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TOPIC: Surging issue 5.0 carb

Surging issue 5.0 carb 21 Aug 2011 15:55 #1

  • spike2450
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Hi
I have a 1998 merc 5.0 2bbl.

I have had a surging issue this year initially it would only happen at reduced rpm 1500 - 1700 and would surge + - by 200 rpm, today it was surging again and when I tried to get her on the plane and got her above 2300 plus it would just die with the rpm jumping anywhere from 1000 to 3000 with a lot of stumbling and hesitation And almost cutting out, sounded terrible, this happened a few times, I did manage after a few attempts to get her stable above 3000 rpm for a short time.

With the surging I had time to check the fuel pick up, anti syphon and they are clean. also checked the accelerator pump and had a good squirt of fuel into both barrels.

Is there anything besides sucking air or fuel supply that can cause this surging??

:)

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1998 2452. 5.0l mercruiser with alpha one gen 2 and 2 bbl :)

Surging issue 5.0 carb 22 Aug 2011 16:30 #2

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Any ideas would be appreciated ;)

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1998 2452. 5.0l mercruiser with alpha one gen 2 and 2 bbl :)

Surging issue 5.0 carb 22 Aug 2011 17:12 #3

  • GrindKore
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When did you perform your ignition tuneup last time? This sounds a lot like what I have experienced early this season. After replacing distributor cap, rotor, spark plugs, and spark plug wires my 5.0 started to run smooth and strong.

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2005 Ciera 242EC
MerCruiser 5.0 w/Alpha I Gen 2
Running Solas aluminum 4 blade 14.75x15 prop

Surging issue 5.0 carb 22 Aug 2011 17:38 #4

  • spike2450
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Hi thanks for your replies.

It's been a couple of years since the ignition parts were replaced, the issue when working on the 2452 is the lack of space when working below the manifolds to check spark plugs etc.!!!!

I'm hoping that someone has other ideas before i throw cash at her, could a failing HT lead for example cause surging etc.

Thanks again :D

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1998 2452. 5.0l mercruiser with alpha one gen 2 and 2 bbl :)

Surging issue 5.0 carb 22 Aug 2011 17:41 #5

  • GrindKore
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The tuneup kit cost me $120, for all parts and about 2 hours to replace everything. At least pop off your thunderbolt distributor cap and take a loot at points, if there is crud on them its time to replace. At bare minimum new rotor and cap will run you about $50-$60, not too bad.

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2005 Ciera 242EC
MerCruiser 5.0 w/Alpha I Gen 2
Running Solas aluminum 4 blade 14.75x15 prop

Surging issue 5.0 carb 03 Oct 2011 06:28 #6

  • Buddy bouy
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Mine was doing that last week. There is a sending unit below the rotor in the distributor cap. It`s easy to replace but I had the same issue. Once you ran it for a period of time it would stop surging. I replace the fuelwater separator, plugs, wires, cap and rotor. It was still doing it. Replaced the sending unit and runs like new.

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Surging issue 5.0 carb 03 Oct 2011 12:00 #7

  • whatadeal
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I am having similar issues with my 2452.
Did the tune-up (cap,rotor,plugs)and replaced the pickup coil in the distributor
Cleaned the fuel pickup, checked the anti-siphon valve, replaced fuel seperator twice and the car b filter twice.
Improved for 2 trips after rebuilding the carburetor then right back at it again.
Pulled it out ot the water last weekend and am in the process of fuel injecting the engine.
Compared the cost of a carb to fuel injecting and figured fuel injection would pay for itself in the long run. Not to mention just hit the key and it is running (no choke to mess with).
Plus we are adding 2 switches to bump the rpms up 100 rpm with 1 switch and 200 rpm more with the other switch, or 300 with both switches.
I do a lot of trolling for salmon and with the carb it is hard to just bump a few rpms when going into wind or waves.

Will let you know how it works out.

Good luck with yours.

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2004 2452
USCG master 50gross ton

Surging issue 5.0 carb 03 Oct 2011 13:09 #8

  • msd58
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I had a similar problem. The problem was fuel related: the bottom of the fuel pick up tube in fuel tank has filter screen on it. When the demands for fuel was increased the problem you described happened. Marina pulled tube out cleaned pick up screen and that was it.

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Port: Sassafras River Georgetown, MD Bayliner 2000 2855 7.4

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Surging issue 5.0 carb 03 Oct 2011 13:36 #9

  • 2850Bounty
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1998 merc 5.0 2bbl.


You have an EST ignition system.... you may want to examine the module.
Ignition timing that is unstable will/may cause surging.

You also have an SI (shift assist) if equipped with an A drive.
Check this out and make sure that the micro switch is capable of fully opening once gear engagement is achieved. If too close to the closed position, it may be suspect!


Unstable high speed fuel metering will/may also cause surging.
This can be caused when the carburetor's fuel demand is not being provided by the fuel pump.
The suggestion of fuel delivery is a good one.... i.e., pick up tube screen, fuel filter, etc.
However, since this occurs at a relatively low RPM (1500 - 1700 rpm) I'd have to say doubtful!
Never say never......, It may still be the most likely suspect!

Check the power supply to the fuel pump.
Power is provided via a N/O oil pressure switch once the oil pressure is up.

The accelerator pump operates during a position change of the throttle, and during further opening only.
IOW, once an RPM position has been established, the accelerator pump is no longer providing any enrichment.
I think that this can be removed from your list!

.

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Rick E. Portland, Oregon
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Surging issue 5.0 carb 03 Oct 2011 19:20 #10

  • whatadeal
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Are there any diagnostics that can be run on a module for a thunderbolt system?

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2004 2452
USCG master 50gross ton

Surging issue 5.0 carb 04 Oct 2011 02:50 #11

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Merc may have some instrumentation that can diagnose a module itself, but if you're asking if engine data can be pulled from a TB module, no!

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Rick E. Portland, Oregon
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Twin 270 HP 5.7's w/ Closed Cooling
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Kohler 4 CZ Gen Set

Surging issue 5.0 carb 04 Oct 2011 06:46 #12

  • Monterey10
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With the engine running, you can look down in the carb bore. If the carb float is sinking, causing a flooding situation, you can see it . The carb will appear normal, then gas will start flooding in from every orifice.. If the engine behaves badly, and the carb appears normal, go to the above mentioned tune up issues. Look closely at the coil. When they get hot, they behave differently than when cold.

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Craig Capitola Village, CA
1988 Bayliner 2556 (BoatAsaurus)
1996 Trophy 2352 (Mystic)

Surging issue 5.0 carb 02 Oct 2017 14:46 #13

  • azlan
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spike2450 wrote: Hi
I have a 1998 merc 5.0 2bbl.

I have had a surging issue this year initially it would only happen at reduced rpm 1500 - 1700 and would surge + - by 200 rpm, today it was surging again and when I tried to get her on the plane and got her above 2300 plus it would just die with the rpm jumping anywhere from 1000 to 3000 with a lot of stumbling and hesitation And almost cutting out, sounded terrible, this happened a few times, I did manage after a few attempts to get her stable above 3000 rpm for a short time.

With the surging I had time to check the fuel pick up, anti syphon and they are clean. also checked the accelerator pump and had a good squirt of fuel into both barrels.

Is there anything besides sucking air or fuel supply that can cause this surging??

:)


did u manage to solve the problem? im having this prob now

azlan
1998 3255 avanti

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Surging issue 5.0 carb 02 Oct 2017 15:37 #14

  • builderdude
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Azlan, this is a super old thread and the OP hasn't logged recently. Best to start a new thread on your issue.

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Dave
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www.baylinerownersclub.org/index.php/for...ansom-repair-my-2556

Surging issue 5.0 carb 05 Oct 2017 03:29 #15

  • azlan
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tq

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