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Discussion Starter #1
The last couple of times I have been out, my motor bogs down between 3000 & 4000 rpm. When it starts to bog down if I put it to WOT it opens up to 5400 without a hitch & will run at 5000 rpm no problem. If I leave it between 3000 & 4000 sometimes it will even quit altogether but if I pump the primer bulb it will keep going. It seems to start and idle fine but every now and then will quit at idle.

Normally I would go to "fuel pump" but the carbs and fuel pump were rebuilt this last winter - may still be that but looking for more ideas before I do the rebuild again.

So here is what I am seeing and what I have done so far:
I attached a pipe to the fuel tank pickup point and can suck and blow on that no problem (so no blockage at the tank). The primer bulb does not get pinched at any speed but does empty itself at the 3000 - 4000 rpm (if I pump the bulb it will keep going). I connected the motor to a portable tank with clean gas & there is no difference to the motor's behavior. I ran iso-heet through the portable tank in case there was water in the carbs - no difference. I replaced the in-line fuel filter on the motor.

Replaced fuel hose and primer bulb - no difference.

I am thinking a small air leak between the fuel hose connector and the fuel pump or maybe a hose that pinches at higher vaccum?

Like I said could be the fuel pump but I am looking for other possibilities. Any help would be most appreciated. I am pretty good with a wrench but this one has me stumped.
 

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The Inferior Fisherman
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It's possible that when you advance your throttle, the throttle advance lever, or arm, in the motor squeezes the fuel line. They are pretty close, and I have wondered about it on mine. I used some tie raps to hold the fuel line away. Check it in your drive, have someone advance the throttle as you watch the movements.
 

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Discussion Starter #4
Looks like it is clear. Part of the problem with trying to work on these engines (even a simple tune-up) is you have to be in-gear, in motion. Great in theory but when you are out in Lake Erie at 20 mph leaning over the outboard while someone else drives can get a little interesting.:C:C:C
 

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Discussion Starter #5
Okay - so here is what I did and here is what I found so far.

I followed the Mercury manual troubleshooting and put a piece of clear pvc hose between the pump and the carbs to check for air bubbles. Well I have lots of air bubbles which go away when I pump the primer bulb.

I bypassed the fuel line connector (fuel line to motor) with a piece of 3/8 copper pipe. Still have air bubbles so it is not sucking air through a bad fuel line connector.

I hooked up my kicker motor fuel line to the 3/8 copper pipe to check the integrity of the fuel line back to the built in fuel tank. Still have bubbles so it is not sucking air somewhere between the bulkhead and the pickup point in the tank.

Also with the engine running I disconnected the kicker fuel line from the portable tank I use for the kicker. The motor sucked the primer bulb flat and the primer bulb stayed flat after I switched the engine off & until I plugged the fuel line back into the portable tank. So it looks like I am not getting the bubbles between the fuel pump and the built in tank.

So it has to be a fuel pump problem that is generating the bubbles.

I have a fuel pump kit on order.

Must have screwed something up when I rebuilt it over the winter. :eek:

I will report back when I have rebuilt the pump.
 

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nice job talking your way thru this problem, I think your on the right track [intr pump problem. that air is com8ng from some where.on a closed system. you,ll find it, got 7 today .off lorain.
 

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Discussion Starter #8
It is the fuel pump. I took it apart and the boost gasket is broken.

My Bad! :( When I assembled the pump last winter I must have had the gasket slightly off center and the thin piece of gasket that separates the pump inlet and outlet compartments has blown out.

Parts are on order. I also paid attention to some of the other possibilities mentioned in the comments & am replacing the hoses, fuel line connector, etc. They may be fine but they only cost a few bucks & I don't want a repeat performance if I am out at the bouy with a storm coming in....

The key was hooking up the clear pvc between the pump and the carbs and seeing the bubbles.

Thanks for your comments. Helped me to think it through.

Joe S.
 

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The Inferior Fisherman
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I took out the fuel line connector at the motor. You don't need it, another connection that can fail. I run the gas line through the hole where it was to the connector inside the motor. I don't think it's a good idea to disconnect the fuel line and run your motor dry, so there is really no reason to disconnect it. It only takes a couple of seconds to loosen a clamp and remove the line if you need to.
 

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Discussion Starter #10
Good point on the fuel line connector.

One other suggestion I received was to replace the standard in-line filter on the line between the pump and the carbs with one of those clear plastic in-line filters. That way you can immediately see if you have a fuel problem.

I went online and got one with several spare replaceable cartridges for <$20 delivered. I am going to look at my kicker too to see how I can add one to that.

BTW while I was at it I found a water separator filter with a "spin-on" cartridge that I added between the built in tank and the primer bulb. I guess these days water separator filters are standard but my boat did not have one. Attached to the bulkhead with 2 bolts. With shipping I paid $25 on-line.

Thanks!
 

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Discussion Starter #11
Oh - and if you ever rebuild one of these fuel pumps, pay attention to ALL the instructions. I missed the one about putting 1/4 inch bolts through the holes in order to align all the gaskets, diaphrams, etc. I just used the fuel pump bolts which are <1/4 inch. This allows just enough play to miss-align the gaskets just enough to allow them to blow out. As I've discovered!
 

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Discussion Starter #12
And one more point to watch on the rebuild is the positioning of the diaphrams relative to the gaskets (this is mentioned in the Seloc manual). On early models the diaphrams are mounted inboard of the gaskets (gaskets outside diaphrams). Sometime in the 90's it appears Mercury switched the positions of the gaskets relative to the diaphrams and the gaskets are now located inboard of the diaphrams.
 

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Discussion Starter #13
I rebuilt the fuel pump and installed it. I swear I did not touch anything electrical but now it will not start. :confused: I checked for spark and there is none.

Anyone got any ideas on why I have no spark? (I did check the dead-man switch).
 

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Discussion Starter #14
Jiggled the kill switch and it started! I am still going to take it into a Mercury Tech to check out the electronics.

If it needs a wrench to fix it I am fine but when it comes to stators, trigger switches, etc I am lost.

Thanks for your help guys!
 
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