My Yanmar (4JH3-HTE) has been faultless albeit a little smokey of late.
I have never really run it too hard and probably even too gentle for a diesel. So today I decided to run it at almost WOT (3500RPM out of 4000) to see if it was a carbon build up issue. Slowly but surely the smoke reduced to almost nothing. BUT..... when I reduced the power back towards idle, the trusty diesel just stoped.
It would run on successive attempts at idle and on increase of power, but every time the power lever was bought back to idle the engine just stopped. It had also been in the past an instant starter. Now it kicks over after about 3 seconds of cranking.
I am hoping all I have done is somehow thrown out the timing. What are the your thoughts 
My guess is that the high revs dragged a lot of (dirty) fuel through the filter and clogged it.
Try a filter change before you panic.
Just a guess though.
Gary
Select to expand quotegarymalmgren said..
Just a guess though.
Your quess is as good as mine... Thanks for the tip 
Select to expand quoteCraig66 said..
At a guess, check the spark plugs are clean
Hi Craig
She is a diesel, so no spark plugs
Regards Don
Select to expand quotegarymalmgren said..
My guess is that the high revs dragged a lot of (dirty) fuel through the filter and clogged it.
Try a filter change before you panic.
Just a guess though.
Gary
I'm a bit late but yes a filter change would be the go. Did the little engine feel a little starved for revs and full throttle? Some people put fuel cleaner additive in there. If you have done this expect your filter to be FULL of sh!t.
The consensus thus far seems to be a blocked (or gunky) filter. I haven't had the opportunity to get back up there (work/kids getting in the way). But at least it would be an easy and cheap place to start.
Cheers 
Select to expand quoteToph said..
The consensus thus far seems to be a blocked (or gunky) filter. I haven't had the opportunity to get back up there (work/kids getting in the way). But at least it would be an easy and cheap place to start.
Cheers
Yeah worth a check
Select to expand quoteToph said..
My Yanmar (4JH3-HTE) has been faultless albeit a little smokey of late.
I have never really run it too hard and probably even too gentle for a diesel. So today I decided to run it at almost WOT (3500RPM out of 4000) to see if it was a carbon build up issue. Slowly but surely the smoke reduced to almost nothing. BUT..... when I reduced the power back towards idle, the trusty diesel just stoped.
It would run on successive attempts at idle and on increase of power, but every time the power lever was bought back to idle the engine just stopped. It had also been in the past an instant starter. Now it kicks over after about 3 seconds of cranking.
I am hoping all I have done is somehow thrown out the timing. What are the your thoughts
Diesels being the fiddly lil things they can be , the diesel fuel could be waxy, organisms maybe, give it a dose of fuel doctor in the tank, maybe if shes never been ridden that hard bores might be a bit glazy, maybe feed it so decarbonizing fluid and get used to running it hard , Yanmars are a good lil motor, there designed to work hard, stick it to her .
My NP300 Navara has a lil Cummins Dieso with twin hair dryers, if I could shove that motor in a boat id be very happy.
Select to expand quoteTopHat 25 Mk2 said..Toph said..
My Yanmar (4JH3-HTE) has been faultless albeit a little smokey of late.
I have never really run it too hard and probably even too gentle for a diesel. So today I decided to run it at almost WOT (3500RPM out of 4000) to see if it was a carbon build up issue. Slowly but surely the smoke reduced to almost nothing. BUT..... when I reduced the power back towards idle, the trusty diesel just stoped.
It would run on successive attempts at idle and on increase of power, but every time the power lever was bought back to idle the engine just stopped. It had also been in the past an instant starter. Now it kicks over after about 3 seconds of cranking.
I am hoping all I have done is somehow thrown out the timing. What are the your thoughts
Diesels being the fiddly lil things they can be , the diesel fuel could be waxy, organisms maybe, give it a dose of fuel doctor in the tank, maybe if shes never been ridden that hard bores might be a bit glazy, maybe feed it so decarbonizing fluid and get used to running it hard , Yanmars are a good lil motor, there designed to work hard, stick it to her .
My NP300 Navara has a lil Cummins Dieso with twin hair dryers, if I could shove that motor in a boat id be very happy.
Cummins in a truck. Nice for doing burnouts. After hearing the sweet sound of a 12v92TTA Detroit Diesel on my fathers trawler. I always wanted to put a 6v53 TT Detroit Diesel (GM) in a truck.
Select to expand quoteJon11 said..Craig66 said..
Sweet sound ??????
Plus all that black smoke 
Dirty spark plugs again
They are good engines those old GMs "Shanty" is right they are loud, Smokey and thirsty. But they will go forever sort of like me. Their parts are cheap as well.
Yes that's true, But shanty has been red carded
I'm sure it won't take him long to set up a new account and continue his ways,
ill keep an eye out for him. 
Take care Mick,
If clearing the filter doesn't work, check for any tiny air leaks in the fuel system. Loose banjo bolt, hardened copper washer, pin-hole in hose, etc are all culprits. This often shows up as loss of power and high revs, but is worth checking as you work through the list of possibilities.
Dodgy lift pump is another possible cause, as is blocked tank breather.
Identical problem with my similar Yanmar. Did a replacement of both filters and checked tank. Turns out tank was lined with black crappy stuff and so was my temporary tank.
All cleaned now and working well
Select to expand quoteShanty said..TopHat 25 Mk2 said..Toph said..
My Yanmar (4JH3-HTE) has been faultless albeit a little smokey of late.
I have never really run it too hard and probably even too gentle for a diesel. So today I decided to run it at almost WOT (3500RPM out of 4000) to see if it was a carbon build up issue. Slowly but surely the smoke reduced to almost nothing. BUT..... when I reduced the power back towards idle, the trusty diesel just stoped.
It would run on successive attempts at idle and on increase of power, but every time the power lever was bought back to idle the engine just stopped. It had also been in the past an instant starter. Now it kicks over after about 3 seconds of cranking.
I am hoping all I have done is somehow thrown out the timing. What are the your thoughts
Diesels being the fiddly lil things they can be , the diesel fuel could be waxy, organisms maybe, give it a dose of fuel doctor in the tank, maybe if shes never been ridden that hard bores might be a bit glazy, maybe feed it so decarbonizing fluid and get used to running it hard , Yanmars are a good lil motor, there designed to work hard, stick it to her .
My NP300 Navara has a lil Cummins Dieso with twin hair dryers, if I could shove that motor in a boat id be very happy.
Cummins in a truck. Nice for doing burnouts. After hearing the sweet sound of a 12v92TTA Detroit Diesel on my fathers trawler. I always wanted to put a 6v53 TT Detroit Diesel (GM) in a truck.
A big 8V92 in a something like and old Dodge mitt a turbo unt a 15 speed cog box, twin stacks, chassis shortened, man thats the stuff of dreams GM 2 Strokes are legendary, Cummins 903T is a good donk, 555 isnt bad, I have seen a 671 in a Dodge with a 13 speed RR, damn thing went like dung off a shovel, bounced around alot but qwik as.
Here's a different thought. Could the throttle cable adjustment be out of whack now that you have almost fully extended it after your WOT. Maybe something slipped. Will it idle if throttle is just moved off idle position.
A good thread. Prompted me to change my primary (is that the correct term for from the tank) on the weekend. It was filthy. Been meaning to switch it for ages but keep putting it off until next week to go sailing instead.
Cleaned my tanks when I first brought my boat and from then on, every drop of diesel that went into them, went through a "Mr Funnel" and then I added in some Diesel Fuel Treatment to (try and) prevent the black death. Also always kept my tanks full. After 10 years I never had one fuel issue and the 2 seperate pre-filter glass bowls were always clear.
I also made my fuel draw point (tube) about 3 mm from the bottom of the keel tank to make sure I wasn't creating my own version of amargeton, that was going to come rocketing through my filters the moment I ran my engine in rough weather. If there was any chance of crap finding its way into my keel tank, it was going to be coming straight back out rather than saving it up for "Murphy' (or Sod) to use at his discretion.
Diesel Engine Basic Rules:
1. Clean Air
2. Clean Fuel
3. Cooling System maintained
4. Oil Changes
5. Never, Never, Never run Unloaded. (An alternator is not enough load. Throw the mooring lines off and go for a run if you want to charge the batteries)
www.mrfunnelaustralia.com.au/buy-online.html
