Merc 5.7 carberated hard start

[Godfirst]

1987 5.7 carberated with alpha 1 1/0 hard starting problem, tried everything of course new quality batteries fuel filter, fuel seperator cleaning carb has the 2 barrel rodchester still when in water have to crank a few minutes really frustrating and be a problem at the docks.

Thanks

 

[86 century]

Re: Merc 5.7 carberated hard start

Is this happening only on cold starts or all the time.

 

[Oshkosh1]

Re: Merc 5.7 carberated hard start

When was the last carb REBUILD? The Rochesters are an easy rebuild...kits run around $30. If it's been awhile... or you don't know...probably a good place to start.

 

[wellcraft-classic210]

Re: Merc 5.7 carberated hard start

Not sure if this is your problem but; Those carbs are known to start hard when the engine has been shut off ofter running hard. The procedure to restart is to move the throttle to full open in nuetral and pull back on the throttle when it starts.

If thats not is can you elaborate on symptoms , hot , cold, throttle setting, does it smoke or smell when it does start;
-- Providing any details may help someone to steer you in the proper direction.
-- You may need to look at fuel quality, fuel supply, fuel mixture ( common issue if debris is in the carb) , ignition spark & water intrusion from the manifolds among the possible causes

 

[NHGuy]

Re: Merc 5.7 carberated hard start

Also remember it's a carburetor, not fuel injection. My motor will start at closed throttle shortly after a shutoff. But sometimes you might need to raise or pump the throttle a bit on restarts.
And pump it 2 or 3 or 4 times to prime it before cold starts. Also on cold starts it can help to lightly feather the throttle just above idle position while cranking after you have pumped.
Once it fires run it at 1100 or so while it warms.

 

[NHGuy]

Re: Merc 5.7 carberated hard start

Just had another thought. You say it takes a few minutes of cranking? Your choke might not be closing when it's cold. To check remove the flame arrestor from top of the carb and see if the choke plate (it's a flap on a horizontal pivot shaft) is closed when cold and open when hot.
If it's always open just pump the gas to get it to start and keep it running fast enough to warm up.

 

[Godfirst]

Re: Merc 5.7 carberated hard start

Happens mainly at cold starts usually the procedure is pump the throttle a few times and give it some gas on average at startups about 6-8 pumps each time with several cranks on the ignition on the throttle then starts have to have it about 1000rpms for a few minutes or it will die, as for the carb I have know idea if it has been rebuilt looks all original even if the original color was black, real pain when at the docks and they are busy..... not talking about my stress.
Thanks

 

[Oshkosh1]

Re: Merc 5.7 carberated hard start

When was the last COMPLETE tune-up...Plugs, cap, rotor?...wire resistance check(Wires should run approx 1kohm per inch)
Also...what about the idle mixture screws? Turned in to lightly seat, back out about 1-1/4 turn...then fine tune from there by ear, or vacuum gauge. Idle should be set around 600RPM...In Gear.
Maybe the choke is sticking...could be gummed up, spray the pivot points and linkage with some gumout and ensure it opens/closes easily.

That's waaaaay too much work to start that motor.

At this point it could be either fuel or ignition...process of elimination.

 

[Godfirst]

Re: Merc 5.7 carberated hard start

Thanks for the info,

I had the carb adjusted when I bought the boat a couple of years ago originally the engine would die even after warmup had shop adjust it including the idle mixture screws, still now to this day has a rough start the carb looks original and the engine probably could use a tuneup, I was told those rodchester carbs had this problem one thing also is out of the water it doesn't have quite the problem the engine seems to idle smooth and does not shake when warmed up.

 

[Oshkosh1]

Re: Merc 5.7 carberated hard start

one thing also is out of the water it doesn't have quite the problem the engine seems to idle smooth and does not shake when warmed up.

Try settiing the idle IN the water.

OUT of the water there is no exhaust backpressure/load from being in gear and the prop spinning.

You need to go to the dock...tie it SECURELY, start it, put it in "Fwd", THEN set it.

But...needless to say...this is all a moot point if the engine isn't tuned-up. Fine tuning the idle should be the LAST step of a complete tune-up.