A little tip for the Mercury brothers with carbureted engine

[fitz73222]

This will probably work on Yammi's and OMC's as well.

A buddy of mine at work was complaining about his 2005 90HP Merc getting harder and harder to start cold. I rigged the boat for him when it was new and he takes meticulous care of the boat and fuel system, keeps it garaged, and like new condition. So we began the process of trying understand what was going on. He went through his cold start process. Squeeze the bulb till hard, push in the key and hear the enrichner click, just crack the throttle open; used to start in 2 seconds and off he'd go. Now she takes a good 10 seconds or more and struggles to stay running without leaning on the primer and eventually stabilizes. This engine may have 200 hours on it so we're not talking about a worn engine. So I start to think about my 60 Bigfoot on the flats boat doing the exact same thing for about the last 2 years. I chaulked my condition up to a 15 year old engine with 800 hours and starting to see a little wear. I've played with timing, syncronization, throttle pick up timing, richening the carbs slightly all set exactly to a factory service manual plus the little tricks I've learned. I've been starting this engine the same way since I took her out of the box and rigged her in '98.

So back to the 90HP; my buddy Dave had started to back track the fuel system and decided to remove the primer line where it attaches to the intake plenum that gets a direct shot of fuel from the primer solenoid to start. Guess what, no fuel even with the solenoid clicking. So he pushed down on the manual plunger and out comes a wad of garbage from the primer hose; pushed it several more times and it was shooting clear fuel again. Hooked it back up and she starts in her normal 2 seconds again. Back to the Bigfoot, same test; no fuel when I push in on the key with solenoid clicking, hit the manual plunger and nothing but clear fuel comes out into a jar BUT it was not working correctly until I excersized the plunger diaphragm manually and she began to shoot fuel like it is supposed to when I pushed in on the key.So went ahead and held the plunger down and squeezed the bulb and a steady stream of fuel was exchanged through the solenoid with the plunger being held down. Hooked the primer line back up to the intake plenum, pushed the key and she started in 2 seconds like she used to.  So if you run into this condition, check to make sure you are really getting fuel out of the enrichener regardless if it is clicking or not. Old dogs can learn new tricks!
So I'm going to do this process to the 115's on the 22-2 next because they also have their day's when I say WTF is going on with the cold start today? I thought I would share this revelation with the brothers...

[FJStretch]

That is great information! I dont know how many times i have heard people talk about this type of problem, hoping to find a solution.  Being very much an amateur-backyard mechanic, its great to pick up new insight and knowledge. It's a good part of why I joined this forum. Thank you for posting this solution!

Stretch

[fitz73222]

Here are some other things I learned about this system that may shed a little more light when it comes to diagnosing a fuel delivery issue. The primer circuit does not pressurize the fuel; it is in fact a solenoid ball seat that opens and closes that receives a fuel charge from you pressurizing the system after squeezing the primer bulb. The primer gets its fuel from a tee fitting from one of the fill lines going to one of the carbs. The primer system relies heavily on the ability for the primer bulb to maintain system pressure via the internal check valves. So if you like to prime your engine before heading to the ramp you may have lost system pressure when you go to crank her up 20 minutes later. Reprime the engine right before you start her to make sure the system is pressurized. So if you have a primer bulb with a defective check valve it will not maintain system pressure to deliver the initial shot of fuel to start. Only after the engine starts will the fuel system become pressurized from the fuel pump.

You only get one shot of fuel when you push in on the key. It lasts about 1-2 seconds and de-pressurizes the system when the fuel charge is deployed into the intake plenum. You can push in on the key 20 times but it won't deliver any more fuel until you reprime with the bulb or the engine starts and fuel pump takes over; then you can bump the key if needed to maintain running quality while the engine warms up.

Now conversely, think about what may be going on if the primer circuit is stuck open or the ball seat is leaking. This is going to cause some significant flooding of the engine not only during cranking but during running also since the primer will continue to dump fuel into the intake as long as the system maintains pressure. I've read a number of posts where the engine seems to be running very rich and idle poorly for no apparent reason. We tend to look at leaking float valve seats in the carb(s) or ruptured fuel pump diaphragm reverse feeding back into the crankcase through the pulse line.

So the lesson here for me is don't take the primer for granted that it is working correctly just because it clicks like it is supposed to. If you think about it, it's probably one of the most neglected components in the fuel system than can cause a host of symptoms that could steer you in the wrong direction (and costly) so take the 5 minute test before you start digging into teardown of components.

[fitz73222]

Just bumping the post before it disappears to page two. I want to make sure you guys read this. We take this component for granted as I did and its worth a first look when dealing with a fueling issue.

[gran398]

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Just bumping the post before it disappears to page two. I want to make sure you guys read this. We take this component for granted as I did and its worth a first look when dealing with a fueling issue.

Glad you bumped it, missed this post over the weekend.

My Merc 75's are running perfectly. I have also noticed they like tight bulbs on the crank.

Got in a hurry last time, cranked without tight bulbs...they spun and spun. Pumped the bulbs tight...BAM...two seconds later, just as you advise, they cranked easily and idled down tight