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Mercarb: Drips fuel under acceleration increase

C

cakley

New member
2000 Mariah 180 4.3l 2bbl mercarb.

Boat ran fine two years ago. Last season from day one it ran like crap. Wouldn't come off idle when in gear (in water). I could use neutral and play with the throttle to get the rpms up. If quick, I could drop it in gear and work the throttle. After several attempts it would come off idle and poorly accelerate. After several more attempts, I could get it on plane and it would run near perfect. Once parked the process was restarted.


  • Fuel pump has 12v at switch and under oil switch circuit. Unknown pressure.
  • Anti-siphon valve is good.
  • new fuel filter
  • fuel looked clean and heet was added
  • Carb was rebuilt with the basic kit. Everything looked good but was rebuilt per directions.
  • carb accelerate pump has three settings and I've tried all three.
  • engine idles and starts. If able to get on plane it will run near top speed.


I can hear that the carb just sounds different under accleration. A different sucking noise. The primaries drip fairly big visible drops.

Am I missing anything other than getting a new carb? If so I am considering the edlebrok 4bbl upgrade.
 
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may need a thicker base gasket if it is less than 1/16 thick I believe there is one about 1/8 thick for this type of issue.....typically a hard stumble off idle is a vacuum leak, a bad one. Did you replace the accelerator pump in the carb? If so did the umbrella have a tight fit? A dripping or over rich carb could be a bad sealing needle (float needle) causing a higher than normal fuel level in carb like a bad float...cant be determined from a computer.lol
Many possibilities
get a vacuum gauge and connect to a intake manifold ( will need to remove a plug and install a barbed fitting for the test) and see what the vacuum reading is should be ~ 15 inches of hg fairly steady at idle if it is very erratic then you need to find out why do a google search for a vacuum chart for engines....other wise the only thing I can think of now (after many beers) is float is too high. Also look closely at the shift interrupter micro switch and if the large V notch is activating the switch it could cause the ignition to be interrupted, this would indicate a bad short shift cable. Also it is not uncommon for a tachometer to take the ignition out so disconnect the tach and retest.

Only other possibility for now may be a bad ignition sensor or timing module.......but one thing at a time........

So to start, pull the plugs. all should be very very close to each other in appearance. If any one is drastically different that may lead you to the root cause. maybe a bad plug, crossed wire, bad wire.....again hard to tell from here........
 
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Base gasket came with the kit. accelerator pump looked good when I rebuilt it and installed a new one.

Vacuum leak will be my next check, after I replace the fuel pump. From what I've read, the fuel pump pressure regulator is prone to issues with ethanol mixed fuels. Since the engine ran perfect before winter storage and then ran like crap. I could see the fuel sitting for that time and damages to the pressure regulator. Excessive pressure running to the carb will cause flooding.

it's almost as cheap and as much work to just buy a new pump than it would be to buy a psi gauge and new plumbing.
 
Cakely, KGHOST is offering some great info......... take heed!

Just an FYI (assuming that you may not know this):
The accelerator pump (and successive fuel spray) is necessary to offset the transition from the "low speed" metering circuits to the "high speed" metering circuits.
Typically, there will be a dead spot during the transition from one circuit to the other..... and it's typically due to momentary fuel starvation.
However, the accelerator pump alone may not fully take care of this if either the low or high speed circuits have an issue.
Make certain that these circuits are clear and free flowing.


If you have the A drive, the Merc SI micro switch is a good suggestion.


.
 
The fuel is dripping when under accleration. You can see drops of fuel.

Accelerator pump sprays a good solid spray. But I am a novice on carbs.

I shall check out the SI switch. But not sure what a SI switch has to do with fuel drops from the primaries.
 
cakley said:
1..... The fuel is dripping when under accleration. You can see drops of fuel.

Accelerator pump sprays a good solid spray. But I am a novice on carbs.

I shall check out the SI switch.

2...... But not sure what a SI switch has to do with fuel drops from the primaries.
Click to expand...



1.... I assume that these drops are coming from an area other than the spray nozzle areas????


2.... Correct..... it is un-related to the fuel droplets.
However, it may be related to the difficultly when coming off idle when in gear and in the water (as you put it), if the SI adjustment is not correct.... and/or if the lower shift cable is now bad!
(the nature of Dog Clutch gear engagement and the necessary SI system! :mad: :mad: )

.
 
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""""Boat ran fine two years ago. Last season from day one it ran like crap. Wouldn't come off idle when in gear (in water). I could use neutral and play with the throttle to get the rpms up. If quick, I could drop it in gear and work the throttle. After several attempts it would come off idle and poorly accelerate. After several more attempts, I could get it on plane and it would run near perfect. Once parked the process was restarted.""""

1. deal with the hard to accelerate issue first.
2. don't worry about dripping fuel at medium to high speeds. If it is at idle there may be an issue. What setting is the float set to and the float drop set to?
3. difficult coming out of gear? is it fuel or ignition related? If fuel then quickly activating the control handle (like pushing a gas pedal very quickly many times) does this overcome the issue even a bit? Is this what you describe as "comes off idle poorly"? This would be lean or vacuum issue or accelerator pump.
4. if not then it may be over rich, too much fuel. Is the choke all the way open? Refer to #2 float settings question.
5. the shift interrupter switch if activated when moving the throttle cable forward ( bad cable or out of adjustment) it will cause the ignition to misfire/cut out. It may not kill it completely (typically does kill it causing a stall but not every time). So watch the v notch and see if it is moving (big shift cable bracket on motor)
6. The fuel pressure should not be more than 6-8 psi. Anything more can force the needle off the seat and result in flooding/over rich. Fuel pressure should be checked.
7 . if the tachometer is bad it can cause a ignition misfire or temporary ignion failure until disconnected from the coil.
8 did you do anything with the spark plug wires? if so maybe one is wrong, if not disregard.
9. please answer these questions asked.

10. if all answers are good and fuel and ignition are normal the it has to be the carb. May need to find someone with a bit more knowledge locally to you to help.
we cant rebuild thru the internet.....lol

need more info.............
 
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kghost said:
""""Boat ran fine two years ago. Last season from day one it ran like crap. Wouldn't come off idle when in gear (in water). I could use neutral and play with the throttle to get the rpms up. If quick, I could drop it in gear and work the throttle. After several attempts it would come off idle and poorly accelerate. After several more attempts, I could get it on plane and it would run near perfect. Once parked the process was restarted.""""

1. deal with the hard to accelerate issue first.
2. don't worry about dripping fuel at medium to high speeds. If it is at idle there may be an issue. What setting is the float set to and the float drop set - set at the directions in the manual. Idles good. No fuel drips at idle. No difference in idle before or after carb rebuild.
3. difficult coming out of gear? is it fuel or ignition related? If fuel then quickly activating the control handle (like pushing a gas pedal very quickly many times) does this overcome the issue even a bit? yes, I can pump it up to speed. Is this what you describe as "comes off idle poorly"? This would be lean or vacuum issue or accelerator pump.
4. if not then it may be over rich, too much fuel. Is the choke all the way open? Refer to #2 float settings question. choke is fully opened.
5. the shift interrupter switch if activated when moving the throttle cable forward ( bad cable or out of adjustment) it will cause the ignition to misfire/cut out. It may not kill it completely (typically does kill it causing a stall but not every time). So watch the v notch and see if it is moving (big shift cable bracket on motor)
6. The fuel pressure should not be more than 6-8 psi. Anything more can force the needle off the seat and result in flooding/over rich. Fuel pressure should be checked - went to the local parts store and was unable to find adapters or gauges to fit. All they had was automotive schrader fittings.
7 . if the tachometer is bad it can cause a ignition misfire or temporary ignion failure until disconnected from the coil. The tach does act up, sometimes. It will read high and I will tap on it and it comes back down. :eek: this will be easy to check, once I get the fuel pump installed.
8 did you do anything with the spark plug wires? if so maybe one is wrong, if not disregard. never touched.
9. please answer these questions asked.

10. if all answers are good and fuel and ignition are normal the it has to be the carb. May need to find someone with a bit more knowledge locally to you to help.
we cant rebuild thru the internet.....lol. ,you've helped a bunch thanks

need more info.............
Click to expand...

In bold.

once I get the boat up on plane and up to speed it will run good for hours. I thought the fuel was an issue, so I ran near full throttle for an hour? I thought burning some old fuel out would had cured the problems... It was slightly slower on the top end. I could slow down and accelerate, with what felt like normal full power. That leads me to think intake manifold leak that swells closed once hot. :confused:

The SI switch, which I knew nothing about until today. I had a bravo drive before and it was very smooth going into gear. This alpha drive has a good thunk going into gear, which I think is normal. It does also easily to into neutral from gear. I've never heard the engine rpms drop when changing gears as if the ignition was killed. But I've never listed for it.
 
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The interrupter switch is supposed to only work when shifting OUT of gear.
A clunk into gear is normal but too high idle rpms will make it louder and harder...not so good. idle should be around 600-650 in gear at idle in the water.

If you suspect fuel related or even a vacuum leak you could very carefully!!!!....try to close the choke butterfly while someone gives it throttle in gear in essence choking it and enriching the fuel. If the boat accelerates properly then it is the carb I would think.....be careful if you do this and who ever does this must be conscious of not choking it out completely....
If you suspect a manifold air leak.....wd 40 or carb cleaner spray when at idle all around carb and intake and if idle changes you have a leak. But a vacuum gauge would show this as I described before.

Make sure to have wet rags/towels and a fire extinguisher at the ready and clean up everything real good when done.

look here

http://www.gregsengine.com/using-a-vacuum-gauge.html

http://www.freeasestudyguides.com/engine-vacuum-test.html

http://www.crankshaftcoalition.com/wiki/Vacuum_gauge_engine_diagnosis
 
Detached wires for the tach from the tach. I only saw two wires on the coil.
Unplugged SI.
Engine was unable to accelerate in the water.

I tried the propane gas trick to find a leak and it didn't work. Can I remove one of the smaller plugs on the manifold to install an adaptor for the vacuum gauge?

Thanks is for the help.
 
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cakley said:
Detached wires for the tach from the tach. I only saw two wires on the coil.
Unplugged SI.

Engine was unable to accelerate in the water.
Click to expand...
Be sure to re-connect the SI.... especially if near the dock or other boats.
Without it, you may not be able to achieve Nuetral.


Have you looked at the progressive ignition advance to see what it's doing?
An engine that is not receiving the correct spark lead, will not perform correctly.


.
 
RicardoMarine said:
Be sure to re-connect the SI.... especially if near the dock or other boats.
Without it, you may not be able to achieve Nuetral.


Have you looked at the progressive ignition advance to see what it's doing?
An engine that is not receiving the correct spark lead, will not perform correctly.


.
Click to expand...

I shut the boat off while in gear then reconnected the plugs before going back to the boat ramp.

I've not checked timing or ignition advance. Distributor cap and rotor looked good.
 
A few of the spark plugs were wet. Smelled like fuel and carbon. These were the rear plugs. The front plugs were clean and dry, nothing unusual.

will be getting a compression check today.

still need to figure how to hook up a vacuum gauge. The square head plug in the center intake manifold. It's not 3/8 or 1/4 drive. I may grind down a 5/16 Allen head to fit the square head. Then hope I can find an adaptor to fit with a barb end for the vacuum gauge.
 
New plugs installed. Sounds much better. Vacuum gauge showed some bouncing between 15-17 at idle. But strong and smooth at high idle and 2500. So that should rule out vacuum leaks. May had just needed a new set of plugs and fresh fuel. Will try it in the lake this weekend,

thanks for the help.
 
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