I changed the motors last month myself from old 1988 merc 135s to 1996 Suzuki 140s that I got a super deal on. I got all the bugs worked out on the hose recently and finally made the trip to the ramp today. They run outstanding but are turning WOT 6000 rpms and only pushing the boat 37mph. The old merc 135s turned less and pushed it 40mph. The service manual says the max rpm range is 5400-5700. The prop is a 18P, if I take the pitch up to a 19 or 20, I know it should drop the RPMs into the proper range, but would it slow the speed or increase it? Would it burn less fuel also.
Thanks
Rick
depends on how much load is in the boat. are you looking for top end speed or hole shot. different brand props make a difference sometimes too. Prop cuppin is something to keep in mind also. If you go from an 18 pitch to a 19 would probably be perfect for you. speed he boat up a little and fuel mileage will depend on how much throttle youll have to use
197 poineer F150
I’m thinking Chris might want to chime in on this. He would need all the info on the boat to offer some insight and solve the issue. Good Luck and I wish you well.
GW 232GT Gulfstream
150Yam x 2
“3rd Day”
Gen. Chap.1 Vs.9-13
Are you running the same prop on the Zukes as with the Mercurys? If it is the same prop, then my initial guess is that the Zukes have a higher gear ratio in the lower unit so it is like driving a car in 4th gear instead of 5th gear on the highway. HP is HP so you should be able to achieve the same speed. You definitely have room to improve your speed by adding pitch and bringing WOT rpm down to where it should be. A 19 or 20 pitch, depending on model, will get you where you want to be…more speed and probably better fuel economy at cruise speeds.
Iain Pelto
Edgewater 185CC “Jumpin’ Bean II”
Native Manta Ray 14
I would go with a 20 pitch, 6000 is over max rpms. one pitch = about 200 rpm drop so you should still be at max rpms range (5600)
26’ Twinvee
Suzuki 175’s
www.creeksidemetalworks.com
Thanks but i found a mistake in my post. My son told me my props were 18P but I just went and looked and the last three of the serial number on them are a 20P. I think they are 20 pitch. Should I go to a 22?
Rick
Your speed seems really low for using a 20P and turning 6000 rpm. With that set up you should be running mid 40s with around 15% slip. I think you have more issues than getting the pitch right; see this post regarding more blade area/diameter to reduce slip.
http://old.charlestonfishing.com/forum/topic.asp?TOPIC_ID=95417
Iain Pelto
Edgewater 185CC “Jumpin’ Bean II”
Native Manta Ray 14
Also, what is you motor height set at?
Iain Pelto
Edgewater 185CC “Jumpin’ Bean II”
Native Manta Ray 14
I am real confused now 
The motor is in the second hole. The cavitation plate is almost level
with the bottom and about where it was with the old motors.
I also think I should easily be in the 40s with a 20P at 6000rpms and twins.
Rick
Rick
23 Center Console
Twin 135s
“Dirty Money”
Happy to say that i have these babies “dialed in”.
Local prop shop hammered them up about 1 1/2 pitches and added cup.
turning 43mp at 5400rpms.
PS. I also fixed my tach problem from an earlier post.
A few more test runs inland and I will be ready to split an inlet open.
Rick
I sold them for $1000 with harness, dual binnacle and gauges and SS props to a guy in NC and they were running strong.
There are some good deals on motors out there if you look and post what you are looking for on several forums.
Rick