1987 Johnson 140hp V4 Loss of high RPM

[TorreyWP]

Hello,

I am new to this site, hoping you guys can help. i have seen a few other posts with problems like mine, but not exactly...

I purchased this engine at the start of the summer to replace a dead Evinrude V6 150. I saw even compression before purchasing and was please with its running condition. It does appear to have a newer powerhead than year I get from the leg. In fact I know it does because the cooling system indicator stream was modified to accommodated the housing. Bottom line, the powerhead looks much newer than the rest of the rest of the engine. I would love to know if there is a way to date the powerhead.

Heres the issue. This engine pushed my boat (20ft Five Island Boat Works, Georgetown ME) beautifully right from the start. I was cruising around 35-40 with a RPM up around 5600. Most recently, If I push the throttle for WOT it will only rev to 3000 (not plane) then all of a sudden come to life and jump on plane. BUT it will not rev up past 5000. I have also noticed it be much less efficient on fuel. Sometimes it will not do the 3000 rev then get on plane but in any case I can not get it up to its ideal operating range any more. In neutral it will rev up fine.

Here is what I have done. I have replaced all fuel filter (water separator and in line filter) I have replaced some checked and cracked fuel lines leading to the fuel pump. I have checked the carbs by taking out all the drain plugs and then priming. They all drain evenly and equally. I sprayed some deep creep in and all around the carbs while I was there for good measure. I have tried priming when it exhibits this issue, no effect. I have tried choking, no effect. I thought this was a fuel issue but I am now suspecting a cylinder with no spark. I plan to diagnose that today and Im hoping someone out there may know if Im on the right track.

Is it correct that if at idle I remove the plug wires one at at time, the removal of the cylinder with no or weak spark will have no effect on the running engine? Or is it best to just get a timing light.

Would a cylinder with intermittent or no spark even cause this issue?

Note: it still starts, idles beautifully as ever.

Thanks for any help


Update:

I went out today and removed all the plugs to see if that gave any clues. I found one bank to be in fine shape and one bank in not so good shape, in fact one plug was very fouled. I cleaned, gaped and reinstalled them with no effect on my symptoms. Them, with the engine idling i removed the plug wire from the plug that was fouled (thinking this may be my culprit "dead" cylinder) and it had no effect on the engine running yet I know there is a spark because I got shocked by a strong spark after removing the wire.

still thinking this is an ignition/electrical problem but just to rule it out, a compression test may be in order.

Still starts easily and runs smoothly, reve up fine in neutral and in gear; bogs before reaching a wot @ 4500-5000 RPM when a month ago it was running around 5600 rpm at wot. No prop changes have ben made!

Help!

 

[fshrgy99]

Re: 1987 Johnson 140hp V4 Loss of high RPM

I just spent a summer with my 1989 140 vro. After totally rebuilding the fuel side from tank to manifold and converting to premix I still ran perfectly ... but only at 8 miles an hour! I starting checking spark and found that it seemed fine at idle. Went running with a timing light on the lake and could not get consistant spark on all cylinders. I was blaming the timing light but (because it was easy and I had an hour to kill) ) I removed the coils and cleaned all contacts and grounds (including on the block) with fine emery paper and electrical cleaner. After 22 years there was a patina of oxidation on most surfaces. Once things appeared shiney and clean I put it back together. Although I went back to the lake equipped to diagnose bad electrical components it immediately ran up to 37 MPH (sorry no tach). I had been obsessed with the fuel side and like to think I fixed lots of problems there. In reality it was probably the ignition side that had me stumped all along. Motors will appear to run well on the muffs with poor spark and/or fuel. Under load problems begin to become more apparent.
Hope that helps point you in the right direction.

 

[TorreyWP]

Re: 1987 Johnson 140hp V4 Loss of high RPM

Very interesting.

I plan to take the boat out of the water over the weekend and really focus on cleaning and inspecting the ignition system more closely. Its too hard to diagnose with the boat in the water.

I will update my findings.

Thanks for your input.

 

[TorreyWP]

Re: 1987 Johnson 140hp V4 Loss of high RPM

I spoke with a marine mechanic friend on the phone today who said to check the thermostat on the bank of cylinders that had worse looking plugs. He said they are notorious on the v4 loop charged block and could be the cause of some or all of this problem.

I plan to let the engine warm up before pulling this weekend and observe the temperature difference between the banks.

Update to follow.

 

[etracer68]

Re: 1987 Johnson 140hp V4 Loss of high RPM

There should be a freeze plug on top of the port side cyclinder, with the model number of the motor. I would see if it matchs the model number on the mounting bracket, if not then the power head is from a differant motor. From what your saying, that it comes to almost full rpm at times, I would think an ingition problem. Sometimes coils will spark, but get weak or better as they get warm, and under a load. I keep a known good coil around just for checking, and if I had a bad one, I replace it with a new one. I have had bad coils that sparked fine at most rpms, then drop out, and start working again.

 

[fshrgy99]

Re: 1987 Johnson 140hp V4 Loss of high RPM

Hi etracer68,
That is precisely what was happening to mine. My problem was when I swapped coils trying to find a bad one I kept getting wierd results. Turned out was poor grounds which makes sense when you consider that my motor is 22 years old.
Torrywp make sure you also check the connections on the port and starboard temp sensor wires. One is for the speed limiting overheat warning system and the other for the quickstart ignition advance. ..... and make sure they are not laying up against a spark plug wire

 

[TorreyWP]

Re: 1987 Johnson 140hp V4 Loss of high RPM

UPDATE:

Today I went out and inspected the ignition system very closely.

Here is what I found/did...

I found that the grounding wires on the coils were all corroded. Some worse than others, I cleaned and replaced all those wires. I noticed that the worst corrosion was on the coil that corresponds to the cylinder that had the most fouled spark plug. I found all of these wires to be routed correctly away from other spark plug wires and to be in good condition.

I then ran the engine and let it warm up. I noted that both cylinder banks were equal temperatures; warm to the touch, not hot.

Then i decided to test it to see if any of those adjustment made any difference. No effect. it still demonstrates the same symptom of not reving up over 5000rpm. It did however not bog around 3000rpm, it got up to 5000rpm rather quickly with little trouble that it used to experience around 3000.

I decided to check the throttle butterflies at wot. So, with the engine off and the carb/air box cover off I advanced the throttle to wot and noted all butterflies open completely and moving in unison. It hard to describe what it feels like when it exhibits this problem. It revs to 5000rpm but the throttle lever still has travel to wot. It just wont get up there. When it does this it almost likes to be backed off a little, it then sounds a little better around 4500-4700 but I dont feel like I am getting the power I used to.

The model number of J140TXCO does match the leg number so my pervious though of this being a newer/replaced power head is debunked. THis actually makes the engine a 1985 so no I realized this thread title is wrong.

I think I will buy a good coil and start by replacing it with the coil that corresponds to the most fouled spark plug.

 

[Solittle]

Re: 1987 Johnson 140hp V4 Loss of high RPM

Before you start throwing parts at it check spark at each cyl with a spark tester. You should get a bright blue spark that will jump a 1/4-3/8" gap.

 

[fshrgy99]

Re: 1987 Johnson 140hp V4 Loss of high RPM

IF you push it to WOT and leave it there ..... and IF the problem is fuel starvation ...... you 'should' overheat (if running lean) .... be careful not to overheat TOO much ...... or don't run with the throttle beyond the 'response point'. But It sounds to me like one cylinder is not performing 100% under load.

 

[TorreyWP]

Re: 1987 Johnson 140hp V4 Loss of high RPM

Yesterday I went out and replaced the coil that corresponded to the plug with the most fouling. The problem of not reaching my optimum rpm range is FIXED. I know ramp right up to 5400 rpm and I have already noticed an increase in fuel economy as well. This was, with out a doubt, the problem. I need to replace the fouled plug and monitor the others but as the season comes to an end her in Maine, Im happy to have corrected the problem before putting her away.

Thanks for the help.

 

[etracer68]

Re: 1987 Johnson 140hp V4 Loss of high RPM

Good to hear its running good again, good luck, and keep the wet side down..

 

[rolander]

Re: 1987 Johnson 140hp V4 Loss of high RPM

Did your motor surge at all when u were having the problem? Like running at 5000 rpm then seem to get a boost of power for a second then back down?

 

[235bajman]

Re: 1987 Johnson 140hp V4 Loss of high RPM

I am new to the site. But this sounds exactly like my problem on my '81 235 Johnson. Everything good to 3/4 throttle. Go to full actually drops a little in power. Back off and it seems to run a little better. I have been fighting this for years. Reply to isom56@hotmail.com if you really found the fix.
Thanks, Isom

UPDATE:
I am new to the site. But this sounds exactly like my problem on my '81 235 Johnson. Everything good to 3/4 throttle. Go to full actually drops a little in power. Back off and it seems to run a little better. I have been fighting this for years. Reply to isom56@hotmail.com if you really found the fix.
Thanks, Isom


Today I went out and inspected the ignition system very closely.

Here is what I found/did...

I found that the grounding wires on the coils were all corroded. Some worse than others, I cleaned and replaced all those wires. I noticed that the worst corrosion was on the coil that corresponds to the cylinder that had the most fouled spark plug. I found all of these wires to be routed correctly away from other spark plug wires and to be in good condition.

I then ran the engine and let it warm up. I noted that both cylinder banks were equal temperatures; warm to the touch, not hot.

Then i decided to test it to see if any of those adjustment made any difference. No effect. it still demonstrates the same symptom of not reving up over 5000rpm. It did however not bog around 3000rpm, it got up to 5000rpm rather quickly with little trouble that it used to experience around 3000.

I decided to check the throttle butterflies at wot. So, with the engine off and the carb/air box cover off I advanced the throttle to wot and noted all butterflies open completely and moving in unison. It hard to describe what it feels like when it exhibits this problem. It revs to 5000rpm but the throttle lever still has travel to wot. It just wont get up there. When it does this it almost likes to be backed off a little, it then sounds a little better around 4500-4700 but I dont feel like I am getting the power I used to.

The model number of J140TXCO does match the leg number so my pervious though of this being a newer/replaced power head is debunked. THis actually makes the engine a 1985 so no I realized this thread title is wrong.

I think I will buy a good coil and start by replacing it with the coil that corresponds to the most fouled spark plug.