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Max Online: 36273 @ 01/23/13 02:34 PM
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#12456157 - 10/06/17 08:26 PM Spark plugs on a 1987 johnson 150 gt
scruboak Online   content
Extreme Angler

Registered: 03/11/03
Posts: 1030
Loc: Cisco,tx
It currently has champion UL77V in it but a parts source shows champion QL77JC4 as plug for it.Only reason I am even looking at plugs is it idles and runs rough at idle speeds but jumps on plane and runs out like it should in fact it screams for it's age.Im suspecting that the Ql77JC4 with proper gap may fix idle and slow running roughness.The motor just is not happy when idling around.Any opinions from the guys that have experience with these old motors?

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#12456296 - 10/06/17 10:42 PM Re: Spark plugs on a 1987 johnson 150 gt [Re: scruboak]
spankyttx Online   content
Extreme Angler

Registered: 01/22/09
Posts: 1043
Loc: Denton Tx.
one thing is resistor and non-resistor, ql is resistor, the ul's could be ring fires/surface gap, my experience with surface gap was they fouled easy, i use the ql's on my older 3 and 4 cyl john/rudes, i'm not familiar with the 6 cyl's but mine seem to like them better than the surface gap plugs, you might even try a little hotter plug, might try some seafoam in the fuel, check the fuel filter and pump screen, a compression test while you have the plugs out wouldn't hurt


Edited by spankyttx (10/06/17 11:36 PM)
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#12456310 - 10/06/17 11:00 PM Re: Spark plugs on a 1987 johnson 150 gt [Re: scruboak]
scruboak Online   content
Extreme Angler

Registered: 03/11/03
Posts: 1030
Loc: Cisco,tx
yeah the UL's are surface gap thats why I think the gap plugs will help.It has been decarbed and all that has water sep.Really runs good all around but idling around which I do alot of scoping electronics.


Edited by scruboak (10/06/17 11:04 PM)

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#12456325 - 10/06/17 11:30 PM Re: Spark plugs on a 1987 johnson 150 gt [Re: scruboak]
spankyttx Online   content
Extreme Angler

Registered: 01/22/09
Posts: 1043
Loc: Denton Tx.
that's what i would start with then
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#12456561 - 10/07/17 10:46 AM Re: Spark plugs on a 1987 johnson 150 gt [Re: scruboak]
gary purdy Offline
TFF Guru

Registered: 05/24/03
Posts: 11162
Loc: Littlefield Tx & Lake A. H. US...
Sounds like you might have carburetor idle circuit problems. At idle pull sparkplug wires on each cylinder to see if all are hitting at idle. If you have one or more not hitting, clean that carb good.
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#12459462 - 10/09/17 02:56 PM Re: Spark plugs on a 1987 johnson 150 gt [Re: scruboak]
PlanoPaul Offline
Outdoorsman

Registered: 12/16/13
Posts: 208
Loc: Plano, TX
I bet those correct plugs may help. But also make sure your ignition system is sending good juice to them. Slap a DVA on a volt meter and make sure you are getting 150V+ on your orange leads down to the coils. If the ignition checks out, then go to the fuel side. Like already said, start with the carb idle circuits.

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#12459646 - 10/09/17 04:50 PM Re: Spark plugs on a 1987 johnson 150 gt [Re: scruboak]
T Bird Offline
TFF Team Angler

Registered: 03/07/10
Posts: 4875
Loc: Temple, Texas USA
Might have better luck using NGK plugs. Here is the conversion part numbers.

Champion QL77JC4

= = = = = = = =

NGK BZ7HS-10

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#12460180 - 10/09/17 11:08 PM Re: Spark plugs on a 1987 johnson 150 gt [Re: scruboak]
scruboak Online   content
Extreme Angler

Registered: 03/11/03
Posts: 1030
Loc: Cisco,tx
I will check all and get back with results.

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