Reply
 
Thread Tools Search this Thread
 
Old 28 August 2008, 14:58   #1
Member
 
Country: UK - England
Town: over there
Length: under 3m
Engine: outboard
Join Date: Aug 2008
Posts: 9
anyone know anything about a 40HP 2stroke mercury?

so i have a 16ft Excedo RHIB with a 40HP 2 stroke mercury on it. and it goes through about 1 tank of 2 stroke oil to every 2 tanks of gas. and the things eats fuel like crazy. and the motor is very hard starting, even after it has been driven for a few hours and gets warmed up. does anyone have any idea as to what this could be? and does anyone know anything about Excedo Canada? that is where i got my boat from. thanks for any help.
__________________

__________________
over there is offline   Reply With Quote
Old 28 August 2008, 16:14   #2
Member
 
Country: UK - Wales
Town: West Wales
Make: Vipermax 5.8, SR4.7
Length: 5m +
Engine: 150 Opti, F50EFi
Join Date: Sep 2005
Posts: 6,298
What size is your 2-stroke tank?
What size is your fuel tank?
How 'crazy' is the fuel usage?
How 'hard' is it to start?

If you could be more specific, you may get a favourable response.
__________________

__________________
Downhilldai is offline   Reply With Quote
Old 28 August 2008, 17:43   #3
RIBnet admin team
 
Poly's Avatar
 
Country: UK - Scotland
Boat name: imposter
Make: FunYak
Length: 3m +
Engine: 2 stroke YAM 20 HP
MMSI: 235089819
Join Date: Sep 2005
Posts: 10,114
if it was an old fashioned engine running "premix" it would probably be on 50:1. So if its using significantly more than 1L of oil for every 50L of fuel its possibly got something wrong. If you spend most of your time at full throttle I would expect it to burn through ~15 L per hour (4 US gal / hr) of fuel.
__________________
Poly is offline   Reply With Quote
Old 29 August 2008, 00:00   #4
Member
 
Country: UK - England
Town: over there
Length: under 3m
Engine: outboard
Join Date: Aug 2008
Posts: 9
i would say the two stroke is about a couple of litres at the most. yes i spend most of my time at WOT soi guess the fuel consumption is about right. what about the RPMs,w here should they be at, cuz the sticker on the motor says max rpm is 5500, and at WOT it is only around 3500rpm. and it is really hard starting, like u have to turn the keyu 4 or 5 times sometimes to get it to stay running and even then it will sometimes bog out on u unless u give it throttle right away. it has a 25Litre gas tank. another thing was when u make sharp turns with the boat at WOT, the motor just revs up and the boat does notg o any where, but the tach does not move when the engine revs right up. it is weird, someone said the prop is coming out of the water and sucking air? any help would be awesome!! is it better to store the motor outside over the winter covered up and winterized or store it somewhere inside where it is warm?
__________________
over there is offline   Reply With Quote
Old 29 August 2008, 01:13   #5
Member
 
Country: Canada
Town: Tobermory, Canada eh
Boat name: Verius
Make: Zodiac Hurricane 590
Length: 5m +
Engine: Yamaha F150
Join Date: Oct 2006
Posts: 1,345
Send a message via MSN to Stoo
If you're grinding to a hault on a hard-over turn, the engine might be set to high. Have you had it in to a good shop for a checkover? The poor starting sounds like it just needs a good tune up. If you're buring too much oil, your plugs could be fouled as well....

Is the engine smoking much? Is there a slick in the water?
__________________
Pump it up and RIDE!

www.wetspotimages.com
Stoo is offline   Reply With Quote
Old 29 August 2008, 04:29   #6
RIBnet admin team
 
Poly's Avatar
 
Country: UK - Scotland
Boat name: imposter
Make: FunYak
Length: 3m +
Engine: 2 stroke YAM 20 HP
MMSI: 235089819
Join Date: Sep 2005
Posts: 10,114
if you are only getting 3500 rpm on an engine specced to do 5500 then you have a problem. could be the propellor is completely wrong for the set up you have or could be an engine problem.
__________________
Poly is offline   Reply With Quote
Old 29 August 2008, 12:39   #7
Member
 
Country: USA
Town: Oakland CA
Length: 3m +
Join Date: Feb 2005
Posts: 6,653
What prop is on the boat? I think it's likely that you are way overpropped, which would account for part of the low rpms at WOT. A 40 on a 16 foot RIB sounds a bit low, so you'd most likely need a fairly low pitched prop.

You should be able to remove the prop with the help of a pair of pliers, an appropriate socket and breaker bar, and a piece of 2x4 (put the lumber between the prop and the anti-ventilation plate to jam the prop, then remove the cotter pin or lock washer, loosen prop nut with socket/breaker bar.) Somewhere on the prop should be a couple of numbers (i.e. 13.25 x 14) The first will be the diameter of the blades, the second the pitch. If you could post what you've got, that will give us some idea of what you're running.

The over-revving and loss of propulsion in a hard turn sounds like classic ventilation. As you turn, the boat heels over on the inside tube, which brings the centerline higher. Since the engine is also no longer vertical, but at an angle, the prop gets closer to the surface (and it's also in the wash behind the boat, which may lower water level just in front of the prop), sucks air, and you lose bite. Typically, it means your trimmed out too far for the turn, or your engine is mounted too high. Something like DoelFins or the like *may* help a bit in this regard, as they tend to keep air from getting to the prop (or perhaps I should say that they are supposed to do so.)

The tank of oil to a couple of tanks of gas is kind of ambiguous; depends on the respective sizes of the tanks. As Polwart and Downhilldai have said, you need to get a handle on exactly how much oil and gas you run through to see if ratios are correct (it's kind of critical; the oil in fuel is what keeps the powerhead from taking itself out.) Then you can address the fuel economy (or lack thereof.)

jky
__________________
jyasaki is offline   Reply With Quote
Old 29 August 2008, 15:03   #8
RIBnet admin team
 
Poly's Avatar
 
Country: UK - Scotland
Boat name: imposter
Make: FunYak
Length: 3m +
Engine: 2 stroke YAM 20 HP
MMSI: 235089819
Join Date: Sep 2005
Posts: 10,114
Any chance you can post a picture of the boat from behind. That would give people an idea if the engine is set too high or trimmed completely wrong or something.
__________________
Poly is offline   Reply With Quote
Old 29 August 2008, 17:04   #9
Member
 
Country: UK - England
Town: over there
Length: under 3m
Engine: outboard
Join Date: Aug 2008
Posts: 9
that is all very interesting. i will get some numbers off the prop and some pictures and post them to see what you guys think. what sould be on it for a motor? a 55 or a 60HP? the model of the motor is 40ELpto if that is any use to you. i am hopefully going to take it to a shop next week for them to take a look at it and they can tell me what they think. thanks for your help.
__________________
over there is offline   Reply With Quote
Old 31 August 2008, 16:14   #10
Member
 
Country: USA
Town: Oakland CA
Length: 3m +
Join Date: Feb 2005
Posts: 6,653
Well, as an example, my buddy runs a Zodiac Pro 16 (15.5', I think) with a 60hp Merc 4-stroke.

The 40 will do for your size boat, don't get me wrong there; it's just that it's probably towards the lower end of the power rating for your hull. The specifications plate (usually on the transom) should give you allowable load and max power (unless it's a fairly old hull, in which case the info may not be there.)

jky
__________________

__________________
jyasaki 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 02:36.


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