mine has the squared off tunnel with the overhanging flared backset transom....make sense? it looks like the transom was moved back from the "normal straight across" position with angular sides to make it act like a built in jackplate....sets back about 10" or so if I recall correctly.

I had a 93 with the flat transom. From talking with others, the flat transom performed better than the setback transom.

Cajunyoung we have the same boat then! they are not known for speed at all! but they are very stable and get pretty shallow... Id say you will run in the upper 30s with with a new 40 4stroke... just a guess of course... The flat transom marshrunners were def a faster boat.

Those marshrunners are heavy boats. If I had to guess, mid 30's. Anything more than that is a bonus. You may wind up turning a 14 pitch prop. That motor with a 14 will get on plane in about 10' distance and hit the rev limiter within 50 yards. You could go to a 15, hole shot will suffer. You may need to do like most of us do, have a river prop and a marsh prop. These units have a 2.08 gear ratio, that usually means that they turn 1" pitch higher than the old 40's and 50's we used to run, they had a 1.93 or 1.95 ratio.
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I always thought that it seemed a little slower than it should be but i have been very happy with it. For the size, its the most stable boat i have had, love that i can stand on the edge of the deck and not have it rocking on me. Thought about selling it a few years ago, but decided to keep it and rebuilt the transom myself. Just thinking about maybe putting a 40 on it now since Lacassine allows it.

[QUOTE=CajunChristian;741003]Those marshrunners are heavy boats. If I had to guess, mid 30's. Anything more than that is a bonus. You may wind up turning a 14 pitch prop. That motor with a 14 will get on plane in about 10' distance and hit the rev limiter within 50 yards. You could go to a 15, hole shot will suffer. You may need to do like most of us do, have a river prop and a marsh prop. These units have a 2.08 gear ratio, that usually means that they turn 1" pitch higher than the old 40's and 50's we used to run, they had a 1.93 or 1.95 ratio.
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When the boat was running before, i had clocked it on my handheld gps at 32 - 33mph rigged for fishing with just me in it on the Calcasieu above Moss Bluff bay. I like my 25 Yammie, and it does okay for a heavy boat, but it always seemed just a little bit short out of the hole. Thank you and everyone else for the advice, i appreciate the opinions.

Another difference to note is the 4 stoke water pump is stronger than the tdli. i have a tdli and love the heck out of it. However in the shallow stuff or grass alarm goes off too easy and engine starts to cut out as a precaution. Cajun Christian has stated the water pump on the 4 strokes is superior by far compared to the tdli.

Thanks, that is definitely a big concern because of fishing in the marshes so much.

I sometimes joke that they stole Mercury's water pump. My 2 stroke Tohatsu's would pump about a dribble at idle, 7 pounds at WOT. The 4 stroke pumps 3-4 pounds at idle and 25-26 at WOT. Love the water system.
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Cajun I have a 1648 alweld semi v and I am in the process of having the Tohatsu 40 HP 4 stroke put on that hull now. What prop would you recommend putting on it?

I am in the process of having one installed on a 1648 semi vee hull what prop set up do you think will be best to set up for fishing and hunting rig

Well, just an update....i want to thank everyone for their opinions, suggestions and information. Went to LAM lasr saturday morning with some questions and got my answers. Talked to Gerald, very helpful and knowledgable person. Decided to go back this coming saturday and get the Tohatsu 40 4stroke for my marshrunner, gonna sell my Yammie, will miss it too. So i may call on ya'lls expertise about setting up a new motor, thanks!

FYI I had 50 TLDI Tohatsu on my 1852. Replaced it with 40hp Tohatsu Four stroke and the four stroke ran faster with equal hole shot same boat same load.

CajunYoung let me know how that 4stroke works out for you.... I wouldnt mind putting one on my marshrunner.

i'll let you know how it does, but it may be a couple of months yet till I get the boat finished and in the water. I am buying the motor now for the pricing and then rigging it later when the boat is ready. did you get my response to your pm a week or so ago? I replied but it never showed that I did, so not sure if it went thru.

no i never got it

Hello everyone just an update picked up my boat from Lake Area marine with the 2015 40 hp 4 stroke Tohatsu on it. Put in at launch and ran it for a couple hrs to on my 1648 semi vee hull .100 gauge. I am very impressed with the motor I had a 2 stoke 40 Tohatsu with ports opened up and 50 carbs installed on it. Once I ran it for several hours I wanted to see what it would do. Do not ever let everyone tell you there is no hole shot on these 4 stroke motors. In about 20' are less its on step and it runs 40mph with a stainless steel Yamaha 15 pitch prop with 2 batteries in front 1 battery in back full tank of gas and trolling motor. Very impressed with it gonna try 16 pitch prop this week if this rain lets up.

What did that boat run before with the 2-stoke 40hp?

I was running between 38-40 but there had been a lot of work done on the 2 stroke. These new motors are strong and they have a lot of low end power the gear ratio in the foot has been changed makes a big difference.

I have run that same unit since last year. I can't find anything I don't like about it. I love everything on the tiller, a LONG tiller.
I got a chance to run a NEW 25hp 4 stroke Tohatsu. It was a rocket. I was very impressed, seems like Tohatsu is listening to it's customers. The 25 on a 1544 AlWeld ran 34 mph with just me, banging on the rev limiter, put Kyle (275+#) on the front deck, motor ran 32.4 mph still on the rev limiter. With a little setup time and the right prop, this will be a legitimate mid 30 mph boat loaded for fishing. It is almost running stock 40hp speeds. That's impressive compared to anything else on the market today. Doubly impressive for a 4 stroke. From dead stop to on plane was just as quick as the 40-50 tohatsu, I was impressed. For the guy that is in love with fishing Miami Corp, this would be the motor to have. I didn't have a chance to measure water pressure, but it was light years stronger than the old 2 stroke tohatsu. I plan on data testing this unit for Lake Area. The numbers will be interesting. I throw that out there for guys thinking about buying a 25 and just don't know where to start looking. Start with this one and then compare everything else to it.
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