4.3 Mercruiser Hard Starting when cold, Starts fine once warm

[synergy141]

Having trouble starting my 4.3 Mercruiser LX, its a 1994. Before I start I pump the throttle a few times in neutral. It will fire up for a second then shut off. What can the problem be?

 

[Bt Doctur]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

choke not adjusted? instead of coming back to neutral, leave it slightly advanced.

 

[synergy141]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

I pump it and then leave it 1/4 throttle, it still dies, then once it turns over I pump it hard and it still dies 1 second after.

 

[dubs283]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

make sure the choke is closed after the initial throttle pump before starting the engine cold

pumping the throttle will give a nice blast of fuel from the accelerator pump well but only about 1 oz. of fuel

when cranking the fuel pump will refill the well and you get that nice blast from the accelerator pump but again, only about 1 oz.

check the choke

 

[synergy141]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

is the choke the one metal flap on the front of the carb or the 2 metal flaps at the back of the carb? . Im guessing its just the one at the front. that one stays closed but will open up a little if I put the throttle to WOT

 

[Alpheus]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

What kind of carb do you have?

 

[synergy141]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

its the 4.3 LX so it should have a 4 barrel Weber

 

[synergy141]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

i tryed to bypass the oil pressure sensor like other people have done, but again the engine would fire up for a second and die.

 

[dubs283]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

the oil pressure sender/switch has nothing to do with the choke operation

the reason it didn't run when you disconnected it is because the fuel pump voltage is received from that circuit

 

[synergy141]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

so you think the choke is the problem? What can I troubleshoot next?

 

[tractoman]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

so you think the choke is the problem? What can I troubleshoot next?

The choke, it should be mostly closed when cold and it is set. Once the engine warms up it will gradually open. If you can't find the merc manual for that Weber, go on the Weber site or Edelbrock site and you should be be able to find instructions to check the choke adjustments. They are virtually the same. On mine, I pump the throttle a couple times, leave it at about 1/8 throttle and turn it over. If it's cold it takes a couple tries, but I don't crank it for 2 minutes. I crank about 5-7 seconds and repeat. It usually fires up after a couple tries. When its warm, no throttle and it fires in a couple revolutions.

 

[Bt Doctur]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

http://www.boatfix.com/merc/Servmanl/18/18C5R2.PDF

 

[synergy141]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

The choke is closed when it is cold with just a little bit of gap for air. So I think the choke may be working. maybe not?

 

[dubs283]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

if the choke plate is closed with the throttle at idle, it is set properly for starting

with the engine off and cold (not been run for a day at least), remove the throttle cable from the carb and manually open the choke plate

fully pump the throttle arm on the carb, you should see two definite streams of fuel being directed down the barrels of the carb

if not, there is a fuel delivery issue or a carb leak issue

 

[synergy141]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

earlier today when the engine was cold I did pump the throttle. ( but without removing the cable like you mentioned) I had a friend look into the carb and he could see 2 fuel streams being shot into the carb bowls

 

[dubs283]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

the streams should be definite, like a squirt gun (best analogy) and you should be able to pump multiple times and see good streams with each pump

i would say, 3 pumps - should see 3 good fuel squirts - after that, there would be no fuel left in the accel pump well

 

[synergy141]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

Im not sure i they were big streams, I would have to see for myself. If they are weak streams what could that be? blocked passages?

 

[dubs283]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

If they are weak streams what could that be?

either a fuel delivery issue or a carb issue

 

[synergy141]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

maybe if I changed the fuel/water seperator that may help

 

[Alpheus]

Re: 4.3 Mercruiser Hard Starting when cold, Starts fine once warm

Originally Posted by synergy141
If they are weak streams what could that be?

That your accelerator pump is going bad, floats are set wrong and not allowing the bowls to fill up completely,check ball sticking.

You may be have a leak inside your carb and flooding your engine(fouling your spark plugs) causing you to have to crank the heck out of it to get it to start. Again this could be a heavy or a un-adjusted float or bad needle and seat.

To diagnose this, prop open the choke and try your normal start up procedure when cold...