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Old 28-04-2006, 09:07 PM   #1
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loss of rpm

Quick question, just back back in from a quick spin around and a couple of times (in about an hour)I seemed to lose around 1k rpm for around 20-30seconds then in would clear and be fine. Apart from whacking a load of carb cleaning spray in what other area should I be checking. Whether its relevant or not I dont know but I`ve got the alien cowl fitted with the 2 air scoops, I`ve fitted V.stacks and have re-jetted the carbs accordingly.
Secondly whats the turn around time at prop revalutions?

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Old 28-04-2006, 11:15 PM   #2
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Not much of a mechanic meself (yet!) but could it be droppin a cylinder now and then? Could be plugs or slight fuel starvation through the pump??
Like I say I'm not much of a mechanic but could be worth a thought??
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Old 29-04-2006, 12:15 AM   #3
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Dan,

I'd double check the fuel line dia and that the fuel filter is allowing sufficient flow. When I 1st fitted my Merc 200 on the Fletcher; I had a situation whereby if I ran at WOT for over (say) 2 mins I'd feel the engine start to hold back as soon as i eased on the throttle the engine would spring into life................. iet was a simple fuel restriction due to 'cheap' hose being used.

Also check the wiring that runs from the main switchbox to the ignition coils (that sequence the firing order) the wire on older mercs is utterly shite............when i replaced it, the motor ran & started a whole load better. In fact, perfic!
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Old 29-04-2006, 01:10 AM   #4
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air scoops in cowl big enough?
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Old 29-04-2006, 07:27 AM   #5
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Re: loss of rpm

Coughing/Spluttering?
Less power as you gave it more throttle?
Or just "down" on power? What rpm was it doing it at, and dropping to what?
M

Quote:
Originally posted by Dan
Quick question, just back back in from a quick spin around and a couple of times (in about an hour)I seemed to lose around 1k rpm for around 20-30seconds then in would clear and be fine. Apart from whacking a load of carb cleaning spray in what other area should I be checking. Whether its relevant or not I dont know but I`ve got the alien cowl fitted with the 2 air scoops, I`ve fitted V.stacks and have re-jetted the carbs accordingly.
Secondly whats the turn around time at prop revalutions?

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Old 29-04-2006, 08:39 AM   #6
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Re: Re: loss of rpm

Quote:
Originally posted by Matt
Coughing/Spluttering?
Less power as you gave it more throttle?
Or just "down" on power? What rpm was it doing it at, and dropping to what?
M
Matt, no coughing or spluttering at all, and it didnt happen as soon as I reached 5800rpm infcat I had been at wot for a while so not really a case of more throttle less power, as you say it just drops down on power. I guess I was around 5800 then a couple of times it just dropped to just below 5, then after a few seconds it picked back up.
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Old 29-04-2006, 08:40 AM   #7
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Quote:
Originally posted by Burty
air scoops in cowl big enough?
I have cut them out since it was fitted, any millage in cutting a hole in the front and fitting the face plate??
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Old 29-04-2006, 09:18 AM   #8
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hi Dan,
I had this problem on a dive boat I was on a few years ago. Cant say its the same problem that your having but the problem I was having was that the pulse line to the fuel pump was clogged up (due to using frikin mineral oil(crappy stuff)), so at high rpm the engine would after a while die down only slightly. Also I am sure yours are fine but I would check the one-way valves in the fuel pumps just to see if there are any tale tale signs there.
Anyways hope you fix it and see you on the water soon
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Old 29-04-2006, 09:33 AM   #9
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Quote:
Originally posted by Dan
I have cut them out since it was fitted, any millage in cutting a hole in the front and fitting the face plate??
Prolly not then, i only have the side scoops and i dont suffer.
you need someone in the back when this is happening to check to see fuel lines / priming bulb are not getting sucked in. changed your fuel filter lately? charged your battery?
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Old 29-04-2006, 09:37 AM   #10
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Quote:
Originally posted by Burty
Prolly not then, i only have the side scoops and i dont suffer.
you need someone in the back when this is happening to check to see fuel lines / priming bulb are not getting sucked in. changed your fuel filter lately? charged your battery?
I`m gunna go and get a new filter and fuel lines today, as for the battery, yep all charged.
Burty, you still coming down tomorrow?
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Old 29-04-2006, 11:21 PM   #11
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no mate, they went today instead and i was busy
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Old 20-05-2006, 10:01 AM   #12
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Sorry to drag this one open again but, fitted all new fuel lines and filters, when out the other day and thought the problem was fixed until mid air revjust died right down (at WOT) and didnt come back up (which meant a very slow crawl back from the breakwater). So, I`ve got a rectifier (thank you very much ) which I`ll stick on today, I`ve checked the plugs they look ok to the untrained eye had a bit of what looked like oil on them. If its still the same after the rectifier I`ll change the stator (and the plugs & leads just to be on the safe side) after than any sugggestions? The engine is not mis firing at all.
Dont know if its relevant or not but when I fitted the stacks I re-jetted the carbs (couple of sizes I think) and I premix at 30-1.
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Old 20-05-2006, 10:06 AM   #13
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30:1 seems a bit much
but prolly not the cause of problem. you can run 40:1 easy which will give you more power.
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Old 20-05-2006, 10:28 AM   #14
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Quote:
Originally posted by Burty
30:1 seems a bit much
but prolly not the cause of problem. you can run 40:1 easy which will give you more power.
Ran 30:1 last year so I`m pretty sure its not that.
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Old 20-05-2006, 11:17 AM   #15
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40:1 its might not be the cause of your problem but your just chucking money away by running 30:1.

If it was rich due to re jetting the carbs it would lose revs on top all the time not spuradically. Check all the wiring around the switch boxxes rectifier stator etc. Look for bad connections, damaged insulation etc. A wire might have rubbed through and be shorting on the block.

Does the tach jump around at all? If it does I would look at the rectifier.

Could also be the stator!!!
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Old 20-05-2006, 11:28 AM   #16
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Quote:
Originally posted by Johnny Boat Dude
40:1 its might not be the cause of your problem but your just chucking money away by running 30:1.
and losing power dude
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Old 20-05-2006, 03:40 PM   #17
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Quote:
Originally posted by Johnny Boat Dude
40:1 its might not be the cause of your problem but your just chucking money away by running 30:1.

If it was rich due to re jetting the carbs it would lose revs on top all the time not spuradically. Check all the wiring around the switch boxxes rectifier stator etc. Look for bad connections, damaged insulation etc. A wire might have rubbed through and be shorting on the block.

Does the tach jump around at all? If it does I would look at the rectifier.

Could also be the stator!!!
No tachs fine no jumping at all. Is there any way of testing the stator or is it a case of trying a new one?
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Old 20-05-2006, 05:44 PM   #18
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Quote:
Originally posted by Dan
I`ve checked the plugs they look ok to the untrained eye had a bit of what looked like oil on them.
As long as they're not cracked anywhere, rusty or badly soiled and the gap in the top should be about the thicknes of the card a fag packet's made of....
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Old 20-05-2006, 06:41 PM   #19
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Dan,

Does it rev fine out of gear and when you put it in gear it dies?
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Old 20-05-2006, 06:48 PM   #20
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Quote:
Originally posted by Dan
No tachs fine no jumping at all. Is there any way of testing the stator or is it a case of trying a new one?
Trouble is it mite only be breaking down when hot or due to vibration.

If you knew which wires went to each coil I supose you could check the DC resistance of each one to see if there's an odd one out, maybe!!!
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