Fuel system question (Fuel pump, Carb?) Goes lean after 15 min.-gctid378492

[Guest]

The last time we used the boat, we started having a problem where the boat would run lean after about 10-15 min of running on plane. The engine would start to ping, sputter, then begin to die. After a couple of minutes at idle, all was well.Recent maintenance was new ignition parts (plugs, coil, wires, cap, rotor). New fuel/water sep filter. Carb rebuilt 2 years prior by carb service in Jax FL.After the carb was rebuilt, we used the boat for one last cruise around Savannah before moving north. No issues.However, here in PA, on the last trip, it started acting up. This was at the end of the season.I asked some questions and list of candidates was not too long.Fuel pumpAnti siphon valveCarbToday I removed the carb and removed the top housing, no problems could be seen. The float level and drop were correct and no gum or varnish. Everything looked ok...... except, one of the screws, the long screw #1 of 8, was loose (see image). Not even snug against the housing. However, all of the other screws were tight. The one screw was at the section between the throttle body and the float bowl. So fuel could have been siphoned in during higher RPM at cruise speeds, emtying the bowl prematurely. The gasket at this point on was stuck to the housing and left gasket material, while the rest of the gasket was easily removed. Additionally, the plugs, recently replaced, appear to show a rich running engine.

[img]/media/kunena/attachments/vb/681952=27331-airhorn.jpg[/img]Today I removed the anti siphon valve and the check ball seems to work as advertised, isn't sticking, the spring isn't too strong and the ball floats when you apply a little bit of pressure.Additionally, I ordered a replacement Mercruiser mechanical fuel pump. The one I removed is the original (circa 1997).Is it possible the loose screw on the carb housing could have been the culprit? Or am I reading too much in to this?Vincent

[Guest]

Perhaps someone more knowledgeable will reply. But to me, it sounds more like the pump. I had to replace mine, it was weak and the engine would die on idle, when docking!

I took the old pump, put my finger on the fuel input, and physically pumped it. A bit of pressure. I took the new pump, did the same, and could feel a real difference. Now to put it on the engine!

Let us know how it turns out.

[Chief_Alen]

A fuel pump should give between 4-7 psi no more no less. This is a 2 barrel carb. You can check it with a gauge. When ordering a new one make doubly sure you ordered the correct one.

Just replied another thread....questions such as this one will pop up all summer long...

http://www.baylinerownersclub.org/forum/showthread.php?70032-05-185-3-0-carb&p=682004&posted=1#post682004

[Guest]

Actually to me it sounds more like a clogged fuel tank vent. Check the vent and hose, or try a runn with the filler cap cracked open, or a remote fuel tank.

[Guest]

akwalker wrote:
Actually to me it sounds more like a clogged fuel tank vent. Check the vent and hose, or try a runn with the filler cap cracked open, or a remote fuel tank.

+1 Check the fuel tank vent. If it was the carb or pump it would give you problems immediately, this sounds like vacuum building up in the tank and starving motor slowly.

[2850Bounty]

I agree with Chief on the fuel pump pressure.

Fuel pumps, fuel lines, filters, anti-siphon valve, etc, should all be capable delivering more fuel than what the carburetor needs to deliver...., if the float level is set correctly and if the fuel metering is working.

I'd have to say that lean conditions are seldom a result of this... if all is working correctly.

Here's your list of knowns and suspects:

No issues with the carburetor prior.

New tune-up parts were installed. No mention of re-timing or checking timing.

Pinging under marine loads is likely detonation.

Spark plugs appear to show a rich condition.

Carburetor gasket suspect to pulling fuel from around it may perhaps equal a rich condition, not necessarily lean. Doubt this is the case... but never say never.

Any change to the grade of fuel used?

The list you posted:

Fuel pump

Anti siphon valve

Carb

No mention of excessive ignition advance (all too often not considered).

Since your ignition system is the Merc TB EST system, you'll want to run this by someone knowledgeable with typical TB module issues, and what/how this may affect and/or cause what you are seeing.... if not carburetor related!

.

[Guest]

Thanks for the advice guys. I should have noted before that we ruled out vapor lock, the problem occurs with the fuel refill cap off.

Since the boat would run fine, for 10-15 min or so on plane, then start to ping, run lean and start stumbling, but recover after idling for a few minutes and run fine for 10-15 min, my theory was the fuel bowl was emptying. If I ran the boat for 10 min, then idled for a minute, then run for 10 minutes, I could go all day with no indications of a problem. It wasn't until I passed that 10-15 min mark, did I start to experience the pinging and subsequent problems.

I am going to go ahead and replace the fuel pump and go from there. I will also check the timing when I get it back together, I wouldn't have thought of this, but it can't hurt and I should have done it when I replaced the ignition parts.

Thank again,

Vincent

[Chief_Alen]

Check the pressure first before buying a fuel pump.

[boatworkfl]

Check your fuel pickup, pull it out and check it, it may solve your problem, and is the least expensive solution, do not become a parts changer, we have enough mechanics in this country that do this because they do not know how to trouble shoot.

[boatworkfl]

Chief Alen wrote:
Check the pressure first before buying a fuel pump.

Pressure and volume may be the issue!