1968 33hp will not rev up

[silverado636]

1968 33hp Johnson. The engine will not open up to full throttle. It will only idle. Last summer I replaced the plugs because it is something I do every year. After I put the new plugs in the engine would not rev up. I put the old plugs back in and same problem, only this time I stripped the bottom plug threads. I pulled the cyl head to install a heli-coil. I discovered badly worn pistons and decided to install .040 oversize pistons and have the block bored. When I started the engine after the overhaul it fired right up and idled fine after a slight low speed carb adjustment. I test ran the engine for an hour revving the engine in gear to try WOT. It revved flat out. I ran it at different RPM to break in the pistons?? When I put the boat in the water this weekend it would only rev a little above idle. All the linkage is moving freely and not binding. If I manually open the throttle plate and advance the timing by pulling on the linkage the engine will rev up. It seems under load it will not rev up. The carb has had a kit installed. <br /> Why will the engine not open up??

 

[Paul Moir]

Re: 1968 33hp will not rev up

Welcome to Iboats, Silverado!<br /><br />If you don't mind, I have a couple questions. You say it will rev up if you manually manipulate the linkages right? Is that in gear or in neutral?<br /><br />A couple (school-marmish) words: reving the engine in neutral is a great way of destroying it. When you do that, the engine is running super lean and so there's inadequate lubrication of parts. Also, reving the engine in neutral - especially that one - can lead to run-away, where the engine runs all by itself and turns up to incredible rpms. This cannot be stopped with the kill switch, only by choking the thing and cutting it's fuel supply.<br />Second, you cannot break in an engine while running it in neutral, no mater what rpms you set it to. The piston rings press against the walls by spring tension, yes, but under load the combustion pressure presses them against the walls as well. Just don't treat the engine like it's fully broken in yet.<br />Sorry if this is making me look like an arse. I don't mean to, just want to give you some warning.<br /><br />An engine will rev fine in neutral and even idle well with one piston not producing power. Of course, once on the water it won't rev up much. Could you pull your spark plugs and have a look at the firing ends? Is there any difference?

 

[silverado636]

Re: 1968 33hp will not rev up

I can rev it up in neutral when I manipulate the linkage. I revved it in gear in my garage was the only time I was able to get WOT guess I'm lucky it did not run away. I realize it will need some hours to break in. I thought idling in neutral would not hurt too much. As for the plugs the boat is now 150 miles away so I will have to pull plugs when I get back to it. Do you think one cyl is not firing properly. At idle the engine sounds good, no misfire.

 

[Paul Moir]

Re: 1968 33hp will not rev up

Yeah, let me add some quick tests for you then. First, make sure you've got really good spark. Rig up a way to make spark jump 1/4"-3/8" to ground. You can get an el-cheapo adjustable spark tester from Princess Auto for a couple bucks, or you can just nail a couple nails into a board 3/8" apart. Connect one of the nails with a wire to bare metal on the engine block (it makes a difference). Fit the spark plug boot over the other.<br />With the plugs out to save your arm, you should be able to draw 3/8" sparks off each cylinder. If an ignition coil is cracked, you'll only be able to draw about 1/8" spark off it.<br />Did adjusting the carb make much of a difference? I don't know if yours had the adjustable high speed mixture or just an oriface in the bottom of the bowl. Have you rebuilt the carb?<br />Another possibility is a leaking fuel pump. Pop it off the engine and squeeze the primer bulb. If any fuel comes out the little hole on the back, it's bad.<br /><br />I'm getting started on a rebuild of a '65 33hp. Where did you find your pistons and such if you don't mind me asking? Price? Thanks!

 

[silverado636]

Re: 1968 33hp will not rev up

One coil has cracks in the clear plastic coating that covers the coil of wire. I remember that from when I had it apart.It does have a high speed carb adjustment and I did a carb o-haul. Adjusting the carb did not make a big difference.<br />I purchased the pistons from Stone & Sons Marine <br />Houston Tx. This is there web address:<br /> http://www.outboard-parts.com/ie4/index.htm <br />Pistons 115.00 ea USD<br />Rings 26.00 ea USD<br />gskts & seals 110.00 USD<br /><br />It could be a couple of weeks till I get to the boat to try these tests. Thanks Scott <br />Could the cracked sealant on the coil be part of the problem

 

[Paul Moir]

Re: 1968 33hp will not rev up

Ah yes, I've heard they're good for that. Thanks! So far I've done fairly well keeping one eye on ebay. Got a .020 over piston to the door for around $30. But I'm going to need another.<br /><br />Yeah, I'de bet that coil is arcing over on you when the revs pick up. Fairly common failure. You can get an aftermarket replacement from themarinedoctor dot com in Saskatoon or marinemanifold dot com in BC, pn 18-5181 for ~20 Canadian each. I like those better than the stock ones, which the dealer quotes to me at around $40 each. The aftermarket ones seem to throw better sparks and are very well made.<br />But run the test first. No sense trying to throw parts at it.

 

[silverado636]

Re: 1968 33hp will not rev up

Are you sure on the part number or should it be 47-5181???

 

[Paul Moir]

Re: 1968 33hp will not rev up

I think 47-5181 is Sierra's old P/N for it. Now it's 18-5181. A number of suppliers change the first two numbers to disguise the product since all Sierra's parts start with 18-. Where did you find that P/N?

 

[silverado636]

Re: 1968 33hp will not rev up

http://www.outboardrepairs.com/coils/

 

[Paul Moir]

Re: 1968 33hp will not rev up

Ahh, that list is as old as the hills. For up-to-date information, get it from the manufacturer:<br /> Sierra