Calling outboard sleuths! Mercury 2004 8hp 2 stroke carb, fuel issues.

[Scoop]

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[FONT=&quot]I am frustrated! [/FONT]
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[FONT=&quot] I’ve taken the carb apart 3 times, fuel filter, and played around with the fuel line all to find a problem that seems to elude me. [/FONT]
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[FONT=&quot]My motor: 2004 Mercury 8hp 2 stroke (model 1008201CD). Carb is a WMC-79a[/FONT]
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[FONT=&quot]This outboard has a diaphragm fuel pump. [/FONT]
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[FONT=&quot]https://www.jamestowndistributors.com/userportal/show_product.do?pid=84106[/FONT]
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[FONT=&quot]History: Motor seemed to run rough and die a few times on the water. Decided to do a carburetor cleaning. I’ve cleaned carbs for other small engines, but this is my first time on an outboard. [/FONT]
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[FONT=&quot]1[SUP]st[/SUP] carb cleaning: The carburetor looked very clean. But, cleaned out all jets and reassembled the carburetor anyway. Put in new fuel filter (although looked very clean). Upon completion, the engine was difficult to start and would run for a minute or two until one could see air form in fuel lines (have clear lines) from carb to air filter (not getting fuel assumed likely cause). Put fuel tank up on front end loader to test fuel pump and engine would run much better/longer. [/FONT]
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[FONT=&quot]2[SUP]nd[/SUP] carb disassembly: After reading, took carb apart. Found gasket from carb to main engine was turned around and the small round hole not in right place. Put gasket on right, and expect this to solve problem. To my surprise, engine ran the same as before – started, but not easily, ran for a minute, while more air than fuel seemed to build in fuel line going to carb, then died after minute or two of struggling. Even more surprising the fuel pump testing (raising fuel tank above carb on front end loader) seemed ineffective. [/FONT]
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[FONT=&quot]3[SUP]rd[/SUP] carb disassembly: Did the carb a third time, with new gaskets and everything. This time, the only possibility I found was the earlier hole in main gasket to engine, looked like it might be a slot. So cut a slot in gasket to match what the engine had on it (saw someone describe this problem somewhere). That said, can’t imagine Mercury making gaskets that need a slot and putting a hole in instead. Could not get outboard started. [/FONT]
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[FONT=&quot]Through this process, I’ve…[/FONT]
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[FONT=&quot]Assumed problem is, in order of likelihood.[/FONT]
[FONT=&quot]a)[/FONT][FONT=&quot] [/FONT][FONT=&quot] 1)[/FONT][FONT=&quot] [/FONT][FONT=&quot]Fuel pump not working. [/FONT]
[FONT=&quot]b)[/FONT][FONT=&quot] [/FONT][FONT=&quot]2) Something blocked in carb (runs for a minute), when pump primer bulb used, gas forced in but air bubble (immovable) in line too.[/FONT][FONT=&quot]
3. Some leak somewhere?
4)[/FONT][FONT=&quot] [/FONT][FONT=&quot] [/FONT][FONT=&quot]Fuel line blocked (this appears to be ok). Remember, none of this was occurring before I started working on carb and fuel filter. [/FONT]
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[FONT=&quot]--put in new fuel filter. Made sure fuel filter tightly seated down. [/FONT]
[FONT=&quot]--new fuel lines from carb to fuel filter (clear lines which were on when I bought it), to fuel filter to fuel inlet. [/FONT]
[FONT=&quot]--put new fuel female adapter on line from fuel tank to engine. [/FONT]
[FONT=&quot]--tested to see if fuel lines blocked (line in tank, connections tight etc). Seemed to get getting fuel from bulb to engine fine. Found no fuel leaks. [/FONT]
[FONT=&quot]--air intake on fuel tank open. [/FONT]
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[FONT=&quot]Some thoughts,[/FONT]
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[FONT=&quot]--when I press the primer bulb, it gets hard. But, there is a lot of air that is in the clear line that I can’t get out before I start it. Is there an area of the carburetor/fuel filter that bleeds air that is blocked?

--When I got the engine started, it ran for a minute of rough running, until air in line rather than fuel (most seemed coming from carb) built up and it dies. However, trying to use the primer bulb as a fuel pump would not keep it running (had very mild effect).

--there was a gasket between part #18 and #27 in Mercury schematic that was on fuel pump when I took carb apart. I put this gasket back on, even though it not shown in schematic.

--fuel lines were not blocked or no problems with fuel tank etc before I started working on it. One can’t assume, but these seem less likely as possible problem because of that. That said, I checked these best I could. [/FONT]
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[FONT=&quot]Does anyone have any ideas? I am not a mechanic (which is probably pretty obvious, at this point). [/FONT]

 

[racerone]

The carburetor is the first thing folks look at.-----What is the compression on this motor ?------Does spark jump a gap of 3/8" on both leads , yes or no ?

 

[Scoop]

The carburetor is the first thing folks look at.-----What is the compression on this motor ?------Does spark jump a gap of 3/8" on both leads , yes or no ?

Thanks so much for the interest and ideas!

I don't think I have the ability to check the compression (need a gauge, never done it). Is there a simple way to rule out compression without expensive tools?

I do understand compression could cause problems with the engine pulling in as the fuel pump in this design requires strong air on downstroke. One issue against compression is that this engine hasn't really been used many hours --before me according to owner or when I bought it. Also, I since the fuel issue occurred suddenly, and after I started working on it, I assumed compression less likely.

I am a newby on engine repair, is there a way to check the spark gap? I am looking that up right now.

I was incredibly meticulous with the third carb redo, and made sure carb cleaner could fly through all ports, jets, and orifices, gaskets aligned, bowl set, etc.

 

[Scoop]

The carburetor is the first thing folks look at.-----What is the compression on this motor ?------Does spark jump a gap of 3/8" on both leads , yes or no ?

Spark test looked ok on both leads.

If its the fuel pump in carb, I still can't figure out why I can't keep it running with the primer bulb, or at least have a positive effect. Primer bulb gets hard and pumps gas through line very well, but I can see lot of air in line that can't be removed before I start it. Runs rough and dies minute or two later as air space visibly grows in line from carb to filter.