Mercury 100 HP 2+2 troubles

[boatinnjax]

Hey fellow Merc owners

I've been reading posts about similar problems on my 1990 Merc 100HP 2+2. Heres my story:
This boat, an 87 Cobia SS 200 and above motor has basically sat for 4 years before I acquired it. It ran like crap when I got it.
I put new plug wires on it, gaped plugs to .40 did numerous carb cinks and tune/set up procedures, cleaned carbs, new fuel tank, line bulb, fittings and filters. Ran great Sunday! But after a 45 minute ride at nearly full throttle it began to bog down. I pumped the bulb which was semi rigid and power came back up briefly, then it wanted to bog again. I'm thinking fuel pump needs rebuilt next. Ideas?

Now heres some more data for you 2+2 owners

> As I understand it, the top two carbs are for Idle and throttle up to whatever RPM, the bottom two kick in as the accelerator pump plunger is depressed by the throttle cam. Right?
> So the fuel line for the bottom two carbs goes to the accelerator pump then out to the carbs, Right?
> I am the third owner of this, and it runs fine mostly. The first owner has a buddy that is a boat mechanic and has worked on this motor a lot.
>I?ve read about some of you wanting to make the motor idle and run off of all 4 carbs, Well I think that was done to mine because all four carbs are fed by a fuel line running to carb 1 then 2 then 3 then 4. Another line tee's off of carb 1 to the accelerator pump and then out to what I?m thinking are the enricher injection points on the Starter side of the motor. Follow Me?

> What do you think?

 

[Laddies]

Re: Mercury 100 HP 2+2 troubles

Yes, it does sound like a fuel pump. No your engine has not been converted or it would idle at 2000RPM+

 

[boatinnjax]

Re: Mercury 100 HP 2+2 troubles

Ahh the guru speaks! Thanks Laddie!
So can you tell me how the fuel lines should be routed? It does not look like routed as it sounds like they should based on how the carbs function. I'll post a picture if it'll help.

 

[boatinnjax]

Re: Mercury 100 HP 2+2 troubles

I've also got a timing issue. The idle timing tab is gone from the throttle arm, I'm attempting to fab and bolt one on. Also the timing marks on the flywheel are almost completely gone, all I can make out are some of the numbers and a bunch of marks, it looks like this:

28 24 20 16 12 8 4
lllllllllllllllllllllllllllllllllllllllllll

I cant see any marks under the numbers or before them either. The numbers degrees of advance right?

Thanks!

 

[CharlieB]

Re: Mercury 100 HP 2+2 troubles

lol
the 2+2 is just misunderstood

Yes only the top 2 carbs have idle circuits

the moment the throttle is moved off idle ALL carbs pass gas and all cyls fire

Just my 2 cents

my 115 runs fine, idles, jumps out of the water with a 4 blade 13 1/2 X 24 on a ProCraft V180FS but tops out at 5250WOT, 43mph, checked by GPS on the lake. Maybe a DO NEED a 175? Nahhh, I'd just burn a LOT more fuel, and STILL wouldn't catch any fish!

 

[boatinnjax]

Re: Mercury 100 HP 2+2 troubles

Yeah, I've had fun tinkering with it and it does run like a raped ape, I can't wait to get it completely dialed in!

Checked the fuel pump today, diaphram looked OK but maybe leaking internally, check valve on pump from the oil/fuel mixing deal may be sticky.

What about gaskets and replacement valves for the fuel pump. Mercurypartsexpress only shows the diaphram kit as being available, anybody have a source for old merc parts?

So can one of you 2+2 owners tell me in some detail how your fuel line to carbs, inricher valve and accelorator pump is set up, I think mine has been changed, not necessarily for the better.