrester wax clean, now has carbon dust on outside.
I can't hear any pinging or missing. The distributed cap looked good. The coil may be original. Any ideas?

 

[Southern Transplant]

New knock sensor, dist cap and coil, Boat gets up on plane better.. just a tiny hesitation. (i couldof lived with that) Still no WOT. Still runs great between 2600 and 3400. Ran for 2 hours at 2850, thought everything was good. Got back to the ramp and it puked out a bunch of nasty carbon. Got home, compression check, all cylinders within 10 psi. Actual reading were between 195 and 205. Not sure why so high..maybe cheap gauge.. was looking for consistency anyway. 3 out of 8 plugs were nasty with dry carbon. 3 of 8 seemed dark, 2 of 8 were like i would expect for good color. Note I did adjust the idle mix to pretty rich.

 

[Scott Danforth]

Check your gauge.....

With compression readings over 150 psi, i suspect your gauge has been dropped, or you have oil or water in all the bores

Compression of 200 psi is what i would expect from a diesel

 

[Southern Transplant]

Cylinders and plugs are dry. This is a cheap gauge. However, when I Checked it with my air compressor this morning the readings alligned with gauges on the compressor. I'll check boat again when it stops raining. My process for checking was... Power off of coil, all plugs out, throttle plates wide open, cranked engine 4or 5 seconds took reading. I could watch the gauge pump up from 130 ish on up to the 195 +. The nasty plug carbon is big concern. Any thoughts on a too rich idle adjust on the mercarb or float adjustment?

 

[Southern Transplant]

BIG Shout Out to marine carburators.com
I decided to purchase a remanufactured carb. It was the best $300 spent to date. Bolted it on, checked timing, Ran some sea foam thru the water separator/filter to try and get rid the carbon build up. Been running fantastic. Sure took the long way around the block to get this thing running. At least I know a lot more now. Thx to all that helped along the way.