Mercury 90 down on power

martin33100 · 31 May 2010, 19:55

Hi, we have a very very good condition 1998 Mercury 90 on our rib, the engine hasn't had a hard life and only let me down today. We went out for an hour at about 33 knots and not a problem. We then went up the Beaulieu river at 5 knots and after a while the engine started to run a little rough (like it had dropped a cyl). Went back out to sea and gave it full chat and up 33 knots again, did this for about an our and then with out a warning dropped back to 18 knots at full throttle. Any views on where to look first?

Turbodiesel · 31 May 2010, 20:13

Could be so many things!, Best to see if it is dropping a cylinder first and identify which one. Once you have got that find out if its lost a spark or is it a fuel problem.

martin33100 · 01 June 2010, 09:06

Quote:

Originally Posted by Turbodiesel

Could be so many things!, Best to see if it is dropping a cylinder first and identify which one. Once you have got that find out if its lost a spark or is it a fuel problem.

I would say its electrical because I could smell lots of un-burnt fuel when I flushed the engine out. My outboard man that looks after our engine said it may be a plug, coil or CD unit that has gone down.

9D280 · 01 June 2010, 10:21

Not sure what flavour yours is, but also check the HT leads if they are independant to the coils.

My going in guess would be electrical too.

martin33100 · 01 June 2010, 21:51

Quote:

Originally Posted by 9D280

Not sure what flavour yours is, but also check the HT leads if they are independant to the coils.

My going in guess would be electrical too.

Its a 90 ELPT

martin33100 · 03 June 2010, 22:39

Just to give you an update, I have put in new plugs and swapped the coils around and its still the midle cylinder that isn't fireing, compression is 140psi on all cylinders so it may be fuel related

9D280 · 04 June 2010, 09:05

sounds like you need to dismantle / clean the middle carb...... or check all electrical connetions between the box of electronics & the plug.

Nos4r2 · 04 June 2010, 16:17

Have you got a spark on the middle cylinder?

If you haven't, after the tests you've already done you'll know it's black box related.

martin33100 · 05 June 2010, 14:44

Just found something very strange, when you disconect the ruber pipe that goes from the middle cylinder to the fuel pump the middle cylinder starts to fire, the fuel pump does have a new diaphram in it.

Nos4r2 · 05 June 2010, 22:24

Clean the carbs. You've probably got a stuck float needle.

uncle al · 06 June 2010, 15:40

if it has sneezed check the pulse hose and connecters for holes from the cyl block to the fuel pump.or if poss give me a ring on monday and i will talk you through it office hours only 01869 326411

martin33100 · 07 June 2010, 17:11

Quote:

Originally Posted by uncle al

if it has sneezed check the pulse hose and connecters for holes from the cyl block to the fuel pump.or if poss give me a ring on monday and i will talk you through it office hours only 01869 326411

Thanks for the offer of talking me through it. I fixed it yesterday morning, middle carb had a blocked main fuel jet, running on all three now and back up to 35 knots in the afternoon

uncle al · 08 June 2010, 09:48

Quote:

Originally Posted by martin33100

Thanks for the offer of talking me through it. I fixed it yesterday morning, middle carb had a blocked main fuel jet, running on all three now and back up to 35 knots in the afternoon

well done