Engine dying in idle

[JimmyDubai]

Guys, after 5 minutes of starting up the engine and keep it in idle, it dies. Shall I start looking at the fuel pump? Any check valve on the way? Where is the location of these two components? The victim is a Mercruiser 7.4 V-8

Thanks

 

[hottoddie]

Is it a carburetor motor? If so sounds like it dies when the choke opens indicating a possible problem with the low speed circuit in carburetor. Possible carb rebuild needed.

 

[Dieseljeff]

Fuel injection or carb?
If carb, maybe choke is sticking closed?
Only check valve I'm aware of on the carburetor engine is in line right after pickup coming out of fuel tank.

Need more info.

Jeff

 

[JimmyDubai]

Oh!! I had no idea that the problem could come from there.... good suggestion. It is a carb unit, correct. Maybe it is time to do it, thanks

 

[dvx216]

Need to find out what your fuel pressure is.You can rent a pressure kit from auto zone .Once you know you got good fuel pressure you can move on to the carb or you can take a stab in the dark without knowing your fuel pressure. To check fuel pressure you are teeing in a gauge in the fuel line right before the carb .

 

[bahamabreisus]

Might start with fuel filter, if not changed in a while.

 

[JimmyDubai]

Need to find out what your fuel pressure is.You can rent a pressure kit from auto zone .Once you know you got good fuel pressure you can move on to the carb or you can take a stab in the dark without knowing your fuel pressure. To check fuel pressure you are teeing in a gauge in the fuel line right before the carb .

Filter was changed a couple of months ago. I will try to do the pressure test that you are saying, thanks

 

[JimmyDubai]

I haven't been able to take pressure readings but I started the engine, checked the choke operation and it looks fine (closed when cold and open a few minutes later). I could see fuel spray on the first two carb openings and I also can see some opening on the back openings of the carb once the throttle is fully engaged.





All seems to be normal to me. Shall I let the engine warm up a bit before sailing off?

 

[scoflaw]

If it runs fine at WOT, forget about it being a fuel pressure problem. Does it load up before it dies ? Black smoke ? No smoke and dies could be a partially plugged idle circuit. Assuming you have tuned the beast ? Plugs, wires ?

 

[SloBurn]

That carb looks really dirty, I'd start by spraying carb cleaner through it.

 

[scoflaw]

That carb looks really dirty, I'd start by spraying carb cleaner through it.

That might make it look better, but will do nothing for the fuel delivery

 

[dvx216]

A little shade tree mechanics. Bump the motor without starting it the best time to do this is when the the motors cold and if you can pull the coil wire. Wait a minute then break the fuel line at the carb. there should be fuel pressure so be careful when doing this it should spray gas all over for a second put a rag under line. What this will tells you is the float valve in the carb is good and the valves in your pump are good.If there is no pressure then you have a leak (you haven't mentioned a external leak) so there for its at the carb or at the pump.If the carb is leaking enough at an idle it will stall due to flooding and if the pump is leaking the motor might not be getting enough fuel until you increase RPM.You haven't mentions how easy the motor starts. This is not the only thing it could be but doing this eliminates things it could be.

 

[JimmyDubai]

Hmmmm..... it takes a few attempts to start after a few days of inactivity. If I do it overnight, it starts fine. No leaks on the carb. No black smoke. I haven't checked plugs or wires for the past 100 hours (one year).

 

[scoflaw]

Like I mentioned earlier.....if it runs right up to normal RPM at WOT, the issue is more than likely in your carburetor idle circuit.

 

[Ruff Life]

I think you finally gave the clue to the problem. When you say it takes a couple tries to start after sitting that indicates the fuel bowl is empty. By taking a couple tries to start the engine you are refilling the fuel bowl with fuel. Quadrajets have fuel bowl plugs that can leak and will empty the bowl in a day or two. It leaks in to the manifold so you will never see it. Also the leaking will cause the engine to run rich at idle as extra fuel is dripping in. This will cause the engine to run very rich and may cause it to stall out at idle especially when in gear. You can just live with this by leaning out the idle mixture a bit or do it right and having the carb rebuilt. When you start the engine and keep it at a fast idle of about 1200 rpm will it stay running? This problem will not be noticed at cruise or wide open.

 

[JimmyDubai]

Excellent, thanks for the advise guys. I will have some work to do over the weekend.
Cheers