1986 90hp inline 6 rpm problems only when in gear,

[MrMikeTN]

I have a 1986 90hp inline 6 serial #0a935296 elpto.
The carbs have been rebuilt (by my buddy)

When I start the motor eveything seems fine, if I idle it up or raise RPMs when not in gear it will go all the way up some where near 5000 according to my tach.

When I put it in gear it runs great untill about 2200-2400 RPMs then it will not get any higher as I increase the throttle to WOT.
If I try to run it WOT at 2200-2400 RPMs for about 5-10 min it bogs and slows, then I have to back throttle down to under 1000 RPMs to keep it running.o
If I shut motor off it will restart and run again as before up to 2200-2400 RPMs.
If I dont push it more than about 1950RPMs itll run all I want for as long as I want.
I have checked to see that the carbs are opening fully, manually while boat was being driven by another person.
Its not a prop issue, i have changed the tank and ran perfect fuel thru it.
The Compression on all cylinders are great, 140+

about once a trip after I shut the engine off it wont restart. maybe after first shut off or after the 6th shut off , sometimes right when I put it in the water. It spins but NO SPARK AT ALL PLUGS.
Dosent happen right after I turn off or after a hours of being off. no patern of when it will happen.
Trying to start it over n over or letting it sit dosent change if itll start either. engine temp dosent matter.
I removed the yellow black kill wires and it didnt change anything.
Removed the rectifier, still no change.
Jiggled wires from ignition/ throttle control all the way back to the motor while try to start, no change.
replaced the Ignition and key, no change (i lost the key is why)
ive hand checked all the nuts, wires and electrical connectors on the powerboxes (SWAPPED THEM),coils, and none look abused or burnt at all.
And then for no reason itll start right up.

Its never failed YET to sooner or later fire up and take me to the next fishing hole or back to the dock.
And up to 2200 RPMs its a SUPER strong good sounding motor.

ARE the 2 issues related?

And What is wrong with this motor and how do I fix it.

NO I havent used a dvi meter, and NO I havent tried running it in gear with the rectifier off ( scared to untill I know it would be ok to test that way).

PLEASE gimme some help.

Mr Mike in TN

 

[Chinewalker]

Re: 1986 90hp inline 6 rpm problems only when in gear,

First - STOP running the motor! NEVER rev a motor to 5000 in neutral! Good way to blow the motor! Compression is good, so you need to isolate the spark issue. Once the spark issue is sorted out then move on from there.

Is the spark consistently missing on any particular plugs or is it random? Could be the trigger/sender under the flywheel.

Rectifier has nothing to do with the ignition system - it's job is to convert AC current of the stator to DC for the battery.

 

[MrMikeTN]

Re: 1986 90hp inline 6 rpm problems only when in gear,

First - STOP running the motor! NEVER rev a motor to 5000 in neutral! Good way to blow the motor! Compression is good, so you need to isolate the spark issue. Once the spark issue is sorted out then move on from there.

Is the spark consistently missing on any particular plugs or is it random? Could be the trigger/sender under the flywheel.

Rectifier has nothing to do with the ignition system - it's job is to convert AC current of the stator to DC for the battery.

it dosent miss.
it just wont go above 2200-2400 rpms

 

[MrMikeTN]

Re: 1986 90hp inline 6 rpm problems only when in gear,

it dosent miss.
it just wont go above 2200-2400 rpms

and when I loose spark I loose spark on all plugs.
Well at least on 1 2 3 4 i couldnt reach 5 6 to test while humped over motor in the lake

 

[MrMikeTN]

Re: 1986 90hp inline 6 rpm problems only when in gear,

Ive been reading alot of forums, and I was about to buy a new stator and trigger after I take off the flywheel and make sure all the magnets are ok.
but I really know nothing about outboard BOAT motors so I didnt wanna throw money down the hole.

i am a Master Millwright and have no problem do any mechanical or electrical work or testing, I have the exploded diagrams, schematics, and books to take the motor apart, and I have about any tool you could ever want except a dva meter.

 

[Chinewalker]

Re: 1986 90hp inline 6 rpm problems only when in gear,

How do the plugs look? Are they all the same color?

 

[MrMikeTN]

Re: 1986 90hp inline 6 rpm problems only when in gear,

yes, I put them in about a month ago and probably havent ran 5 total hours on them.
the plugs I replaced also looked new.
I just went outside and pulled them all again except #6 (bottom).
they all look great, maybe #4 has a little bit darker area to one side kinda brown.
put the foot in my water barrel and I fired the motor up, shut it off 2 times before it could warm up, started back every time.
Let it totally warm up and shut it off 3 times over 10 minutes and it fired back up every time.
Left for about 20 min, came back and POW, IT WONT START, NO SPARK ON 1 2 3 so i didnt pull 4 5 6.
went back and twisted every wire and connection I could find, still no start, so I had my gilfriend operate the ignition and I re wiggled, twisted and moved every connection while she tried to start it, still no spark.
But I know if I just wait or maybe a bird flys by itll start right up.

Makes NO sense to me.

 

[MrMikeTN]

Re: 1986 90hp inline 6 rpm problems only when in gear,

I even pulled the black and yellow wires again to make sure it wasnt a ground kill signal doing it.

 

[Maxz695]

Re: 1986 90hp inline 6 rpm problems only when in gear,

Try unpluging the wire harness from the boat to the motor and try to see if the spark is there. You may have just a bad connection there and it will eliminate the key switch lanyard switch if there is one etc

 

[MrMikeTN]

Re: 1986 90hp inline 6 rpm problems only when in gear,

Im assuming your talking about where the wiring harness goes into the motor housing then vertically up the front, there is a large "pigtail" looking connector there.
You saying unplug it and then plug it back in and try to start it?

or am I not understanding you?

 

[Maxz695]

Re: 1986 90hp inline 6 rpm problems only when in gear,

unplug it and turn the engine over if not by key jump the starter and check for spark although yes there may be a problem in the cconnector plug as well. if you have spak then i would start looking through the harness to the keyshwitch and throttle

 

[MrMikeTN]

Re: 1986 90hp inline 6 rpm problems only when in gear,

I guess Ill have to wait till it wont start again to try unplugging the harness..
I went outside and just turned the key and it FIRED right up.
Brought the Idle up to 1000, then back down, put it into forward gear, then reverse, then shut it off and it started the next 3 times over 9 or 10 minutes.

 

[Maxz695]

Re: 1986 90hp inline 6 rpm problems only when in gear,

there is most likely some kind of a bad connection causing this check the grounds on the engine and the bat teminal. by disconnecting the harness will eliminate half of the electrical and make it easier to diagnose.

 

[MrMikeTN]

Re: 1986 90hp inline 6 rpm problems only when in gear,

ill run continuity on the throttle/ignition/choke/tach to motor portion of the harness when it does it again.
Ive starting it a few times in the last couple hours and let it idle a little but its "restarted" every time.
also the last 2 times I started it its running a little rough, kinda like a miss,then itll sputter slightly and then runs perfect.
But I think that more to do with what ever problem im having with decreased RPMs.
Ive got an inductive Electrical tester that will record and hold information when spark plugs fire for an 8cyl.
Im gonna hook it up and see if its missing now and which ones are missing.

Im gonna take it out on the lake tomorrow, im taking my big trolling motor and 5 extra batteries just in case.

 

[Maxz695]

Re: 1986 90hp inline 6 rpm problems only when in gear,

I like the reasured method of getting back home you have. I just redid my motor and statred it tonight same deal runs fine then a miss after a bit changed 1 plug ran better for a while. I think I may have damaged one of the reed blocks but I have 2 more. I need to do more testing before I decied to rip it all back down again. RRRR I,m gonna pull the plugs tommarow and clean em in fuel mix reinsert them and check the low speed timing even though there is no information on my 70 HP having a low speed timing which I believe is 7 BTDC. Overall seems to run fairly well. It may be the gas mixture sat too long as well as working out the bugs after changing pistons rods and the crank

 

[MrMikeTN]

Re: 1986 90hp inline 6 rpm problems only when in gear,

LOL amazing what a Motorguide Tour Edition 82lb 24 volt trolling motor can do to get a 30' and loaded Pontoon/Catfish Slayer down the Tennessee River and back to the Dock.
But KnOCk On WoOD ** The "Tower of (Almost) Power" has not let me down yet.
It might be Cranky and needing WAY more of a mechanic than Ill ever be, but when It Does decide to act right it flat out can move the Pontoon boat faster than I want to go.

 

[MrMikeTN]

Re: 1986 90hp inline 6 rpm problems only when in gear,

I Got a super deal on a NIB trigger, im gonna swap it for the one on it, any DO's or Donts Beyond the service manuals I might need to know.?

 

[aussieflash]

Re: 1986 90hp inline 6 rpm problems only when in gear,

When you say no start sometimes...is it cranking or completely dead?If the latter id be checking starter solenoid for faults or bad connections.
Another good practice is to clean ALL ground connections till shiny then re attach tight.
Not getting over 2200 rpm could be blocked jets in carbs or faulty stator.
On this site you can make your own DVA for a few $$.Then you can test Stator properly.For now you can Ohm test it with meter.

 

[MrMikeTN]

Re: 1986 90hp inline 6 rpm problems only when in gear,

It cranks.
There is a certain sound, kind of a nothing free spin no fuel no spark sound when you flip the kill switch and try to fire the motor,
this is NOT the sound it makes when It wont start.
It sounds like it should or could start, BUT IT WONT, for a while, then it will.
I have pulled evey wire connection and screw post and scotch brite cleaned them that I I can find excluding the harness connection between the throttle box and the motor.
Gonna take it out on the lake tonight and see if it still does the sometimes NO START / no fire at the plugs .
Im gonna replace the Trigger, and the stator BOTH this week, if still not above 2200 rpms then im buying 2 switch boxes.
Tired of not knowing whats the problem so Ill throw parts at it till its new I guess.

 

[Maxz695]

Re: 1986 90hp inline 6 rpm problems only when in gear,

I wouldn,t normally think its not the trigger or the stator. One switchbox Black white wire to the (either condeser or capacitor) not sure which it is could be bad. Try disconnecting the blk wht wire see if it helps. ususally only one switchbox goes bad not both. you said you where losing spark on 135 but not 246 to me I would think (Not know) that the switchbox for the 135 plugs has a bad capacitor.(Mis interpeted) Edit After re reading the post #1 you lose all fire on all plugs Less 5 and 6 (Unchecked) to me the trigger has a short in it when heated up