New Yanmar Not Starting Straight Away, What do I Check?

[monte]

Gday,
One of our new Yanmar 40hp (3JH5CE) with 60 hrs on it isnt firing straight away, or it fires and starts for 5 seconds then stops. Giving it some revs will keep it running and once running its fine. Im just wondering where to start looking to resolve the problem. It has recently been serviced (20 hrs ago), oil and filters changed.
The other engine is fine and fuel is the same in both.
I'm assuming seeing as it runs its not likely to be air in the line as that would have gone by now?
Not likely to be filters.
Maybe the idle speed is too low?
Any suggestion on what to take a look at will be much appreciated.
Thanks
Monte

[monte]

Actually the mechanic didn't touch this filter. I'm wondering how to service, drain the water from it. Does it also have a serviceable filter that needs replacing? Thanks again

[a64pilot]

I would suspect air in the fuel lines, unless of course it's idling lower than spec, but I still bet air.
You need to find someone to show you how to change your own filters, drain water from the pre-filter and bleed air from the system, it's a skill you will need to have as eventually you will be faced with having to do it without a mechanic available.

[monte]

Thanks, I loosened the lower nut and let about 100ml of diesel out. It didn't seem to have water or debris in it. I then retightened and ran the engine for 10 mins to make sure there was no air in the lines. I assume if it runs ok there's no air as it would soon run rough. Is this correct ? I watched the mechanic change the oil and diesel filters and bleed the fuel line so I can manage that when needed. It was the 50 hr service so needed to be done by a yanmar agent.
I guess there is a filter cartridge in the water separator so I will have to find the type and have some spares on board. Is the filter in the photo the primary filter, and the one on the engine the secondary?
Thanks again for any advice. Also curious if I should bleed the fuel line even though it is running ok..

[a64pilot]

If you bled fuel out, then there is almost certainly air in it, Usually there is a water separator / filter that is supplied by the boat manufacturer that connects to the secondary, finer filter that comes with the engine.
In my opinion, you need spares for both as well as the knowledge of how to replace them and bleed the system so that you are comfortable doing it at night in adverse weather, seems these filters clog more readily when the boat is being tossed about and the crud in the fuel tank is being stirred up.
Your hard start / dieing soon after start sounds exactly like loss of prime to me
Rarely will an engine self bleed, usually you have to bleed them

[monte]

Thanks. Regarding the bleeding, im a bit confused. Can there still be air in the line even though the engine is running fine? I thought bleeding was just necessary if the engine doesn't run after changing filters, low fuel tank etc. Won't any air in the fuel system soon be exhausted as the engine runs?

[MarkJ]

Originally Posted by monte

ran the engine for 10 mins to make sure there was no air in the lines. I assume if it runs ok there's no air as it would soon run rough. Is this correct ? I watched the mechanic change the oil and diesel filters and bleed the fuel line so I can manage that when needed. It was the 50 hr service so needed to be done by a yanmar agent.


.

Did you have the problem before the mechanic did the service?

If the problem has just started after the service and you havent run the engine for long after the service then it maybe a problem I have when I change filters...

After I change filters and bleed, then start-up I can have a flickering tacho for maybe the first 20 to 30 minutes. I think its because when you change filters theres air bubbles inside the final filter. I think these may take a while to get chased out. I could be wrong because I am no mechanic! Now, I make sure to fill the final filter with diesel and tap it.

BTW Running the engine at idle for 20 minutes may not be long enough. Mine takes that long under load.

the other point is if its started from when the mechanic touched it he can come back and fix the damn thing for free, eh?!

[noelex 77]

Originally Posted by a64pilot

I would suspect air in the fuel lines, unless of course it's idling lower than spec, but I still bet air.

+1.
Classic symptoms for air in the fuel line.
There is likely to be a poor joint in one of the fuel fittings.

They can be buggers to find, but at least its not expensive to fix.

[DeepFrz]

A connection in the fuel line that slowly lets a little air into the system can cause your system. It could be just about anywhere, but I would suspect downstream from your primary filter and even close to the engine. When sitting you get a little air in and the engine has to purge this out before it runs properly. By the way, cracking the throttle open part way is an okay procedure. In fact your operators manual probably calls for you to do that when starting.

[leftbrainstuff]

There is often an anti drain back check valve somewhere on the fuel suction side. In many Racor filters it's part of the filter. It's purpose is to maintain the prime when not running.

If you can't find any suction leaks the check valve might be worth a look.

Sent from my SM-N900T using Cruisers Sailing Forum mobile app

[monte]

Thanks for the feedback. W didn't have the problem before the filter change which was about 20 engine hrs ago. Since then we have used the engine maybe 10 times for extended periods and it's run fine. The issue is only the last couple of start ups, after which it runs fine. Just trying to isolate the cause in case it continues or won't start when we need it to (and learn some stuff along the way).

[Target9000]

We had the same problems after installing a new engine. Once the engine was running it ran fine. Left the boat for a few days and you had to bleed the system to get it started. It turned out to be that one of the hose clamps on the fuel line from a fuel pick up tube wasn't tight enough, it must have been ever so slowly allowing air into the system.

I would start by going from the engine all the way to the tanks slowly and meticulously checking each fitting, hose and connection.

[marlinmike]

Filter gasket/o ring or like another OP stated anti siphon valve. sometimes when you place the throttle full forward it helps bleed out some of the air to get started, be quick to pull it back once it gets going. Bottom like it sounds like who ever did the work created a problem.

[monte]

Thanks. Why pull the throttle back fast? I have it out of gear, and yeah I've Been pulling it back, just wondering why you say to do it?

[marlinmike]

Just didn't want you to think you could leave it there and have it rev up to the governor. Once it kicks off just bring back the throttle, maybe fast was not the right word.

Originally Posted by monte

Thanks. Why pull the throttle back fast? I have it out of gear, and yeah I've Been pulling it back, just wondering why you say to do it?