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Bets BD3 Strange fuel issue


onanov

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Hi,

 

Our boat is powered by a Beta BD3 with about 4000 hrs on the clock. With a full fuel tank it runs like a dream, starts first time with no issues. However, when the fuel gets to below 1/2 a tank, the engine then gets slightly harder to start. It will start, and then die immediately. Leave it for 60 seconds & try again, and it starts no problem. Runs fine when started. Topping up the tank cures the problem.

 

Can anyone make any suggestions what might be going on?

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What is the lift pump arrangement on this engine? It could be faulty. I'm thinking that the engine is being gravity fed by the contents of the full tank but at some point the weight of fuel in the tank is not enough.

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29 minutes ago, Tony Brooks said:

Sounds as if air is getting into the system with anything but a full tank. Where I have no idea.

That sounds plausible. we have a Fuelguard filter on the system (with a glass bowl) and that tends to run with the bowl 1/2 full. Never checked whether this only happens when the tank is getting low, but it is a possibility So as you say looks like air is getting in somewhere. Question is where. we have no fuel leaks as far as we can see.

 

It is strange as the engine runs like a dream if the talk is full, even if the fuel filter bowl is only 1/2 full

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1 minute ago, onanov said:

Not sure what you mean by lift pump. as far as I am aware there is only 1 pump on the system, and that is the one on the engine.

Trace the fuel line from the tank to the engine. You will likely find the in line fuel filter, then a small piece of equipment attached to the engine block through which the fuel lines go. This is the lift pump. 

4 minutes ago, onanov said:

That sounds plausible. we have a Fuelguard filter on the system (with a glass bowl) and that tends to run with the bowl 1/2 full. Never checked whether this only happens when the tank is getting low, but it is a possibility So as you say looks like air is getting in somewhere. Question is where. we have no fuel leaks as far as we can see.

 

It is strange as the engine runs like a dream if the talk is full, even if the fuel filter bowl is only 1/2 full

 Check the breather on the fuel tank. If it doesn’t let air in as fuel is burned, then this may be causing a partial vacuum in the tank, and giving you the problem you describe.

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Thanks, never know that was called a lift pump :) - (I am not an engineer) - yes faulty pump was my thought. However, Tony's suggestion re Air sounds V plausible too - given other symptoms - (see my post about the Fuelguard filter).

 

Thoughts? 

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Now you know where it is, a photo of the lift pump would be helpful. A common type has a rubber diaphragm which can fail. There is a coarse filter too which can block but I doubt the gravity feed would work if that was blocked.

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3 minutes ago, philjw said:

Now you know where it is, a photo of the lift pump would be helpful. A common type has a rubber diaphragm which can fail. There is a coarse filter too which can block but I doubt the gravity feed would work if that was blocked.

I will take a photo next time I am down at the boat. In the meantime, I found this pic on line. Its a BD3, its not our engine, but the fuel pump looks V similartTIUCTD.jpg 

5 minutes ago, onanov said:

no diesel heater

No diesel heater - heating is Gas

The boat did have a diesel heater at one time, but this has now been removed. The fuel line for this is still in place (capped off) - it came direct from the tank on a separate line.

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I would say that the diaphragm on that pump would be between the two halves (top & bottom) and will be visible when the screws are removed.  I wouldn't do that without having a repair kit on hand though and, of course shutting off the diesel supply.  The filter I mentioned will be under the domed part, accesed by removing the bolt at the top. 

Is there a priming lever? I can't see one in that photo. If there is then I would guess that if there is a problem with the diaphragm, working the lever would not pump any fuel through so there would be very little resistance felt. I stand to be corrected by those (Tony B?) who know more about such things though.

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There is no priming lever. Really value your input, but the lack of a fuel leak on the pump (I would have thought that fuel would leak out if air can get in) plus the air in the filter suggests an air leak somewhere closer to the tank - As per Tony b's suggestion. My thoughts would be on the fuel pick-up. That might also explain why the symptoms only occur when the tank is getting low, and why there are no fuel leaks on the system.  

 

Next question is how to get to the fuel pick up!

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4 minutes ago, onanov said:

but the lack of a fuel leak on the pump (I would have thought that fuel would leak out if air can get in

I was suggesting a split in the diaphragm which is internal to the pump not a leak from its connections. A split would mean that no fuel would be delivered by the pump.

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57 minutes ago, Stilllearning said:

Trace the fuel line from the tank to the engine. You will likely find the in line fuel filter, then a small piece of equipment attached to the engine block through which the fuel lines go. This is the lift pump. 

 Check the breather on the fuel tank. If it doesn’t let air in as fuel is burned, then this may be causing a partial vacuum in the tank, and giving you the problem you describe.

would a split in the diaphram also be consistent with the fact that that issue only occurs when the tank is > 1/2 full?

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I'm speculating (and it is just speculation) that the weight of a full tank of fuel is enough to feed the engine with sufficient fuel even though no assistance is coming from the lift pump due to a split diaphragm. When the tank is less than full there is too much resistance from filters etc. to feed the engine's needs.  Do check the breather as Stilllearning has said and answer the point re the filterbowl - I would have expected this to be completly full. 

Getting to the fuel take off is probably all but impossible but you could try back flushing the pipework in an attempt to clear any detritis from around the pick up.

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I had this problem several years ago on my Beta Kubota engine  - solved in the end by changing the primary fuel filter regularly - i.e. once per annum.

Do you have a primary filter or does your installation rely on the engine mounted filter only?

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This just might be "diesel drainback". Beta mention this in some of their documentation. I think this is when fuel drains from the fuel system back into the tank via the return line.  I sometimes get similar symptoms on our JD3 if I let the tank get very low, but sometimes, not every time. I think the valves in the lift pump play a part in this too.

 

We do have a priming lever. When this problem occurs I note that I can mostly get a good clean start by pumping the priming lever and it takes a lot of strokes. When the problem is not present then only a couple of strokes will get the the fuel system up to pressure.

 

Its on my long list of things to investigate one day.

 

.............Dave

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Had exactly this on our old CRK3 powered boat, bugger to start with low fuel level, ok with full tank.

Did all the checks round joints and the lift pump and filters, etc. This made things better but never cured the problem.

The fuel take off from the tank was via a dip tube fitted to the top of the tank, It turned out that that the tube had corroded and had pin holes in about half way down, probably at the fuel / air boundary, the previous owner didn’t run the engine much as it was on shoreline in a marina.

New take off tube fitted and started every time regardless of fuel level.

  • Greenie 1
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35 minutes ago, steve hayes said:

Had exactly this on our old CRK3 powered boat, bugger to start with low fuel level, ok with full tank.

Did all the checks round joints and the lift pump and filters, etc. This made things better but never cured the problem.

The fuel take off from the tank was via a dip tube fitted to the top of the tank, It turned out that that the tube had corroded and had pin holes in about half way down, probably at the fuel / air boundary, the previous owner didn’t run the engine much as it was on shoreline in a marina.

New take off tube fitted and started every time regardless of fuel level.

Not all that uncommon. 

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12 minutes ago, WotEver said:

And fits withTony’s ‘pulling air’ diagnosis. 

Yes, I've found this problem on a couple of boats over the years and on a couple of old Ford Transit diesel vans. One got ridiculous as the owner reckoned that if he kept the tank fairly full he'd suffer on. The corrosian pin holes gradually crept up the pipe until he had to keep the tank almost full, stopping to top it up about ever 30 miles. At that point he got me to fix it.

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4 minutes ago, bizzard said:

The corrosian pin holes gradually crept up the pipe until he had to keep the tank almost full, stopping to top it up about ever 30 miles. At that point he got me to fix it.

:D

 

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