idle instability with water depth

[james_shoemaker]

I have a 1976 55Hp johnson on my pontoon boat and it idles beautifully as long as the water level hits the motor at the same place. If I take someone along and they walk to the front of the boat, raising the back of the boat the idle speed increases. If they walk to the back it reduces, often to the point of stalling the motor.<br /> Is there something to deal with this issue, or do I just make everyone sit still.<br /><br />James

 

[james_shoemaker]

Re: idle instability with water depth

Additional, it could (I suppose) be related to the angle rather than the depth, as they change as well.<br /><br />James

 

[angus63]

Re: idle instability with water depth

The deeper the exhaust in the water, the more backpressure is created. More backpressure equals lower idle rpms. Adjust the idle as low as possible with the motor as deep as possible and be sure the water intake always remains submerged.<br />This is normal and expected.<br />Good luck<br />and Welcome to the forum!!

 

[james_shoemaker]

Re: idle instability with water depth

Any way to minimize the effect? It goes from stalled to racing by moving from the back to the front of the boat?<br /><br />James

 

[angus63]

Re: idle instability with water depth

You can adjust the height of the motor so it is as deep as possible when stern heavy. The difference in rpm from deep to shallow should only be 100-200 rpm. You could also trim up when stern heavy to increase idle rpms and trim down when bow heavy. Try to find a happy medium but pontoons can be like a see-saw and make this difficult. You can shift your loads (coolers, in-laws, noisy kids, fuel, batteries, water, etc..)to help minimize effect. Adjustable height motor mounts are also an option.<br />Good luck

 

[james_shoemaker]

Re: idle instability with water depth

Could there be something wrong with the motor that could magnify the issue? I think I have slightly leaky reeds (air puffs out the carbs at idle), would that affect this?<br /><br /> No trim on this motor so that is out.<br /><br /> No budget for fancy jack-plates, only have $700 in the whole boat including $500 for the used 55Hp outboard, will live with it if that is the alternative.<br /><br /> Thanks.<br /><br />James

 

[angus63]

Re: idle instability with water depth

If you have air puffing OUT of the carbs at idle , you do indeed have reed issues. That will make having a steady idle near impossible until it is addressed.

 

[james_shoemaker]

Re: idle instability with water depth

It does idle a bit rough. Are reed valves a replace or service item?<br /> If replace, ballpark cost?<br /> If service, what steps are involved (I am not shy about working on it, but haven't done much with 2Cycle)<br /><br />James

 

[CATransplant]

Re: idle instability with water depth

"You can shift your loads (coolers, in-laws, noisy kids, fuel, batteries, water, etc..)to help minimize effect. "<br /><br />Hmm...coolers, batteries, water...all necessary things. In-laws? Shift 'em back to the dock. Noisy kids? Cut back on the sugar, eh?<br /><br />Come to think about it, maybe the solution here is to go out alone and just sit and fish. Sounds good to me.

 

[james_shoemaker]

Re: idle instability with water depth

When I go out alone, I would take another boat (probably the sailboat), the pontoon was obtained for handling the crowds and it is quite annoying when it stalls at the dock because it is lower than when I tuned it.<br /><br />James

 

[james_shoemaker]

Re: idle instability with water depth

The target is to get it running good enough so the wife can handle the pontoon fodder and I can go back to sailing.<br /><br />James

 

[BoatBuoy]

Re: idle instability with water depth

Originally posted by james_shoemaker:<br /> Are reed valves a replace or service item?<br />Replace<br /><br />If replace, ballpark cost??<br />$82.34 ea.(ishopmarine.com)Need 2. Part # 0387431 <br /><br />If service, what steps are involved ?<br />Short answer - to replace, remove carb then remove leaf plate assembly.<br /><br />Some here have reported having good success at truing a warped leaf plate by placing it on a piece of emory cloth on a plate glass. Work it in a motion similar to an orbital sander until it appears flat.

 

[james_shoemaker]

Re: idle instability with water depth

Is it the leaf or the block that they seal to that I am lapping on the emory?<br /><br /> $82.34 for a thin little piece of sprint steel? Or is that for the block? Anyway it is too much for my blood, will try the other method.<br /><br /> How do I determine if they are sealing properly, light?<br /><br />James

 

[Chinewalker]

Re: idle instability with water depth

It's possible that the issue is with the exhaust. Are you getting much exhaust out the idle relief holes in the rear of the motor leg? They may have mud-daubers or the like making a home in there... The relief ports are there to prevent exactly what is happening to your motor...<br /><br />- Scott

 

[BoatBuoy]

Re: idle instability with water depth

Originally posted by james_shoemaker:<br /> $82.34 for a thin little piece of sprint steel? Or is that for the block? Anyway it is too much for my blood, will try the other method.<br />

$82.34 for "leaf plate assembly". See here: http://www.ishopmarine.com/ishop/js...~A0000022~M0016802~M0016821~M0016823~C0248557 <br /><br />

How do I determine if they are sealing properly, light?<br />

That's my understanding from those who've done it. Maybe someone will chime in here with actual experience.

 

[Basscat 1]

Re: idle instability with water depth

You will need to remove the reeds and hold a flashlight up to the reed block. If you see any light around the edges, you need to replace them. You will sand block the reed block with a flat piece of glass, not the reed leafs themselves.<br />If they make Boyesen reeds for this motor, thats what I would use. I am sold on those things, but thats just me.