1978 mercury 850 fuel pump spring

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Ifkyk

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I have a 1978 mercury 850 and have been having a lot of problems with idle and will not start without giving it gas and even when it does it sounds like it’s so loaded up that it takes a second to catch up I picked the motor up for 300$ so I’ve cleaned carbs replaced spark plugs rewired everything still didn’t help my issue when it’s running from 1/4 to 3/4 throttle runs decent just spits and sputters but when I give it full throttle it runs for a minute or so then starts bogging down figured it wasn’t getting enough fuel so I started to replace diaphragm seals and check valves on fuel pump but there was a little black plastic piece with a spring behind it so when trying to put it all back together the spring shot off and I have lost it but when I go to the parts diagram I can’t find the plastic piece or the spring is it sopposed to be on the motor? Or is there a way to bypass The Whole fuel pump with a small electric pump? What’s the psi coming out of the pump sopposed to be? Any help or ideas would help.
Thanks In advance!!
 
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Chris1956

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What kind of shape is your wiring harness? They often go bad on those older motors.

Is she running on all 4 cylinders? A bad fuel pump diaphragm can cause bogging at idle. I would rebuild the fuel pump thereby making sure the fuel pump is operating properly. and then see how she runs.
 
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Ifkyk

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Chris1956 said:
What kind of shape is your wiring harness? They often go bad on those older motors.

Is she running on all 4 cylinders? A bad fuel pump diaphragm can cause bogging at idle. I would rebuild the fuel pump thereby making sure the fuel pump is operating properly. and then see how she runs.
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Okay I’ve rebuilt the fuel pump last week still not running right in fact that’s when it started bogging at wot I have gone through the harness and rewired as far as I can it has a new trigger and cdi box the last time I hooked a timing light to it I was getting fire to all 4 cylinders witch was when I put the trigger and on still had the same idle problem then I’ve rebuilt carbs I pulled the intake cover off yesterday to take a look and that’s when I lost the spring I just looked at Crowley marine and couldn’t find the plastic piece nor the spring there
Thanks for all the help! It’s greatly appreciated
 
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racerone

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It might be a 76 model.----Decals look like colored " hockey sticks " by any chance ?
 
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Chris1956

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Check the spark plugs to make sure they are the same color. If one is real clean, you may have water infiltration into that cylinder. Even with good spark, water puts the fire out.
 
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Ifkyk

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Pulled the plugs yesterday there all the same color looks to be a little fouled put new ones in still the same thing hooked the timing light up all 4 getting fire timing looked a little off but maybe a few degrees from what I’ve been able to find it’s sopposed to be 6deg atdc at idle sound right? Can’t find the specs thanks for all the help any more ideas?
 
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Chris1956

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The 4 coil ignition system (versus Distributor and 1 coil), idle pickup timing should be 0-9* ATDC. Max spark advance s/b 21* BTDC.
 
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