will go back to idle on its own

[npaul]

I have a 1976 55 johnson , while boating at top speed 35 mph, ( is that good ? ) after about 10-15 minutes, without touching anything the motor will slow right down to 10 mph on its own, till I bring it to shore and will do the same thing the next day, I replaced the powerpack thinking that it maybe the problem, I'm a new member and it the first time I'm writing, I switch tanks and check all gas lines filters ect,, I'm convinced it not a fuel problem, any suggestions folk would be greatly appriciated

 

[Silvertip]

Re: will go back to idle on its own

Are the fuel tank vents open? Does the primer bulb get sucked flat? Fuel pump test and compression tests are in order. May be losing compression as the engine warms up. Whether 35 MPH is good on a boat we know nothing about is impossible to answer.

 

[npaul]

Re: will go back to idle on its own

thanks for the quick reply, upinsmoke. yes the vent is open and the primer bulb is still hard, I'll be doing compression test next, can you please tell me how much compression I should expect? my boat is a 15 foot runabout

 

[willamettejeff]

Re: will go back to idle on its own

Can we assume the problem is not just the throttle handle moving back on its own like they tend to do?<br /><br />If thats a fiberglass 15' runabout then your doing really well with a 55hp motor, IMHO.

 

[npaul]

Re: will go back to idle on its own

The throttle is fine it don't back off on its own, one more thing that I failed to mention that may be of some help is when I go back to neutral and give it full throttle again it will make an effort and go like hell for about a minute or so and I could pull the trottle back and forth and the engine sound barely changes

 

[djzyla1980]

Re: will go back to idle on its own

How do the carbs look???

 

[npaul]

Re: will go back to idle on its own

That the thing Dave, they look ok, but who knows,it the last thing I'd want to tangle, I'm tempted to replace my coils one at the time, do you know if its a points and condencer under the flywheel or is it electronic back in '76. I appreciate all your help gentlemen

 

[Goodoleboy]

Re: will go back to idle on its own

I would run a spark test and see if it will jump at least a 7/16 gap. good snappy blue streak.<br /><br />If you have points and condencer it mite not be able to jump this much. The electronic ignitions are hotter.<br />Mabey 1/4 is good for your engine. But still should be good snappy blue spark.<br /><br />Then the next time you have a shut down try spark test again.<br /><br />I kinda think your troubles are in your fire not in your fuel.<br /><br />You can buy a spark tester from auto parts store. or build one. do a search on spark testers here on this forum.<br /><br />Sounds to me like something is breaking down when warmed up.<br /><br />You can test coils with hair dryer in your drive way while running on muffs. Might save a frustrating trip to the lake.<br /><br />Good Luck!

 

[npaul]

Re: will go back to idle on its own

Thanks for all the info. Gents, I'm of to the cottage, i'll get back to you Sept. 7 , with my findings

 

[npaul]

Re: will go back to idle on its own

I'm back from my cottage and yes the compression is 130 at both cyls, the spark jumps fine,I put the muffs on while running and I notice the water coming out some kind of peep hole in the front, is that ok ? there water coming out of the exhaust and out of the sides where the screens are, but some of it is coming from the peep hole in the front at the lower end and underneath the u shape thing that looks like a clamp that hold the motor in place, what happened is I got stuck in the mud and the sound and light came on at the trottle area so I clean the lower parts of the motor the best I could, after about 15 min. the sound came on again, it there a thermostat on this engine? 55 hp 2 cyl, could the mud be out of the impeler and pump area and pluged in the cylinder head ?, I'm sorry for all theses questions, one more thing, a spring from the carb flew out, it seems that it came from the throttle plates, is that spring available in a carb kit?

 

[andy6374]

Re: will go back to idle on its own

What RPM's are you getting at 35MPH.

 

[wilde1j]

Re: will go back to idle on its own

doréman, this sounds like a typical fuel starvation problem. Could be an air leak on the suction side of the fuel pump, trash in the tank covering the pickup screen, etc, etc. BTW, water coming from the drain holes on the LU is quite normal. I would check all of the following:<br /><br />A. Idle or high speed needles set too lean.<br />B. Carburetor not synchronized.<br />C. Leaking gaskets in induction system.<br />D. Obstructed fuel passages.<br />E. Float level set too low.<br />F. Improperly seated or broken reeds.<br />G. Fuel pump pressure line ruptured.<br />H. Fuel pump (punctured diaphragm), check valves stuck open or<br />closed, fuel lines leak.<br />I. Poor fuel tank pressure (pressurized system).<br />J. Worn or leaking fuel connector.<br /><br />I would also recommend getting an OEM shop manual if you plan to do work on the motor without getting lost.