4.3 lx starting problem

raa711

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Jan 12, 2009
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Two years ago I purchased a 1996 donzi with a 4.3lx merc powerplant. The problem I have is if the boat sits for more than a few days, it will not start. My guess is the fuel in the carb is either evaporating or there's something wrong with the fuel pump. I understand this engine has a oil pressure senor switch that will not allow the electric fuel pump to work without the right amount of oil pressure. I've had number of opinions on this including installing a switch to tickle the pump until the carb is full of fuel. I guess what I'm asking is this a fuel evaporation problem, or is there problem with the pump. I've "hot wired" the switch at the oil pressure sender and this seems work. But there has to be a better fix than that. Once she's running, it starts right up.
 

Chris1956

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Mar 25, 2004
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Re: 4.3 lx starting problem

I had the same problem on my old mechanical fuel pump 4.3LX. It started doing it one day, and never stopped. For years before it was fine. I ended up pumping the throttle when cold starting it. Thaty was my workaround, and it was pretty effective.

When I think about it, it could have been a lazy choke, or some sore of leaking antisiphon valve, in combination with some gas boil off.
 

Bondo

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Re: 4.3 lx starting problem

I guess what I'm asking is this a fuel evaporation problem, or is there problem with the pump.

Ayuh,.... Neither,.... The Fuel Bowls are Leaking...
 

Don S

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Re: 4.3 lx starting problem

I ended up pumping the throttle when cold starting it. Thaty was my workaround, and it was pretty effective
That's how it's done on carbed engines. You young guys that have never had a carb in a car just don't understand how to start them.
\
\The electric fuel pump also starts pumping when the starter is engaged and within a couple of seconds has the carb fulll of fuel. If the carb is leaking fuel out, try pumping the throttle and cranking the engine at the same time.
 

chiefalen

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Re: 4.3 lx starting problem

Go to the adults only section at the top of the forum click on it, than click on how to start a cold carbed motor.

See if that fix's the problem post back the results.

Good luck !
 

raa711

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Re: 4.3 lx starting problem

I've done that...hammered that throttle handle many times and no fire. If there's no gas in the carb ???? What I've been told is that fuel pump doesn't kick in until there is sufficient oil pressure. If the motor has enough fuel to start, then, no problem. When it doesn't that carb has to be filled with gas some way.
 

Don S

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Re: 4.3 lx starting problem

I've done that...hammered that throttle handle many times and no fire.

Maybe a bad accelerator pump in the carb. If it's bad, you are just exercising your arm with pumping the throttle.
After it has been settig for awhile, look into the carb and see if gas squirts in while someone else is pumping the throttle


What I've been told is that fuel pump doesn't kick in until there is sufficient oil pressure.

Well, I don't know where you heard it, but they were wrong. There is a purple/yellow wire that comes off the starter solenoid that energises the pump when the starter solenoid engages.

Here is the drawing from the OEM service manual that shows it.

FuelPumpWiring.jpg
 

JustJason

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Re: 4.3 lx starting problem

when the engine been sitting for a few days..... remove the flame arrestore and hold the choke open by hand, have another guy put the shifter in neutral and give it a firm pump. If your not getting 2 streams of fuel out of the accelerator pump nozzles then your carb is leaking.
 

raa711

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Re: 4.3 lx starting problem

No gas at the carb when it sits for any length of time has been the problem all along. So my question is: is it evaporating, or leaking. If so, is there a fix. Should I be able to hear the electric fuel pump when I turn the key on.
 

Don S

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Re: 4.3 lx starting problem

No gas at the carb when it sits for any length of time has been the problem all along. So my question is: is it evaporating, or leaking.
Not sure how long "any length of time" is exactly, but the gas will not evaporate out of a carb in 2 or 3 weeks. I've taken carbs apart that sat all winter that still had fuel in the bowl. Did you take the top off the carb and look to see if it was empty, or just assume, since it doesn't pump, that the carb is empty. PS, if you do take the top of the carb, you need a new gasket. Don't try to reuse the old one.

Should I be able to hear the electric fuel pump when I turn the key on.

No, because it doesn't come on till you start cranking the engine with the starter. Just turning the key to the run position does not energiize the pump.
 

raa711

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Re: 4.3 lx starting problem

If the boat sits for more than a week or so, I have the problem. With the flame arrestor removed you can look inside the carb and see that there's no gas when you work the throttle handle.
 

Don S

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Re: 4.3 lx starting problem

With the flame arrestor removed you can look inside the carb and see that there's no gas when you work the throttle handle.

My guess is you need a new accelerator pump. Basically, a carb rebuild. There is probably gas in the carb, it just won't pump out.
 

Bondo

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Re: 4.3 lx starting problem

Ayuh,.... I guess it's Leaking then.....

Probably otta Rebuild the Carb...
 

bpmcl00

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Oct 22, 2008
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271
Re: 4.3 lx starting problem

My 4.3 lx has the same issue. if i leave mine sitting out for a while it wont start.

i have just been using starter fluid.

but i will try pumping the throttle.

also whoever had my boat beofre me put the regulator from the fuel pump before the carb
 

Don S

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Re: 4.3 lx starting problem

Three things.

Throw the starting fluid away before you damage your engine.

Learn to start a carbed engine

There are no external regulators on marine fuel pumps
 

TomP

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Jul 12, 2007
Messages
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Re: 4.3 lx starting problem

I had the same problem with a 97 Mercuriser 4.3 LXH. I had the engine tuned and the accelerator pump checked. I also made sure that the oil pressure switch was working correctly. I eventually got frustrated and put in a new fuel pump, and it has started on the first try ever since. For some reason that I don't understand, the old fuel pump didn't always engage when the engine started cranking. The old pump seemed to work fine, however, once the engine finally started. Good luck.
 

bpmcl00

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Re: 4.3 lx starting problem

Don S-

instead of using starter fluid. would squirting some gas down the carb work also???
 

Bondo

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Re: 4.3 lx starting problem

instead of using starter fluid. would squirting some gas down the carb work also???

Ayuh,.... But Fixing it would be even Better....
 

J JACKSON

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Re: 4.3 lx starting problem

what carburetor do you have i have the webber (carter) carb on mine and i have the same problem i have read on here that its is normal for these type of carbs to siphon the fuel out the venturis when sitting emptying the float bowl i would love to find a fix for this
 

Bondo

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Re: 4.3 lx starting problem

i would love to find a fix for this

Ayuh,....

I remember a few years ago,... Achris posted on How to fix it,...
Unfortunately,...
I remember it, but wasn't paying Attention,+ don't remember the Fix...

To bad too,... I've now got the same carb, doing the same thing....
 
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