Reply
 
Thread Tools Search this Thread
 
Old 12 March 2011, 07:11   #1
Member
 
neil.mccrirrick's Avatar
 
Country: UK - England
Town: Oldham
Boat name: Nemanda
Make: Aluminium
Length: 6m +
Engine: 140hp Tohatsu
MMSI: 235065639
Join Date: Jan 2008
Posts: 869
Merc 90 loss of power

Hi All,

At the end of last season my outboard, (merc 90), lost power at cruising or high revs. Not at first, after about 15 to 20 mins playing around at different speeds etc. If I throttled back sometimes it picked up, other times it didn't, but if I pumped the bulb, or selected neutral and let the engine rev on the idler all was good again for a while.

It felt like it was either down to it not venting properly, at first so I checked that, and switched between tanks, (I have two connected by a three way switch). Same problem.

So I changed the fuel filter and tried that, same problem.

The weather got too cold and so I left it as it starts no problem on the flush muffs, so I know I need to be on the water to test it.

Since then I've re routed the fuel line, (it did look like it may have been under some pressure the way it was, and today went to change the plugs. The top plug was really loose, loose enough to come undone without the socket, so my question is do you think that could have been causing the power drop off?

I've taken the airfilter off, and all looks clean, clearly the next step is to strip the carbs to check for debris, but I don't want to go that far if you think this may be enough for another water test, now the weather is hopefully getting warmer.

I would just drop it in the water, but its a 90 minute tug to get to the nearest water etc etc
__________________

__________________
neil.mccrirrick is offline   Reply With Quote
Old 12 March 2011, 07:40   #2
Member
 
Country: UK - England
Town: Worthing
Boat name: None
Make: Narwal
Length: 4m +
Engine: Suzuki DF60
Join Date: Jul 2008
Posts: 48
Hi,
You do not say which Mercury 90 you have or the age. So, lets suggest its is a two stroke 3 cylinder model. It looks as if your problem is fuel related. I would suggest you change the fuel pump diaphragms. It comes as a kit with diaphragms, gaskets and non return valve discs. If you have the early type discs made of rubber they get weak and soft over the years and get sucked through the housing, therefore not locking off the fuel and allowing the fuel to run back. This makes the pump run overtime to keep up any pressure. The new discs are clear plstic and impervious to fuel.
I would also look at the fuel primer bulb. If it is a genuine Quicksilver item it will have two non return valves. Remove it and try to blow through it from the outlet side (there is an arrow showing flow direction) back through. If you can blow through it change it for a new one. Aftermarket ones mostly only have one non return valve, not as good. get a Genuine Quicksilver one.
Lastly, I would remove the carb float bowl drain plugs and prime some fuel through. This should clear any dirt or water from the bowls. Put some rag below the carbs to catch the fuel. You need fresh fuel also. Do not use fuel from last season.
Water test the boat as it needs to be under load.
Let us know how you get on.
Regards,
Aquatec
__________________

__________________
aquatec is offline   Reply With Quote
Old 12 March 2011, 07:53   #3
Member
 
neil.mccrirrick's Avatar
 
Country: UK - England
Town: Oldham
Boat name: Nemanda
Make: Aluminium
Length: 6m +
Engine: 140hp Tohatsu
MMSI: 235065639
Join Date: Jan 2008
Posts: 869
All great advice, and well guessed, it is a 3 cyl model and I think 2001 if memory serves, based on what you've said I think the fuel pump diaphrams are defo a good bet

Thanks
__________________
neil.mccrirrick is offline   Reply With Quote
Old 12 March 2011, 09:35   #4
Member
 
Country: UK - England
Town: Southampton
Boat name: SMH Rib / War Shot
Make: Ribtec / Scorpion
Length: 4m +
Engine: 10hp Yam / 150hp opt
Join Date: Sep 2003
Posts: 1,894
RIBase
Primer bulb

Worth changing the primer bulb before diving into the carbs.

Had all sorts of problems with Tempo ones.

Is yours a genuine one?
__________________
Searider is offline   Reply With Quote
Old 12 March 2011, 12:31   #5
DJS
Member
 
Country: UK - N Ireland
Boat name: *
Make: replacement soon!
Length: no boat
Join Date: Jul 2010
Posts: 143
I had a similar problem with mine (same year and model of engine as yours) just after I bought it and on the first run out! After a thorough inspection I discovered it was drawing air at a compression joint. Hence worth checking every connection!
__________________
DJS is offline   Reply With Quote
Old 12 March 2011, 13:17   #6
RIBnet admin team
 
Nos4r2's Avatar
 
Country: UK - England
Town: The wilds of Wiltshire
Boat name: WhiteNoise/Dominator
Make: Ballistic 7.8/SR5.4
Length: 7m +
Engine: Opti 225/Yam 85
MMSI: 235090687/235055163
Join Date: Jul 2005
Posts: 12,645
RIBase
Hold your tank above the engine when it starts playing up if you can and see if it suddenly improves. If it does, it's fuel pump for definite.
__________________
Need spares,consoles,consumables,hire,training or even a new boat?

Please click HERE and HERE and support our Trade Members.

Join up as a Trade member or Supporter HERE
Nos4r2 is offline   Reply With Quote
Old 14 March 2011, 16:52   #7
Member
 
neil.mccrirrick's Avatar
 
Country: UK - England
Town: Oldham
Boat name: Nemanda
Make: Aluminium
Length: 6m +
Engine: 140hp Tohatsu
MMSI: 235065639
Join Date: Jan 2008
Posts: 869
The primer bulb is a quicksilver one, so there's a good thing

Ordered the fuel pump service kit, so hopefully it will be here before the weekend so I can fit it and get out Sunday to test.

Moving the spare fuel tank will be awkward to do Nos, but if the kit is not here for the weekend I'll do it to try it and prove the fault, thanks for the top tip.

All being well I'll post next week with the problem resolved

Thanks all as ever

Neil
__________________
neil.mccrirrick is offline   Reply With Quote
Old 19 March 2011, 07:32   #8
Member
 
neil.mccrirrick's Avatar
 
Country: UK - England
Town: Oldham
Boat name: Nemanda
Make: Aluminium
Length: 6m +
Engine: 140hp Tohatsu
MMSI: 235065639
Join Date: Jan 2008
Posts: 869
Ah well, fuel pump service kit has not arrived, but I have separated the fuel pump, (I was hoping the postie would turn up with the kit mid job, but he's just been and all he brought was bills ).

The discs are plastic and look ok. I was hoping to see a load of dirt, or some holes, but sadly not. I'll re assemble and take to the water tomorrow, you never know something I have done may fix this, and if not it moves me on.

I will see if I can use the spare fuel tank as Nos described, the problem here is I don't think I've any spare fuel line to do it easily, which means trying to detach the main fuel line, (not an easy job as the main tank is crammed, and I do mean crammed, under the centre console, obviously I can get it out, but it involves a lot of swearing

Update next week.
__________________
neil.mccrirrick is offline   Reply With Quote
Old 21 March 2011, 08:56   #9
Member
 
neil.mccrirrick's Avatar
 
Country: UK - England
Town: Oldham
Boat name: Nemanda
Make: Aluminium
Length: 6m +
Engine: 140hp Tohatsu
MMSI: 235065639
Join Date: Jan 2008
Posts: 869
No update on this yet I'm sorry to say. We attempted to launch at Knott End, Fleetwood on Sunday. The sea was a little choppy coming over the slip, so we launched off the side, off me new rollercoaster trailer.

Went in absolutely fine and all was good, until a wave picked the rib up just as it was broadside to the trailer.

For those that know rollercoasters, there is a pin in the bar for the extensions off the trailer that is there to hold the lightboard. Well I can only wish I'd noticed it earlier and covered it in foam or even took them off as I don't use them, but one of them did this, see pictures.

An inch higher and it would have been the rubbing stake, 10 seconds loger and it would have been the handle, both of which would have just been a warning for the future, ah well.

Repair is set for Thursday evening, and hopefully back out next weekend to test.
Attached Thumbnails
Click image for larger version

Name:	photo1.jpg
Views:	162
Size:	43.4 KB
ID:	57766   Click image for larger version

Name:	photo.jpg
Views:	140
Size:	60.9 KB
ID:	57767  
__________________
neil.mccrirrick is offline   Reply With Quote
Old 21 March 2011, 12:19   #10
Member
 
Country: UK - England
Town: bicester
Length: no boat
Engine: outboard only
Join Date: Feb 2009
Posts: 894
your problem reads like a classic fuel pump diaphrams, which is usually cured fitting a diaphram kit,the diaphrams dont have to be punctured to be defective just stretched.I know the slip at knott end by the coast guard station i have launched some coast guard boats from there for sea trials after servicing them, many moons ago
__________________

__________________
uncle al is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 23:19.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.