1978 Merc questions

[redneckpunk]

I took a break from my resto today to pull the boat out of the garage, gather some info on the motor, fire it up and do a compression check. I bought the boat and motor last year and the motor has had me stumped a bit. The boat is a 1993 that has been repowered with an older o/b. There is no serial # plate anywhere. The wrap around cowling says 1150. The stickers on the lower unit say 1500. Under the cowling is a sticker that say 1978 and gives specs for 1150 and 1400. I cannot find any other numbers.

So here's what I've got for compression (1-6);
132
130
135
135
135
140

so here are some of my questions. are these comp numbers within a reasonable range? Next question is about the prop. The boat is a 19ft deep v dual console aluminum fishing boat dry weight listed at 1300lbs. Last year with just two adults in the boat at sea level WOT the RPMs was only 4400 with top speed of 32mph. I'm not looking to have a speed boat so mph isnt biggest concern, but I do know these motors usually WOT around 5000-5500rpm. The prop is an aluminum 13.25x17. My understanding, which may be completely wrong, is that for every drop in pitch (ie 17 to 15) I should gain about 400+/- rpm. is this correct? My other concern is I certainly dont want to lose too much "hole shot" because currently its on plain almost instantly.

Any help, comments, or suggestions would be greatly appreciated. I've received differing opinions while speaking with fellow fisherman, including changing pitches and changing diameters, but I think I trust the experts here as iboats forums hasnt failed me yet and has been the inspiration and tutorial source for my resto project

~RNP

 

[Chris1956]

Re: 1978 Merc questions

Compression is good. If you are sure tachometer is accurate, you may be overpropped. Does motor have PTT? If so, trimming may help with max RPM. I would think a 17P prop would be pretty close to optimum for that boat.

There was no Merc 1500s built in 1978. 1977 was last year for 1500. 1400 and 1150 did exist in 1978. Post serial number and someone can tell HP for sure.

 

[redneckpunk]

Re: 1978 Merc questions

Compression is good. If you are sure tachometer is accurate, you may be overpropped. Does motor have PTT? If so, trimming may help with max RPM. I would think a 17P prop would be pretty close to optimum for that boat.

There was no Merc 1500s built in 1978. 1977 was last year for 1500. 1400 and 1150 did exist in 1978. Post serial number and someone can tell HP for sure.

thanks for answer. wish I could post serial # but there isnt one anywhere I can find. The plate has been removed and dont know where else to look.

 

[Chris1956]

Re: 1978 Merc questions

look for freeze plug with serial number, on block. Post part number of block. Look on transfer cover side of block, about 1/2 way up.

 

[redneckpunk]

Re: 1978 Merc questions

Thanks for the replies.

Still looking for numbers, but no luck so far. However, I got her out on the water for a shakedown this past sunday and was pleasanlty surprised. I topped off the 39gallon tank and added a can of Sea Foam on the way out of town. At the beginning of the day she was running much like when I garaged her last fall. However, after several hours of some fairly hard running she was turning 4800-4900 RPM and between 35-37mph. I also noticed just before launching a slight "bend" in one of the prop blades and a small "nick" in another. I will be picking up a new prop, same size, soon to see if theres a difference. However, for the age of the motor and size of the boat I;m thinking she's doing very well.