Mercruiser starts but then dies! need help

[franktank11]

alright guys i am running out of ideas....i have a 3.7 mecruiser 470 model inboard motor i have spark and fuel. i have recently replaced the spark plugs, wires, tune up kit, fuel pump and rebuilt the carb. the motor starts for a second or two then dies. there were a couple of times where it runs for like a minute or so then dies. i am thinking that i may have a choke problem. i am doubting my work on the choke, does anyone have pictures or a how to adjust the choke. i looked in the book and it mentions a "choke baffle" i dont remember there being one before i took it apart. can anyone steer me in the right direction to get this thing running. i am close to getting this boat in the water. thanks in advance

 

[Pete104]

Re: Mercruiser starts but then dies! need help

Your choke plate should stand straight up & down. If you remove the flame arrestor the first thing you see is the choke. It's called that because it , when closed doesn't allow air into the engine. Get it? It must be open for the engine to run.
You can prop it open oneway or another but don't let anything fall into the intake.
Sounds like you might be able to take it to the next step. Give it a shot!

 

[franktank11]

Re: Mercruiser starts but then dies! need help

here is what i was thinking and correct me if i am wrong.....i have an automatic choke my understanding was that it automatically opens as the engine warms up, and it starts off shut with the minimum opening (.011 mm). my thinking was that it was getting too much air thats why it wasnt starting. am i wrong for thinking this? thanks

 

[franktank11]

Re: Mercruiser starts but then dies! need help

Another question just came to mind.....is the housing of the choke thermostat suppose to me HOT? when it sits there motor not running that choke housing is pretty hot.

 

[Stamey]

Re: Mercruiser starts but then dies! need help

What is supposed to happen is right along what you are thinking. When cold, the choke should close most of the way. I can't close completely because the engine needs air to run in any case. Note: many carbs will close the choke all the way when the engine is not running and is cold, but the choke will open just a little as soon as the engine starts due to the vacuum of the engine. This is normal. In most cases the choke will be open from the last time the engine was run, and you need to actuate the throttle to allow the choke to automatically close, when engine is cold. This is because there are throttle stops connected to the choke linkage to raise the idle speed of the engine while the choke is engaged. This has an added side affect to also actuating the accelerator pump and squirting a little gas into the carb.

Once you have set the choke as described above, you should attempt to start the engine. Once the engine has started. the heat up sequence begins. This includes the heating of the engine and the heating of the choke control thermostat. This will be a manifold thermostat or and electric thermostat. Either is supposed to get warm as the gine heats up. In the case of the electric, because it is independent of the engine for the heat source, if you leave the key on the choke thermostat will get hot and release the choke whether the engine is running or not.

If you suspect a choke issue, you can put a rag and your over the carb to simulate the action of the choke.

Chris

 

[franktank11]

Re: Mercruiser starts but then dies! need help

if i put a rag over the top will this shut the motor off if it was running or will this allow it to run? thanks

 

[dn010]

Re: Mercruiser starts but then dies! need help

be careful using anything to cover the top of the carb as it can get sucked into the intake... Why not just have someone hold the choke open/closed and try to start? If it is closed too much you won't be able to start at all unless you have the throttle full on which forces the choke open. I just went thru this with my 470, I put the choke cover on wrong which held the choke too closed, readjusted and it runs great for once!

 

[dn010]

Re: Mercruiser starts but then dies! need help

Forgot to mention that the auto choke will get hot if you have the key on - engine running or not. The heat is what expands/contracts the spring inside the choke to open or close the choke plate. The choke is supposed to start closed (.11) and then open as it warms up. On a hot day the choke may start open and not even close at all (don't think mine ever close..). There should be a cut in the plastic of the choke thermo which you line up to the middle notch on the top of the choke housing - then you adjust the plastic piece a few notches lean or rich if needed. Bending the arm for choke adjustment is a different story.. Also make sure your choke isn't binding and it opens and closes easily.

 

[franktank11]

Re: Mercruiser starts but then dies! need help

i will definetly try those reccomendations.....when you set your choke plate do you use the electric choke cover (utalizing the thermostat spring) to make your adjustments (.11mm) or the idle bolt? the choke plate is loose and opens and closes easily

 

[Stamey]

Re: Mercruiser starts but then dies! need help

The way I adjust the electric chokes is, when the engine is stone cold, to turn the choke thermostat until the choke closes fully. Make sure you have the throttle above an idle, perhaps half throttle, so that the high idle linkage, if yours has one, can move freely. You can get more scientific, but this method works well in most cases.

So, getting back to your problem, why do you think it's a choke problem, or is that just where you are starting?
Is the engine just cold-natured (doesn't want to run when cold), or is it that every time you start the engine it just cuts off immediately or soon after?

Chris

 

[franktank11]

Re: Mercruiser starts but then dies! need help

well on saturday i took the carb apart agian and did the adjustments on the float and went ahead and poured fuel into the reservoir and put it all back together and opened up the butterflys to squirt a little fuel in the intake and started it up and ran a little longer than usual and tapped the choke plate open and it made pop sound and shutdown. i just was never comfortable with the re-install of that choke valve. when you push the throttle back is the choke suppose to open with it or is it just altogether seperate from the throttle? right now i have the fuel pump disconnected from the carb and just adding fuel to the reservoir as needed. i am not sure when the last time this motor had been started i picked it up about 2 months ago. the last time this boat had been registered was in '99. but i do tell you this when it does run it sounds solid, no tapping.

So not being comfortable with it thats where i wan't to lean to. but any other suggestions are welcome

 

[mxcobra]

Re: Mercruiser starts but then dies! need help

sounds like you are starving for fuel make sure ur fuel pump is working and pumping good gas?

 

[franktank11]

Re: Mercruiser starts but then dies! need help

sounds like you are starving for fuel make sure ur fuel pump is working and pumping good gas?

i have the fuel pump disconnected right now (cleaning out the old fuel in the tank) but the reservoir is full of fuel.

 

[dn010]

Re: Mercruiser starts but then dies! need help

So not being comfortable with it thats where i wan't to lean to. but any other suggestions are welcome

So then take it all apart and start from square one, make sure you have everything installed and configured correctly. A rebuild should be more than just removing old gaskets and putting new ones in-if you haven't, make sure all the little passages and ports are clear, sometimes people drop gasket pieces where they shouldn't be. Also - did you touch the 2 adjustment screws that are sticking out of the throttle base plate? If you're not sure they are set correctly, turn them all the way in and then back them both out 1 turn and start from there.

You also said you're not sure the last time the motor ran - tune it up with some new plugs, wires, points, etc. You'll also need a constant source of fuel if you want to test how it runs; it will run dry fast with just filling the bowl by hand...