91 Johnson 150 missing 1000 RPM's after rebuild.

[Old Coasty]

Model J150GLEIS. On 91 Lund Pro V 18 ft. 14 1/2 x 21 aluminum prop. I had motor rebuilt in August. (See post from 7-25-05 "91 Johnson idles rough and dies when put in gear"). It's now broken in enough to go WOT. It tops out at 45-4600 RPM's @ 45MPH on boat gauges. It used to do 55K RPM @55 MPH when running good before motor problem. I told mechanic (certified Johnson shop that did rebuild) and he said to bring it back. He put in his tank with load and said it ran up to 5800. He said everything looked good but he did change the timing from 18 to 20 deg. We agreed to try a 14 1/2 x 19 prop to see what would happen. With 19" prop it ran up to 5500 very quickly. I had to back off throttle to keep from over rev. Next day I put the 21" back on and it ran like it used too 55K RPM @ 55 MPH. I thought all was fixed. Fished for a while. On way back to dock tried WOT and the best it would do was 45K RPM. Where do I start? FYI-new fuel, champion QL78YC plugs. I'm still running double oil in fuel for break in.

 

[Chris1956]

Re: 91 Johnson 150 missing 1000 RPM's after rebuild.

Sounds like you are fouling a plug. Check to see if any one plug is oil fouled compared to the others. Also look for one plug to be "steam-cleaned" (very clean) compared to the others. This indicates water in that cylinder.

 

[Dhadley]

Re: 91 Johnson 150 missing 1000 RPM's after rebuild.

Which 91 150 do you have? Since you mentioned 20* timing we'll assume you have the 60* looper.<br /><br />Start by continuing with the dealer as you have been. He rebuilt it and should want to see it run correctly to protect his work (warranty). It sounds like you may be losing spark to a couple of cylinders or the timing isnt staying up like it should. Youre on the right path. Stick with the dealer to whom youve paid a lot of money.<br /><br />BTW -- 5500 is not "over-reving", its border line lugging.

 

[Old Coasty]

Re: 91 Johnson 150 missing 1000 RPM's after rebuild.

The motor is 60*. By over-reving, it went from 4K to 5.5K so fast it felt like it was going to keep going so I back down the throttle. At 5.5K I had throttle left.<br /> <br />I just talked to the mech again. I will run this tank of fuel out, which has the added oil. Change the plugs and see if it makes a difference.<br /><br />Question: Can the timing slip or change? Could going from 18 to 20 make the differce in RPM that I saw? That was the only variable that was intentionally changed. <br /><br />FYI- I pulled the plugs in between prop changes. They looked good, concidering double oil. I also did a compression check for the hell of it. 101, 105, 105, 110, 110, 110.

 

[Old Coasty]

Re: 91 Johnson 150 missing 1000 RPM's after rebuild.

The story continues. New gas, new plugs. The last three times out this happened. Idles smooth, throttles right up to 5.5K rpm, slow down and repeat no proplem. Stop and fish for half hour, restart and it will only turn 4.5K rpm. Repeat throughout the day only 4.5K. I come back to the lake the next day or weekend and she revs right up to 5.5K until I shut it down to fish for a while. I then only get 4.5K out of it. The last time out I pulled one plug wire at a time and five of six dropped 1500 rpm but the center starboard only dropped 500 rpm to 4K.<br /> <br />Why would this be intermitten? Should I move coil locations and see if problem follows. <br />Does this sound like a power pack problem?

 

[Walker]

Re: 91 Johnson 150 missing 1000 RPM's after rebuild.

I would first, inspect the coils for cracks. Then I would take an inductive timing light to the lake with you and when the motor gets into its 4500rpm mode I'd check each sparkplug wire with the timing light. Sounds to me like you are dropping one cylinder with the most likely culprit being a coil or a bad coil ground.

 

[MCM]

Re: 91 Johnson 150 missing 1000 RPM's after rebuild.

Hi,<br /><br />Sounds like that would be a good place to start.<br /><br />A coil's definately cheaper'n a p/pack. At least on my motor <br /><br />Mike

 

[Solittle]

Re: 91 Johnson 150 missing 1000 RPM's after rebuild.

Why are you messing with this? You risk your shop voiding your warranty by trying to fix it yourself. Let them fuss with it as Dhadley has advised.

 

[Old Coasty]

Re: 91 Johnson 150 missing 1000 RPM's after rebuild.

SoLittle I wish it was that simple. I took it back to the shop (as Dhadley suggested) and he put it in his tank and it ran just fine. I take it back out on the lake and it fails. The mechanic is aware of the problem but he can't fix it if he doesn't see the problem. <br />The other thing is, this appears to be a secondary problem which has nothing to do with rebuild. In other words, he wants money to fix it. <br />I have been using the advice of the forum, my own knowledge, (which is limited when it comes to outboards) and the advice of the mechanic to figure this thing out. Thanks to all of your help I think I am close to finding this problem.<br /><br />Forgive me if I am wrong but isn't that what the forum was designed for. Letting the average guy figure out some of these problems so he doesn't have to pay a mechanic a summers worth the gas to fix it.

 

[MCM]

Re: 91 Johnson 150 missing 1000 RPM's after rebuild.

You got a point there. so you got any progress no the problem?<br /><br />Mike

 

[Old Coasty]

Re: 91 Johnson 150 missing 1000 RPM's after rebuild.

I moved the coil from the center to the top of the stack. First I will see if just moving the coil makes any difference (a bad ground or something). If not, I will see if the missing cylinder follows the coil. The mechanic said he has a used coil I can use to swap out with the bad one at that point. Hopefully this will correct the problem.