5.7L mercruiser choke problemr

[ericz103]

Hi everybody, I'm new here.

I have a 1996 5.7L mercruiser alpha one 2barrel carb. When I went to take my boat out for the first time this year it would not start. I got it to fire on starting fluid but that was it. I didn't have many tools on me so it was time to take it back home.

At home it had fuel going to the carb, but just to be safe I changed the fuel filter/water separator, it needed done anyways. I also cleaned the vent line that runs from to the fuel pump to the carb. I don't think it was completely clogged but it did have a lot of gunk in it. Still nothing when I tried to start it.

So I go to at least partially clean the carb. It was getting plenty of fuel in the bowl. None of the jets I removed looked clogged but the bowl did have alot of debri in it. I cleaned all the jets that are accessible with the top plate of the carb off, and also the float mechanism. Go to start it afterwards and still nothing....

Then it hit me, the top choke plate is always wide open. So i rig it most of the way close with wire and it fires up. It seem to run fine on fast idle and beyond once i open the choke plate back up... but would not idle. This was on ear muffs in my driveway. I did not run it for a super long time, it was not even all the way warm...

So I think I just have a problem with the choke. I have not really messed with carburetors too much, I am a younger lad and most everything I have worked on has been fuel injected. So my question is, I am assuming this is just an electric choke problem correct? The actual mechanism is plenty free moving. I measured voltage to it running an it had zero volts(plate wide open). So when should the plate be closed, just cold starting? I am assuming voltage applied to the choke closes it. What controls when and how long it is on? The wires kinda went back to where it would be hard to trace, just following them but I guess I did not give it too much effort.

Any help, or pointing to literature that would educate me would be appreciated. I am a handy guy, I just have never worked on boat motors or carbs really before.

Thanks
Eric

 

[NHGuy]

Welcome Eric. If you go to the stickies at the top of the forum and go into the Mercruiser information page there's a link to boatinfo which has read only info. You can't down load it but it's still the shop manual. That will help you a lot.
Your choke should close when cold, when the power is applied on startup it will slowly open. It sounds as if someone disconnected it and adjusted it open. Some do this intentionally because a proper running motor will usually run after about 30 seconds of high idle in summer weather. And the choke takes a few minutes to open.
See if your motor will idle when warm. If it won't idle warm you could have plugged idle circuits or if you are lucky someone might have turned the mixture screws in too far.
When it runs watch that clear line from the pump to the carb, if it gets fuel in it shut down. That's the replace fuel pump indicator. Fuel there means the pump diaphragm is leaking. It can cause poor running too, because it brings too much fuel into the carb bowl.
Let us know.

 

[ktbarrentine]

I measured voltage to it running an it had zero volts(plate wide open). So when should the plate be closed, just cold starting? I am assuming voltage applied to the choke closes it. What controls when and how long it is on? The wires kinda went back to where it would be hard to trace, just following them but I guess I did not give it too much effort.

Any help, or pointing to literature that would educate me would be appreciated. I am a handy guy, I just have never worked on boat motors or carbs really before.

Thanks
Eric

When you read the stickies as mentioned above, you will figure out that the choke coil gets voltage all the time when the engine is started/running. As the coil heats, it "unwinds" (metal expands when it gets hot) and opens the choke plate. The stickies have the steps to adjust the choke, but basically, you loosen the three screws on the choke coil and rotate it (with engine cold) until the choke plate is all but 1/8" closed (I use a 1/8" drill bit). Then tighten the screws. You need to find out why you dont have voltage to the choke coil. Choke plate should move to full open w/in a couple minutes of running.
Remember, though... after you get the choke adjusted, you need to cycle the throttle open abit to "set" the choke in the cold starting position. (after you turn off a hot engine, the choke stays in the open position (there is an idle adj screw on the carberator throttle shaft that bears on the choke shaft cam. Once you move the throttle, the screw comes off the choke cam and the choke re-closes, assuming the choke coil has cooled off, i.e when your engine has cooled off).

I had the exact problem as yours a few years ago. Once I figured it out and got my choke adjusted properly, my starting issues went away.

 

[ericz103]

Thanks for the help guys. I went and looked on youtube after posting this for setting an electric chokes seems easy enough. I should mention that it ran fine when put up last winter. I had it professionally winterized too. I cannot see why any adjustment on the carb would suddenly be out considering its running in the same conditions it always has(temp,elevation, type of gas)....

This is my 3rd summer with the boat, 1st boat I've owned. I guess I could see the choke being disabled the whole time, it always did take some work to get cold started, but I always just chalked it up to being carbed. It had never really caused a problem before.

I'll check out the manual too. Off the top of their head does anyone know what voltage I should see at the the electric choke? 12V?

I'll check for gas going down the vent line too. I should mention that when I cracked the infeed gas line at the carb it sprayed pretty good. I know carbs/mechanical pumps don't run a whole lot of fuel pressure. I don't have a fuel pressure gauge but my hillbilly watch out hard it sprays test, it looked like it passed...

Hopefully I get to it this weekend. I'm recovering from ACL replacement surgery, so I can't wakeboard or waterski this summer anyways. Good time to learn about my boat! I think I have been lucky on having zero problems for this long.