difficult cold start despite recon

[Mistroma]

If it helps, I started my old DV20 for 23 years with about 1/3 throttle when cold. I found it difficult to start when I bought the boat but fine once I found the correct throttle position. Never had any starting problems afterwards.

DV20 doesn't have any method of warming up fuel or air prior to start as standard. I'd heard that they were sometimes a little difficult to start from cold. So I assumed the 30% throttle opening was normal. So I wasn't at all surprised to see your message about starting problem without any throttle.

 

[Stu Jackson]

...but key is in cabin while throttle is in cockpit, so I hoped to avert that, but if a bit of throttle is all it takes though I'll be OK with that!#

btw tickover is adjusted to 1000rpm which feels right.

Have you considered either relocating the key or adding one in parallel in the cockpit? I would imagine that in the event you needed to start the engine in an emergency, going down below to do so would be a tad harrowing.

We have glow plugs on our 21 hp Universal, but I still engage the throttle to almost half to start.

 

[chewi]

Thanks all for the replies, it seems to be common practise to start with throttle, so I am a little less bothered about it.

I was not present whern the engine was started with some throttle yesterday pm, but it was better apparently. After a while running I dropped it to tickover and it was running at a lumpy 750 rpm and struggled to rev up so I have readjused that. That suggests it was being very fuel starved for a tickover start, and that may well be the shole problem, I won't know until I try again from stone cold prob. next week.

An aspect of the starting I didn't mention is that both before and after the recon it took a few coughy false starts on the way to running up properly from cold, and I don't really understand what is happening.
It's as if each cough is a single ignition of accumulated unburnt fuel in the cylinder that is insufficient to run until more is collected and a further cough happens, but what would break that cycle to afterwards achieve a proper start if it were so fuel starved as not to run at the first ignition?

 

[chewi]

Much now learnt on this, and the answer is very Bukh specific.
There is a governor stop on the stbd top of the rear casing, 10mm head srew and locknut. It is not shown in the workshop or users manual, nor the exploded diagrams. It limits revs at full load, independently of the throttle tiller stop adjustments.

In my case it was adjusted in so deep the engine could not readily accelerate or pickup from firing. Unscrewing it a whole turn has transformed the engine and I no longer fear I have wasted the refurb.

Norman Griffiths at BUKH UK says there is no prescribed adjustment technique for this screw(!), but unscrewing will give more fuel and vice versa (within limits), but the stop valve must also be correctly adjusted as per the manual.



Result!

 

[wotayottie]

why does it restart easily at T+24hrs but not T+7days?

I would suspect a small slow air leak into the fuel system. There would be no residual heat after 24 hours but there would be residual oil in the bores giving a better compression if the bores / rings werent quite right.

 

[chewi]

I would suspect a small slow air leak into the fuel system. There would be no residual heat after 24 hours but there would be residual oil in the bores giving a better compression if the bores / rings werent quite right.

others have said this, but my fuel tank is wholly above the engine, the fuel pressure must be above air pressure so I think a leak is only likely to put diesel in the bilge. Time will tell, but I think since I fised the governor stop all is well.

 

[Rafiki]

My experience with 4 Bukhs ( 3 x20 and 1 x24) is that they start just with about 50% throttle when absolutely cold unless we are down to low single figure temperatures in which case simply warming up the air with a fan heater (assuming you are in a marina!) works a real treat.
As you say even after 24 hours they start perectly from cold. I've always assumed this was the oil helping to seal up the piston rings in some way so that the compression was improved.