1975 50 hp wont idle

oldboatsrule

oldboatsrule

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Apr 11, 2010
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I have a 1975 50 hp Evinrude mounted on a 1960 Wizard cabin cruiser. The motor is new to me.. and most of my experiance lies with the older omc big twins.

Here's what i've got..
.
carbs are clean.. runs well at speed.. but wont idle when in the water.
On the muffs it idles fair.. new plugs, powerpack, good compression in both holes.. has me stumped ... fluttering the choke seems to help it stay running.

When I 1st started this motor.. parts of a wasps nest came out of the exhuast vent ... is there a chance this passage is clogged, making too much back pressure while in the water to idle ? And if so.. can it be cleared without too much disassembly ?


Thanks in advance
 

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fireman57

fireman57

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Re: 1975 50 hp wont idle

you just need to set the idle while on the water. If you take your cover off and manually "give it gas" without it running you will see an armature turn under your flywheel. It will in turn run into a stop with a long bolt on it. Use a screwdriver to turn that bolt in so the engine will idle a little higher. You can also adjust your throttle cable with wheel adjuster where it goes into the engine compartment.
 
oldboatsrule

oldboatsrule

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Re: 1975 50 hp wont idle

Fireman67,Thanks for the quick reply...

I re-adjusted the link and sync per the OMC manual today. 3 degrees btc and the pointer aligned with the roller... In order to put the timing light to it.. I had to hold the throttle (at the carb) open a bit.. is that normal ? ... Also.. I adjusted the idle on the water as you described. ran out of screw and had to use the cable as well.

Seems the idle adjustment screw shouldn't be bottomed out.
 
fireman57

fireman57

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Re: 1975 50 hp wont idle

No it shouldn't bottom out. Could be your cable is just old and stretched. You can also adjust your cable in the control box to an extent. Might free up just enough that you need.
 
oldboatsrule

oldboatsrule

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Re: 1975 50 hp wont idle

I think I found it... While putting my hand in front of the top carb, I feel air pulsing out...

Reeds need to be cleaned or replaced ?
 
oldboatsrule

oldboatsrule

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Re: 1975 50 hp wont idle

OK..I'm back at it today. carbs are rebuilt..still no change.. while running on the muffs today I noticed when I put my hand over the top carb there is not much sucking going on.. and the motor doesn't die.. cover the lower carb and the motor will die. Also.. a light mist can be seen coming from the toop carb at idle.. nothing blows out while running at higher rpms though (only tested on the muffs)

Is it possible for reed valves in these motors leak causing a low intake vacume condition in one cylinder only ?

PS compression is an even 155 psi
 
fireman57

fireman57

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3,811
Re: 1975 50 hp wont idle

When you take your carbs off get a flashlight and look back into the reed assembly and see if there is an errant screw or something laying against the reeds. They usually don't bad.
 
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