Fuel problem?

[NickAllinson]

Having some kind of fuel issue...
The engine starts and idles fine for about 3 minutes, then dies. Starts again no problem, idles for 2-3 minutes then dies unless the throttle is turned up.
I've tried this with the gas cap on and off, thinking the vent is blocked, no difference.
It'll drive forward for hours at idle, I just won't idle in neutral.
I don't have a working tach, but used a friend's timing light to get it idling around 900.
Also, there's a surge...
Also also, as the engine warms up the idle increases.
Also also also... The motor quits at idle, shifting from forward to neutral... ***.
This is our first year with the boat. It has a rebuilt carb and fuel water filter and clean fresh fuel. It also has an adjustable main jet. I've done all the Moyer tuning...

The annoyance is that it dies when in neutral usually as you're docking.

Any ideas?

[zellerj]

This is opposite from my engine. My engine decreases RPM in gear (friction in the system and the prop turning through water) and speeds up a little in neutral. My idle is around 1100 rpm because it will stall if I set it lower, especially when shifting into gear, and as you pointed out, stalling is no fun when docking. I know I am not getting ideal fuel economy but I am not worried about fuel economy.

Surging - hunting some call it - rpms increase and decrease at idle, could be because of an air leak. Did you install new gaskets? Were the two halves of the carb checked for flatness, so they seal properly?

Take out the bowl drain screw and drain the bowl into a clean glass jar and look for debris. Sometimes debris is from putting hoses on rough barbs and perhaps pieces of teflon tape if that was used in the install. This debris floats around in the carb bowl and periodically plugs the jet causing stalling and rough running.

Finally when I had carb trouble, I could never fix it with a rebuild. Perhaps it was my lack of skill, perhaps the carb was just at the end of its useful life. A new carb from Moyer was a good investment, because the last 10 years have been trouble free. A cheap (1/3rd boat bucks) fix when one considers trouble free docking.

[Surcouf]

if you are 100% sure it is the fuel and not ignition (dying coil?), you would have to rule out items one by one:
- first should be a pressure indicator just before the carb. Would allow you to rule out any safety valve electrical issue, blocked tank vent (you already did that one), pump or filter issue etc...
- any chance it could be bad fuel? water in seperator? this could be ruled out by rigging a temporary tank right before the pump
but I agree with the previous advice: with your description it could be more a floating debris in the carb bowl.

Once you treat all the usual suspects (ignition, timing, fuel and compression), do not forget that a partialy blocked water discharge could also be an issue.

[Dave Neptune]

4 things?

First welcome to the forum.

#1 Do you have a mechanical or electric fuel pump?

#2 Have you checked the centrifugal advance? This is done by removing the distributor cap and twisting the rotor to see first that it is moving and moving smoothly and returning smoothly as well. Do you have points or an electronic ignition?

#3 How have YOU adjusted the idle? please explain.

#4 Did you check ALL of the fuel line connections from the tank to the carb?

By answering these it may give us an idea of the source of the problem or problems .

Dave Neptune

[joe_db]

Finally when I had carb trouble, I could never fix it with a rebuild. Perhaps it was my lack of skill, perhaps the carb was just at the end of its useful life. A new carb from Moyer was a good investment, because the last 10 years have been trouble free. A cheap (1/3rd boat bucks) fix when one considers trouble free docking.

Our carbs seem to have a finite lifespan. I think it relates to the metals used and ethanol. I found that eventually no amount of cleaning and fixing would keep it running for long and a new carb fixed it all.
At the rate I use my boat I think the carbs are good for about 10 years.

[ndutton]

Our carbs seem to have a finite lifespan. At the rate I use my boat I think the carbs are good for about 10 years.

I’ve run mine on a steady diet of E10 for 17 years with zero carburetor problems.

[Dave Neptune]

Very durable carb

Like Neil, I ran the same fuels in the same carb for 34 years. I had it apart many times playing with jets, air correctors and float levels to get the carb the way I liked it. I did replace the bowl gasket during each jetting episode. I did start with a new carb when I bought the boat as it had been submerged and the engine was frozen tight.

Dave Neptune

[capnward]

You have come to the right place. Sounds like a fuel issue, or an idle issue. I'm guessing idle, since it runs well enough at higher rpm. To the excellent advice above, I would add that you should check your choke to make sure it opens completely. If it doesn't, then you would be running too rich. That could explain why you need more throttle to keep it running, and why it shuts down after a while.
Or your fix may be as simple as turning the idle mixture screw out a bit to make it leaner. One full turn out from the seat is the standard adjustment, maybe 1.5. Also, turn the adjustable main jet all the way into its seat, then back it out 1.5 turns, maybe a little more. This can dislodge an obstruction in the jet. Turning out the main jet richens the mixture. But if you've done all the Moyer tuning you have already done this.
Assuming you have an electric fuel pump, you may have a slight leak in a fuel line connection which does not drip gas but allows enough air into the fuel line to build up in the pump and stop it pumping. Mechanical fuel pumps which have more suction overcome small leaks in the line which should not exist anyway. They may leak fuel when the engine isn't running.
A fuel pressure gauge just upstream of the carb will indicate restrictions or air in the fuel line. A working tach would also help you know if your idle is consistent.
Another possible reason could be the idle ports, the small holes in the side of the carb throat near the throttle valve,

are clogged. They enable idling.
The only time my engine wouldn't idle was because of a barely visible blockage in the idle jet, only noticed when the jet was removed and held into the light. A thin wire cleared it. I have what may be the original late model carb and avoid ethanol. The brown gelatinous goo I used to get in the filters and carb no longer occurs. Those who always keep any water out of the fuel tank can run ethanol in their gasoline.
In my experience, it is normal for the rpm to increase as the engine warms up initially. I don't know why it does that. It stabilizes after a minute.
Your report that the engine will operate in idle under load, but not in neutral, mystifies me, unless you are increasing throttle in gear to keep it running. If I have an idle problem, it occurs when I throttle down, especially when in gear. Putting it into gear at low rpms shuts it down. Taking it out of gear increases rpm and keeps it running. But on my primitive boat, the shifting and throttle controls are separate. It may that be on your boat you have to throttle down to put it into neutral, and putting it into gear also increases throttle. This would explain why it stalls in neutral, runs in forward.
Once you get a working idle, you are all set. Good Luck!

[Sam]

A few years back I had an intermitent idling and surging problem. I change fuel lines to low permentation, changed fuel pump, cleaned carb. What really solved the problem is I completely emptied the gas tank. The bottom few gallons were a combination of water & gas and some crud built up over last 40 yrs. Now with ethanol etc I make it a habit to drain the bottom gallon or so every season. This year it looked fine. [To empty the tank I rigged up an old electric fuel pump on a board with battery connectors with one line going into the tank and another to a container. Now I use a telescoping transfer stick pump which runs off two D cell batteries and reaches the bottom of the tank from the cockpit]. I think you have a tank - water -fuel issue.

[capnward]

Maybe fifteen years ago I went to a gas dock, and they filled the tank with diesel. I said gasoline but they didn't believe it. Then they pumped out the tank somehow using a hose that snaked its way down the fill tube into the tank. I was surprised they were able to do that, because I once hired a guy who cleans fuel to clean my tank, but he said he needed a port in the top of the tank which I didn't have, and my fuel fill hose had too many turns in it, so he declined the job. I didn't get to see what the gas dock pumped out; it all went into a 50-gallon drum. Not long after that I began using non-ethanol gasoline. Since then, I have had no issues with junk in the filters and carb. Of course, I change filters and clean the carb every spring. It may be the non-ethanol fuel, but it may also be the tank was cleaned that day.

[joe_db]

I’ve run mine on a steady diet of E10 for 17 years with zero carburetor problems.

What happened to me was the zinc coating of the carb started creating this white goo that would clog the carb. No amount of filtering could prevent it, the reaction was happening in the carb itself.
I did some Googe-Fu and found out this is a result of ethanol interacting with the metals in the carb. I got a new carb and ALWAYS ad SeaFoam to the gas, according to Practical Sailor it is both cheap and does a good job preventing metal corrosion. No issues at all on the replacement carb that must be about 10 years old now.

[ndutton]

What I find interesting is the difference between your experience and mine, Dave's too. Either our carbs are not identical in terms of their casting alloys and coatings or something else is going on.

My gas additive is MMO @ 1%

[capnward]

I really don't see much difference. Both put either MMO or Seafoam in the fuel and have no corrosion issues. Evidently either of the additives does the job. I believe that the lack of ethanol also plays a part in preventing corrosion, but I have only anecdotal, not scientific proof. The theory seems to be that ethanol bonds with any water in the tank and sends the stuff down the line, where it is combusted in the engine or corrodes the filters, pump, and carb, depending on your point of view. Lack of water in the tank is the main goal. Either way I like MMO in the fuel. Never seen any white stuff in the carb. I doubt the alloy in the carbs varies much. I had no idea they were coated with anything but the oil in the gas.

[Dave Neptune]

Nick, any questions or answers?

Dave Neptune

[joe_db]

I think the key is keeping water out. All the bad chemical reactions with metal and ethanol are vastly worse if there is water in the mix to provide an electrolyte. (tons of info on Google if you care) Once the metal is eaten into, it just keeps corroding. Whatever protective surface coating or oxide layer or whatever is gone and not coming back.
I put a new O-ring on the fuel cap when I replaced the carb and have used MMO or Seafoam with pretty much every fill and now decade old carb has been totally trouble free so far.