1978 35 Evinrude?

[Rivernut]

Got this motor last fall. Comp. is 125 in both cylinders. Runs well, but doesnt push my 16 ft. lund as fast as it should. The 25 merc. on the 700 lb starcraft I had prior would have blown right by this rig. Granted it was 15 yrs. newer. Any simple things to try before going to shop? Have a 20" transom and the motor has an extra long shaft. Dont know if that matters much.The Lund is about 500 lbs. Thanks in advance. Rivernut.

[delcecchi]

In 78 horsepower was calculated at the power head and more optimistically. That motor later was a 30 or a 25. But maybe it needs some carb or ignition work too.

[jasper60103]

Compression is fine. My guess is it probably running on one cylinder.

[marine_man]

How fast does it sound like the motor is running, RPM wise? You could need to re-prop it, depending on what's on the motor now, or if it came off a pontoon for example.

marine_man

[boatfixer]

If you say it runs well I would think its running on both cylinders. If the ignition drops on one cylinder on a 2 cylinder engine, it likely wont even idle and will run extremly sluggish at wot.

I think more than likely your problem is the length of the shaft. There is more drag than you may think. I have yet to see this combination perform like a properly set up rig. Marine_man's suggestion may help things if its not propped right and letting the engine reach max rpm.

The loss of power through a gearcase is approximatly 10%. So even if you figure in the powerhead vs propshaft HP, the 35 should still have more net HP.

I would look for a motor with a long shaft.

[SkunkedAgain]

I had a '79 evinrude 35hp motor for a few years until the clutch dog failed and stripped the forward gear. I really liked that motor. I'm right with boatfixer that you're probably getting a bunch of drag since you fit the wrong shaft length to your boat. If you like the motor or want to really test this, build a strong motor lift onto the transom. Do it right or that motor will end up at the bottom of the lake though!

If I remember correctly about these motors, the 35hp rating was more equivalent to a modern 28hp. You should be competitive with that newer 25hp.

[Rivernut]

Thanks for the replies. The cavitation plate was originally causing water up over the transom. Fixed that. Didnt know there was such a thing as an extra long shaft. Just long 20" and short 15". It doesnt sound like it is running at top rpm. Seems like there should be more throttle for sure. I"ll check into the prop. Keep you posted. Thanks again

[Rivernut]

What I have now is a 10 1/2 X 11

[jwmiller33]

I have a 78 35HP Johnson long shaft tiller as well. last spring I had to replace the seals as well as the clutch doggy and the forward and reverse gears. besides that, the motor runs like a charm. It is a really good motor, almost always starts in a 2-3 pulls.

How fast does your 35hp push your 16ft boat? I have a 16ft aluminum Lund, 2 batteries and about 75-100lbs of additional wood used to construct a floor and front casting deck, and my 35hp tiller pushes my boat about 25 mph (gps speed) with 2 guys fully loaded, about 23 mph with 3 guys.

how fast do you think you should be going in your boat? i'd bet that having the extra long shaft is your main problem. its causing a lot of drag and putting all of the thrust from the motor in the wrong spot in the transom to make the boat drive the best.

[Surface Tension]

Fine tuning the height a fraction of and inch will increase performance on an outboard that is matched to the transom height.

Mounting a X-long shaft on a 20" transom will greatly reduce the speed and nothing else you do will overcome the mismatch.

You need a longshaft (20") outboard on a 20" transom.

[Rivernut]

If I had to guess about 20-22 mph. Just me, 2 batteries and usual stuff. I actually picked this up as a package deal. Might check into a different motor.

[jwmiller33]

You could look into getting your extra long (25") shaft swapped out with a long (20") shaft. if you can find the used part (the 20" shaft), most boat mechanics should be able to swap it out for you. I'm not sure how much that would cost you in labor to do the swap, nor am I sure how much the shaft would cost or how hard it is to find. I'm just letting you know this is an option you have. If the motor is in as good as condition as you say (there are no major problems with it i.e. bad compression, worn forward or reverse gear, bad clutch doggy, lower unit seal issues, etc) I would look into seeing how much you could get a shaft for. If you found the right used motor parts guy, maybe you could work up a deal if you gave him back your extra long shaft so it would decrease the aggregate cost of doing the swap. Those old Evinrudes and Johnsons will run forever if you treat them right

[Rivernut]

Thanks Jake. Thats what I was thinking. Maybe try and get a long shaft lower unit. It really is a clean smooth runner.

[TUMBLEWEED]

A 20 inch transom should be fine with a long shaft.

There are very few 25 inch transoms out there.

Have you tried to adjust the trim? There should be

a drift pin with a keeper. Adjust so the motor is

a spot or two up from where it is now. That might

plane you up out of the water and bring the speed

up??

[jwmiller33]

A 20 inch transom should be fine with a long shaft.

he has a 20 inch transom with a extra long shaft, not long.

[grizrunner]

What I have now is a 10 1/2 X 11

I have an '82 35 Johnson. OEM prop, and is 10x13.(actually I think it's 10 1/8) I have it on a 14', 70" wide v-hull aluminum boat(pro customized/rigged) that weighs about 600-700 lbs. Two guys and gear can get 26 mph. By myself and minimal gear I get close to 30. As it has a decent hole shot, I was thinking of getting a 10x14 prop for a spare, and see if I can squeak out another mph or two. I also use a hydrofoil as it helps stability.

I guess I never heard of a 25" shaft...probably made for a pontoon? I'm guessing it was, with that low-pitch prop(power instead of speed)

If you find a solution to the shaft length, change props, too.

[jwmiller33]

If you find a solution to the shaft length, change props, too.

+1

[Rivernut]

Will do. Thanks, I will post as I go. You are correct, the motor originally came off of a pontoon. Hence the prop pitch. All starting to make sense. Thanks again.

[Rivernut]

Going to try a 10x13, now has a 10.5x11. What, if anything, is the .5" dia. difference going to make? Thanks as always.