Requires open throttle to start

[pauldo]

My 2004 50hp Mercury is requiring an open throttle to start. What does this mean? Clean and rebuild carbs? Carb adjustment? Timing? It runs great but hard to start if it sits for more than 15 minutes or so. When throttle is open it immediately fires at very high rpm. Plugs, fuel filter, and primer bulb have been replaced. Also, I have verified that the choke/enricher is functioning properly.

[sliderman]

It actually sounds like you are running ethanol fuel that has absorbed some water. The need to open the throttle shutters indicates a flooding condition. I'd take a fuel sample and inspect for the presence of water before I removed the cowling on the motor.

[MDCrappie]

I agree with the "flooding" aspect, but not sure how water in the fuel would cause this. My guess would be the needle/seat leaking and when you are pumping the ball the fuel is going right into the cylinder(s). Is it a 2 or 4 stroke?

[pauldo]

Its a 2 stroke with 3 cylinders. For the entire summer I ran ethanol free gas and I got the same result. I thought seafoam would have been my cure but it has also failed. Will the carb rebuild kit include all parts needed to fix a leaky needle seat? Is it possible that the low speed jets have some degree of clogging.

[sliderman]

Water saturated fuel is less combustible. It requires a richer mix. If the fuel is dry, I would inspect it in this order.
Tilt motor slightly to a positive trim angle. (like a moderate shallow water drive position). Squeeze primer bulb. It should firm up solid after 4 or 5 full squeezes. If fuel begins pouring from a carb, you need the carbs cleaned as you have at least one needle valve that's not closing completely. If no fuel leaks but the bulb never gets completely firm. Squeeze it slowly. If you notice that fuel is still being moved upstream, you have a bad diaphragm in your fuel pump that's allowing fuel to travel directly into the block. If no fuel leaks and bulb firms up, walk away for 15 mins. Return and again squeeze the bulb. If you find that it is no longer firm and requires one or more squeezes to firm up, you have a bad primer bulb that is letting fuel pressure bleed back down. You may also want to elaborate on your test of the enrichener. Also, I've seen many folks that don't push in on the key until the starter is engaging. (a habit that comes from the days of choke shutters). With the enrichener, key on, push and hold, start engine. It makes for quicker starts.
You indicate that the motor runs fine once it's started which goes against the norm if a carb circuit is stopped up. Considering the age of the motor and the fact that ethanol fuels and additives made now aren't necessarily friendly with older made rubber components, it may be a good idea to have the fuel pump rebuilt with a new kit, have the carbs cleaned and adjusted and have the entire system checked over by someone who's in tune with the common problems of that particular motor design.

Be easy with the sea foam and other snake oils. They can be useful in keeping a motor in top shape. But they are used way too much in my opinion and cause problems that are difficult to diagnose.

[sliderman]

If you are scratching your head trying to figure out how a bad primer bulb could possibly cause this. As the fuel gets passed the bad check valve in the bulb and returns down hill to the tank, it will have a siphon effect and drop the fuel pressure into the negative. The enrichener requires positive pressure in order to function. Which means the motor would have to spin over several times in order for the fuel pump to build pressure and bring the enrichener into operation. And most all motors will turnover faster with open throttle shutters. If that makes sense.

Also, if your fuel line is the original gray colored line, it has most likely become stiff. It stiffens as a result of the most inner layer becoming brittle. When it does that, it flakes off and the particles end up messing up the primer bulb, creating obstructions in the fuel pump and create problems in the carb among other things. If you have the gray line, replace it with an expensive ethanol resistant line from the auto parts store. It's less expensive and will outlast the ready made stuff.

[pauldo]

I checked the enricher by turning key to on position and pushing the key inward; I was able to hear it click. Also, on initial startup if the engine tries to shutoff I can push inward on the key and it picks up again. Today, after reading your posts, I tilted the motor and pumped the bulb - the bulb got fairly firm but just a tad fleshy and no leakage from carbs. After 20 minutes the bulb retained the same level of firmness and still no leakage at the carbs. In addition, I held constant pressure on the bulb once it was firm and it did eventually start to collapse but just a small amount (1-2 minutes). Not sure if this is normal. Thinking back to when I changed the primer bulb, I also changed its lower hose because I could see where the interior was crumbling. I didn't change the upper hose because I was unsure about removing the factory metal clamp at the quick connector. My next move will be to replace the mercury gray hoses with 5/16 hose from the part store. Should I use zip ties at the quick connector or a traditional metal hose clamp? Maybe I should invest in a water separation filter.

[SeaRay]

I was unable to get a zip tie tight enough to not leak when I changed mine. I went with worm gear metal clamps.

[sliderman]

A cheap zip tie tool will tighten the zip tie enough. If you prefer the clamps, go for it. Since it is recommended to always disconnect the fuel line from the engine when not in use, take an extra minute to make sure that the zip tie or clamp is free from sharp edges. Nothing worse than reaching over to pull the line and cutting a finger.
Sounds like you are on top of your game on this thing. Diagnosing from long distance has it's limitations.

I need some clarification on this, does this motor require that you give it 'some' throttle in order to cold start or is this a problem requiring the throttle be set wide open before it will start?
Also, has this problem always existed? Developed following a service or just developed over the course of a summer?

[pauldo]

I start with throttle nearly wide open and once running I back off of the throttle; however if I back down too quickly it will die. This condition has existed every since I purchased the boat last spring. Didn't think much of it because I could tell the boat had been sitting for awhile. I have never taken it in for service but if I can't resolve the current issue with a simple solution I will definitely seek professional help. Just hate to fork over that kinda cash. Call me cheap if you like.