1981 Johnson 35hp and 1984 Evinrude 20 hp

[piscesplaypen]

I'm trying to find out whether the 1981 Johnson 35 hp motor and the 1984 Evinrude 20 hp motor are the same basic engine. Are the carburetors and intake manifolds interchangeable between these motors or are they completely different motors?<br /><br />I have access to the 35 hp for parts and was thinking if it is compatible with my 1984 20 hp, I would consider obtaining the 35.<br /><br />Are these two motors close to the same gross dry weight?

 

[G DANE]

Re: 1981 Johnson 35hp and 1984 Evinrude 20 hp

Hi GeorgeN<br /><br />Theese two motors are based n exactly the same powerhead. The 35 has a different intake manifold, carbureator, cylinderhead, midsection and lower unit. The strongest motor build from theese two would be using the 20 powerhead with all the rest from the 35HP. If the 35 HP is electric start it will be like 10-15 lbs heavier. Another obtion could be using intake manifold, cylinderhead and carb on the 20 Hp which would give you around 28 - HP.

 

[piscesplaypen]

Re: 1981 Johnson 35hp and 1984 Evinrude 20 hp

Hi,<br /><br />So, if I understand you correctly, I could actually take the carb and intake from the 1981 35hp motor and use it on the 1984 20hp motor and everything would play okay.<br /><br />The 20 hp motor has excellent compression, but has some sort of elusive problem with the fuel system that no one has been able to solve. Many have tried including some very savy mechanics.<br />Also the butterfly shaft on the carb has play in it.<br /><br />If the 35hp motor's carb and intake are in good shape I'd rather do a rebuild on the carb and change my 20 hp to a stronger better running motor by switching the intake and carb. Why would I have to change cylinder heads??

 

[G DANE]

Re: 1981 Johnson 35hp and 1984 Evinrude 20 hp

The cylinderhead on the 20 Hp is different from the others, lowering compression, to reduce HP. You will however have no problems using carb and intake alone, i did this once, worked fine. Changing carb and intake will make the biggest power jump, exhaust and lower unit the next big jump upwards. Head means less, only topend.

 

[piscesplaypen]

Re: 1981 Johnson 35hp and 1984 Evinrude 20 hp

Okay,<br /><br />First of all I'm sorry to say a made a mistake on the year of the 20hp motor. It is a 1988 Evinrude 20 hp not a 1984. Are the parts we discused still compatible? If so, then the following applies......if not then I guess it's a futile effort.<br /><br />So, if the 1981 35hp Johnson and the 1988 20hp Evinrude are still compatible as far as the carb, manifold, and cylinder head are concerned, read on<br /><br />With today's fuel I'm not so sure that the lower compression wouldn't be better then hyping up the compression to the max. What do you think? Like I said if I get the 35hp I'll have access to all the parts so I suppose I should make the decision about the cylinder head swap before I do the carb and intake since the cylinder head would require taking it all apart.<br /><br />Thanks, <br />George

 

[Mercathode]

Re: 1981 Johnson 35hp and 1984 Evinrude 20 hp

Hi George<br />One thing to consider on parts swapping between these engines if your not carefull you can lose ground and open new problems. Also consider the 88 20 is prop rated and the 81 35 is flywheel rated. The 20 would be more like a 25 in 81 and the 35 would be more like a 30 in 88. <br />LW

 

[G DANE]

Re: 1981 Johnson 35hp and 1984 Evinrude 20 hp

Hi again George. As I mentioned, parts will fit. The compression on neither the 20 HP nor the 35HP will reach hights to require premium fuel. <br /><br />If you dont feel comfortable about swapping heads, leave them, it wont add much, as I mentioned. I once rebuild a 35 HP using a block from a 20HP, and afterwards discovered that the heads were different. I swapped them, but gained almost no speed from that, only faster hole shot.<br /><br />Besides from that, swapping heads is no big deal, just make sure the thermostat you transfer with the other head is good, and at this opportunity check your if deflectors are fine and in right place. ( I never experienced any problems there, if not badly overheated, though ) Good luck.

 

[G DANE]

Re: 1981 Johnson 35hp and 1984 Evinrude 20 hp

But one thing, George. When you are done, borrow a tach and check your wot rpm, not to exceed 5800. If they do, go to a higher prop pitch, theese twin crossflows dont like to overrev, can cost you a cranckshaft.