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Max Online: 36273 @ 01/23/13 02:34 PM
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#12343997 - 07/17/17 10:08 AM 1987 Johnson 140
PlanoPaul Offline
Outdoorsman

Registered: 12/16/13
Posts: 192
Loc: Plano, TX
Hey guys,

Got a Johnson 140 V4 looper that has developed a dead spot around 2800-3000rpm when coming out of the hole. Outside of this dead spot, the motor runs perfect. Starts fine,idles fine, and will run 6000rpm all day long. I can work through the dead spot if i just hammer down on it, but if i hit the dead spot and just hold it there, the motor will completely die and i have to restart. The motor is basically running out of gas when i hit this spot, as i can hit the choke and it will keep it from dying, so i know it is a fuel starvation issue.

Here is what i have done:
*checked compression - 140-135 psi every cylinder
*checked ignition - all is good
*rebuilt carburetors - they are spotless
*replaced all intake gaskets to make sure it wasn't a vacuum leak
*checked reed blocks and gaskets - all good
*all throttle linkage is properly adjusted and timing is correct
*checked all fuel lines and the gas tanks
*new fuel pump
*new fuel filter

I have read things about these motors having a "heat soak" issue in the summer time when it gets hot. This is my first summer with this motor as i acquired it this past winter, so i don't have any past history with it. But it somewhat makes sense because the motor jumps right out of the hole first thing in the morning, but as the day goes on and i run the motor more, the issue gets worse. So it does seem that heat is doing something to it(no it is not overheating, it has a new water pump and thermostats).

Anyways, i am pretty much at a deadend with troubleshooting this thing, other than taking it to a shop to have a mechanic offer an opinion. I'd greatly appreciate any info y'all might have on this.

Thanks!

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#12345029 - 07/17/17 08:58 PM Re: 1987 Johnson 140 [Re: PlanoPaul]
gary purdy Online   content
TFF Guru

Registered: 05/24/03
Posts: 11086
Loc: Littlefield Tx & Lake A. H. US...
Check the base timer to see if it is sticking at that throttle position. That compression actually sounds high for this motor. Could be a carbon issue. More heat causes more compression.
_________________________
“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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#12345242 - 07/17/17 11:07 PM Re: 1987 Johnson 140 [Re: PlanoPaul]
scruboak Online   content
Pro Angler

Registered: 03/11/03
Posts: 726
Loc: Cisco,tx
just decarbed My 150 and it made a ton of difference.Mine is 87 gt-150


Edited by scruboak (07/17/17 11:11 PM)

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#12345580 - 07/18/17 08:54 AM Re: 1987 Johnson 140 [Re: PlanoPaul]
PlanoPaul Offline
Outdoorsman

Registered: 12/16/13
Posts: 192
Loc: Plano, TX
Thanks for the replys guys. Just a little more history on the motor. I bought this motor(and boat) extremely cheap from a guy this past winter as a rebuild project - rebuilt motors before so not a newbie. The water pump went out on him and he fried it. It was pretty bad, he had seized the rod bearings on #1 and all that fun stuff. Anyways, i repaired/replaced everything that needed it and sealed her back up. All through break-in and the first few months of use the motor was absolutely flawless, ran like it was brand new. But now that the hot weather has set in, this little "dead spot" has appeared. I have looked at and inspected everying i know to look at and just can't remedy this dead spot. Anyways, the rebuild might explain the strong compression numbers, they have come down a bit since day one, and have settled in around 135psi.

So to answer your responses, yes trigger has been checked, and because it's recently rebuilt it doesn't have much carbon buildup yet.

The only thing i haven't tried is to run non-ethanol gas, which i am going to do this weekend and see if it changes anything.

Also read that richening the intermediate jets could help, but that sounds more like a band-aid than a fix??

Thanks again for y'alls interest in the post.

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#12347263 - 07/18/17 11:31 PM Re: 1987 Johnson 140 [Re: PlanoPaul]
scruboak Online   content
Pro Angler

Registered: 03/11/03
Posts: 726
Loc: Cisco,tx
If you didn't replace jets that old may be some out of spec.

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#12347535 - 07/19/17 08:31 AM Re: 1987 Johnson 140 [Re: PlanoPaul]
PlanoPaul Offline
Outdoorsman

Registered: 12/16/13
Posts: 192
Loc: Plano, TX
Funny you say that, i've got new jets on the way that will here Friday cheers

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#12349334 - 07/20/17 12:18 AM Re: 1987 Johnson 140 [Re: PlanoPaul]
scruboak Online   content
Pro Angler

Registered: 03/11/03
Posts: 726
Loc: Cisco,tx
Let us know how it goes. I have feeling I have all this coming down the road a bit.

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