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Spark plugs on a 1987 johnson 150 gt
#12456157
10/07/17 01:26 AM
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Joined: Mar 2003
Posts: 1,349
scruboak
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Extreme Angler
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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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Re: Spark plugs on a 1987 johnson 150 gt
[Re: scruboak]
#12456296
10/07/17 03:42 AM
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Joined: Jan 2009
Posts: 1,645
spankyttx
Extreme Angler
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Extreme Angler
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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
Last edited by spankyttx; 10/07/17 04:36 AM.
LI-SI-WI-NWI
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Re: Spark plugs on a 1987 johnson 150 gt
[Re: scruboak]
#12456310
10/07/17 04:00 AM
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Joined: Mar 2003
Posts: 1,349
scruboak
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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.
Last edited by scruboak; 10/07/17 04:04 AM.
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Re: Spark plugs on a 1987 johnson 150 gt
[Re: scruboak]
#12456325
10/07/17 04:30 AM
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Joined: Jan 2009
Posts: 1,645
spankyttx
Extreme Angler
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Extreme Angler
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that's what i would start with then
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Re: Spark plugs on a 1987 johnson 150 gt
[Re: scruboak]
#12456561
10/07/17 03:46 PM
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Joined: May 2003
Posts: 11,586
gary purdy
TFF Guru
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TFF Guru
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Posts: 11,586 |
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.
The world will not be destroyed by those who do evil, but by those who watch them without doing anything. Remember what He has done and remember that He is not done yet!-- GOD IS GOOD
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Re: Spark plugs on a 1987 johnson 150 gt
[Re: scruboak]
#12459462
10/09/17 07:56 PM
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Joined: Dec 2013
Posts: 459
PlanoPaul
Angler
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Angler
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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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Re: Spark plugs on a 1987 johnson 150 gt
[Re: scruboak]
#12459646
10/09/17 09:50 PM
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Joined: Mar 2010
Posts: 25,659
T Bird
TFF Guru
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TFF Guru
Joined: Mar 2010
Posts: 25,659 |
Might have better luck using NGK plugs. Here is the conversion part numbers.
Champion QL77JC4
= = = = = = = =
NGK BZ7HS-10
Okie by birth, Texan by choice. USAF "Thunderbirds" Alumni 1985-1989
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Re: Spark plugs on a 1987 johnson 150 gt
[Re: scruboak]
#12460180
10/10/17 04:08 AM
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Joined: Mar 2003
Posts: 1,349
scruboak
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I will check all and get back with results.
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Re: Spark plugs on a 1987 johnson 150 gt
[Re: scruboak]
#12474421
10/22/17 03:25 AM
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Joined: Mar 2003
Posts: 1,349
scruboak
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Had a bad battery and now it idles better but tach is going crazy now reading more rpms than it was before at wot.went all the way to 7000 rpm when before reading would be 5500 to 6000 rpms.
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Re: Spark plugs on a 1987 johnson 150 gt
[Re: scruboak]
#12474603
10/22/17 01:56 PM
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Joined: Dec 2013
Posts: 459
PlanoPaul
Angler
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Angler
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Interesting, Ive always been told that the battery is just to start it. After its started you can throw the battery over the side of the boat and nothing will change, at least on the ignition like you have on that GT150. Id be interested to hear opinions from others on this.
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Re: Spark plugs on a 1987 johnson 150 gt
[Re: scruboak]
#12474627
10/22/17 02:17 PM
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Joined: Mar 2010
Posts: 25,659
T Bird
TFF Guru
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Had a bad battery and now it idles better but tach is going crazy now reading more rpms than it was before at wot.went all the way to 7000 rpm when before reading would be 5500 to 6000 rpms. On back of tach. is a round cylinder # rheostat switch. Rotate it multiple times and then set it to the correct number of cylinders your motor has. Have seen this cure many erratic tach. readings. Think switch contacts get some build up on them over time.
Okie by birth, Texan by choice. USAF "Thunderbirds" Alumni 1985-1989
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Re: Spark plugs on a 1987 johnson 150 gt
[Re: scruboak]
#12474680
10/22/17 02:55 PM
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Joined: Jan 2009
Posts: 1,645
spankyttx
Extreme Angler
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Extreme Angler
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recheck the battery ground cable, and check voltage at the battery while running to make sure your getting around 14v, i'm leaning towards the rectifier now
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Re: Spark plugs on a 1987 johnson 150 gt
[Re: scruboak]
#12474705
10/22/17 03:15 PM
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Joined: Mar 2015
Posts: 499
Cat finder
Angler
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Angler
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Hey do you mind posting a pic of the front of that tach? From the looks of it i have the same minus the sticker and was wondering why it never responds to the engine rpm properly. Thanks!
Last edited by Cat finder; 10/22/17 03:16 PM.
If the fish don't bite your not baiting right...
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Re: Spark plugs on a 1987 johnson 150 gt
[Re: scruboak]
#12474730
10/22/17 03:54 PM
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Joined: May 2003
Posts: 11,586
gary purdy
TFF Guru
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Posts: 11,586 |
I use to think that the battery had no effect on the ignition but was proven wrong. 200 Merc had no power and found after a lot of work that the owner had connected the on-board charger up to the cranking battery backwards. Corrected the chargers connections and the motor ran great.
The world will not be destroyed by those who do evil, but by those who watch them without doing anything. Remember what He has done and remember that He is not done yet!-- GOD IS GOOD
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