Priming ball losing prime after long idle

[2100greenmonster]

If I idle for a long time my priming bulb seems to lose prime. If I'm running hard and check it it seems fine it's just after a long idle. I'm gonna replace the bulb and line and rebuild the pulse pump. Is there anything else I should check. The motor runs strong, just don't want to run into a lean problem.

[EuropeanAM]

You could also remove the antisiphon valve from the fuel tank pickup and check it for debris, obstructions, or sticking.

Incidentally... when you say "it's losing prime"... are you referring to it being "soft", or "sucked flat"? Is it an OEM primer bulb?

One must remember that the primer bulb is a "pumping device to prime fuel into the fuel system of the engine". It places the fuel line between the bulb and the motor under "pressure" after you pump it firm.

Once the engine is started, the same portion of the line will come under "low pressure" (you would know this as a vaccum). That's because the pulse fuel pump is "sucking" fuel through the line... the primer bulb essentially is just "along for the ride".

[2100greenmonster]

It's just soft, it's completely possible that it's always been like this and I'm just recently conscious of it after reading a recomentdation to pump it up at every start up. It runs strong with zero issues, just want to keep it that way.

Is the anti siphon valve in the elbow going into the tank for fuel pick up.

[EuropeanAM]

Yes, the anti-siphon valve will look just like a "screw-in nipple" (it actually has a check ball and spring inside it).

[Strokerdean]

Not to hi-jack the post but I have never had to squeeze the prime bulb since the motor installation. The motor starts after a couple of revolutions (300xs), it does seem to crank slow even with the larger battery (900cca). Is it recommended, if so, why.

[EuropeanAM]

It is recommended, and here's why:

1. Pumping the primer bulb ensures that the VST is full of fuel. It can prevent situations where you key up the ignition, the VST is dry (fuel evaporation or vaporization occured), and damage to the fuel pump occurs.

2. With today's fuels (and the prevalence of ethanol), it is highly likely that at some point throughout the year, you will find yourself faced with a "fuel vaporization issue". On EFI/Optimax Models, you may not even realize it occured. It may present as difficult starting, a short lag on acceleration, a complete "fall on it's face failure to accelerate", or in extreme cases, a hard "lean sneeze" upon acceleration that blows EVERY SINGLE REED BACKWARDS THROUGH THE REED BLOCKS. And yes... I've seen the last one TWICE.

Fuel vaporization occurs at lower temperatures when the fuel comes under "low pressure" (or vaccum). So... if you've run the engine on a hot day... shut down, and fish for 45 minutes, it is entirely possible that upon starting, the fuel line is actually full of "vapor", rather than fuel. The pulse fuel pump was designed to pump "liquid"... so the possibility of any of the scenarios in #2 above exists.

Simply pumping the bulb "firm" will usually purge the vapor through the VST (Vapor Separator Tank ), leaving fuel where it SHOULD be. At the very least, it will compress the vapor, raising the "boiling point" of the fuel/vapor in the line, and allowing for faster purge of the compressed vapor.

Hope this explanation helps some....

[CRIMSONGAMBLER]

Does anyone reccomend a fuel pump anymore.Would it hurt a 97 225 EFI Merc? Used to run them a long time ago on the carb engines.. I know it has one in the cowl.

[EuropeanAM]

External fuel pumps not recommended on your model (actually only recommended on a very select number of Racing models).

Factory mounted/supplied pumps are "more than adequate" for the fuel demands of the engine (provided the pump(s) are in good, functional shape).

[CRIMSONGAMBLER]

Thanks,

[Strokerdean]

Thanks Don for the explanation, I will start pumping the bulb first thing in the morning.