Wrong Prop, bad tach or both ?

[greasemonkeyjmj]

steelespike, I pulled one of the main jets and it is a 45D the jets in my old carb is a 50D

 

[greasemonkeyjmj]

Additional info, i was looking at pictures of before i pulled the engine for the rebuild, when i reinstalled the engine, i mounted it as low as it would go, it was originally in the nex to the bottom hole.

 

[steelespike]

Any jets I've checked were simply marked in thousands. Can we assume a 50D is larger than a 45D?
I don't think lowering the motor would affect your rpm that much. Wouldn't hurt to raise it if you had no ventilation issues.
Your numbers still don't add up.I don't think it is the ultimate problem but we may want to manually check the gear ratio.
We feel the new tach is accurate,9" pitch,13 mph,3500 We are assuming 2.42 ratio with the tach being accurate
The next suspect is the ratio. We need our calculations to make sense 13 mph calculates to negative slip.
A numerically lower ratio would calculate to a more normal slip.
Pull the plugs and turn the motor by hand count motor revolutions to one prop revolution

 

[greasemonkeyjmj]

I will do that this afternoon, Thanks Steelespike, and on a positive note, a friend gave me a complete 50 Evinrude, here to hoping that it is a year model that will give me the correct lower to put on my engine. He believes it to be a mid 80's model

 

[greasemonkeyjmj]

well guys thanks for the help on this, But I think i am at the point to where it is best to throw in the towel and cut my losses. raising the engine and swapping the jets made no change at all. On top of that, now the engine is running rough at sounds like a totally different engine than it did yesterday. i checked the compression its at 148 on top and 135 on bottom. looks to me like a internal problem brewing.

 

[greasemonkeyjmj]

I just wanted to give a update on this post , I bought a used 70 Horsepower Evinrude and put it on in place of the 48 SPL and solved my problems, but I was lying in bed and thinking about the 48 last night and a thought popped in my head. So today I pulled the upper carb off of my engine and rounded up the original carb from my engine. I measure the throat at the rear of the carbs, my original is 1.5 inches across, or 38MM, the carbs i was running measures 1.2 inches or 31mm across,.

 

[steelespike]

Like it's maybe from a smaller motor.
You want to give us your present numbers to see if we can fine tune your setup.

 

[greasemonkeyjmj]

Thanks steelespike, but right now I am going to keep running the 70 and keep an eye out for a replacement Carb for the 48, once I find one, then I will decide if I am going to keep the engine, or sell it.