Starting procedure

[Jcris]

My boat has an electric fuel pump that doesn’t get power until the motor builds enough oil pressure. I believe that’s normal. After the boat sits for a couple days it’s always difficult to start cold. To start it cold I crank the motor until the oil pressure alarm stops ringing. I then turn the key off and advance the throttle full twice to get some fuel in the carburetor. Then, with neutral bypass engaged , I advance the throttle about 1/2 way and try to start. It will usually start but run very rough until the choke opens. At which point it begins to idle smoothly. Does this sound right?
I don’t like how rough it runs initially
let me know what you think
thanks

 

[Furbird]

Replying because I want to see what the experts here know. I have a 4.3 with a TKS engine but the previous owner replaced the TKS with a Rochester (just found that out today). He was having a cold start issue too so he put a primer bulb in the line just in front of the engine and manually pumps it on cold start. However, the fuel pump not coming on because of oil pressure does seem a little strange because that's one of the things I checked today and mine gets power as soon as you start trying to crank it. Are you sure you don't have a bad oil pressure switch or sender that may be creating more problems for you? Also sounds like you have a choke issue because that should pop closed the first time you engage the throttle to pump some fuel in.

 

[Rick Stephens]

Merc fuel pumps get power two ways: one off the oil pressure switch and the second off the outboard starter lug which powers during cranking.

Sounds like your anti-syphon valve isn't sealing well enough to keep your fuel lines full of fuel. If I start up my motor after sitting for months then I prime the motor by shorting the outside lug on the starter to the battery lead coming in at the top of the solenoid. But otherwise, your fuel system, if everything is working, should not drain all the fuel back into the tank.

 

[Rick Stephens]

Here's the wiring diagram with modification added to insert a relay to power the pump: The bottom diagram is how your boat is wired with the purple yellow going directly to the pump.

 

[achris]

That diagram looks familiar.

If you want to be a bit clever, you could run a wire from the relay (terminal that runs to the pur/yel wire) to the dash. Connect it to the purple from the key via a momentary push button. When you turn the key ON, push the button to run the pump to prime the carb.... Then do your throttle pumps and start....



Chris.......

 

[Jcris]

Last year before I rebuilt the carburetor I installed a momentary switch on the fuel pump. I would cycle it for 5-10 seconds before I pumped the throttle. That would always get fuel into the bowl and make starting easier.
But, it also began starting as if it were choking on too much fuel. Smoking, running rough and smelling rich. Once the choke opened up the rpms increased and it began idleIng smoothly. Just started so rough I thought maybe The switch adding fuel was flooding the carburetor. So I took the switch out I began starting it by the procedure outlined above. Which seemed to work but Now it’s back to its rough cold start scenario. I’m going to look at the anti siphon valve today. I did once before and seem to remember it was just a check ball in a hose barb located right at the tank. Once I get it started my first order of business is going to be a compression check. And of course a check of all ignition components. Which are all essentially new. Thanks everyone for the help

 

[Lou C]

Question and suggestion:
1) are you raising the idle speed with the shift system dis-engaged to approx 1200-1500 rpm for cold starts? Carbed engines with chokes need that to run relatively smoothly after a cold start, they will not run smooth at 600 rpm like an EFI engine when cold.
2) with the choke set up, you can set it so it just barely closes, and make sure that the choke pull off is opening it the specified amount after a cold start, if the choke is adjusted too tightly or the choke pull off does not work you will get that rich chugging after a cold start.

 

[H20Rat]

Last year before I rebuilt the carburetor I installed a momentary switch on the fuel pump. I would cycle it for 5-10 seconds before I pumped the throttle. That would always get fuel into the bowl and make starting easier.
But, it also began starting as if it were choking on too much fuel. Smoking, running rough and smelling rich. ...h adding fuel was flooding the carburetor.

Shouldn't be happening. The float valves should close up once the bowl(s) are full and shut down flow.

 

[achris]

Sounds like the choke setup needs adjusting... The maximum pressure those pumps can make shouldn't overcome the needle and seat in the carb...

Chris...

 

[nola mike]

That diagram looks familiar.

If you want to be a bit clever, you could run a wire from the relay (terminal that runs to the pur/yel wire) to the dash. Connect it to the purple from the key via a momentary push button. When you turn the key ON, push the button to run the pump to prime the carb.... Then do your throttle pumps and start....



Chris.......

I was thinking about doing something like this, didn't know if it was needed. Also didn't know if there was some sort of timer that could be used to prime for a few seconds when the key was first turned on

 

[nola mike]

He was having a cold start issue too so he put a primer bulb in the line just in front of the engine and manually pumps it on cold start.

Pretty sure this is illegal.

 

[achris]

Pretty sure this is illegal.

Not illegal.

When I had the 4.3LX I also had an outboard fuel primer in my fuel line, for the same reason... My engine had the dribbly Weber, and after shutdown the carb continued to drop fuel into the engine. Given enough time (overnight) the carb would empty, leave the needle and seat open and the fuel would then drain back to the tank. As the electric pumps aren't 'valved' they can't self prime. If they're empty and you spin them, they stay empty.... Quick couple of pumps on the primer and we're good for the day...

Chris....

 

[harringtondav]

I cheat. ...don't hate me, and don't let your children try this at home.

I keep a harness jumper in my glove box for the first start after winter layover. I disconnect the harness at the oil pressure switch and jump it with my jumper. I can hear the electric fuel pump working at key on. This fills my carb float bowl.

After the engine starts and warms up I shut down and remove the jumper and reconnect the harness.

Thereafter the engine starts fine. I crank for a few seconds to get the fuel pump to charge up the carb. One pump on the throttle to give the carb a shot of gas through the accel pump, back to neutral and just a slight touch of throttle to get a little higher rev when the engine touches off. And it always does.

 

[Jcris]

Checked anti siphon valve and it works good. Blow in direction of flow (tank to filter to carb) the ball releases. Other direction flow is stopped ( no flow toward tank). No issue there. The choke is set so minimal pressure allows it to open. The pull off opens to about 1/8” when I give throttle on cold motor.
sound right?

 

[Jcris]

So, once the bowl in the carb fills the float shuts off flow. But the pump continues to run? What is an appropriate length of time to run the pump? 5 seconds? 10? Or?

 

[achris]

Nope, keeps running... That's why you have 'pressure'. If the pump stopped, there'd be no pressure....

Chris...