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popping at idle

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ss/409

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85 mercury A144113 compression 120 both cyl. cleaned walbro 3 carb replaced fuel pump new plugs and wires thinking might be reed valve...and can you have good compression with bad reed valve?
 
racerone said:
Reed valves have nothing to do with compression in the cylinders.
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thanks for verifying that...but 2 days prior on a different lake it was not doing the popping sound but couldn't get higher than 4000rpm so back at camp i made a couple checks and adjustments...checked to see if throttle plate was going to WOT which it wasn't... maybe 3/4 at WOT...so i readjusted the new plastic throttle shaft lever that replaced the old cracked lever that was probably brittle and the original and adjusted the tiller cables to remove some the slack to make for better tiller response so after those adjustments thats when popping started and never left the dock. i noticed that to keep it running i had to keep choke partially closed and idle mixture screw was approx 1.5-2 turns out so my question is can a lean mixture give a popping sound and when i had the crankcase halves apart a month prior to replace both crankshaft end seals all the reeds looked good and in spec.
 
ss/409 said:
thanks for verifying that...but 2 days prior on a different lake it was not doing the popping sound but couldn't get higher than 4000rpm so back at camp i made a couple checks and adjustments...checked to see if throttle plate was going to WOT which it wasn't... maybe 3/4 at WOT...so i readjusted the new plastic throttle shaft lever that replaced the old cracked lever that was probably brittle and the original and adjusted the tiller cables to remove some the slack to make for better tiller response so after those adjustments thats when popping started and never left the dock. i noticed that to keep it running i had to keep choke partially closed and idle mixture screw was approx 1.5-2 turns out so my question is can a lean mixture give a popping sound and when i had the crankcase halves apart a month prior to replace both crankshaft end seals all the reeds looked good and in spec.
Click to expand...
 
Throttle plate needs to be CLOSED at idle.----Andjust that new plastic piece.-----Common issue with these plastic bits broken !
 
racerone said:
Throttle plate needs to be CLOSED at idle.----Andjust that new plastic piece.-----Common issue with these plastic bits broken !
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since our last contact i wound up locating an old school friendly marine tech through a charter boat captain on Lake Erie who gave me his number and he might have solved my problem over the phone but can't verify till i get it in the water and that might be a week or two away. after giving him the low down on everything that I've done to this 9.8 he asked if i checked spark quality with a tester which i didn't and yet i have the tools to do it and didn't think of it since new plugs and wires i put on, so told him i set plugs at .044 was told to bring them down to .035 he said these engines always ran better with a gap set at less than book spec...so me being automotive tech since 1967 i had high energy ignition stuck on the brain and gapped plugs at .044 to trying to burn off the excess fuel on the plugs. so maybe seeing something that looks like a module threw me a curve ball and not realizing low energy or old school coil output either way hope this simple adjustment cures it and will be in touch and let you know how things turn out. sometimes you can just kick yourself for missing the basics but the books don't tell you they run better with a smaller plug gap. so thanks for all your time invested so far. hope it gets better than 4000rpm cause that's all it was putting out. we'll see.
 
A 1985 model MERURY 9.8 has electronic ignition.-----Capable ( 40,000 volts ) of jumping a gap of 7/16" or more.----A gap of 0.028" or 0.045" does not matter that much.
 
racerone said:
A 1985 model MERURY 9.8 has electronic ignition.-----Capable ( 40,000 volts ) of jumping a gap of 7/16" or more.----A gap of 0.028" or 0.045" does not matter that much.
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WOW that's a bummer... but he did ask if my spark could jump a 1/2in gap which I'm going to check that out today and I'm not doubting you at all, i know that 40k should have no problem at book spec of .040 or what i set it at .044. At this point I'm going to check ignition output which might be weak before i put it in a lake for the test run... came back home and now my water barrel is 135mi south at camp. i didn't think that those coils put out that kind of voltage since the guy said bring the gaps down to .035. one other thing that i should mention the plugs that that were in the 9.8 from the previous owner NGK B9HS that looked almost like new and it fired up on the second pull and seemed to run really good, but i wound up putting CHAMPION L77JC4 is what the MERCURY service manual printed 1993 called for. actually seemed to run better with the NGK when i bought it with the Lowe 1467wt boat will try the NGK's and see if i notice a difference. well till then I'm hoping for the best but maybe not...water tank testing is really deceiving, it doesn't give you the whole picture...
 
85 9.8 mercury walbro3 carb just would like to know what the fiber gasket in the 18-7815 sierra fuel pump kit is used for... on disassembly has one stacked on the duplicate rubber type diaphragm but yet the 93-mercury service manual shows none...use the fiber or not... read somewhere its for ethanol fuel...use both or one or the other...confusion.
 
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