jslu
Seaman
- Joined
- Jul 31, 2010
- Messages
- 74
1987 35 HP MERC Serial No. 0B111943
The above serial no. appears on the transom bracket which I recently bought for cheap money, basically in good condition.
I've kinda focused in on these 1980's vintage 35 Mercs as a way to enjoy my retirement by bringing them back to life with a very marginal profit, mostly just for fun. I currently run one of these 35's on my 15' fiberglass Starcraft Select 150.
However, it did not take me long to figure out that the serial no. as mentioned above has had a powerhead swap and is now featuring a 1983 40 HP, aka M40. i'm OK with this.
My question is this.------My Merc Manual covers both of these powerheads and it is puzzling to me why both engines have the same displacement (33.3 cu. in.) but yet develop their horsepower at different RPM. Strangely the 40 HP (M40) is rated at 5200 to 5500 RPM, 35 HP (M35) is rated at 5400 to 6000 RPM, both at full throttle. Seems reversed.
The only difference I see is the timing data as stated in the timing decals on each engine, pictures enclosed.
Just curious. Is this really a 40 HP powerhead??
Thanks,
John
Is this timing difference enough to make the extra 5 HP or did methods of HP rating change somewhere around 1984? The carbs look the same relative to main jet size. The carb vent jet on the 40 HP is .002 larger???
Different fuel qualities or requirements??
The above serial no. appears on the transom bracket which I recently bought for cheap money, basically in good condition.
I've kinda focused in on these 1980's vintage 35 Mercs as a way to enjoy my retirement by bringing them back to life with a very marginal profit, mostly just for fun. I currently run one of these 35's on my 15' fiberglass Starcraft Select 150.
However, it did not take me long to figure out that the serial no. as mentioned above has had a powerhead swap and is now featuring a 1983 40 HP, aka M40. i'm OK with this.
My question is this.------My Merc Manual covers both of these powerheads and it is puzzling to me why both engines have the same displacement (33.3 cu. in.) but yet develop their horsepower at different RPM. Strangely the 40 HP (M40) is rated at 5200 to 5500 RPM, 35 HP (M35) is rated at 5400 to 6000 RPM, both at full throttle. Seems reversed.
The only difference I see is the timing data as stated in the timing decals on each engine, pictures enclosed.
Just curious. Is this really a 40 HP powerhead??
Thanks,
John
Is this timing difference enough to make the extra 5 HP or did methods of HP rating change somewhere around 1984? The carbs look the same relative to main jet size. The carb vent jet on the 40 HP is .002 larger???
Different fuel qualities or requirements??
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