Mercury 2.5 200 problems

Paul E · 29-05-2011, 07:20 PM

I got my boat out for the first time on Friday. It's running a '99 carb'd 2.5 200 on an offshore leg and 2 hole CLE. I've ditched the oil injection, premixed on premium plus at 40:1, and it's running the stock fuel pump. For now it's on a 23" Yam Pro M prop.

On the first run it jumped straight on the plane and went up to 6200rpm really nicely, then after around 30 seconds it lost power and got gradually worse. The wires coming from the stator had cooked (it was 40A at this stage).

We swapped the Stator, flywheel and rectifier for 16A, timed it to 23-24 degrees, but now it won't run properly under load, 4,500rpm max. Swapped the stator for another 16A that's known to be ok, ran it in gear on the trailer and still didn't seem happy under load.

Has anyone got any suggestions?

Cheers

Paul

Paul E · 30-05-2011, 07:50 PM

Any suggestions? After doing a lot of reading I suspect a switchbox. Will check each cylinder tomorrow to check it's running on 6, a faulty switchbox would mean only 3 I gather? Which is hard to tell at idle?

maz928 · 30-05-2011, 09:57 PM

It sounds like its running on 5 cylinders ,try to get hold of 6 plug testers (Any motor shop)which fits onto the plugs and then put the leads onto the testers.
Run it up on the hose pipe and check for sparks in the testers.If its running on 5 change the switch boxes(inner and outer) over,if the no spark goes to a different cylinder its the switch box but if it stays on the same cylinder check out the coils/leads etc.
It also could be the stator which may run up on all 6 cylinders as it has high speed and low speed outputs.

hope this helps

Steve

drew · 30-05-2011, 10:01 PM

Quote:

Originally Posted by maz928

It sounds like its running on 5 cylinders ,try to get hold of 6 plug testers (Any motor shop)which fits onto the plugs and then put the leads onto the testers.
Run it up on the hose pipe and check for sparks in the testers.If its running on 5 change the switch boxes(inner and outer) over,if the no spark goes to a different cylinder its the switch box but if it stays on the same cylinder check out the coils/leads etc.
It also could be the stator which may run up on all 6 cylinders as it has high speed and low speed outputs.

hope this helps

Steve

shepster · 30-05-2011, 10:19 PM

Hi, as above but you could also pull a ht lead off in turn to see if that cylinder is firing. Just make sure you have some insulated pliers so you don't get belted!!
If there is one thats playing up carry on as above to find the cause.

Superjetjim · 30-05-2011, 10:33 PM

Quote:

Originally Posted by shepster

Hi, as above but you could also pull a ht lead off in turn to see if that cylinder is firing. Just make sure you have some insulated pliers so you don't get belted!!
If there is one thats playing up carry on as above to find the cause.

You can remove all six plugs at once then plug them back into the leads and rest them as they hang down against the block - get someone to crank her over and look at which plugs spark and which dont - no shocks and no worries, simples

You'll most likely have a coil down, easy to swap round to see if the fault moves with it. If a box had gone down you'd loose all three.

Jim

Superjetjim · 30-05-2011, 10:38 PM

Why did the wires from the stator cook? - Did the flywheel rub through the wires and ground out? Guess this could have placed other loads on the electrics further down stream (like coils/switch boxes)

Jim

maz928 · 30-05-2011, 11:14 PM

I like to use plug testers as it tests plugs under compression and I recently had a merc 200 which had a coil breaking down at 1800rpm and over as it puts more load on the ignition with higher revs.

just be careful cranking the engine over with plugs hanging down on the leads as if you dont get a good earth you can blow a switch box which can take a switch box just for one cylinder not all three !!

Steve

Jay Smith · 30-05-2011, 11:42 PM

Steve is right on....
If you spin the motor doing checks the switch boxes and coils MUST eliminate their high voltage charge to a ground on ALL plugs OR it can fry a switch box ( s )..

I use whats called a spider that tests not only spark but spark strength with a means to widen the air gap ..

If a wire fries on the charge system like that its a direct short, look for a ground and a positive some way became married.

If you have converted to 16 amp from 40 did you install a rectifier? If not and your trying to use the old 40 am voltage regulator system , can them and wire like a 260 Hi Per motor it should lower the possibility of wiring errors by going back very simple.

Good luck,
Jay

Paul E · 31-05-2011, 10:41 AM

Thanks for all the suggestions guys. A 16A rectifier was installed when the stator and flywheel were done on Friday I believe.

I'm off down there shortly, on my way to get 6 spark testers (the little light up jobbies that fit between plug and lead) and see what happens when we crank it. If that's ok then we'll dip it in the water on the trailer and try it under load.

Paul E · 31-05-2011, 03:02 PM

Well all 6 are sparking when it's being cranked over on the battery... I know the coils and leads are ok as Sean1982 used them on Saturday to see if they cured his issue, and they turned 6000rpm. Now I'm stumped. Could it be a switchbox issue when the revs/load are increased?

Superjetjim · 31-05-2011, 04:56 PM

Have you changed all 6 x plugs? - Had an issue similar to this on another 2 x stroke and it turned out to be a plug breaking down under compression as revs/loads increased.

Paul E · 31-05-2011, 05:05 PM

Nah I haven't changed them but they only have an hour on them at the most. The fact it ran faultlessly to 6200 before the 'issues' with the 40a stator surely mean it's somewhere in the ignition system? I need this wind to bugger off so I can go and give it some stick out at sea, as in gear on the trailer probably isn't a realistic simulation of what the motor experiences if it's allowed to spin up...

Paul E · 31-05-2011, 10:07 PM

Right, the plot thickens

Compression tested all cylinders, all good (gauge read 160 on all 6, although I'm unsure how accurate that is. As long as they're all the same I'm happy!) Went for another run - exactly the same situation, Idles perfectly, starts on the button with no throttle, but no guts and 4500 max rpm.

My dad mentioned the problems to a yamaha tech he knows, first thing he said was fuel starvation. The fuel lines, primer bulb and filters are all brand new, and I stripped the pump yesterday and all looks well... However on getting the boat in the workshop I took the drain plug off each carb in turn. The top and bottom were full of fuel, whereas the middle carb just trickled a bit out. Unfortunately I didn't have any imperial allen keys to get them off but I'll do that tomorrow. Stuck float or something starving 2 and 4 of fuel mixture? I hope so!! The ignition issues may be a red herring and I was too quick to blame the 40A system possibly?

Superjetjim · 31-05-2011, 10:59 PM

Could be but I would expect a stuck float to allow fuel to pour in assuming it's stuck open and not closed.

Humour me for a moment - you did block off the oil pump presssure take off on the side of the crank when you removed the oil injection didn't you, the large Nipple/pipe on the starboard side? Could that be an air leak into the crank by the middle pots causing the lean issue?

Also I would strip and rebuild your carbs for sure, easy job (with the right tools!) and removes an obvious possible issue.

When your next out get someone to pump the primer bulb as you hit it and see if that clears it, if it does your defo got a supply issue.

Jim

Paul E · 31-05-2011, 11:05 PM

Yeah Jim I definitely blocked off that pipe. Will tear down the carbs tomorrow and report back

only 2 out of 3 carbs working properly would explain my symptoms though I reckon. If a float is stuck up surely that would stop any more fuel entering?

Superjetjim · 31-05-2011, 11:09 PM

Quote:

Originally Posted by Paul E

Yeah Jim I definitely blocked off that pipe. Will tear down the carbs tomorrow and report back

only 2 out of 3 carbs working properly would explain my symptoms though I reckon. If a float is stuck up surely that would stop any more fuel entering?

Possibly... More likely the carb is blocked up with sh1t from before you changed the filter etc. Tooth brush and carb cleaner will have em cleaned in no time. tooth brush gets into the tiny holes for the low end circuit.

Jim

Superjetjim · 31-05-2011, 11:12 PM

And one other thing - the primer bulb, it's not an eBay cheapey one is it? If it is bin it - caused me loads of grief with one of those randomly blocking internally.

Paul E · 01-06-2011, 05:56 AM

Nah the primer bulb is a brand new yamaha one, £17!! Gonna get the carbs off this afternoon and see what the problem is

Paul E · 01-06-2011, 02:21 PM

Well the middle carb wasn't getting any fuel... The float was stuck down which I thought was odd. Turns out the little brass bit that the needle valve sits in (sorry I don't know if I'm using the correct terminology!) had wound itself out locking the valve in the closed position. All tightened up, all 3 carbs cleaned, and it's time for another run out tonight!