Complex and strange

[S C Wootton]

Any help truly appreciated! I have a 4.3LX Alpha 1 Merc on a 20ft. Fletcher cuddy sportsboat, 4bbl Weber carb with electric fuel pump. I have a misfiring problem that I thought was cured...<br /><br />The boat is on a tidal estuary where the speed is restricted, so, it takes around half an hour to get to the open sea. For all of this part of my trip the temperature guage doesn't register. Once at sea I run at 3600rpm - around 32mph - and all is well for another 20 to 30 minutes. The temperature guage will rise slowly to around 150, but rises and falls continually - although slowly, not flicking up and down.<br />Then the fun starts - the engine will start to sound rough and eventually pop and bang like it is too lean. Backing off the revs to 2000rpm will see the motor run smooth again. Any further attempts at getting past this speed will cause further pops and bangs. The onset of this noise is effected by how much throttle is applied - i.e. running at 3000rpm will be OK for longer than if you run at 4000rpm - suggesting fuel starvation.<br />This started last summer and I thought was cured when I couldn't get the motor to run for more than a few seconds before cutting out. This was diagnosed by a local repair guy as a problem with the fuel supply. The fuel filter was replaced although no sign of dirt or water was found in the old unit. The oil pressure cut off switch to the fuel pump was replaced. The electric fuel pump was replaced. The problem was finally traced to a poor connection in the loom whuch has now been by-passed. Result:engine starts and runs OK until I go on a longer trip like today...<br /><br />I'm thinking that this must be something to do with the temperature fluctuation / rise as the problem occurs very predictably after 20-30minutes of running.<br /><br />The starboard head area feels only a little warmer than the port side and I can't believe that this is hot enough to evaporate the fuel in the metal pipe to the carb - although this is close to the starboard head.<br /><br />Any ideas or suggestions gratefully received!<br />

 

[imported_Mike_M2]

Re: Complex and strange

I don't understand how your Temp problems are fuel related. Have you tried installing a new thermostat? If it is sticking, the guage would rise and fall without flicking as you state. It would move slower, but fast enough usually that you can watch it move. Could your popping problem be from heat? It's possible, and it's possible it's something else. I would concentrate on the temp problem first, it may just cure everything.

 

[S C Wootton]

Re: Complex and strange

Thanks Mike - I'll get that stat looked at.

 

[Bondo]

Re: Complex and strange

Well,<br />Have you checked the Color of the Plugs ??????<br />Have you Looked at the Hi-speed circuit, Or Any of the Carb. ??????<br />I'd say your T-stat Might be Sticking Open at low speeds,<br />But is Working Perfectly at High Speeds.....<br />The Fluctutations you see are the T-stat Openning + Closing......<br />What's the Highest Temp.s noted in these trials ?????<br />Most All marine engines run Slightly Warmer on 1 side or the other......<br /><br />I Think you're Still dealing with a Fuel Issue......<br />Even thou you've got the Merc/Weber carb.... Go to this site, It's the Exact Same Carb. as Your's....!!!!<br /> http://www.edelbrock.com/automotive/index.html <br /> Lower end left menu > Technical Information > Installation Tips > scroll down to performer carbs. > click on Owner's Manual<br /><br />Oh Ya......<br />All the Parts are Interchangable Too.........

 

[S C Wootton]

Re: Complex and strange

Thanks Bondo - I'll check the colour of the plugs. The maximum temperature I saw yesterday was around 165°F - but only for a few seconds before the slow descent and climb back. The sea temperature here is about 55°F at the moment, is my max temperature OK?<br /><br />As to the carb, this was removed by my local "expert" as a part of another fuel problem that came after this intermittent problem. The problem where the motor ran for a few seconds then died was fixed by this guy and I hoped the intermittent one too...<br /><br />I saw the inside of the carb when it was in pieces and there was no dirt anywhere apart from a single spec of red paint in one of the internal mesh filters.<br /><br />This guy was always keen to rip the floor out of the boat to get to the tank in case of a suspect pick up - but surely this wouldn't kick in after 20-30 mins of running??

 

[BRIAN03]

Re: Complex and strange

What year? There is an updated sensor coil.

 

[imported_Mike_M2]

Re: Complex and strange

"This guy was always keen to rip the floor out of the boat to get to the tank in case of a suspect pick up - but surely this wouldn't kick in after 20-30 mins of running??"<br /><br />Surely the guy would test first before doing this? Run the line to a test can of gas to determine, but i doubt it.

 

[S C Wootton]

Re: Complex and strange

Brian - it's a '96.<br /><br />Mike - he did use a remote tank but only when I had the more permanent problem.

 

[BRIAN03]

Re: Complex and strange

When the problem occurs does the tach. die. Sensor coil problem or coil problem. Put a timing light on it as you run the boat and watch the timing light.

 

[S C Wootton]

Re: Complex and strange

Tach doesn't die Brian - it just reflects the loss of revs as the problem is just about to occur. I get a slight loss of power combined with a kind of labouring sound - as if the boat is going "uphill" - and if I apply more throttle at that point I get the bangs. My only way of geeting home then is to slow down to about the 2000rpm mark.

 

[dmorley]

Re: Complex and strange

If the engine sputtering only takes place once the engine warms up there is a good chance that the source is electrical. Specifically, the coil and ignition moduel in the distributor will first start failing when they warm up prior to totally going out.

 

[S C Wootton]

Re: Complex and strange

Thanks Don - definitely seems temperature related to me so this could be a good place for me to start.

 

[LubeDude]

Re: Complex and strange

Sounds like you have the fuel system functioning ok, I suspect an electrical prblem as well, Logically the desributor. Could very simply be a condensor. Change over to a pertronix electronic ignition if you can find one that will fit this application. Change it all, wires, coil, and cap.<br /><br />In salt water use you really do not want 165 degrees as I understand you can have salt crystalizing in the cooling system at that temp, I believe the correct thermostate for that engine is a 140-145.

 

[Bondo]

Re: Complex and strange

"Could very simply be a condensor. Change over to a pertronix electronic ignition if you can find one that will fit this application. Change it all, wires, coil, and cap." <br />The 4.3LX uses the ThunderBolt IV system....<br />There's the under-cap Sensor, or the Module....<br />That's It.....

 

[LubeDude]

Re: Complex and strange

I missed the 96 part.

 

[S C Wootton]

Re: Complex and strange

Thanks for the temperature hint Lubedude - and the Thunderbolt IV info Bondo.<br />To get to the dizzy on my boat you need to be a conortionist - crazy design! So I'm taking it to the nearest dealer this week - just hope he's feeling supple...<br />Thanks again guys.

 

[S C Wootton]

Re: Complex and strange

That should have been CONTORTIONIST!

 

[S C Wootton]

Re: Complex and strange

Just an update - the temperature gauge problem turned out to be a stuck open thermostat. This led to the choke never being fully opened as it was running too cool. New stat fitted ($45) Spotted a leak in the water pump and significant play in the pulley. New pump ($165) ran much quieter - good news. Boat ran on test for 35 mins with no popping and banging - good news.<br />BAD NEWS - found metal in the oil / filter when oil was changed. BAD NEWS - quiet water pump now reveals strange rumbling noise (previously masked by worn out bearings) coming from crank area. <br />Local MerCruiser dealer recommends new engine or burial at sea...<br />Decided to sell up and become a land-lubber as the rates for labour round here are just too steep - equivalent to $80 per hour. <br />New engine not feasible on my '96 boat.<br />Thanks for all your help guys - much appreciated.

 

[imported_Mike_M2]

Re: Complex and strange

Hey, i got it right! I wish you had more to celebrate tho, sorry to here you got bigger problems. Hey, why not tackle the labor yourself? Start pulling that puppy apart?