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lean condition?

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LostAnchor

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New to this forum hoping you guys could point me in the write direction. 1984 wecraft with a 5.7. Boat run great last weekend today it was runnig good but I noticed when I would come off plane and out of gear it was idleing rough so rev it up and black soot out the thru hull. ThenI take off figure I will run her and blow it out. At 4200 rpm it acts like its running out off fuel so I back off the throttle and it starts popping throught the carb. Bring it to idle and your good to go till you open her up any ideas?
 
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Let me add th this. Rebuilt 4 barrel goudrojet 2 summers ago. I removed the mechanical choke when I changed intakes. New fuel/ water seperatore new filter in carb this season. Base timming 8btdc. Boat run great last time out. I also noticed a slight vibration like a cylinder misfire. It idles great starts great just wont hold wot losses power and as soon as you let of throttle it starts popping through carb. I guess I will empty my filter and check 4 water. Ideas welcomed?
 
Ok hers what I found #5 cylinder was running lean and burnt the electrode of the plug. I did a compression test and that cylinder is down 140 psi all other cylinders ar 160. Next step new plugs and a vacuum test.
 
most manifolds are dual plane, meaning 1/2 of the carb feeds 4 cylinders. If it a carb issue 4 plugs would show up lean
 
Im starting to wonder if I have an intake leak? Also shoult I run the mr43lts or mr43ts plugs long or short. This engine is out of a 1990 pickup marine converted.
 
LostAnchor said:
Im starting to wonder if I have an intake leak? Also shoult I run the mr43lts or mr43ts plugs long or short. This engine is out of a 1990 pickup marine converted.
Click to expand...

Ayuh,... The short plugs are used up to 1996, 'n the Vortec heads,.....

Sounds like there's crud in the carb,..... Rebuild it again,....
 
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