1993 4.3LX Mercruiser Cold Start Issue

[1993Baja180]

I have a runabout with a 1993 4.3LX Mercrusier engine. Since owning the boat for the past 6 years, I have simply lived with its cold start issue. To start the boat after it has been sitting at least 3 days, I have to prime the engine (by pumping the throttle) at least 75 times. Typical cold start process is as follows: prime 25 times and briefly attempt to start; again prime 25 times and briefly attempt to start; again and again until fuel is available and she starts. I rebuilt the Weber 4bbl carb about 1.5 years ago thinking I had a carb issue. No luck there, the boat ran/started exactly the same.

I am now thinking I either have a fuel filter issue, a fuel pump issue, or an anit-siphon valve issue (assuming I have an anti-siphon valve). As far as the fuel filter goes, the engine is not setup with the typical remote fuel filter (that looks like an oil filter). If it has a fuel filter, it must be inline of some older style. Needless to say, I have not replaced any fuel filter (other than filters in the carb). If it is the fuel pump, after 6 years I would have expected other issues (like not starting at all). Maybe the anti-siphon valve (assuming I have one near the fuel tank) is allowing the fuel to flow down from the carb when it sets for an extended period of time?

Any thoughts appreciated

 

[180shabah]

Re: 1993 4.3LX Mercruiser Cold Start Issue

Momentary switch feeding the fuel pump will fix it. Hold the switch for 5 - 10 seconds, pump twice, hit the key. If this doesn't work, you need a new fuel pump.

 

[mkast]

Re: 1993 4.3LX Mercruiser Cold Start Issue

Have you verified the accelerator pump is working?
If the accelerator pump is working, don't you think pumping the throttle 75 times would flood the engine?

 

[180shabah]

Re: 1993 4.3LX Mercruiser Cold Start Issue

Accelerator pump....leave it to me to skip step one.

secondary power feed to the pump will help diagnose this. If there is no gas in the carb, there will be nothing to pump. Run the pump until you here the pitch change, then pump the throttle, should see two solid streams of gas squirting.

 

[Don S]

Re: 1993 4.3LX Mercruiser Cold Start Issue

Sounds like accelerator pump circuit problem to me too.
Have you actually looked inside the carb and operate the throttle and see if gas squirts out the jets?
If, the carb is empty of fuel in 3 days, a momentary switch on the fuel pump does nothing but hide the REAL problem of why the carb is empty. When the engine is cranking, the fuel pump should be running, and it will only take a couple of seconds to get fuel to the carb.

 

[ziggy]

Re: 1993 4.3LX Mercruiser Cold Start Issue

I have not replaced any fuel filter

seems to me that might be part of step one too. probably where i'd go on my engine 1st. but mines old and his is new. but he still has a fuel filter.
hard to argue that acc. pump possibility. but what if no fuels going past the fuel filter... fuel would never make it to the carb to fill up with fuel so the acc. pump has fuel to pump..

 

[Don S]

Re: 1993 4.3LX Mercruiser Cold Start Issue

IF your fuel filter was plugged up and wouldn't let fuel to the carb for starting, I doubt it would ever get on plane and run at WOT.

 

[180shabah]

Re: 1993 4.3LX Mercruiser Cold Start Issue

4.3LX = weber carb and electric fuel pump. Both of these items commonly exhibit unusual "failures". The carb can actually drain itself through the jets. Do a search of posts by achris, he had to video it and send it to edelbrock(same carb) to prove that fuel could "flow uphill" Just came out as a slight dribble, but over night or a couple of days and the carb was empty. The fix - to date there still isn't one.

BTW - what ever happened to achris?

The electric fuel pump - frequently fails partially. Like an old fan with a dirty motor. Turn it on and nothing happens, give the blades a little bump to get them started and it will run all day. These pumps do the same thing.

My first post was poorly worded(I was Itouch typing), should not have said that the switch will fix it. Don is right, it will hide it. However, on these setups a secondary power source for the pump is an invaluable diagnostic aide. If it turns out, you have a weber with the "siphon" feature, leave the switch installed, it will make you life so much simpler. If you pump is giving you advance warning, replace it before it fails completely.
Don't forget the other items, fuel filter, AS valve that could be stuck in the open position and allowing tank drainback.

 

[1993Baja180]

Re: 1993 4.3LX Mercruiser Cold Start Issue

Thanks for all of the posts. I originally thought it was the accelerator pump as well, which is why I rebuilt the carb. I replaced the accelerator pump with a new one. Once the boat is started, it runs like a dream all day. I can stop and restart it with ease. The problem is definitely lack of fuel in the carb. Once fuel is there, the jets spray as designed.

The issue with the weber carb "uphill flow" sounds like a strong possibility. Also, could fuel flow back down through the fuel pump to the tank over several days?

With regard to the anti-siphon valve, which way is the valve designed to prevent flow?

 

[Don S]

Re: 1993 4.3LX Mercruiser Cold Start Issue

Gas is not leaking out of the carb and back into the tank. That would mean the gas jumps up out of the float bowl through the needle and seat, into the line, and then leaks back to the tank. I think not.
The anti siphon valve is just that, an anti siphon valve. It prevents a siphon in case a hose breaks off the fuel pump, it can't drop below the tank and siphon gas out of the tank. It is not a check valve to prevent gas from running out of the fuel system.
The carb is probably leaking, NEEDS FIXED, not something to mask the problem and let it leak, but you wouldn't be the first to re-engineer something so the actual problem wasn't a problem no more. Doesn't cure anything, just covers it up.

 

[1993Baja180]

Re: 1993 4.3LX Mercruiser Cold Start Issue

So if fuel cannot flow from the carb bowl back into the fuel line to the tank, then it is leaking into the carb, or possibly evaporating?


When I rebuilt the carb, I used a complete carb rebuild kit. All gaskets, filters, floats, accelerator pump, etc were replace with new and adjusted to specified settings. If it were leaking, seems like rebuild would have fixed the problem. After carb rebuild, same hard start problem continued. At least I didn't introduce a new problem!

Were would a carb leak from?

Also note, I have never smelled any order of fuel in the engine compartment.

Also, I really don't want to install the bypass switch unless absolutely necessary. Does seem to mask true prob.

 

[Don S]

Re: 1993 4.3LX Mercruiser Cold Start Issue

Gas isn't going to evaporate out of those enclosed areas in 3 days, and like I said, it's not going to jump UP and out of the carb.
I would guess that it's leaking into the manifold somehow. Might look for that article by achris. I really haven't had any of the Weber's with that complaint or with any complaint for some time.
Trust me, rebuilding any carb does not guarantee success. It just means you took it apart and put it back together.

 

[mkast]

Re: 1993 4.3LX Mercruiser Cold Start Issue

You state that the accelerator pump was replaced.
Have you physically removed the spark arrestor, prior to starting the engine, and have another person move the throttle while you are looking at the carburetor to see if the accelerator pump is in fact working?
The last time the complaint was, "Cranking forever to start the engine" turned out to be a bad ignition switch.

 

[Maxumum]

Re: 1993 4.3LX Mercruiser Cold Start Issue

Guys: I have the exact same problem and have checked that fuel is present in the carb and the pump sends a stream of fuel when pumping the throttle. After sometimes hours of trying / recharging the battery etc it'll start up and run perfectly out of the blue. Can't figure it out.

 

[achris]

Re: 1993 4.3LX Mercruiser Cold Start Issue

Welcome to the wonderful world of Weber carbs.... They dribble... empties out the float bowl overnight... Nothing can be done to fix them, it's just a design fault. My previous engine was a '94 4.3LX, I fixed it , read my signature.

Chris.......

 

[Maxumum]

Re: 1993 4.3LX Mercruiser Cold Start Issue

I read in here somewhere that oil pressure sensor could be at fault. Is there a failsafe that keeps the engine from starting if no oil pressure is detected? The way my engine behaves I seem to think it is fire not gas causing the problem.

 

[achris]

Re: 1993 4.3LX Mercruiser Cold Start Issue

I read in here somewhere that oil pressure sensor could be at fault. Is there a failsafe that keeps the engine from starting if no oil pressure is detected? The way my engine behaves I seem to think it is fire not gas causing the problem.

The oil pressure switch kills the fuel pump, not the spark....

 

[Maxumum]

Re: 1993 4.3LX Mercruiser Cold Start Issue

Thanks Chris. Amazing amount of good info can be had through this forum.

 

[Maxumum]

Re: 1993 4.3LX Mercruiser Cold Start Issue

Gotta wait another few weeks before I try it again, still winter here in Eastern Canada.

 

[DeepBlue2010]

Re: 1993 4.3LX Mercruiser Cold Start Issue

@ Achris, I have the 94 4.3 LX. What did you do to fix yours? Can the carburetor be replaced with equivalent that doesn?t have this design flaw?