boat engine surging

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diymirage

diymirage

HP@idle > hondaHP@redline
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evening guys

the last few times i have had the boat out, i noticed the engine surges, mostly during the no wake speeds

it seems to idle fine, and it seems to haul fine (3000 RPM and up)
when it does surge, it surges 3-400 rpm and kinda rocks to the point of me worrying about it stalling out
(it actually did stall on em twice today)



i replaced the fuel filter 2 years ago, new plugs and such at the time too

i plan to take a look at it over the weekend, or next week, any suggestions what i should look for?


it is a 1994 mercruiser 3.0 4 banger with an alpha one outdrive
 
pauly said:
Running fresh rec gas in it?
Click to expand...
No, I'm on my second fill of over the counter 87 of the season

And I don't believe I treated the gas that was in there at the end of last season with anything iether
 
Couple thing to look at....
Wiring check loose connections / intermittent short from rubbing, etc.
Plug wire resistance, coil, cap, arching.
Battery charge state.
Out of the box, disconnect tach.
Clean out the carb
 
The fuel pump on those things consist of these little plastic valves that pulsate to provide gas flow. They succumb to old gas pretty readily and can get brittle or perform oddly at low rpm. Take a peak at your pump too.

cheers
 
Surging at Part-Throttle is gonna be an AFR problem.
Could be in the carb, or could be an air-leak into the crankcase. But on a 2-cycle could also be in the ringseal, as in rings or cylinders.
Because the idle is affected intermitantly, I'm gonna go with a vacuum leak; or, as mentioned the fuel pump or it's signal line.
And don't forget the rest of the supply line. Primer-bulb connections are a known trouble-source.
 
My boating friends travel miles to get gas with no alcohol in it. Between that and Seafoam very few issues. With alcohol they were replacing fuel tanks and fuel lines.
 
AJ/FormS said:
Surging at Part-Throttle is gonna be an AFR problem.
Could be in the carb, or could be an air-leak into the crankcase. But on a 2-cycle could also be in the ringseal, as in rings or cylinders.
Because the idle is affected intermitantly, I'm gonna go with a vacuum leak; or, as mentioned the fuel pump or it's signal line.
And don't forget the rest of the supply line. Primer-bulb connections are a known trouble-source.
Click to expand...
It's a 4 cylinder 4 stroke engine

The fuel pump looks an awful lot like the Carter on my duster

I sprayed the base of the carb with carb cleaner while it was running and found no change in idle

I cleaned out the fuel inlet filter in the carb but it wasn't terrible


The annoying thing is, I can't replicate the issue on land
 
diymirage said:
evening guys

the last few times i have had the boat out, i noticed the engine surges, mostly during the no wake speeds

it seems to idle fine, and it seems to haul fine (3000 RPM and up)
when it does surge, it surges 3-400 rpm and kinda rocks to the point of me worrying about it stalling out
(it actually did stall on em twice today)



i replaced the fuel filter 2 years ago, new plugs and such at the time too

i plan to take a look at it over the weekend, or next week, any suggestions what i should look for?


it is a 1994 mercruiser 3.0 4 banger with an alpha one outdrive
Click to expand...
Time to check the floats and clean the carb.
 
I can help with pics if it's an AFB style Edelbrock or Carter. I currently don't have any Holley's but can borrow one from my Brother to take pics if you really need.
It's most probably just some gunk stuck in a passage from ethanol evap or old fuel.
A secondary thought is vapor lock, I find it interesting that it only happens on load which points to vaccum leak.
How do the plugs read?
 
Stop haulin around them foe hunnit fiddy pound fat women.
 
EDIT. LOL runs fine high RPM. I got nottun

Plugged/ gummed up carb idle circuit
 
Deltatech said:
I can help with pics if it's an AFB style Edelbrock or Carter. I currently don't have any Holley's but can borrow one from my Brother to take pics if you really need.
It's most probably just some gunk stuck in a passage from ethanol evap or old fuel.
A secondary thought is vapor lock, I find it interesting that it only happens on load which points to vaccum leak.
How do the plugs read?
Click to expand...
Click to expand...

I will pull them on Tuesday and post some pics
RustyRatRod said:
Stop haulin around them foe hunnit fiddy pound fat women.
Click to expand...
Click to expand...

hate the game, not the player

AJ/FormS said:
well then, maybe check for evidence of the water pump sucking air.
Click to expand...
Click to expand...
I believe it sucks in fresh water through the outdrive, and im not sure how to tell if it is sucking air?

67Dart273 said:
EDIT. LOL runs fine high RPM. I got nottun

Plugged/ gummed up carb idle circuit
Click to expand...
.
Click to expand...

It idles fine though
Really the only thing I can think of is an issue with the power valve
That seems to control the range where I'm seeing issues

I intend to pick up a carb rebuild kit tomorrow
 
Check the fundamentals, timing etc.
Volvos surge with too much timing .
Water in float bowl moving with boat motion/attitude sucks water. Marine carbs often have a bowl drain .
 
Another thing that might happen. You might have something in the distributor, if it is mechanical. Worn, sticky, etc, or wrong / weak springs, advancing timing can/ usually increases engine speed. I'm not sure how it works. I assume that something triggers the advance (it unsticks)--advances, engine speeds up, then runs out of idle mixture and falls back. Anyhow examine the dist advance for problems, wear, etc, and re-check timing.

LOLOL^^^^I hit enter right after you posted^^^^
 
Ok, this is ALL I've done

I did some general cleaning of the carb and engine

Cleaned the inet strainer of carb

Shot some carb cleaner down it

I added 16 gallons of gas (now the tank reads 3/4 full on the trailer, but 4/4 on the water)

I also added half a bottle of seafoam to the tank

And the steel fuel line running from the pump to the carb was missing one tie down and it was vibrating like crazy
So I found a bolt to run that down and secure it



After all that I spent about an hour and a half on the water today and the boat did fine

She started easier then usual, ran great and never a sign of surging

So whatever the issue was, it's gone now
 
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