TOPIC: Whats the Max RPM and Rec RPM for a 1975-76 1500?

I'm starting to do some research on Props, and need to get the specs on the merc 1500. I thought my motor was a 76 but the decals suggest it is a 75.

Now that I have a working tach, I can get some useful info.

about 4800-5400 recomended max only my opinion 6000

The Mercury Manual states 4800-5800 RPM for the 1500. Like Dave said up to 6000 RPM is still pretty good and a LOT better than lugging it down under 5000 RPM. I run mine at 6000 RPM a lot and it performs nice at that RPM.

Amigoid wrote:

I'm starting to do some research on Props, and need to get the specs on the merc 1500. I thought my motor was a 76 but the decals suggest it is a 75.

Here's a chart with serial numbers so you will know "FOR SURE"
It's for 1968-1996 115-150 HP Outboards

www.raylinrestoration.com/BoatStuff/Technical/MercuryModelID.htm

I also have LOTS of technical stuff uploaded for both Merc and JEGO outboards, painting/repair tips, Gauges, wiring diagrams.... etc

HERE: www.raylinrestoration.com/BoatStuff/Technical/technical_information.htm

Ray

I run my '77 1500 at a constant 6000 with max timing at 20 BTDC with ethynol 92 octane and 50:1 AMSoil.
I run my '87 115 to 6300 constant - BUT no,...I don't recommend it.
My formal recommendation for both would be 57-5800 with a maximum wide open throttle timing set at 20 BTDC on any inline-6 built after 1970. (or in other words,...Any with direct charge pistons)
Proper oil and the best gas you can find at a proper ratio with periodic use of a de-carbonizing agent to keep the rings and domes clean is critical.
If you compression readings aren't good or you don't know the true condition of your rings and domes I would red-line at 56-5700 and mix 40:1 AMS or Quicksilver semi-synthetic.
I strongly recommend installing a fuel filter/water separator with a clear bottom section and petcock and monitor it very frequently when running today's ethynol.
Install the filter between the prime bulb and the engine.
(others may suggest install between the tank and the prime bulb, but between the prime bulb and the engine is what was recommended to me by several CMTs. (Certified Marine Technicians)
I also recommend use of Star-Tron or Stabil Marine and a decarb agent like Sea Foam or OMC Engine Tuner.
Star-Tron or Stabil Marine (blue fluid not red) every tank and de-carb every other tank of fuel mix.
These old beasts will perform very well when properly cared for.
Impeller replacement every year or two max is critical due to the crummy design of the impeller.
Thom

Dr_Frankenmerc wrote:

I run my '77 1500 at a constant 6000 with max timing at 20 BTDC with ethynol 92 octane and 50:1 AMSoil.
I run my '87 115 to 6300 constant - BUT no,...I don't recommend it.
My formal recommendation for both would be 57-5800 with a maximum wide open throttle timing set at 20 BTDC on any inline-6 built after 1970. (or in other words,...Any with direct charge pistons)
Proper oil and the best gas you can find at a proper ratio with periodic use of a de-carbonizing agent to keep the rings and domes clean is critical.
If you compression readings aren't good or you don't know the true condition of your rings and domes I would red-line at 56-5700 and mix 40:1 AMS or Quicksilver semi-synthetic.
I strongly recommend installing a fuel filter/water separator with a clear bottom section and petcock and monitor it very frequently when running today's ethynol.
Install the filter between the prime bulb and the engine.
(others may suggest install between the tank and the prime bulb, but between the prime bulb and the engine is what was recommended to me by several CMTs. (Certified Marine Technicians)
I also recommend use of Star-Tron or Stabil Marine and a decarb agent like Sea Foam or OMC Engine Tuner.
Star-Tron or Stabil Marine (blue fluid not red) every tank and de-carb every other tank of fuel mix.
These old beasts will perform very well when properly cared for.
Impeller replacement every year or two max is critical due to the crummy design of the impeller.
Thom

What the man said!
(although my boat came with the water separator between the (belly) talk & the bulb which is in the engine well, I haven't had a problem as far as I am aware??)

Thank you for the advice. Could you please recommend a good compatible fuel/filter water separator? I have a regular fuel filter in line before the squeeze bulb right now.

Impeller was just replaced, as part of a flat $150 lower assembly lube. Now I need to find the correct water pressure gauge (need 0-15psi instead of my current 0-30/35

I run a Racor FF/WS unit, but Frank found the same unit at NAPA for less money! Spin on 2 micron filter and a clear bowl on the bottom with a petcock to drain any water. You can go to NAPA online and search Water Separator to find them.

I was going to retitle the post "Its the end of the world and you know what? The Merc runs fine..."

Took it out to the lake this weekend!
Keep in mind this is at the Cherry Creek Reservoir in Colorado, mile high elevation.

WOT Max RPM was around ~5500 rpm and Max speed was ~40mph, using a traditional water pressure speedometer, not a GPS. Manually played around with the trim to get it just before the point it starts porposing. 15p 3 bladed cupped aluminum prop. 18 Fiberglass nordic with 2 adults, 1 teenager, and a dog.

Lake conditions were windy and cold, but I was able to make some speed runs along the dam where the water was smooth.

It choked out and died a couple times when I tried to aggressively accelerate. Cruises comfortably around ~30mph with ~4500 rpm.

I have a Racor water/fuel separator on order, will replace the current fuel filter with this unit as soon as it arrives. marinefilters.net had it for $58 so I ordered it online. No local stores stock it, and their price shipped from their warehouse was $98.

The throttle will not hold position at WOT, I have to hold the trottle down, or it slides back to a crusing speed. The water pressure gauge needs to be swapped for a 0-15psi instead of the 0-35psi I have now.

Okay, couldn't resist.
Hey if its the last day, I'm grabbing the family and heading to the lake.