Yanmar sb8 hard to start only after heavy sailing

[kielboatsa]

I have a yanmar sb8 in my 1978 hunter 27. The engine starts on the first crank normally, unless I have been out sailing in heavier winds. After sailing healed over in 15+ knot winds, the engine is hard to start. It requires opening the throttle almost full and cranking the engine a lot for it to start. Once it starts, I can shut it down and it will start back up on the first crank again. I currently have it at my boat yard for service, but they tell me that it is hard for them to diagnois without the problem actually occuring. Has anyone else ran into this that can help me figure out what is causing this?

 

[Don S/V ILLusion]

Pretty difficult to diagnose without lots more info, e.g., hard to start when engine still warm? only starts immediately when cold? how is cranking speed? only difficult to start after battery partially drained? condition of fuel and filters, hoses? only a problem after heeling for a while?

You can get many wild guesses but it might help to narrow down the possibilities

 

[kielboatsa]

easy to start if engine is warm or cold, cranking speed is always good, filters were changed this April, fuel is new this year. The problem is only after heeling for a while. It seems as if it is having a hard time getting fuel after being heeled. Once the fuel is there it starts and the problem goes away, untill the boat is heeled for a while again.

 

[Witzend]

Maybe air getting into fuel line, but more info is needed to diagnose.

 

[kielboatsa]

Why would air only get into the fuel line after heeling. If there is an air leak would it not also show up after the boat sat level for a while?

 

[RichH]

Suggest you retighten each and every 'connector' , filter housing, etc. on your fuel delivery system; plus, evaluating all the rubber 'hoses' for cracks (especially the hose that runs from the tubing TO the engine). Your symptom is possibly due to an air leak.
If re-tightening all the components etc. does not solve the problem, then check the lift pump - check valves (leaking back) or pin-hole, etc. in the diaphragm of the lift pump.

 

[RichH]

Why would air only get into the fuel line after heeling. If there is an air leak would it not also show up after the boat sat level for a while?

Could be a 'crack', etc. in the rubber hosing that runs from the tubing TO the engine. The engine 'leans' (moves) to one side or other during the heel and thus may be opening/enhancing a small crack, etc. in this hose allowing air to be 'sucked into' the system.

Other possibility is that the tank's dip tube is not deep enough in the tank or that your fuel level (not enough fuel) in the tank is too low to 'cover' the inlet to the dip-tube; thus, sucking air into the system.

 

[kielboatsa]

The fuel tank is 3/4 full. Sounds like checking the hosing and fittings is first step.

 

[Don S/V ILLusion]

It does sound like an air leak but if that isn't the case, the next best bet would be crud in the bottom of the tank which gets agitated causing the pickup tube to intermittently clog. This is unlikely but conceivable based on your description and it's always a good maintenance chore to periodically draw some fuel from the bottom to visually inspect.

 

[Deadline2]

Clarification

Just to clarify, your problem seems to be the engine not the starter. I had chronic problems restarting the engine after a day's sail, owing to a voltage drop. If that indeed is your problem, I have the fix and the entire thread to walk you through it. Do tell.

 

[kielboatsa]

I spoke to the mechanic at my boat yard today, and he indicated that the problem appears to be in the pick-up tube in my fuel tank. He is going to replace the pick-up tube and I will post back on the results.

 

[RichH]

If the dip tube is partly plugged/restricted AND the fuel has a lot of entrained air (not 'visible' air but air that is essentially included with/as 'emulsions' in the fuel) the high vacuum due to the 'resistance' caused by the fouled/restricted dip tube 'may' cause the air to 'coalesce' out of the fuel (usually on the downstream side of the filters) and then form 'large air bubbles' in the system. Air entrainment can be caused by filling the tank 'too fast' and such as when the tank develops a lot of 'foam' when **rapidly filled**, such air emulsions can be very stable and do not 'separate' by the formation of physical bubbles (which rise) later-on.

This air entrainment separation should be a 'very rare' problem in diesel fuel systems such as in boats with 'small' engines - but should be considered if you dont identify the location of 'easy' problems. In large fuel delivery systems air-entrainment/separation is often encountered where the system is not 'well designed' .... not designed so that such that the 'now free', 'coalesced'/trapped bubbles can freely migrate and that become trapped in 'high-spots' in the system - the inlet to the injector pump being a 'high spot'.

added/edited-in Air Entrainment Phenomenon documentation: http://www.parker.com/literature/Racor/Mobile_Air_Separation_In_Diesel_Fuel.pdf

As stated before Yanmars are virtually 'self bleeding' and usually start with 'small' amounts of air in the delivery system.

 

[Bill Roosa]

I'd say very rare

Air entrainment and coalescing??? Been around diesels for 40 years and that is the first time I ever heard of that.
If air is entering the system then it would surly take a few minutes of running to get to the engine. ie the engine high pressure side of the fuel system should stay primed even if air has just entered the pick up tube.
I suspect you have an air leak near the injector pump on the low side that leaves an air bubble that gets dislodged when you heal the boat.
in any case it should not happen on a full tank.

Does it only do it on one tack or both?

 

[RichH]

Bill ...
Not an unknown to many who work in high flow fuel/chemical systems engineering.
Sure, I'd give this a 0.01% chance. But such a search/evaluation 'may' lead to the location of the usual simple 'oh my gosh', "well, I'll be damned' solutions/fixes.

Cracked/loose tubing connector/fitting. pin hole in the lift pump diaphragm, improperly installed fuel filter gasket, .... 99.99% of the time. Could even be an improper "S" bend in the delivery tubing that 'allows a burp of entrapped air' when the boat is over on its ear.

 

[sailingdog]

I'd point out that heeling the boat may cause a section of the fuel system that is normally low enough that it doesn't normally airlock or leak to airlock or leak. A common point for this to happen at is banjo bolts, since over-tightening the banjo bolt can result in a very slight leak at the crush washer, and the crush washers are not designed to be reused very often.

 

[kielboatsa]

Well I picked the boat up this weekend and had enough air to test out the repair. It turns out that the pick-up tube was on the far port side of my fuel tank and the tank is starboard. When on a starboard tack and heavily heeled, the pickup was no longer in the fuel allowing air into the line. That pick-up was abandoned and a new one is now installed at the center line of my tank. This appears to have solved my problem. Fortunately an easy and inexpensive fix!