Merc 4.3 problem 1991

[ryanr623]

I have a perplexing problem. My boat starts cold with the flick of the key. If i turn it of, wait 15 seconds, and try and start her again....boom, fires instantly.

However, if i let it sit for more than 30 minutes it has a really hard time starting. IE giving a little gas and cranking for 30 seconds. I originally thought the motor was flooding, so i took it to the sand bar, shut it off, and waited 30 minutes and tried starting it without giving gas. Same thing, 30 seconds of cranking and when it is about to fire, i have to give it a little gas.

After having the hard starting problem, i took it to the dock and let it sit for 3 hours. Came back out and fired instantly. It appears i may have a heat soak problem? I know its winter blend gas in the boat, but i never had this problem with my merc 120? Is this what it sounds like to you?

 

[ryanr623]

Re: Merc 4.3 problem 1991

Bump

 

[Don S]

Re: Merc 4.3 problem 1991

Sounds to me like the choke is closed, and not opening. Does the engine idle ok warm at 650 rpm?

 

[ryanr623]

Re: Merc 4.3 problem 1991

Sounds to me like the choke is closed, and not opening. Does the engine idle ok warm at 650 rpm?

Yeah, it idles fine at 700rpm-800rpm whether cold or hot. And even after its hard to start (30 seconds of cranking), the motor idles great and sings beautifully at 4800rpm WOT

 

[searay3]

Re: Merc 4.3 problem 1991

When it dies, check for both spark and fuel. Pull the flame arrestor and look at the choke plate like Dons suggests. Could be a broken spring or a power issue to the choke...

 

[ryanr623]

Re: Merc 4.3 problem 1991

When it dies, check for both spark and fuel. Pull the flame arrestor and look at the choke plate like Dons suggests. Could be a broken spring or a power issue to the choke...

It doesn't ever die, sputter, cough or anything. It always runs beautifully. Just once it sets for 30 minutes to 2 hours it's hard to start.

 

[searay3]

Re: Merc 4.3 problem 1991

The idea here is to eliminate subsystems. If it won;t start and you have spark, you can rule out the ign. Move on to fuel. Some of those carbs have plugs at the bottom of the carb that can leak into the intake. If that is happening, it's flooding simply sittig there. To start a flooded carb engine, hold the throttle wide open to clear the engine but be ready to pull back the throttle quickly when it starts. The guys on this forum concentrate on troubleshooting. As I stated before, that is the art of elimination....

 

[ryanr623]

Re: Merc 4.3 problem 1991

The idea here is to eliminate subsystems. If it won;t start and you have spark, you can rule out the ign. Move on to fuel. Some of those carbs have plugs at the bottom of the carb that can leak into the intake. If that is happening, it's flooding simply sittig there. To start a flooded carb engine, hold the throttle wide open to clear the engine but be ready to pull back the throttle quickly when it starts. The guys on this forum concentrate on troubleshooting. As I stated before, that is the art of elimination....

Gotcha. Will do. Sounds more like flooding to me now too. Because once i hear it start to want to start i have to hold it wide open to start. It rushes obviously, but i back off the throttle quick.

 

[Bondo]

Re: Merc 4.3 problem 1991

Gotcha. Will do. Sounds more like flooding to me now too. Because once i hear it start to want to start i have to hold it wide open to start. It rushes obviously, but i back off the throttle quick.

Ayuh,... What carb are We talkin' 'bout anyways,..??

 

[ryanr623]

Re: Merc 4.3 problem 1991

Ayuh,... What carb are We talkin' 'bout anyways,..??

The dealer where I bought it said 190hp, but i only see 175 or 205 for a 1991. Im assuming that it is 175hp 2 barrell, although i haven't been back to the marina to check.

Also, i always thought holding the throttle wide open would make the flooding worse, i guess not?

 

[ryanr623]

Re: Merc 4.3 problem 1991

How long does it take a leaking carb to "flood" an engine? If it can take 30 minutes im almost sure its flooding. Because from what im hearing vapor lock isn't all that common.

 

[Bondo]

Re: Merc 4.3 problem 1991

The dealer where I bought it said 190hp, but i only see 175 or 205 for a 1991. Im assuming that it is 175hp 2 barrell, although i haven't been back to the marina to check.

Also, i always thought holding the throttle wide open would make the flooding worse, i guess not?

Ayuh,... It's either a 2bbl. or 4bbl. carb...
Take the flame arrester off, 'n LOOK...

If it's the 4bbl. carb, those Merc/ Webers leak off internally...
Going to Wot to start it usually Helps...
Holding it Wot, clears the flooding...

 

[ryanr623]

Re: Merc 4.3 problem 1991

Ayuh,... It's either a 2bbl. or 4bbl. carb...
Take the flame arrester off, 'n LOOK...

If it's the 4bbl. carb, those Merc/ Webers leak off internally...
Going to Wot to start it usually Helps...
Holding it Wot, clears the flooding...

Yeah i know how to check, i just haven't yet, since the marina is 15 miles away. You say they leak off internally.... i have heard on another forum there is no fix for this (and its early 4.3's only) and mercruiser refuses to even acknowledge the problem. If so that's ridiculous.

So basically, if the carb is leaking we are looking at:

If two barrel, a rebuild
If four barrel Live with it..... WOT hot starts, great.

 

[Bondo]

Re: Merc 4.3 problem 1991

Yeah i know how to check, i just haven't yet, since the marina is 15 miles away. You say they leak off internally.... i have heard on another forum there is no fix for this (and its early 4.3's only) and mercruiser refuses to even acknowledge the problem. If so that's ridiculous.

So basically, if the carb is leaking we are looking at:

If two barrel, a rebuild
If four barrel Live with it..... WOT hot starts, great.

Ayuh,.... I haven't heard either way,...
But, if the Edlebrocks don't Leak,...
They're a Carbon Copy of the Merc/ Weber...

They're Both Carter AFB clones...

Reasonably inexpensive too...

 

[ryanr623]

Re: Merc 4.3 problem 1991

So i just look down the barrels to see if fuel is leaking correct? Should i wait a couple minutes after i shut her off? I heard the carb leaks a little for a couple minutes immediately after shut down. IS this true?

If its not, i'll leave the doghouse off, to determine if its vapor lock. I'll also idle for three minutes and run the blower.

Thanks for all the help already, its much appreciated!

 

[ryanr623]

Re: Merc 4.3 problem 1991

Someone told me that the (mechanical ) fuel pump could be the problem. When it gets hot a ball or something gives a little and not deliver the correct fuel pressure.... I thought this was only on fuel injected motors?

 

[Harte3]

Re: Merc 4.3 problem 1991

I had a similar starting issue when warm. Finally shut it off, pulled the spark arrestor and looked down the carb...it was dribbling gas. I had the carb rebuilt this last winter.

 

[90stingray]

Re: Merc 4.3 problem 1991

Mine was doing the same thing! I rebuilt the Mercarb and it still did it. Later on i found there are two types of needle and seats. You need the one with the spring NOT the solid needle. I just rebuilt her again and no more issues. Starts hot with a bump of the key