'65 33 hp Evinrude speed question

[1973Chieftain]

I just purchased a 15' aluminum Starcraft Jet (about 450 lb) powered by a 1965 33 hp Evinrude. So far, I have only been able to get up to 16 mph with it wide open, with 2 adults in it. On the face of it, does this seem right? I had thought that with as light of a boat as mine, and from reading on these forums of others with similar boats, that a 33hp should be large enough to push it faster. There is no tach on the boat so I am unsure of my RPMs, and I did not notice any sort of roughness in the engine which seemed to be running smoothly. The hull is rated for 50 hp, so I know I'm a bit on the low end for power, and I am trying to determine if there is a problem with my engine, or if I should repower with something larger. I understand that there are many factors related to the speed of a boat, it just struck me as slow. Any thoughts or guesses?

Thanks for the advice!

 

[BonairII]

Re: '65 33 hp Evinrude speed question

I had a 14' Glasspar fiberglass (400-ish lb range) with a 35hp Bigtwin. It did 24mph(if I remember correctly) with 2 people and wasn't running perfectly.

Any idea what your compression is on your motor?

How many lbs of gear/people are you pushing? Does it get up on plane? Def a lot of factors affect speed.

A tach would def help

 

[kfa4303]

Re: '65 33 hp Evinrude speed question

Hi Chieftan. I had a '66 33hp and it was screamer. I think you should definitely be going faster. I'm thinking you may only be running on one cylinder. It's amazing how well these old gems will run on just one can. Only three things to check: compression (over 80 psi and within 10% of each other should be good), spark (Should jump a 1/4" gap), and fuel (50:1). If the motors been sitting a while, then it almost certainly needs its carb rebuilt. The points probably need to be cleaned and rest to .020", or replace them better yet. New s'plug wires make a huge difference too. Napa sells 7mm copper core wire for about $3 a foot. Check out these links they can walk you through a good all around tune up. You've got a great old "Big Twin" motor there. Well worth the effort of keeping it running. Keep us posted. Good luck.


http://www.duckworksmagazine.com/04/s/columns/max/24/index.cfm
http://forums.iboats.com/showthread.php?t=158086
http://forums.iboats.com/showthread.php?t=167352

 

[1973Chieftain]

Re: '65 33 hp Evinrude speed question

Update- I bought a compression gauge and the top cylinder is about 87 and the bottom is 90. I finger tightened the gauge in both cases, and when I removed the bottom one I found that I had completely stripped the threads on the engine! I'm not sure how I did, since it threaded nicely and correctly. HELP! Is this fixable or did I just completely screw myself??

 

[kfa4303]

Re: '65 33 hp Evinrude speed question

No need to panic Chief. Do a search in the forums for "helicoil" and you'll find out all you need to get it fixed.

 

[BonairII]

Re: '65 33 hp Evinrude speed question

I had completely stripped the threads on the engine! I'm not sure how I did, since it threaded nicely and correctly.

It was probably cross-threaded at some point(s) in the past and the threads were weakened. Just has the same prob myself, but I was lucky enough to have spare heads to swap 'em out.

If you don't want to do it yourself...call an auto shop and get a price quote. The heads is prob going to have to be removed to do the work, so you might as well order a head gasket now.

 

[jasper60103]

Re: '65 33 hp Evinrude speed question

Update- I bought a compression gauge and the top cylinder is about 87 and the bottom is 90. I finger tightened the gauge in both cases, and when I removed the bottom one I found that I had completely stripped the threads on the engine! I'm not sure how I did, since it threaded nicely and correctly. HELP! Is this fixable or did I just completely screw myself??

Chief,
I've done the same thing. The threads were probably weak. I used Save-A-Thread to repair my head, but you can find a replacement if you prefer. It's a DIY fix if you feel comfortable pulling the head. My motor has been running great for two seasons. Good luck.

 

[1973Chieftain]

Re: '65 33 hp Evinrude speed question

I called my local Autozone, and they had a spark plug thread repair kit. Basically a two step tap and threaded inserts, which for even a thumbs-only mechanic such as myself was very easy to accomplish. As per the advice above, I very liberally greased the tap up, and about 4 times backed it out, cleaned the metal shavings off and regreased it. It did not look like many of the chips fell off the tap and the grease caught most. My question is should I remove the head anyways in case there are a couple of shavings that fell in? I'm a very poor mechanic, but it looks fairly simple to unbolt and use a new gasket when it goes back on. I really would prefer not to if I don't have to, since with me unexpected problems are the norm (such as the above "simple" compression test)! Thoughts?

 

[freddyray21]

Re: '65 33 hp Evinrude speed question

your motor, but not hard to pull the head and make sure it's clean.

 

[jay_merrill]

Re: '65 33 hp Evinrude speed question

I would remove the head. Its not hard to do and well worth making sure that there are no shavings in the cylinders.

BTW, the reason why you stripped the threads, is probably because you used the compression gauge with the long reach insert adapter. If you look at your gauge, you'll most likely notice that it screws off, revealing a threaded section behind it, with a shorter reach. That prevents the piston domes from contacting the compression gauge insert, thus trying to drive them out of the head.

As far as the speed of the boat is concerned, you should try to determine the pitch of the prop. If the motor sounded like it was running at very high rpm, chances are that you are under-propped and losing top end because of this. With a boat at the weight of yours, you should be able to use a 14" pitch (the highest stock prop available for that motor) and the boat should run in the low 20s, at least.

To assist in prop selection and just to be able to determine the engine speed in general, you may wish to purchase an induction operated, digital tachometer, such as the two stroke Tiny Tach model. They are relatively inexpensive and very handy.

http://www.tinytach.com/

 

[1973Chieftain]

Re: '65 33 hp Evinrude speed question

I would remove the head. Its not hard to do and well worth making sure that there are no shavings in the cylinders.


As far as the speed of the boat is concerned, you should try to determine the pitch of the prop. If the motor sounded like it was running at very high rpm, chances are that you are under-propped and losing top end because of this. With a boat at the weight of yours, you should be able to use a 14" pitch (the highest stock prop available for that motor) and the boat should run in the low 20s, at least.

To assist in prop selection and just to be able to determine the engine speed in general, you may wish to purchase an induction operated, digital tachometer, such as the two stroke Tiny Tach model. They are relatively inexpensive and very handy.

http://www.tinytach.com/

Is there a way of measuring the pitch? I read on these forums that the prop should be stamped with the info, but nary a mark do I see either on prop currently on the engine, nor the spare. Thanks for the advice on the head, I've got a new gasket on the way!

 

[jay_merrill]

Re: '65 33 hp Evinrude speed question

A prop shop can determine what pitch your prop is. In some cases with the props for this motor, you can tell the 14" version by sight, but that's not the best way to determine what you have.