Running rough at cold start

[Lager]

Im new to mercruiser 3.0 so excuse my ignorance.
I bought this 1988 3.0 and it runs very rough at initial start up, in our 40 degree temps. I found that the choke plate is in the completely closed position until the engine is running for about 2 minutes, then it starts to open and then the engine runs smoothly.
There are three hold screws holding the electric choke mechanism in place and if this were an automobile engine, I could adjust the electric coil to reduce choke closure allowing a smooth engine start, meaning less misfire.But I cannot.
I read on another forum that this is normal operation. The 3.0 will misfire/run rich until the electric choke plate opens allowing better mixture rate.
Is this true? If so, its dumb, it does not have to be this way.
Second,what is the vent line running from the top of my carb to the top of the fuel pump for?
Ive been an auto mechanic for the past 35 years and Im looking at this I/O, thinking why?
Ideas?

 

[thumpar]

Re: Running rough at cold start

My 2.5l did the same thing. If you want the choke to open more just turn the key to run and let it sit for a 30 seconds or so then start it. To me it was normal.

ETA: I would run mine at a high idle speed for the warm up also. Somewhere around 1500-1600 RPM.

 

[model14]

Re: Running rough at cold start

Loosen the screws on the choke housing and rotate the cover to change the choke closure, or better yet, just wait 2 minutes after turning on the ignition switch and the choke will have opened enough to allow smooth running. The choke spring is heated by a heating element that is powered through the ignition switch. It has nothing to do with actual engine manifold temperature. Take the flash arrester off and watch it happen.

The line running from the fuel pump to the carb is to allow raw fuel to go directly into the carb and flood the engine to shutdown, in the case of a ruptured diaphragm in the fuel pump. Otherwise it would collect in the bilge.

If you are going to work on this engine yourself, get a manual for it and learn to love YouTube, and this forum. I speak from experience, having just restored a 1988 2.5L.

 

[thumpar]

Re: Running rough at cold start

Model14 is correct. That line is a "telltail". You don't want fuel in the bilge or crankcase. If there is fuel in that line you need a fuel pump.

 

[Lager]

Re: Running rough at cold start

I thank everyone for their responses.
I understand now about the overaggressive choke plate, I guess it is what it is.Thanks for the tips on how not to foul my spark plugs.
There is an adjustment, but its not effective. OK I can deal with that.
Concerning the vent line from the fuel pump to the carb, this has got to be one of these Marine regs that make no sense.
Automobile engines that have used mechanical fuel pumps for a long time used the same sort of pump, the upper chamber was not vented to the carb but sealed. If the diaphragm were to rupture, it quit pumping fuel, it didnt leak fuel anywhere.
OK, Im good with that also.
My many thanks, now it all makes sense, sort of. LOL
So, Im good to go !

 

[littlebookworm]

Re: Running rough at cold start

JWelcome to the forum and the boating world. ust to add a few notes to the question on the fuel hose: Never replace a marine fuel pump with an auto pump. They make look the same but an auto pump doesn't have the fuel return hose and is illegal and unsafe in a boat. That hose becomes cloudy and brittle over time. When you replace it, always use hose specifically designed for that purpose. Do not use clear hose you buy at a home center. I definitely agree that you should get the manuals for the engine and outdrive and review postings on this forum and others regarding your engine and drive and boating in general. Many details about maintaining a marine setup are the same as for maintaining an auto setup, but there are differences and you should be aware of them. Maintenance is critical. You don't want to be stuck on the water. You can't walk home. Hy

 

[thumpar]

Re: Running rough at cold start

JWelcome to the forum and the boating world. ust to add a few notes to the question on the fuel hose: Never replace a marine fuel pump with an auto pump. They make look the same but an auto pump doesn't have the fuel return hose and is illegal and unsafe in a boat. That hose becomes cloudy and brittle over time. When you replace it, always use hose specifically designed for that purpose. Do not use clear hose you buy at a home center. I definitely agree that you should get the manuals for the engine and outdrive and review postings on this forum and others regarding your engine and drive and boating in general. Many details about maintaining a marine setup are the same as for maintaining an auto setup, but there are differences and you should be aware of them. Maintenance is critical. You don't want to be stuck on the water. You can't walk home. Hy

Especially if your boat is on fire. The regs make sense. On my last inspection (they are random on the water) the officer told me must a week before a Fiberform had an explosion in the bilge because the guy used an auto alternator. There was a kid sitting in the seat next to the doghouse. He would go into details on damages/injuries.

 

[harleyman1975]

Re: Running rough at cold start

Yepper, what they said! The starter, carb, alt, fuel pump and dist have all been "marinized" to prevent fire...and even though all this has been done there is still a danger of fire. Always turn on the blower 2-3 minutes before you start. (I always open the hatch and take a look and a whiff when I am getting ready to start the engine). Fire on water is bad cause there is no place to go.

 

[Bondo]

Re: Running rough at cold start

I thank everyone for their responses.
I understand now about the overaggressive choke plate, I guess it is what it is.Thanks for the tips on how not to foul my spark plugs.
There is an adjustment, but its not effective. OK I can deal with that.
Concerning the vent line from the fuel pump to the carb, this has got to be one of these Marine regs that make no sense.
Automobile engines that have used mechanical fuel pumps for a long time used the same sort of pump, the upper chamber was not vented to the carb but sealed. If the diaphragm were to rupture, it quit pumping fuel, it didnt leak fuel anywhere.
OK, Im good with that also.
My many thanks, now it all makes sense, sort of. LOL
So, Im good to go !

Ayuh,.... Welcome Aboard,.... Yer gonna have to look closer at the next automotive diaphragm fuel pump ya see,...

A diaphragm type pump, can't/ won't work unless the backside of the diaphragm is Vented,...

On a car, it'll drip on the ground, in a boat, into the bilge,....

Gas in the bilge is the next to the last step before an Explosion,...

 

[Lager]

Re: Running rough at cold start

Good answers from everyone, I had no idea that that even the starter and alternator were specific for a closed compartment .
Littlebookworm said it best, " You cant walk home on the water"
Im not new to boating and I do agree with his statement, plus Im from Florida and enjoyed the outer swamp areas so Im pretty picky about safety and maintenance.This is just my first In board engine, Ive always had outboards so Im new to this setup.
My thanks again for the education I just received and Member Bubba 1235, I am too and so do I.
This Sunday, its gonna be 55 degrees and clear. I have to replace the trailer bunks so Im going to splash it into the water and take it for a lil spin, then replace the bunks.

 

[NHGuy]

Re: Running rough at cold start

If you can't adjust the choke plate by turning the choke pulloff mechanism take it apart and look. It's designed to be adjustable, maybe the last person who put it together assembled it wrong.
Pretty much like a GM electric choke. Wait, it is a GM electric choke!

 

[Lager]

Re: Running rough at cold start

NH Guy, I thought it would be adjustable also, but the cap is indexed to one location by a tab on the cap.But,If I were to grind the tab off, this would allow me to set the cold start choke plate position to where I want it to be.This would eliminate the severe engine missfire and the shaking of the engine that stresses the engine mounts.
Thanks for the idea.

 

[airdvr1227]

Re: Running rough at cold start

Hehe...every vehicle I ever owned until 1985 ran rough when it was cold.

 

[Scott Danforth]

Re: Running rough at cold start

try this next time.

2 pumps of the carb, move the lever to a fast throttle (disengage gear select) then start it. I usually bring the RPM's up to about 1500 for a few minutes.

unlike a car, there is no fast-idle cam on the choke. this is by design so that you dont try to put it in gear with the engine screaming at 2000 rpm

 

[thumpar]

Re: Running rough at cold start

try this next time.

2 pumps of the carb, move the lever to a fast throttle (disengage gear select) then start it. I usually bring the RPM's up to about 1500 for a few minutes.

unlike a car, there is no fast-idle cam on the choke. this is by design so that you dont try to put it in gear with the engine screaming at 2000 rpm

That is exactly how I would start my 2.5l. The fast idle is a much smoother way to warm it up.

 

[Lager]

Re: Running rough at cold start

Member Thumpar, hit it right.
Turned the ignition switch on and let it sit for about a minite maybe more.
Two pumps on the go lever.
Hit the gear disconnect switch and pushed the throttle to the fast idle position, hit the starter and it ran smoothly.
Im pleased as punch now,Thanks Thumpar.
Hitting the water tomorrow for the first time in this thing.Supposed to be nice, 55 degrees.

 

[thumpar]

Re: Running rough at cold start

Have fun. Our highs are still about freezing. Can't wait for summer.