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28 September 2005, 09:58
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#1
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Member
Country: UK - England
Town: Chester
Boat name: Escapism
Make: Narwhal
Length: 4m +
Engine: Yamaha 55
Join Date: Jun 2004
Posts: 45
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Yam 55 down on power
As you might have noticed from my previous post "worth repairing?" my Yamaha 55 suffered a terminal fault recently. I did however manage to find another 55 on Ebay with a knackered gearbox for £100 and swapped the powerheads over.
I've set the timing, overhauled the carbs, fitted new plugs, checked the compression (both cyinders in the 140-145psi) etc etc.
Both plugs are the perfect tan colour so the mixtures right but it just hasnt got as much power my old 55 had. It doesnt accelerate as well and is about 5kts down on top speed. Top engine speed is now 4900rpm not 5500rpm as it used to be.
Is there something I'm missing? I'm sure they never came out of the factory with so much variation in output.
Anyone got any suggestions?
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28 September 2005, 10:57
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#2
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Member
Country: UK - England
Town: Gosport
Boat name: April Lass
Make: Moody 31
Length: 9m +
Join Date: Aug 2001
Posts: 4,951
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Is the throttle opening fully, that would explain the loss of 600 revs and slow acceleration.
Pete
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28 September 2005, 11:01
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#3
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Member
Country: UK - England
Town: Cumbria
Length: 4m +
Join Date: Jul 2005
Posts: 126
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Craig,
when you say you swapped the powerheads over what do you mean exactly:
1. Undressed the old, failed powerhead and transferred everything onto the "new" powerhead.
2. Lifted the "new" powerhead lock, stock and barrel and swapped over.
If it's option two then you've swapped ignition components from the "new" engine?
Have you checked the temp that the "new" head is running at?
Did you decoke the "new" head or just transfer it straight across?
Did you compare engine numbers and the year of manufacture of the powerheads.
Sorry for all the questions but the more info we have the better the chances that we might collectively spot the problem.
Good luck
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28 September 2005, 11:50
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#4
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Member
Country: UK - England
Town: Chester
Boat name: Escapism
Make: Narwhal
Length: 4m +
Engine: Yamaha 55
Join Date: Jun 2004
Posts: 45
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Quote:
Originally Posted by stan_deezy
Craig,
when you say you swapped the powerheads over what do you mean exactly:
1. Undressed the old, failed powerhead and transferred everything onto the "new" powerhead.
2. Lifted the "new" powerhead lock, stock and barrel and swapped over.
If it's option two then you've swapped ignition components from the "new" engine?
Have you checked the temp that the "new" head is running at?
Did you decoke the "new" head or just transfer it straight across?
Did you compare engine numbers and the year of manufacture of the powerheads.
Sorry for all the questions but the more info we have the better the chances that we might collectively spot the problem.
Good luck
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Lock stock and barrel, allthough I did swap some components: Ignition coils, carbs, starter motor, thermostat and fuel pump since these were all in better condition on the old head.
Running temp is around 130F (54C), wich is about 10F (5C) warmer than the old. The thermostat in these is about 60C so taking in to account the gauge error that seems OK
new engine is 3 yrs younger but most of the parts including the carbs are the same.
Didnt de-coke, had a look in both cylinders through the spark plug holes and they look clean enough, could be worth a try though.
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28 September 2005, 11:53
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#5
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Member
Country: UK - England
Town: Chester
Boat name: Escapism
Make: Narwhal
Length: 4m +
Engine: Yamaha 55
Join Date: Jun 2004
Posts: 45
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Quote:
Originally Posted by Pete7
Is the throttle opening fully, that would explain the loss of 600 revs and slow acceleration.
Pete
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The butterfly is opening to within about 5 degrees of horizontal. Theres no adjustment for them since they're opened by a cam connected to the throtle/timing controler. This is probably my number one suspision but I cant see how to improve it.
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28 September 2005, 17:36
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#6
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Member
Country: UK - England
Town: Cumbria
Length: 4m +
Join Date: Jul 2005
Posts: 126
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Craig I just re-read your original post and you say the plugs are tan?
That's great in a car but suggests you may be running slightly weak in a two stroke. Brown and with a "damp sheen" is what you really want.
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28 September 2005, 18:30
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#7
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Member
Country: UK - England
Town: Chester
Boat name: Escapism
Make: Narwhal
Length: 4m +
Engine: Yamaha 55
Join Date: Jun 2004
Posts: 45
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Quote:
Originally Posted by stan_deezy
Craig I just re-read your original post and you say the plugs are tan?
That's great in a car but suggests you may be running slightly weak in a two stroke. Brown and with a "damp sheen" is what you really want.
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electrode brown, electrode surround tan - brown, and black around the end of the metal case!
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29 September 2005, 00:18
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#8
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Member
Country: Other
Town: brighton
Length: 10m +
Join Date: Aug 2005
Posts: 14
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are you using a different prop?
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04 October 2005, 13:41
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#9
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Member
Country: UK - England
Town: Swindon
Boat name: na
Make: Oldenberg
Length: 5m +
Engine: Outbard
Join Date: Sep 2005
Posts: 3
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Spare Parts
I have a Yam 60 with electrical problem when its warm, would you consider selling the spare electronics you have, I can collect
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06 October 2005, 23:00
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#10
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Member
Country: UK - England
Town: Chester
Boat name: Escapism
Make: Narwhal
Length: 4m +
Engine: Yamaha 55
Join Date: Jun 2004
Posts: 45
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Quote:
Originally Posted by rama
are you using a different prop?
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Same prop!
Have adjusted the butterflies by using thinner gaskets!
Ran it for 4 hours up the Menai today, still down on power, poor acceleration & top speed. plugs still the right colour, engine still smooth, its driving me mad, what can it be???????????????????
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07 October 2005, 10:31
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#11
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Member
Country: Other
Town: Oakley
Boat name: Zerstörer
Make: Ribcraft
Length: 5m +
Engine: Suzuki DF 140
MMSI: 235050131
Join Date: Jun 2003
Posts: 3,931
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I have a similar problem on my engine which I hope to solve today.
I think its dirt in the fuel. The engine fuel filter is very dirty and their is some sand like material in the bottom of the bowl.
I am going to replace the engine filter, fit a new in line filter, clean the tank filter/pick up and clean the bowl.
I'm hoping that will sort it.
Maybe that might help you..........
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07 October 2005, 11:12
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#12
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Member
Country: UK - England
Town: Chester
Boat name: Escapism
Make: Narwhal
Length: 4m +
Engine: Yamaha 55
Join Date: Jun 2004
Posts: 45
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Quote:
Originally Posted by Biggles
I have a similar problem on my engine which I hope to solve today.
I think its dirt in the fuel. The engine fuel filter is very dirty and their is some sand like material in the bottom of the bowl.
I am going to replace the engine filter, fit a new in line filter, clean the tank filter/pick up and clean the bowl.
I'm hoping that will sort it.
Maybe that might help you..........
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Thanks biggles, I allready threw out my old fuel, cleaned the tank and filters and changed the fuel pipes!!!
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07 October 2005, 16:47
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#13
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Member
Country: UK - England
Town: Chester
Boat name: Escapism
Make: Narwhal
Length: 4m +
Engine: Yamaha 55
Join Date: Jun 2004
Posts: 45
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Now I know the answer!!!
Just took the head off to de-coke and found that the liner in the top cylinder has rotated by about 10 degrees, half closing all the ports!
Has anyone seen this happen before?
And more importantly does anyone know how to put it right?!
Thanks very much to all those who have allready offered advice, its very apparent at times like this that there’s a fair bit of knowledge to be found on these pages.
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08 October 2005, 10:05
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#14
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Member
Country: UK - England
Town: Cumbria
Length: 4m +
Join Date: Jul 2005
Posts: 126
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Craig, thanks for the feedback and for passing on what the problem was
For info, I have never heard of the liner moving in this fashion. No wonder you were having problems
How did the cylinders look when you got inside? Was there a lot of carbon build-up?
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08 October 2005, 19:43
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#15
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Member
Country: Other
Town: Oakley
Boat name: Zerstörer
Make: Ribcraft
Length: 5m +
Engine: Suzuki DF 140
MMSI: 235050131
Join Date: Jun 2003
Posts: 3,931
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There was a post on iboats about this sort of thing.
It was a smaller engine and the guy had to put the block in his oven, sent the wife out obviously, and then managed to twist it back.
Do a search of www.iboats.com and see what comes up.
Regards Nick R.
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26 October 2005, 20:35
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#16
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Member
Country: UK - England
Town: Hoylake,Wirral
Boat name: Deerider and Beast
Make: Beufort and Avon
Length: 8m +
Engine: Outboards
Join Date: Oct 2005
Posts: 19
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Quote:
Originally Posted by Craig H
As you might have noticed from my previous post "worth repairing?" my Yamaha 55 suffered a terminal fault recently. I did however manage to find another 55 on Ebay with a knackered gearbox for £100 and swapped the powerheads over.
I've set the timing, overhauled the carbs, fitted new plugs, checked the compression (both cyinders in the 140-145psi) etc etc.
Both plugs are the perfect tan colour so the mixtures right but it just hasnt got as much power my old 55 had. It doesnt accelerate as well and is about 5kts down on top speed. Top engine speed is now 4900rpm not 5500rpm as it used to be.
Is there something I'm missing? I'm sure they never came out of the factory with so much variation in output.
Anyone got any suggestions?
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Have you drained the gearbox since running the new engine to make sure it is not metallicy it could be the box braking down and causing poor excelleration and top end speed (unlikely but desprate times and all). otherwise it sounds like a fuel problem have you tried changing the carbs over from the dead engine.
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