Replaced carb - engine won't start (oil in flame arrestor)

[bgilbert]

At loss here.

I had purchased a new cab about a month ago, installed, engine running fine, but there was a leak in the carb (upper gasket). MM replaced the carb for me, sent me a new one and I installed. Everything seemed fine, engine fired right up, ran for about 30 seconds, then slowely started to die out (as if not enough fuel). I increased throttle and she stayed alive for about 15 more seconds, then stalled.

Now she won't start, turns over (I can hear a low pitch wizzing - flywheel?). There is fuel in the carb, I removed the flame arrestor. Then I noticed that the flame arrestor had an oil/gas mixture in it. I've never seen this and have had the flame arrestor off probably 4 times in the last 2 years.

Any thoughts? I'm back on the boat today to check plugs, etc.

[Marian Claire]

Questions... Is this a late model carb with the scavenge tube? Is the flame arrester your old one? Do you have the crankcase breather running to the flame arrester? How is the choke set when you are starting/trying to run? Have you checked for an air leak in the manifold? Mechanical or electric fuel pump? How do the plugs look, wet/dry? Dan S/V Marian Claire

[bgilbert]

So I just had a chance to get to the boat, looks like the oil in the crankcase is diluted with gas (a lot of gas). I'll take a look at the fuel pump.

It did start this morning, but did the same thing as described above.

Dan - thanks for the quick reply. To respond, late model w/scavange tube. Original flame arrestor w/breather. Choke is open, plugs look wet. Mechanical pump.

I haven't worked on the pump before, so this should be a joy ride....

[Marian Claire]

I believe the fuel in the crankcase is a sign of a bad diaphragm in the mechanical fuel pump. I have an electric pump so others may have better info but a rebuild of the pump and a few oil changes should take care of that issue. The wet plugs are confusing, is it fuel, water, oily/fuel? Drain some fuel from the carb and see what it looks like. Dan S/V Marian Claire

[bgilbert]

I'll have to check what was on the plugs later this week.

While I have the fuel system torn apart (and can at least access the engine now), is there any other likely causes of oil in the crankcase? If the tools are out, might as well repair / perform maintenance on any likely causes.

Thanks.

[Dave Neptune]

Careful

bgilbert, if there is a smell of fuel in the oil and the level of the "OIL" has risen in the crankcase~~STOP. This is a classic case of a failed diaphram in the fuel pump an easy fix . An above full oil level can splash around in the block much more and bits of the oil instead of just fumes can escape the VENT line that feeds the spark arrestor and that could drastically affect the mix and performance.
Check the oil level and most important to note if it has mysteriously risen due to fuel leaking from the diaphram directly into the crankcase.
First decide if you want to rebuild/replace the mechanical pump (my preferance) or go with the electric pump, they both work fine. When replacing the pump of your choice install a cheap fuel preassure gage between the last polishing filter if so equiped and the carb. It will save you much time in diagnosing any futere problems.
Rebuilding the pump is easier than getting it off the engine as one of the bolts is a bit tough to get to easily. When reinstalling use a "allen" type cap screw and instalation/removal will be much easier.

Dave Neptune

[bgilbert]

Thanks. This is where I'm at. I have the fuel pump off, surprisingly easy with a 3/8 socket and 5" extension from Ace Hardware.......heard some horror stories, but will reattach w/allen screws.

I have the pump apart, will order repair kit tomorrow.

That being said, what is the benefit of the electric vs. mechanical pump?

And has anyone installed a manual fuel valve to shut off fuel between pump and carb to guarantee no leakage when engine not in use?

[hanleyclifford]

You should have a shut off valve at the fuel tank and that is sufficient to meet USCG requirements. If you do put a shut off valve between fuel pump and carb make sure it is well supported so that vibration cannot over time cause a cracked nipple or other line component failure.

[CalebD]

That being said, what is the benefit of the electric vs. mechanical pump?

Mechanical vs. electric fuel pump

The electric fuel pump requires you to use an oil pressure cutoff sensor in the ignition circuit. The reasoning for this is that if you left the ignition key in the 'on' position the electric pump would pump fuel while the engine is not running. The oil pressure sensor solves this problem. I have heard of cases where the oil pressure sensor malfunctioned causing an otherwise healthy engine to stop running. The fix in this case was to replace the sensor.
The mechanical pump needs no oil pressure sensor as it only works when the engine is being turned over by the starter motor or the engine is running. When the engine stops the mechanical pump stops pumping. A common failure mode of the mech. pump is that the diaphragm can leak allowing fuel into the oil in the crank case. The fix for this involves replacing the diaphragm in the pump and changing the engine oil.

And has anyone installed a manual fuel valve to shut off fuel between pump and carb to guarantee no leakage when engine not in use?

I know that some here have added another fuel valve between the tank and engine in order to make it easier to access the shut off valve. You could add fuel valves anywhere you like in the fuel line. Personally, I like the simplicity of having only 1 valve in our fuel line which is installed immediately downstream from the tank.

[Marian Claire]

bgilbert: Pros and cons for both types of fuel pumps. Maintenance and proper installation play into it. IMO. The one thing that the electric provides me that a mechanical does not is ease of swapping in a hurry. I have a spare electric pump mounted in the engine compartment. Two hoses and a wire and off I go.
Full disclosure: I also carry a mechanical pump and a rebuild kit. A third small facet electric pump and the inline primer bulb can be used to keep the engine running. Dan S/V Marian Claire

[Dave Neptune]

Shut off

bgilbert, as was stated you should have one at the tank. I also mounted one to my "CHEAP" fuel preassure gage which is fed by the polishing filter and feeds directly to the carb. The gage is a good place to support the valve and not much fuel is left in the line to the carb. My practice is to shut off the valve and then shut down the engine when I am going to leave the boat after a cruise.

Dave Neptune

[Dennis Mominee]

Dave, where do you find fuel pressure gages? Are they in line or part of a tee? Any part numbers?

[smosher]

Check Ebay for the gauge and a local h/w store for the fittings.

It is basically a T fitting for your size hose, with a 1/4" port for the gauge.

I have a mechanical fuel pump and my gas pressure is always a little over 3 psi.

I use a racor filter to the pump, polishing filter, fp gauge, then carb.

Steve

[Dave Neptune]

Gage

Dennis, I'm using a std Stewart Warner 0~15 PSI gage with a "tee" mounted to it. the fueu comes in and on the way out it goes through a 1/8 SS ball valve and the valve has a short run to the carb.

Dave Neptune

[bgilbert]

Thanks everyone. Repair kit seemed to fix the problem. Now having a bit of an issue with stall when put in to forward gear. Neutral RPM is just about perfect, but when I place in forward, she either stalls out or sputters a bit. If it increase throttle, no issues. Suspect I'll have to work with either mixture or throat setting.

Thanks again. Brody.