Mercury 1750 '76-77 Timing?

**SWA91** · 07-05-2021, 11:13 PM

I am at my wits end with my '76 Mercury 175hp and could really use help from the experienced. I have no top end power above 4000 rpm however great low end torque. At 4000-4200 is max RPM and I can feel that it's just not smooth until I back off to around 3800 or less which then runs great.

All electronics (coils, stator, switchbox, trigger, rectifier, wires plugs) were replaced with new during the rebuild (bored '.015), carbs were gone through 3X to insure no issues, jetting @ .076/78 as per service manual, 4-5lb psi on fuel (new pump diaphragm), confirmed spark is good at 7/8" gap, CCM reeds, proper break-in schedule followed. Running a 21" SS 3 blade prop or 4 blade 21" aluminum on a 18' CeeBee Avenger which both ran @5400 prior to rebuild.

What is odd to me is the timing per the Merc service manual which is 15` BTDC for the '76-'77 and is where I am set. (Lync and sync confirmed, TDC identified with dial indicator on #1 cyl)

I am hesitant to advance the timing any more to 18`-22` which is where most of the earlier model 2.0/2.4/2.5 Mercs are at.

So my question to this group is:
1) What could cause the lack of top end power/RPMs issue?
2) What would I be risking if I were to advance timing to 18 or 20, would I gain RPM's?
3) If spark gap is strong (fire), plugs and top of pistons look good (fuel) with thumb sized wash on exhaust and intake, what else would keep the RPM's from reaching 5000+?

**faztbullet** · 07-07-2021, 05:07 AM

What series carbs??? Sound a bit rich for a 2L

**SWA91** · 07-07-2021, 10:18 AM

Faztbullet...these are WH-1's which were on the motor previously and worked great. Even now, piston wash is near perfect. The jetting wasn't changed and is per the book. .078 on #1&#2, .076 on #2 thru #6 (if I remember correctly).

**Capt.Insane-o** · 07-07-2021, 07:45 PM

If this isn't a heavy boat 25 degrees on those motors is fine.

**Capt.Insane-o** · 07-07-2021, 10:26 PM

If you went through the carbs with aftermarket parts over the past plandemic year I have been having a REALLY tough time with aftermarket needles and seats.

**SWA91** · 07-07-2021, 10:53 PM

Capt. I was able to re-use the floats, needles, and seats all looked good. I replaced gaskets and seals only for the rebuild. I hear you on the the parts. I bought new Sierra needles for another carbed motor and definitely could see the difference in height difference of the hangers.

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I lack experience with timing a 2 stroke...why would the book say only 15` BTDC for max timing and the motor wont get the RPM's. Im hesitant to move up to 25 but can certainly get it in the water and slowly advance timing.

**nitro_rat** · 07-08-2021, 10:54 AM

I usually replace the bowls on those early carbs with the late style and drill for the primer system and ditch the choke flaps. Makes cold starts much better. The old orange foam floats will dissolve in ethanol if the orange coating gets damaged. The newer bowls and plastic floats eliminates that possibility! There's a post on here somewhere that I made that details the conversion...

**silverfox** · 07-08-2021, 11:39 AM

SWA91
I looked in the manual and the timing for the vertical valve 175 is 18 degrees but 20 degrees at cranking speed. Your jetting is correct according to the manual. I didn't see anything in the manual for 15 degrees.
Bill Hoch

**SWA91** · 07-08-2021, 11:50 AM

Nitro_Rat…the floats on these WH1 carbs are plastic, may have been switched out before me? Although I have no starting issues, I hear you on the primer/enrichner solenoid. I have this on another motor with WH-31 carbs and it makes starting easier.

**SWA91** · 07-08-2021, 12:47 PM

Bill…you are correct on timing for the ‘78 and newer but the ‘76-‘77 is 15* BTDC “one punch” on the flywheel. I’m now second guessing my carbs, (even though piston wash is near perfect) so I’m gonna through these again to insure proper flow. Then I may mess with the timing.

**silverfox** · 07-08-2021, 12:52 PM

SWA91
Was is the serial number on your motor? I still haven't found that 15 degree timing yet.
Bill

**SWA91** · 07-08-2021, 01:31 PM

Silverfox....this is a 1976 1750 #4303623 ELPT. Service Manual # 90-86133-3, Section 2, Part C, Page 1

All stock except all the cylinders bored .015 with ProMarine pistons and CCMS reeds.

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**silverfox** · 07-08-2021, 02:39 PM

I learn something new everyday. Even though my manual covers the 175 vertical reed it only goes back to the ser #4838074.Thanks for the update.
Bill

**99fxst99** · 07-13-2021, 12:06 PM

Make sure the carbs are opening.....voice of experience here......on a 1976 175!

**SWA91** · 07-13-2021, 03:42 PM

99fxst99...when you say "carbs are opening", are you referring to the butterflies or something else? Carb sync is good but then again, you never know if something came loose. I had planned to pull the carbs off once more and go through them, making sure nothing is gummed up. Even though my stator is fairly new, I'm planning to confirm with my DVA just to make sure Im getting the correct voltage on the high side. I just learned my regulated rectifier (CDI 193-5114) is getting extremely hot when running, even at idle, and wondering if my stator is causing all these issues. Ground is all good everywhere, double checked last night and battery is fully charged with a good connection.

I can't think of what else could be causing my issue of no HP after 4200 RPM's.