Mercury 175 slower than expected?

**Baker343** · 08-27-2021, 11:09 PM

Love these years of the 2L. Exhaust chest and dump was opened way up by mercury. Built for top end back in the day.
These motors can take a beating with the block built around the steal sleeves. We run these 40 plus year old blocks over 7k in roundy round races and just under 7k for 4hrs running Enduro's.
Compression looks good. Check all your ground connections especially your coils.
My guess would be the carbs. If original, I think they came with foam type floats. If one or more of your floats are heavy or out of adjustment your carbs might be puking fuel out the emulation tube and getting sucked back into the intake causing you to run fat. Floats could be breaking down and soaking up fuel and messing with your fuel level in the carbs. If your still running the stock air box, remove it and start it on a hose and see if it's puking.
Awesome and simple motors that still have a lot of potential to rip, even being in their 40"s.
Compression, spark/grounds and carbs

Listen to Tlwjkw he's been beating on these first and second generation motors for a long time

**johnboy 88 vegas** · 08-27-2021, 11:31 PM

Originally Posted by mrichartz

Which that guy mistook for omc motors ? They need WOT in gear unload at rpm... Thats omc.

Why just OMC? Bout 8 years ago watched another mechanic rebuild a motor three times because of a bad idle box advancing the timing and burning up pistons on a stock 200 Merc. The timing was going off the chart on the flywheel once the motor was up and running. I'll take the wot at the boat ramp to be sure with a timing light on Merc or OMC after a rebuild or any changes to the electrical system.

**Baker343** · 08-27-2021, 11:43 PM

I don't believe the early 2L had timing advance modules.
Could be wrong

**tlwjkw** · 08-28-2021, 04:07 AM

Originally Posted by Baker343

I don't believe the early 2L had timing advance modules.
Could be wrong

yeah, they've been on tha V6 since its '76 show up time.. jus took some time for guys ta figure out they sucked.. called 'em "idle speed control"... took 'em (merc) a few years ta figure out that "stabilizer" sounded better.........

**Glastron1987** · 08-28-2021, 07:23 AM

Did you check the plugs after a hard run to see if one of the cylinders is at fault? Could be electrical or fuel.

**blackmaxonly** · 08-28-2021, 12:04 PM

Thanks for all the responses guys! I just did some electrical tests with the voltmeter and the stator / trigger / coils all were within spec of ohms (I dont have a DVA to do 'proper' measurements). My model does not have an idle stabilizer, maybe the previous owner removed it but there is no indication of one ever being on this motor. They do have the original foam floats, so I will order those after I try another new set of plugs. I will get a fresh look at the plugs after a hard run and see if there is an indication of anything. I will also run it with the airbox off to see if fuel is coming back out! Will keep you guys updated when I get around to it again on sunday

**mrichartz** · 08-28-2021, 12:34 PM

Originally Posted by johnboy 88 vegas

Why just OMC? Bout 8 years ago watched another mechanic rebuild a motor three times because of a bad idle box advancing the timing and burning up pistons on a stock 200 Merc. The timing was going off the chart on the flywheel once the motor was up and running. I'll take the wot at the boat ramp to be sure with a timing light on Merc or OMC after a rebuild or any changes to the electrical system.

I didnt say just omc.. but omc definitely have to be because unload wot they can pickup over 4 degrees of timing...I haven't worked on a merc in years so i dont remember exactly why but for sone reason they dont need to be... BUT im not commenting on the timing or giving advice on mercs.. And like baker said Tlwjkw been running these and knows..

**Whaaaaat** · 08-28-2021, 01:00 PM

Anybody know why omc would spec this. I'm curious. I can't think of a reason timing would change from loaded to unloaded unless some part of the crank was made out of gumby rubber.

**mrichartz** · 08-28-2021, 01:08 PM

Originally Posted by Whaaaaat

Anybody know why omc would spec this. I'm curious. I can't think of a reason timing would change from loaded to unloaded unless some part of the crank was made out of gumby rubber.

Its electrical not mech why.. I honestly cant/dont remember.. to be honest i vaguely remember but not positive so...
I will say that when i use all digital cdi 8500 rpm it doesn't happen...
BUT I WILL STILL check under load every damn time to much time and $$$ not to.
Why i cut props up etc to make it easier

Not really helpful but

**blackmaxonly** · 08-30-2021, 10:08 AM

Hey guys, as promised on Sunday I ran some more tests and got a couple of videos:
#1: Video of running
#2: Closeup of fuel line
#3: Water stream on top of engine?

I also retook compression on all cylinders (cold) and they were higher than I mentioned, the lowest is 111 and the highest is 117.

#1: The first video may be an indicator to someone if they have a better trained ear / eye than I do. I confirmed there is strong spark at all 6 cylinders
#2: Would this amount of air cause the issues I am seeing? The fuel lines are brand new, including a new filter and pump ball. The air is coming in from either the ball, which is the 2nd new one Ive tried, or from inside the fuel tank itself, which I am not sure how I would end up fixing.
#3: As a bonus maybe someone can answer this: Where is the water line from the top of the engine supposed to run to? It is NOT on the water flow diagram in my manual, and came without any tubing connected. You can see I ran some tubing to just below the cowling for it to drain to, it is a strong stream. The telltale does not work unless the engine is at temp.

I did not have any fuel puking from the carbs when I took the airbox off.

**David - WI** · 08-30-2021, 10:15 AM

3. to the water pressure gauge on your dashboard.
2. the air itself doesn't hurt anything... the carb bowls are vented and floats / needle & seat will keep them full BUT it looks like you have a leak in the suction line somewhere; so you might not get enough fuel flow at WOT?
1. sounds normal to me.

**tlwjkw** · 08-30-2021, 10:28 AM

another thing ya might wanna check.. night time, remove cowl and run it while ya take a long screw driver and run it along spark plug wires ta ground.. try it with all wiring..

**mrichartz** · 08-30-2021, 10:50 AM

Yea if those are the old plug wires.. x2 on checking at night
I would change them either way if they are old
Need to find out why your sucking that much air in the fuel line most likely a cracked line.
Its amazing how SOMETIMES its just something small.

**mrichartz** · 08-30-2021, 11:13 AM

Oh do you have a water pressure gauge hooked up yet?
I would get that hooked up too sooner than later.. you never know... Easy enough to do since its already in the block.
The plug wires if they are cracked or leaking they could be fine while sitting there checking but when you start moving (driving it around) the cracks in the wires will start leaking and losing spark..

**blackmaxonly** · 08-30-2021, 11:22 AM

I will try at night to see if there is an issue with the wires. They were replaced in 2016, as well as both switchboxes. While cranking there is a clean jump across 1/2 gap from my tester on all wires. My hull does not have a water pressure gauge - should I install one or can I just cap off this water flow? I plan to get a small 6gal tank and try to see if there is any air in the line after that, as I have traced it to be before the primer bulb

Thanks for all the great information and stuff to test