Mercury Lightning XR 40HP (Tohatsu M40D2)

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Post Options Post Options   Likes (0) Likes(0)   Quote SufixRockMan Quote  Post ReplyReply Direct Link To This Post Topic: Mercury Lightning XR 40HP (Tohatsu M40D2)
    Posted: 17 Mar 2018 at 6:41pm
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Hi folks,

My Mercury Lightning XR 40HP is loosing power above 4000RPM, below this she runs well, idle is smooth etc

Typically what happens is that I'm under power, moving along well and then the power drops off, she sounds fine at this point but even if I push the throttle forward nothing happens. Turning the ignition off for 10 seconds and then starting the engine again she comes back with full power. More often than not it seems like the power comes off when I hit a wave too hard 😂

The engine has had a full service including the spark plugs being replaced, all cylinders are within 10% of each other.
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Post Options Post Options   Likes (0) Likes(0)   Quote funandfunction Quote  Post ReplyReply Direct Link To This Post Posted: 17 Mar 2018 at 8:06pm
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Sounds like it's starving of fuel.... have someone sit down the back when you're running and as it looses power at higher revs give the primer bulb a few squeezes and see if the revs pick up. The bulb will feel soft   when you first pump because the fuel line is under negative pressure so don't worry about it not being hard.
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Post Options Post Options   Likes (0) Likes(0)   Quote Durban Quote  Post ReplyReply Direct Link To This Post Posted: 17 Mar 2018 at 8:16pm
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Another thing you can check is see if you have enough spark ,when the timing is advanced , to do this you need a spark tester. and set at 7/16 or 3/8
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Post Options Post Options   Likes (0) Likes(0)   Quote SufixRockMan Quote  Post ReplyReply Direct Link To This Post Posted: 17 Mar 2018 at 8:16pm
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Okay, awesome advice regarding fuel. Thank you - if that is the issue what are my options to have it fixed permanently?

Just for information, the engine has done approx 150 hours.
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Post Options Post Options   Likes (0) Likes(0)   Quote OneWayTraffic Quote  Post ReplyReply Direct Link To This Post Posted: 17 Mar 2018 at 9:43pm
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Have you tried cleaning out the carb?
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Post Options Post Options   Likes (0) Likes(0)   Quote DIY Quote  Post ReplyReply Direct Link To This Post Posted: 17 Mar 2018 at 10:43pm
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I’ve got a workshop manual and parts book for my Lightning, it’s a 2007. I can send it to you if it helps.
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Post Options Post Options   Likes (0) Likes(0)   Quote pjc Quote  Post ReplyReply Direct Link To This Post Posted: 18 Mar 2018 at 7:45am
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buy a new bulb for starters,150hrs would still be under warranty?dont  merc give 5yrs?
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Post Options Post Options   Likes (0) Likes(0)   Quote SufixRockMan Quote  Post ReplyReply Direct Link To This Post Posted: 18 Mar 2018 at 7:58am
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Thanks PJC, already replaced.
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 18 Mar 2018 at 10:26am
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MNost common issue with bulbs is they make leak back between while stopped at a fishing spot, have to pump up again.
Often the bulb is replaced and still does it.
 Reason, the bulb must be mounted with out let above the inlet.. if not the little ball bearings in the non return valve fall out of the valve stop sealing..

 Check easy stuff 1st.

Your issue sounds most likely fuel starvation.
 1/ check fuel filters for crap
2/ check ALL fuel lines for any suspect air leaks at joins. 
Ideally cut back re fit and re fit the stainless jubilee clips.
 This also eliminates the possibility of a flap of fuel hoes interior being peeled off when fitted onto fittings previous time.
3/ check the pick up in the tote( assume tote) is clean clear, no carp in the tote tank.
4/ Check tote tank breather is actually breathing WELL.
 5/ Old school vintage/ hot rodding , side of the road carb fix. Run engine, take rpms up to fast idle or little more. put hand over carb inlet, create a good suck vacuum, without stalling the engine, then suddenly remove your hand... repeat 4 to 5 times.

Running an engine, espec engines like outboards chain saws garden blowers etc, that are in the high performance league, lean is serious slow death to the engine...combustion temps get very high
 Note: Combustion temp and engine running temps are 2 very different things.

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Post Options Post Options   Likes (0) Likes(0)   Quote SufixRockMan Quote  Post ReplyReply Direct Link To This Post Posted: 18 Mar 2018 at 4:05pm
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Thanks Steps, I'm going to contact the shop who did the work on the outboard a couple of months prior to me buying it (it was taken in to fix this exact issue). I will put these suggestions!
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 18 Mar 2018 at 4:40pm
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Im is just the simple/ cheap stuff to start with
 Do not write off Durbans stuff/ post above.
 One would assume  the shop would have covered these simple things... 
on the other hand A55 U & Me is just that with a lot posts made her over the yrs of a lack of professionalism/ by professionals
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Post Options Post Options   Likes (0) Likes(0)   Quote SufixRockMan Quote  Post ReplyReply Direct Link To This Post Posted: 18 Mar 2018 at 5:16pm
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Yeah, one would assume so. Maybe it's hard to test or my tot tanks are being dicks.

I guess the strangest thing is that it does come right immediately after turning the ignition into the off position waiting for a few seconds then starting her up again. If she was running lean wouldnt you expect poor(er) performance throughout the rpm range?

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Post Options Post Options   Likes (0) Likes(0)   Quote Bigfishbob Quote  Post ReplyReply Direct Link To This Post Posted: 18 Mar 2018 at 9:59pm
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Sounds like it's getting hot and tightening up, even 10 seconds stop and the ramp down and back up can be enough to get the temp down to let it free up. Check you water pump and thermostat.

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Post Options Post Options   Likes (0) Likes(0)   Quote SufixRockMan Quote  Post ReplyReply Direct Link To This Post Posted: 19 Mar 2018 at 7:49am
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Hey Bigfishbob, unfortunately both have been replaced last month.
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Post Options Post Options   Likes (0) Likes(0)   Quote Tagit Quote  Post ReplyReply Direct Link To This Post Posted: 19 Mar 2018 at 8:42am
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Bad ignition will more usually cause a miss rather than 'a drop in power but still run smooth'. Fuel starvation seems more likley but strange that you can turn off/on and then be good again. Don't know that engine so hard to try and guess what might be happening. Another possibility though could be that the engine is losing it's timing advance. That could drop power without causing a miss. 

If the engine has an ECM rather than a more simple mechanical ignition control etc than it could maybe be an issue with the ECM getting hot or similar. That is where the service agents can hopefully diagnose using factory software tools if they have them.

Most obvious checks from what you have described would be fuel lines in case they are collapsing internally (maybe had ethonal fuel through them etc), tank pick-ups and vents (but it seems you are on totes?), filters, and as above the primer bulb. Also need to check for air leaks in the fuel system as that can also cause similar issues. Maybe also check the fuel pump although with low hours that is a less likley issue.

The idea above of pumping the primer bulb hard when the condition comes on is a good test as it may at least give some indication of whether the fuel system is faulty i.e. if it helps the condition then the fuel system is probably the issue. If this has been happening on one particular tank then also try opening the tank cap to prove that it isn't a tank vent issue. 

Last thing is that this could be a carb issue with some dirt affecting the fuel flow and then dropping out of the way again when you turn off the engine and hence fuel pressure. If they decide to clean the carb it must be done really well. There is no such thing as a quick carb clean.

One simple thing you could do yourself is to drain the carb bowl(s). There is usually a drain plug you can undo. Drain what is in there into a clean container so you can check for any gunk. If there is gunk just leave the drain plug out and pump the primer bulb to flush clean fuel through the carb until you are confident that it is perfectly clean.
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 19 Mar 2018 at 9:17am
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 it does come right immediately after turning the ignition into the off position waiting for a few seconds then starting her up again.

 A slight air leak in a fuel line will do that.. faulty breather, crap in filters, partly blocked fuel line/ breather,/pickup.
Air bubble collects floats up.. line between engine and where leak is becomes solid fuel.. fire up , low rpms/ load, fuel flow small, get a solid line of fuel to the engine..
 open up , suck/ flow of fuel increases, air gets sucked in... many not even pull air at lower fuel flow..

 and so will a faulty breather valve..starts to lean out at high fuel flow (speed/ rpms) due to vacuum in fuel tank.. and or/ fuel restriction...stop, breather allows tank vacuum to equalize... Fire up, all good at low fuel flow, higher speed.. back to lean out.


 If she was running lean wouldnt you expect poor(er) performance throughout the rpm range? 

As mentioned above.. faster you go, the more load on the engine the more energy required , therefore more fuel therefore  more fuel flow 

Lean .. a little lean makes a engine run strong more hp.. with very high combustion Temps.. Notice when a chainsaw or lawn mow runs out of gas, that last few rpms when goes lean, it speeds up the dies?  thats lean burn. melts tops of pistons etc.
 If run over lean for too long,  kill the engine, you pull the spark plugs and examine under a very good magnifying glass you will see very small round balls of melted piston alloy.

Lean out further and the mixture gets above air fuel ratio around 16:1 to one the engine starts to miss.
ideal is about 14.2:1  lean idle cruise around 14.8:1  rich WoT power down 11 to 12.5 to 1. Bit over simplified  as cylinder pressure/rpms/ EGR/ cam and ign timing/ engine temps etc all influence.

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Post Options Post Options   Likes (0) Likes(0)   Quote SufixRockMan Quote  Post ReplyReply Direct Link To This Post Posted: 22 Mar 2018 at 8:19am
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Hi folks, thanks for all the advice - the issue was at high rpm some gunk was getting sucked into the carburetor and restricting the fuel intake. Turning the engine off broke the seal/vacuum releasing the gunk. I had previously replaced the fuel lines but some crap had made it through. Anyway, have had the carburetor cleaned out and all the lines etc rechecked.

Weather forecast is for flatter than hammered **** this weekend, looking forward to getting out for a blat!
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 22 Mar 2018 at 10:41am
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I had previously replaced the fuel lines but some crap had made it through.

Very similar to a very common issue after restoring a vintage or a hot build  type of thing.
Lines / tanks dry out, grunge drys up.. Finish build on the road and next day going to do a road trip , or some distance up .
Say Auckland Taupo.. all good get 3/4s or so of the way, engine starts missing.. The crap but scale whatever, goes down the lines jambs the float valve so will not fully close off ( Holley type carbs).
 Generally other/ vintage carbs will drop crap in a port or capillary tube...
 Either way if after storing / building for couple yrs .. or have done work on tanks fuel lines..start to miss.. will be crap.
 And 99% of the time the side of the road 'fix' above sorts the issue..
 Not the holley float valve issue thu.
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Post Options Post Options   Likes (0) Likes(0)   Quote MikeAqua Quote  Post ReplyReply Direct Link To This Post Posted: 22 Mar 2018 at 1:14pm
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Do Tohastu's not have a secondary filter on the engine?
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Post Options Post Options   Likes (0) Likes(0)   Quote 4 stix Quote  Post ReplyReply Direct Link To This Post Posted: 27 Mar 2018 at 7:29pm
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I have had the same problem twice over a 2 yeay period, after checking everything I removed the carb fuel drain bungs & flished 2-3 L thru & both times it want away. this saved the job of removing the carbs which i didn't want to do at the beach.
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