Logo
FULL SITE MENU

1993 43LX Merc Cold Start Problem

M

msuel

Guest
"I have 1993 4.3LX Merc with a

"I have 1993 4.3LX Merc with a Weber 4BBL that has a cold start problem. In order to get the engine to start, I have to prime the engine (by putting the throttle in neutral and pumping) 20 or 30 times, then crank the engine for 4 or 5 seconds. Then I have to prime the engine another 20-30 times, crank again. I repeat this process 3 or 4 times and she finally starts. I can get the engine to start everytime with this process, but it shouldn't require this effort. Also, once it is started, it runs and starts perfectly all day. Starting is only a problem if she has been sitting.

I first suspected a choke problem. However, the choke works perfectly, closed when cold. The problem is definitely lack of fuel. I removed the flame arrestor and watched as the throttle was pumped and engine cracked. Eventually, the jets started to spray fuel into the carb and the engine started. I suspect a problem with the accelerator pump in the carb (losing its prime) or a problem with the fuel pump. Any info appreciated. Any suggested troubleshooting tests to isolate the problem?"
 
The boat is difficult to start

The boat is difficult to start if it has been sitting for 3 or more days.
 
"Check the fuel tank vent to s

"Check the fuel tank vent to see if it's clogged. If it is and the air around the tank (and therefore, the gas in it) cools, it contracts. This could create a condition very similar to vapor lock and it will be hard to start."
 
"Mike: Does the engine run at

"Mike: Does the engine run at the correct temp or is it hot when you shut it down after the last run? You have described a lack of fuel in the bowl at a cold start. Fuel may be boiling off if it runs hot, hence the throttle pumping and engine cranking before it sprays fuel from the jets. Is it a spray or a pair of strong streams of fuel like a squirt gun? Weak streams spell failing accel. pump.

You may also have a failing fuel pump or if equipped, a failed anti-drain back valve in the fuel line which is siphoning the fuel out of the bowl overnight."
 
"The engine is running at the

"The engine is running at the proper temperature. Also, the tank vent is clear as I found this out at my last fillup at the gas station. The jets looked more like a strong stream similar to a squirt gun, however that was my first look at jets so nothing to compare against.

Where is the anti-drain back valve located (if equipped)?

I am considering pulling the gas line going into the carb and cranking the engine to see if I am getting gas flow up to the carb."
 
"The anti-[i]siphon[/i] valve

"The anti-siphon valve is on the fitting where the gas leaves the tank, usually in a right angle fitting. It's not anti-drain-back, it for a case where the fuel line is cut and if it's missing or stuck open, the gas would siphon out of the tank if the hose is lower than the fitting.

Remove the bottom of the pump and look at the filter."
 
"valve between the pump and ta

"valve between the pump and tank, I think. If you test the fuel pump that way, disconnect the coil + wire and use a long hose to pump it into another fuel tank outside the boat. Have a helper nearby w/a fire ext. ready to use!!!! Watch out! A little static spark and KABOOM! You and the boat are history. If you need a pump, check with NAPA--best price I found. Ask for instr. to replace pump. if mech. type."
 
"To shed a little light on the

"To shed a little light on the static thing- kneeling on carpet with long pants in dry weather is a great way to build up enough static to cause a problem. If you want to be safe, go to Radio Shack and buy a static clip/wrist band. They're cheap and all you need to do is attach the clip to a good ground and remember that it's there.

If the gas fumes are really strong, vent them before doing anything. It's the fumes, not the liquid that causes the risk."
 
"Mike, I have the same problem

"Mike, I have the same problem with my '88 4.3LX. I didn't always have it though. I suspect fuel is draining from the carb, but have not tried to verify it. The 4bbl Rochester on my motor has the carb inlet needle in the bottom of the carb. I never thought to see if it drains back into the tank."
 
"Thanks for the safety tips, I

"Thanks for the safety tips, I will definitely heed the advice.

Chris's comment above brings up a good point. Unfortunately I don't know how (where) the fuel enters the fuel bowl. I need to look at a schematic of the Weber carb. In order for fuel to "drain" from the fuel bowl, it would seem that the fuel inlet (and needle) would need to be at the bottom of the fuel bowl. If at the top, as I understand is often the case, there should be fuel in the fuel bowl available for starting. This is why I have tended to suspect the accelerator pump losing its prime (needing replacement). If I can verify fuel at the carb, then this would probably point to the accelerator pump. Thanks for all of the input."
 
Might be a good time to put a

Might be a good time to put a gas shut off valve ahead of the fuel pump. It is a good safety device; and by shutting it off you will see if fuel from the bowl is draining back into the line.
 
"I have the same problem with

"I have the same problem with my '96 4.3 LX with 4 bbl Quadrajet. If it sits for much more than a week, it takes 10-15 seconds of cranking along with several throttle shots in the neutral lockout position to get going. Once started, all is well thereafter until the next week or more layup.
Does anyone know if an electric fuel pump can be retrofitted so as to fill the carb bowl up before cranking over. This would eliminate the problem entirely."
 
"I also have a 96 4.3 LX that

"I also have a 96 4.3 LX that HAD exactly the same problem. As you are probably aware the electric fuel pump will not start pumping until either the engine has Oil Pressure, or the starter is engaged IE cranking. Only then will the electric fuel pump start. While the engine is cranking the battery voltage will drop to about 11 volts so the electric fuel pump will run quite slow and take awhile to fill carb bowl. Two ways to overcome this problem 1) bypass the oil pressure switch so electric fuel pumps starts when you turn the key on. however this will remove the safety factor of having a fuel spill from your carb if the float valve does not cut off !!!. 2) other option is to install a fuel primmer bowl into the fuel line between the tank and electric fuel pump, (similar to ones on most outboards) give this a pump up when engine is cold (while you are in there checking the oil and water) this will insure the carb bowl is full before you start cranking. Also make sure the auto choke is adjusted properly. If it is closing with to little spring tension the air sucking down through the carb will pull it open and it will have know choking effect. The dash pot will pull it open 3/16" as soon as the engine starts. Finally engines will start alot better cold if they are turning over at the right rpm on the starter. Mercruiser were a little mean with the starter cables I replaced mine with heavy battery cables both the live (+) to the starter and the ground (-) cables with descent lugs properly crimped on and it made a huge different to the starting speed. All fairly minor things but made all the difference. My engine starts like a new car every time hot or cold with only one pump on throttle before starting when cold. All the best. Roger"
 
"Thanks rchris; what you say m

"Thanks rchris; what you say makes sense.
Mine kicks right over and starts within 1 second or so cold, as long as it has not been idle for a few days. Once it has sat for a while it seems like the fuel either evaporates from the carb bowl, or leaks back down into the tank, and then it just takes a long while for the engine driven mechanical pump to refill the bowl. So if I put in an electric pump, I would have to wire it to run whenever the key is on, and bypass the oil pressure switch. This seems OK to me, as it has the warning system for low pressure, high temp, or low drive oil level.
Where can I buy the correct pump?"
 
"Update.

I removed the gas

"Update.

I removed the gas line coming into carb. The line was dry at this high point. Don't know if this is normal. I was expecting fuel to spill a bit from the line when I removed it. I routed a hose from the fuel line, out the drain and to buck outside the boat. Then I cranked the boat over for a few seconds and checked the buck. A fair amount of fuel was present indicating it was pumping well.

I reconnected the fuel line to the carb. Then I primed the engine (pumped the throttle in neutral) 3 or so times and checked to see if fuel had come out of the jets. No fuel from the jets. Then I cranked the engine over for 5 or 6 seconds and primed the engine 10 or so times. This time fuel was expelled from the jets and she started right up.

Conclusions: Either the fuel bowl was empty or the accelerator pump wasn't functioning properly. The boat was last run 3 1/2 days ago. This doesn't seem like enough time for evaporation and boiling off is highly unlikely. Thus, how could there not be fuel expelled from jets when initially primed as the fuel bowl should be full? However, the dry fuel line does make me suspect fuel is falling back down towards the tank. I did locate the anti-siphon value coming out of the tank. I am going to replace this for good measure since it is a $10 part with easy access. Enough rambling."
 
M.S. Just a thought; have you

M.S. Just a thought; have you tightened the carb base nuts and the carb top screws? Fuel will evaporate from the smallest opening.
 
Guy: A friend recommended thi

Guy: A friend recommended this so I did tighten the base nuts a couple weeks ago.
 
Poor / dirty needle & seat

Poor / dirty needle & seat / float adjustment allowing fuel to drain back?
 
"Rod and Mike,
Firstly Rod y

"Rod and Mike,
Firstly Rod you should already have an electric fuel pump on your engine, it will be wired to only operate if the engine starter is engaged or the oil pressure is up. If you want it to start pumping and fill carb bowl before you start cranking the engine you will need to by pass the oil pressure switch.
Mike this is also the same reason your bucket had fuel in it after you started cranking the engine over.

Cheers Roger"
 
"Hah! You guys don't know

"Hah! You guys don't know about the "Fastjeff Easy Re-Starting Technique":

Assuming you can let the motor cool down thoroughly after using the boat, here's what to do. (This works best if the motor is stone cold):

Simply restart the motor and run it for 10 seconds before leaving the olde girl. That refills the carb with fresh, cool gas. Makes a hellova difference.

Jeff"
 
"Roger;
From what I can see,

"Roger;
From what I can see, you are correct. I can see the electric fuel pump on the wiring diagram that is in the Installation manual that came with the boat and drive.
I also note the oil press switch that controls it and it is separate from the switch that gives the audio warning. So I beleive that if I can find the former switch and jumper it, the fuel pump will run as soon as the ignition is switched on, thus filling the carb before cranking, plus I will still get an audible alarm if oil pressure is lost. I think this will completely solve the problem.
Anyone with a similar problem should be able to do the same thing.
Thanks, Rod"
 
"If you have an electric pump,

"If you have an electric pump, by all means add a momentary jumper switch and run the pump for 10 seconds BEFORE trying to start it. (Did that on my old boat--worked great.)

The reason the manufacturers don't make this part of the starting system is this: If the motor died because a fuel line ruptured, the pump would dump raw fuel into the bilge as you tried to restart--not good! Using a momentary button can avoid this hazard (assuming one is smart enough to take a look in the bilge before trying to restart a motor that "mysteriously" died).


Jeff"
 
"Jeff;
What you say makes sen

"Jeff;
What you say makes sense. I guess the best arrangement would be a momentary contact switch that you would hold down for a few seconds before a cold start. The switch would in effect jumper the oil pressure switch to acitivate the fuel pump. Once she starts, you would then still have the protection of the oil pressure switch to shut off the fuel pump in the event of a fuel line rupture.
I think this is the way I will go at this.
Thanks all for the help.
Rod"
 
"Roger, Jeff; I have a new pla

"Roger, Jeff; I have a new plan that keeps the new wiring to a minimum. Why not jumper from the hot side of the bilge blower to the hot side of the electric fuel pump. That is a very short run or wire, and the fuel pump will then be enabled anytime you run the blower. After you are rolling and switch off the blower, you are back to normal with all safeguards intact.
Only issue is whether the blower wiring and breaker will handle the extra load of the fuel pump. Do you know what amps the pump draws?
Mike S.; my apologies to you, I kind of hi-jacked your original topic, but I think we both (and who knows how many others) have the same problem/issue.
Peace,
Rod"
 
"Gentlemen:
Let us remember

"Gentlemen:
Let us remember that our boats are floating bombs just waiting on the fuse, a tiny fuel leak, because it already has many ignition sources to set it off.

For the safety of all on deck, only use the momentary "push to make contact" marine grade sealed switch with an "ON" LED (10,000 hour life) indicator lamp wired parallel to the switch.

The power source needs to be a separate 12V fused or breaker controlled circuit for the electric fuel pump. There should be a fused panel with spare circuits under the dash somewhere. All you need to do is install the correct fuse and attach the hot wire to the + side of the fuse panel buss bar. The ground wire can be attached to the - side buss or the engine main ground. No fuse panel available; then use an in-line fuse installed as close to the 12V source as possible. Size the switch and fuse or breaker and wiring to the maximum draw amperage of the fuel pump. Use stranded 16 ga, or 14 ga. for a long run.

Consider using the smallest volume pump you can get since it has only a small job to do which will also control the amount of fuel dumped into the bilge by accidental leakage. Consider installing a gas leak monitor alarm in the bilge area.

Safe boating for all."
 
"..."Why not jumper from t

"..."Why not jumper from the hot side of the bilge blower to the hot side of the electric fuel pump"

Not sure I like that idea. First of all, I NEVER turn my bilge blowers off (knowing full well I would regularly forget to turn them back on when I need them most). Second of all, that would defeat the reason for the oil pressure circuit and that's not what you want to do.

I like the "jumper the oil pressure switch" idea, or power the pump directly, but using only a momentary contact button. And I agree the switch needs to be marine approved (as mine was).

Jeff"
 
"In my <u>opinion</u>, the mom

"In my <u>opinion</u>, the momentary switch is masking the problem. However, I'm sure it will work well. My friend has a 1994 5.7L w/Carb. It starts immediately when the key is turned regardless of how long it has been sitting. Mine should be doing the same thing."
 
"M.S.: Your problem with fuel

"M.S.: Your problem with fuel loss from the bowl has to be something that is repairable. Is the carb original? Has it been rebuilt? If not, rebuild it. If yes, has it been rebuilt recently? Perhaps the rebuilder left out a washer type seal in one of the jets that is allowing it to leak out. I would go over the carb with a fine tooth comb. Fuel loss from the bowl is either evaporation, leakage or siphoning."
 
Back
Top