Classic 50 won't start

[bstig60]

I have an 88 Mercury Classic 50 which will not start. I have good spark and good compression and fuel in the carb bowls but the engine will not start. I pull the plugs and there is no smell of fuel at all and the plugs are dry. If I squirt a little fuel mix into the cylinders the engine will start and run for a few seconds. Supposedly, the carbs were recently rebuilt, or so says the PO.....
A little history, I just bought the boat recently. The PO started it in his driveway when I picked it up. It ran rough, but it ran. Wouldn't idle without the spark advanced a bit. I started it at home and ran it for a minute or two the day after I got home with it. I put it in the lake a few days ago and it was hard to start and seemed to be missing on one cylinder. It didn't want to idle without the spark advance up somewhat. I idled it out of the marina and gently brought the throttle up to get the boat on plane, after a minute or so, the engine just died like it was out of fuel and wouldn't restart. I spent some time today checking things out, even pulled the upper carb to be sure fuel was in the bowl. It was and the fuel was clean. Didn't pull the other carb. Any thoughts on why fuel isn't getting into the cylinders........

Bill

 

[roscoe]

Welcome to iboats.

Kind of need to go through the process of elimination to diagnose.

First, check spark and compression on all 4 cylinders.


Are you new to operating an outboard?

It could be something as simple as your starting procedure,
Review the following.
Don't be afraid to ask questions.


Open fuel tank vent
Check the kill switch, place in "run" position
Open fuel tank vent.
Squeeze fuel primer bulb till firm.

Advance the throttle 3/4 way, without putting it in gear. -- This is done by either pushing a button in the center of the controls, or pulling the shift handle toward the driver, or raising the fast idle lever, all depending on what control unit you have.

Turn the key to the on/run position.
Activate the choke by pushing in on the key. Its only activated while the key is being pushed in.

Turn the key to start while continuing to hold the key in.
Release the key and choke when it starts.
3-5 seconds of "choke", is usually enough.

Be ready to pull the throttle back toward the idle/neutral position, when the engine starts and the revs increase.
Continue to pull the throttle back as the engine warms up.
You should not have to use the choke much, if at all, once the engine has warmed up.
Engine should start within 10 seconds of turning the key.

Since the po claimed to have cleaned the carbs, they likely need to be adjusted to their factory starting point, then fine tuned.

​Also, carbs may have an air leak between the carb and the manifold.
Or an air leak in one of the fuel lines.

 

[bstig60]

I am not new to OB's or to engines in general.I have spark and compression and fuel to the carbs, just nothing getting into the cylinders. No gas smell or wet plugs when plugs are pulled. Plugs are newly installed.

 

[bstig60]

It turns out the po did not rebuild the carbs but replaced a leaking bowl gasket. He is supposed to be sending me the remainder of the kits. As mentioned above, fuel is getting to the carbs but not into the cylinders, I have a service manual but it doesn't go into any detail regarding these carbs. Is there one available that does?

 

[bstig60]

Are there any thoughts on why I can't get fuel thru the carbs? I have tried the procedure outlined above several times. The fuel lines are all new as is the bulb. No apparent air leaks. Problem still exists.

 

[Michawilden]

Did you rebuild the carbs yet? If you are realy sure that there is fresh fuel in the carbs you could have two problems. One is that the jets are clogged with debris. I don't think it is likely that your main jets are all clogged but the idle jets/ passage could be blocked. The other problem is that you have a lack of compression. To low compression means a small underpressure in the case. If the underpressure is not big enough, it won't draw fuel from the bowls. You state that the engine has good compression so that is probably not the issue.
In such a situation I usually squirt a little gasoline in the throttle body's to get it started just to make sure it does have compression. A compression test will also do no harm. this will give you a decisive reading instead of a 'feeling that the compression is good'.

 

[bstig60]

I located and corrected the problem today. I think. Thought was to rebuild the carbs, but I decided to check the pilot screws and see what they were set at. The top carb was at 3/4 turn out from a soft seat and the bottom carb was not quite 1 turn out. I adjusted them both to 1 1/2 turns out plus 1/4 turn and the engine started. I will have to do some tweeking of the mixture when I get it in the water but it runs and idles on all 4 cylinders. I will try and attach a video..... File too large.......

 

[bstig60]

Put the boat in the watter today to see if it would run OK. Had a little trouble getting it started, but it started and warmed up setting at the dock. I idled it out of the marina and slowly gave it throttle. It wouldn't get the little boat up on plane, so I babied it a bit and got the engine up to operating temp and then tried again. It sputtered a bit, then took hold an came up on plane and took off like a shot. I ran it for a few minutes and then decided to slow down and troll for a little while. The engine idled down OK and seemed to be running on all cylinders. I shut it down and fished for a 1/2 hour or so. When I got ready to head back to the dock, I got the engine started but it would not come up on plane when I added throttle. So I idled it back to the dock. It seems if was not hitting on all cylinders. I noticed that when I was adjusting the pilot screw that the upper adjustment didn't seem to make any difference where the screw was set. That tells me that maybe the jet is plugged up. I will have to pull that carb and try and clean it out. I will check to see if the top two plugs are fouled. Any other thoughts would be appreciated......

 

[GA_Boater]

Check the float level on the top carb. If the float is keeping the needle closed - No gas and the idle screw will have no effect.

 

[Oldcraneguy]

Sounds like you just need to pull the carbs and go thru them, Id stick a kit in the pump as well as an inline filter and be done with it, its all pretty easy and gives you a fresh start on a fuel system that you shouldnt need to mess with for a long time provided you use it regularly or run it out of gas when its gonna set for long periods....OCG

 

[bstig60]

Put the boat in the water today and adjusted the carbs under load as suggested. Ran the engine up on the triailer in gear to full speed and it ran find. So I idled it out to the main lake and gently brought it up to full power, It did just fine for about 100 yards and then started to cut out. I ran it back to the dock and shut it down and pulled the covers off the engine. It was hard to start so I pumped the bulb and it started and idled OK. I did some small adjustments to the carbs and decided to take it back out. Again it ran up to full RPM for about 100 yards and started to cut out. I reached back and pumped the bulb and it came back up to full RPM. I was able to keep it running fine as long as I pumped the bulb ever little bit. I am assuming this is the fuel pump. It keeps enough fuel in the carbs to run at low R's but when I bring it up to full power, the fuel pump can't keep up....... Thoughts..........

 

[eggcanada]

check the fuel pump, or change the bulb.

 

[bstig60]

Changed the fuel pump and still have the same problem.... Bulb is new....