Going Back to 2 Stroke Jet!

I've decided to stop wasting time and money trying to improve my Mercury 4S 40 Jet's performance with my boat to a point where I'm satisfied with it and am going back to a 2S. I'm planning to buy a used 75-90 HP motor and converting it to a jet since the new 4S factory jets in anything bigger than a 40 HP are so expensive, not to mention heavy. What I would like to do is find a Yamaha 90 2S since they are about the lightest motor going in that size. The problem with that is my boat has Mercury controls and I'm not sure I can do the electrical work needed to swap out the controls to Yamaha controls. I can do all the mechanical parts with no problem since I've done it before several times.

The boat is a center console and has binnacle controls and a separate start switch which makes it even more complicated. Of course, the easy way to go would be to just find a used Mercury 2S 90 which I might end up doing if I can't figure it out. I've already been quoted a price of over $1000 for parts and labor just for installing and wiring up a Yamaha control to my boat. :shock:

Anyone here done a control swap similar to what I'm talking about? Any advice would be appreciated.

Hey Larry, I have done many jobs consistent with replacing controls, mainly Yamaha's. That price is a little high but not by much. Yamaha controls and parts are expensive, but they make a good product.

if I were to buy your parts to rig your boat with all new controls fit to a Yamaha 2 stroke 90 it would be roughly 685.00 (my cost) before shipping. If your married to binnacle controls, stick with the 704 series, this gives you the ability to plug and play with all the components. basically you plug everything in to the appropriate terminal hook up you shifter/throttle cables and go, no wiring necessary.

I can give you some suppliers if you'd like to tackle it yourself, its not hard at all.

I would appreciate it. I would like to stay with binnacle controls. The price of labor I was quoted was 4 hours at $95 per hour. Surely it wouldn't take 4 hours to hook up the wiring if I did the other installation work.

No way it should take 4 hours, I pm'ed you the info. Good Luck.

Appreciate it.

Found a 2007 Yamaha 70hp 2S (prop) on eBay. It's a little overpriced according to NADA, but not bad. Thing is, even though it's rated 70hp, it has the same size motor as both the 60 Yamaha and the pre-98 60/40 Merc 2S (51.8 ci). I can't help but wondering if there is actually a noticeable difference in the 60 & 70, especially after being converted to a jet. I still want to try to find a 90hp Yamaha 2S to convert, but I can't help but wonder if the 70 would be worth considering. Any thoughts?

I know there are a few people here running Mercury jets with the 51.8 motor. Do they perform as well as the 59 ci motor used in the 98 t0 05 Merc jets?

The 70 won't be much improvement over a 60 yamaha the main difference is I believe they just had larger carbs maybe a different exhaust tuner kind of like the difference between a 60 and 70 3cyl evinrude/johnson the 70 has a slight edge mostly up top it might be able to spin the impeller a little faster netting in a slight top speed gain hole shot will be similar. Go with a 90 if you want a marked improvement. You can find omc 4cyl 90-115 pretty cheap too they were pretty good engines as well. They are heavier than a yamaha 90 but the later 4cyl omc engines went up to 130hp so they put out a decent bit more power. The yamaha 90 2s is a great engine one of the better power to weight ratios out there. The plus to the omc 4cyl is a decent number came as factory 80-90hp jets so one that's already a jet might be easier to come by. No matter what brand you go with go with a 90 that way you really see a difference they turn much larger impellers than any 60-70hp engine which most of which spin a 6 7/8" impeller. The bigger impeller is what will really make noticeable difference. The 4cyl omc's have their down sides fuel consumption being the biggest down side and some issues, but they are pretty good engines and can usually be had for cheap. The merc 3cyl 90hp 2s were pretty good engines as well. My point is be it merc 90, yamaha 90, omc 90-115 they can all be good engines. with older engines what will make the bigger difference is if they were cared for or left to just sit all the time.

Pretty much my own thoughts, Andy. I'm keeping a look out for OMC and Mercury 75-90 horse 2S as well as the Yamaha 90's. It would be nice to find a factory jet, but I doubt that I would be that lucky.

I'd be all over an older Merc 90/65 if I were you. What about a 90 or 115 Opti?

redrum said:

I'd be all over an older Merc 90/65 if I were you. What about a 90 or 115 Opti?

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I'm looking at a couple of Merc 2S 90's. Haven't had any luck finding a 90/65 jet though.
Used Optimax motors in the mid-range sizes are almost impossible to find and Mercury doesn't make them in anything less than 200hp anymore. At 375 lbs, hey're also heavier than I would want to put on a 16' boat.

LarryMc said:

redrum said:

I'd be all over an older Merc 90/65 if I were you. What about a 90 or 115 Opti?

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I'm looking at a couple of Merc 2S 90's. Haven't had any luck finding a 90/65 jet though.
Used Optimax motors in the mid-range sizes are almost impossible to find and Mercury doesn't make them in anything less than 200hp anymore. At 375 lbs, hey're also heavier than I would want to put on a 16' boat.

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55" wide boat will handle a heck of a lot of weight. Its all in what you are comfortable with for sure. A 90/65 Merc would be great. Does your boat have a tunnel? My friend has a Lowe 1655 and his came factory with a jet tunnel.

Mine doesn't have a tunnel.

crap no tunnel that thing outta fly I thought it was a 18ft boat you had. My 1554 which is a heavy one the 70hp evinrude is just right. I wish my boat was a 18ft wouldn't be faster but would plane a heavier load out easier might lose a little top speed but from what I've seen with 60/40 boats the 18 footers aren't that much slower than 15-16ft ones when you have a load in them of a couple guys fishing or hunting. The 16 footers if loaded light and built light are way faster but I'm usually more concerned with drafting less while drifting and getting on plane quicker.

Larry,

The swap is easy. That being said, I know where a Yammie 90/65 jet is located, and the guy will ship it if you want. I will PM you the details.

That being said, a 4 cylinder OMC 90hp is 92 cu in!!! Thats a screamer! They go up a block size from 75hp -90 hp, unlike yamaha who uses the same displacement engine for their 60-70hp motors (52 cu in). The step up the the 75hp is where its at, the block is 70 cu in. Many of the Merc 70-90hps are 71-84 cu in blocks. Just depends on how much weight you want to carry, but those 3 cylinder Yammie 70hps are a little low on the displacement side for a 70...........

Update to this thread. I am still in the process of switching back to a 2S motor for my Lowe 1655CC. Since I already have Mercury controls, I decided to go the easy and considerably less expensive route with a rebuilt 2005 Mercury 90hp 2S from Outboards Unlimited in Astor, Florida. The owner let me buy it without the prop lower which saved me a little money. I ordered a Jet lower from OBJ to fit the motor, but was disappointed to find that they had about a four month order backlog. I contacted the Jet Doctor in Ellington, Missouri and found that they had a new jet kit in stock that would fit a Mercury 90hp 2S motor other than having the wrong shaft. They offered to get a new shaft from OBJ and sell the kit to me for the same price as OBJ. I took them up on the offer which cut my waiting time down to about three weeks and cancelled the order to OBJ. The motor is supposed to come in this week and the jet kit should be here in about two more weeks.

I considered having my transom raised to fit the longer shaft of the 90hp motor, but instead opted to install a Heavy duty Versa-Jac jackplate with a 4" setback from Bob's machine shop. I figure using a jack plate will make it easier to fine tune the motor height. The jack plate has already been delivered and I bought a new water pump kit to install on the jet lower.

So waiting for the motor and jet kit is where I am right now.

Also still need to sell my 2016 4S Jet 40 to ease the financial pain a bit. :mrgreen:

Cool, be interested in seeing the performance of the 90 on your hull, basically the same as mine only mine has the tunnel.

dearl said:

Cool, be interested in seeing the performance of the 90 on your hull, basically the same as mine only mine has the tunnel.

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Probably be a while before I get it done, but will definitely post the performance numbers.

Going to be a little longer than I anticipated. The motor came in and I immediately discovered that it's not a good idea to buy a 12 year old used outboard from Florida sight unseen. I didn't expect a new motor, but I did expect that someone rebuilding a powerhead would pick a motor in fairly good shape. I was wrong. I could not believe the amount of corrosion on the motor. :shock:

I sent it back the next day. Luckily, the seller didn't give me a hassle about sending it back and he was good enough to pay the return freight and refund my money. So I'm out the original freight costs and back to looking for a Merc 90hp 2S.

I have bought three new jet boats thru the years from the jet doctor, I live close to Ellington. Blazer boats are made in Ellington as well. Anyway, you might ask The jet doctor about a motor, he might have one or know where there might be one. I also would suggest joining the Facebook page semojetboatenthusiests, you may already be a member, but if your not, lots of people selling motors and stuff on there, most already setup with a jet. If the jet doctor doesn't have a motor your looking for, you might try current river marine in Doniphan, West boat shop in Winona, Luttrels boat sales in Bunker, and I don't know name of the shops, but there are two boat shops in Van Buren that might have a motor, I want to say ones name is Holts and the other is Reds. You could call Blazer boats, they could tell you the names of the dealers in Van Buren, they sell boats to both places. All those places are in Missouri. I would think one of those places would have what you are looking for. Hope this has helped. Good luck.


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Thanks!