Johnson 48 spl rough idle/low speeds

[adamst]

Hello,

I have been having some issues i just cant get fixed on my 1988 Johnson 48 spl model # j48eslccc. When out on the lake when the motor is idling it spits a little bit jerks side to side and just idles fairly rough not rough enough it wont stay running it does some time die but always starts back up. Also when in gear idling around say about 5mph looking at my side imaging it runs pretty poor spits and kinda misses sometime it will die. But when your running up on plane it runs fantastic never missed a beat. I have done a lot to the motor in the last 2 years trying to catch up on maint and fix this issue. I have replaced/fixed the following items.... Rebuilt both carbs with complete kits did a lync and sync per the oem manual after rebuild, last week i pulled the high and low speed orifices again to make sure nothing was plugged, rebuilt fuel pump, replaced every fuel line on the boat and motor, installed a fuel water separator, Install new plugs QL77JC4's gapped at .040, tested compression on both cylinders top was 140 bottom was 138, Installed new thermostat on relief valve, checked overheat alarm works great, rebuilt lower unit had broken tooth on forward gear, checked reed valves nothing looks out of place, the only thing i haven't done because i haven't figured out how to do it is check the timing. im just at a loss on what the issue could be is there something im missing with the carbs? My father bought this boat new in 88 i have every receipt and record of everything that has ever been done to it. I know it has ran smoother then it currently does just not sure where to go next??

Thanks for any help. Adam

 

[sumocomputers]

You sound like me the last few weeks

You didn't mention checking spark with a gap tester. Does it jump consistently 7/16" on both?

 

[adamst]

Oh good call haven't done that yet i will get a tester tomorrow and check it and let know. If it had week spark would it still run good at high rpms?

 

[sumocomputers]

Oh good call haven't done that yet i will get a tester tomorrow and check it and let know. If it had week spark would it still run good at high rpms?

I am too much of an engine noob to answer that, but I do know that good compression, spark, and fuel are required for an engine to run right, and so it is probably just good to know where you stand on these.

Make sure you get the kind of tester that is an open gap so you can set it longer or shorter yourself. I got this:

http://www.amazon.com/gp/product/B0002STSBM

I am sure you can pick one up locally.

 

[adamst]

anyone else have any ideas

 

[adamst]

Checked spark today checked first at a 7/16'' gap and it jumped it no problem and was bright blue also checked at a 1/2'' gap with the same results. I also rechecked compression with a quality snap on gauge (not my 30 year old hand me down) I had 145 top cylinder and 144 on bottom cylinder. I also rechecked the gap on my plugs with a feeler gauge they were at roughly .044 so i reset them to .035. Not sure where to go next?

 

[racerone]

Check the flywheel key ?

 

[adamst]

ill go pull it and take a look

 

[pn]

try running some seafoam thru it to decarb, i shoot it right into the carbs while throttling up. also you might check that your intake manifold bolts are tight and your wires arnt rubbing on your cowl.

 

[adamst]

I checked fly wheel key its still in one piece, I did 2 decarbs on it last year and it didnt make it run any better. I will check the torque on intake bolts.

 

[racerone]

You removed flywheel to inspect the key ?

 

[adamst]

yep pulled it off with my harmonic balancer puller the key was in one piece so i reinstalled the fly wheel and torqued the nut to 100 ft/lbs.

 

[adamst]

???