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Surging issue

Flying_Lavey

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So for the first time in..... well maybe the entire 12 years I've owned my boat, I habe a slight issue with the engine that is not from my doing (as far as I know so far). First, the motor is an '86 Merc 200 without oil injection (never even had it, no mounts on the motor for it). It has a hard time ideling (have to keep it about 1k to keep it alive), and once the motor warms up it surges. Even while on plane and moving. It seems the higher the RPM's the less the surges. It's got a new water pump 2 months ago and runs about 12 psi at speed and about 7 ideling. I'm leaning towards the reeds being shot but I haven't had a chance to open it up and take a look yet. I was wondering what the congregation thought before I dove into it.
 

stoker2001

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sounds like reeds,are they original?do compression check first,then check spark on all six
 

Flying_Lavey

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sounds like reeds,are they original?do compression check first,then check spark on all six
I'm not too sure. I wouldn't be surprised though. I know they are at LEAST 12 years old (as long as I've owned the boat). I haven't done a compression test in years so that probably wouldn't be a bad idea. I figured I'd used my inspection camera either way to inspect the cylinders too.
 

HST4ME

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Put a clear piece of hose from the primer bulb to the motor and see if it drawing air, rebuild the fuel pump anyway.

If it still has the steel reeds and it ate one it's more than likely there will be bore damage.
 

Flying_Lavey

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Put a clear piece of hose from the primer bulb to the motor and see if it drawing air, rebuild the fuel pump anyway.

If it still has the steel reeds and it ate one it's more than likely there will be bore damage.

That's what I'm most concerned about, extensive bore damage.

I know it's been debated many times over, but I do run a low pressure electric fuel pump so I'm not too concerned about fuel supply to the carbs. And the surge lessens with high R's. I'd imagine it'd get worse if it was a fuel supply issue.
 

HST4ME

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Take the air box off and see if it's pushing fuel past a needle.
 

Flying_Lavey

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Finally got around to checking everything out. Used my endoscope to check the cylinders and reeds and all looked good. Turned on the fuel pump and let it run for a bit and sure enough HST4ME hit the nail on the head. The bottom carb needles don't appear to be seating fully and the fuel was pushing right passed them. I pulled the carb off bit haven't had a chance to really dive into it yet. Glad it's something simple though. 20170718_194426.jpg
 

Mr. C

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Off topic. Curious what Prop you run and speeds you see with your 200.
I'm running 14 1/4 x 19 on my '87 150 and see roughly 50mph at 5800 - 6k RPM
A friend has 20 pitch on his '79 200 and beats by a couple MPH.
 

Flying_Lavey

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Off topic. Curious what Prop you run and speeds you see with your 200.
I'm running 14 1/4 x 19 on my '87 150 and see roughly 50mph at 5800 - 6k RPM
A friend has 20 pitch on his '79 200 and beats by a couple MPH.
I have low water pick-up and run my motor high which allows me to run more prop. My big prop is a 26 Ron Hill chopper. I haven't GPS'd it in forever but light load and ideal conditions the slip numbers decrease greatly and it runs about 65ish at about 6500. I'm leaving a lot on the table though with my trim tabs (rams aren't mounted high enough so they don't allow the boat to air out as much as it would like) and the fact that I haven't had the funds to play with correct props. My 21 Laser II will run right about 60 with the same RPM but will almost jump out of the hole with 6 people in the boat and a full load.
 

Flying_Lavey

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So took it out yesterday evening and the surge is gone and it is running somewhat smoother. I think it may habe fouled a plug though. Can definitely hear a miss occasionally at idle and can feel it drop a cylinder while running. I guess it's time to change the surface gap plugs. It's only been 12+ years. Lol!
 

Flying_Lavey

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Alright, so it only took a month but I took the boat out again Saturday with the new plugs. Still not running right. It doesn't do the same thing as often (feels and sounds like a misfire). But it will all of a sudden drop about 1k RPM for a quick second and come right back up. It really only seems to do it at about 5k RPM though. And getting on plane is no issue at all, no hiccups, no nothin. I don't think it's a spark box (would imagine it's be having a hard time getting on plane if so) and it seems too intermittent to be a stator. What do you guys think?

1986 Merc 200 carbed. No oil injection no thermostats, new water pump at the beginning of the season.
 

Warpt

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How old are the fuel lines? They could be coming apart and restricting flow when your running? Bowls are full alowing you to get on plane but restrict flow while running.
 

Flying_Lavey

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How old are the fuel lines? They could be coming apart and restricting flow when your running? Bowls are full alowing you to get on plane but restrict flow while running.

Possible but doesn't really seem like it. It's only at 5k and just for a second. Didn't do it at all above 5k.
 
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