59 Johnson Over-reving

[Mick_Michigan]

I have a 59 Johnson 35 hp motor i just replaced the coils and points on and when i have it in the water it runs gret while ideling but once i get to a certain point on the throttle it takes off to wide open and even if i back the throttle off i have to choke it out to slow it down. I'm wondering sense I have all gas control in my hands is it the cam getting stuck causing it to over-rev?

 

[ICEMAN]

Re: 59 Johnson Over-reving

Hi Mick_Michigan, One possibility is that when you replaced the coils under the flywheel, they are not adjusted properly, directly below the coil, where it sits on the plate, the edge of the coil must be lined up so it does not stick out further than the area on the leg it sits on. Another possibility is that if the coils are adjusted correctly is that plate they sit on is loose where it sits on the top of the motor or the upper bearing for the crankshaft is worn and allowing the plate or crankshaft to move off center as you increase speed. Take the flywheel off and see if the coils have marks on them indicating they have been touching the flywheel magnet area. the flywheel and the plate rotate, but should not have any side to side, or forward to rearward play. This could cause the problem you have. Did it look like the old coils hit the flywheel?

 

[Dunk]

Re: 59 Johnson Over-reving

Ice, you're loosing me here with the coils. If the flywheel was hitting the coils it would be grounding out and missing or it wouldn't even start.<br /><br /> Sounds like to me the return spring on the throttle plate shaft is broken or disconnected. The throttle plate should snap shut when you back off the throttle. If the spring is gone then the air flow would open it all the way once you got to a certain rpm. The spring should be very visable on the starboard side of the carb around the throttle shaft.

 

[Dunk]

Re: 59 Johnson Over-reving

On second thought I've got a 53 25hp Rude that uses a straight spring to pull the carb shut. It's on top of the carb. My 70 40hp rude uses a spring around the throttle plate shaft. Your being in the middle of those years could use either one. Either way that throttle plate should snap closed by itself when you back off on the throttle.

 

[dcparizo]

Re: 59 Johnson Over-reving

I have a similar motor that I'm trying to work on. In a different discussion with someone, they referenced a "vacuum cut-off switch". No other details except that this was put in place to prevent just the problem your describing. <br /><br />Evidently the switch would temporarily ground out the lower plug or mag and slow the engine.<br /><br />someone with more knowledge than I will have to interpret my babbling if this is the case ...<br /><br />Hope this helps<br />Computer Geek

 

[Chinewalker]

Re: 59 Johnson Over-reving

There should be a single black wire leading from the magneto to a small square (approx. 2"x2") of bakelite with a metal dome on it. There's a post coming out of the dome that the wire leads to, and there's a hose nipple that leads to the crankcase. That's the vacuum cutout switch - shorts out one cylinder to reign in the revs. The old Big Twins had the habit of running away from you while they were in neutral and this was OMC's fix for it...<br />- Scott

 

[dcparizo]

Re: 59 Johnson Over-reving

Can you elaborate a little.. Is there only one wire magnito to domed center post?<br /><br />I also had (and schematic shows) a wire going from<br />the dome to the solenoid. also a wire leading from<br />a corner post grounded to the engine block.<br /><br />This could also be my problem.<br /><br />Thanks in advance.

 

[rwise]

Re: 59 Johnson Over-reving

Just a thought, but it could also be the floats in the carb set to low. Fuel pump weak and not keeping up with fuel demand. Air leak/s in fuel line. 2 stroks tend to “run away” when they have a lean condition.<br />Richard

 

[Lark40]

Re: 59 Johnson Over-reving

The vacuum cut-off switch is not involved in causing your over-revving, as that is what it would stop. Also, the coil and magneto alignment issues would impede performance, not enhance it.<br /><br />The carb issues mentioned in the other posts would seem the obvious suspects.

 

[alcan]

Re: 59 Johnson Over-reving

If the throtle is suddenly closed while the engine is running at fast idle in neutral, crankcase vacume increases rapidly. This can cause erratic cylinder firing, increasing engine rpm sharply even though the throtle closed. To prevent this problem a vacuume cut-out switch momentarily shorts out the lower cylinder breaker point when crankcase vacuume is high. The starting circut safety switch is also incorporated in this circut to prevent the cut-out switch from operating at full throtle. <br /> <br /> Mick Recheck your point adjustment and then check the link and sync. Test your vacuume cut-out and safety switches and circuts. I think you will find the problem in the linkage. Check all the sugestion given as they are all valid. I have had to pull more shop rags out of the carbs on these than I care to admit. There's a tip. While in the test tank keep a shop rag handy. When it starts that runaway monkey business stuff a rag in the carb.