2005 700lx Mercury 90

[Moparman926]

I'm getting ready to start my 3rd fishing season with my Nitro 700lx, and I'm still struggling on prop and engine setup. The boat came with a 23P aluminum prop. I was able to get 44-45mph with gps. After talking back and forth with my local boat shop, I ended up buying a 21P Solas Saturn SS prop. With this prop at WOT I was pushing 5800 RPMs with myself and gear in the boat. The engine clearly says on the serial number plate Max RPM 5500. The guy at the boat store argued with me and said this was a 6000 rpm engine and it was good to run it that fast. Performance wise, the top speed dropped to 40 mph and hole shot was incredible. After running with this setup for 6 months, I ended up sending the prop to New England Propeller to add cupping. This dropped my RPM to 5500 at WOT and increased speed by 1 mph. I still don't feel like the boat is propped right. In my opinion I shouldn't have lost so much top end speed going to a SS prop. Also, the boat rolls really bad and pulls incredibly hard until I get it trimmed right. When I do get the proper trim, I have issues with porpoising if I don't keep my speed pretty high. I checked motor height and the cavitation plate is about in line with the keel.

Do you think my issue is the prop? Should I look at raising the engine? Or installing a jack plate? Right now the engine is mounted in the center mounting holes. At WOT, what should my max RPM be? I appreciate any help you guys can give me.

 

[Bill Willette]

I had a 2002 640lx with a 90HP mercury and mine came stock with a 23p aluminum prop. I switched to SS and I went with a 22p Laser II which worked out very well. Yes your boat is a bit heavier but 21p doesn't seem like enough so adding the cupping was probably a good idea if it brought down your WOT to correct. The 700 and 640 have the same transom and I want to say my 90 was also mounted in center holes and all was good. I wonder if I can find a picture to confirm mounting. I do remember the dealer stating that with a 90 on the 640lx I should get a 24p Laser II because the 22p would make WOT too high. I searched for information available on the web and somewhere read the 24p would be too much for the 90/640lx combo, giving a slower hole shot and incorrect WOT. The 22p worked out just right in my case. I know these things are expensive but if you are still thinking something is off, maybe look into the Laser II if its still available. The 22p Laser II lasted the entire 16 yrs I had the rig which has me biased for sure!!! Also - I think you are right on the 5500 for WOT, dealer number doesn't sound right for a 2005 2 stroke 90hp. My 640 did pull until trimmed just right. I didn't have a trim gauge but didn't seem to really need it, I just trimmed up until it stopped pulling. Good luck with your boat and happy fishing!

 

[Moparman926]

I may check into a 22P Laser II. I've seen some good deals on eBay on used ones. I'm just curious, what kind of top speed were you getting with your 640?

I've also been having issues with my trolling motor wires getting hot around the plug. The boat has the factory Motorguide 46, with factory wiring. I noticed the factory used 8 AWG wire. Everything I have read online says I should use a minimum of 6 AWG for that length of wire (16-17 feet). I'm considering replacing this with 6 AWG wire just to be safe. I also plan to upgrade trolling motors in the future, so the larger wire will give me more flexibility. I'm currently running 2 Interstate 27 Series Deep Cycles in parallel to power my trolling motor. This gives me plenty of battery life. The 46 seems a little weak to me. I'm considering either a 55 lb or a 24V system at 70 lbs. Since I already have the dual batteries, it would be very simple to switch from parallel to series wiring.

Any thoughts on trolling motor upgrades for this boat? Is 70 lbs too much thrust?

 

[Bill Willette]

I may check into a 22P Laser II. I've seen some good deals on eBay on used ones. I'm just curious, what kind of top speed were you getting with your 640?

I was around 48mph on the GPS, I want to say around 5300RPM. This was loaded with my normal gear and just me. With a partner it was lower, around 46mph. I looked on bassboatcentral as my numbers used to be there but I don't see them listed anymore. There are two 640lx with 90's listed there and they run 24p that I thought was too much and claim top speed over 50. I never broke 50 with the 22p but was certainly happy with 48 and my hole shot was good, maybe I overload my boats. I did kill my factory MG 46 at some point, I really did abuse it in shallow conditions. Its speed settings seemed either not enough or max was to much. You've added the extra weight already with the batteries & really up to you on 55 vs 70. 70 seems like a lot but if you have lots of wind or current it may make sense. I wound up replacing my MG with a Minnkota, I want to say it was 50 something and it worked out fine. Cheers!

 

[Robert haas]

With a ss prop you will have a better hole shot but not top end. I had a few flats boats and needed to get on plane quick.

 

[Matt Smart]

Hey guys, so I’ve been dealing with similar issue. My Nitro 700lx is 1998 with a 90hp Mercury. It came stock with a 23p and previous owner changed it to a Solas 13.25 x 17 and I’m lucky to get 38 mph and zero holeshot if water is in Livewell I have to empty it to take off. I don’t recall my rpm’s right off since it was August last time I was out in it. I’ve been told to go to a 4 blade spitfire. But by far more people say laser II is better... According to spitfire the correct prop would be a 17p for a 90-115 and laser I’ve heard 21-22p... I guess my question would be what is better? I don’t care about speed since I just sport fish. I want acceleration and plane out good. Also is 13.25 correct diameter?