84' 90hp johnson

[rob711]

i was given this motor and it did run great ...its a 90hp with the vro...it used to idle nice but no more..the first sign of trouble is when it would start up no problem and idle all day...it would run at the slow speeds through channels...once it was running at higher rpm...no tach so i have no numbers..it would run fine for close to 20 minutes then just completly die out...i'd wait a minute it would start up no problem..away i'd go and then again after 15 minutes running on plane at crusing speed it would die out again...i tried changing the fuel filter today but it almost seems worse..the b ulb is never really soft plus its one of those water seperaters and there is always fuel in the bottom clear part..it does not really wanna idle and i'd have to start it every time with the throtte lever up almost all the way....put it down quick then jam it into gear to stop from stalling...its strange because its hard to duplicate. any ideas!!!!!!!!

 

[jtexas]

Re: 84' 90hp johnson

Do the cylinder drop test: with the engine idling on the muffs, pull then reattach the spark plug wires one at a time. RPM's should drop noticeably, otherwise that cylinder's not making power. If that's the case, check for spark. To avoid a good dose of electro-shock therapy, use a plastic spark plug boot tool or insulated pliers, or ask your mother-in-law to help.

Just a hunch - check the throttle/spark advance rod - there should be a plastic ball joint style bushing on both ends - see if maybe one of those broke.

Report back with the cylinder drop test results. Also what do the spark plugs look like? Should be champion QL77JC4 at .030

 

[tashasdaddy]

Re: 84' 90hp johnson

that's good advice. let us know the results.

 

[rob711]

Re: 84' 90hp johnson

ok i did as u said and it seems one cylinder is not fireing..when i check for spark its at the plug but when the motor is running there is no difference in sound...so how do i know if its the coil or the power pack...thank for the help....and wow mother inlaws are useful!!

 

[rob711]

Re: 84' 90hp johnson

i just tried switching the coils on the same side...i swapped the plug wires and half forced the plug that goes to those 2 coils 180 degrees...my idea was 2 seperate that coil...well the problem stayed at that same cylinder...i'm going to go borrow a compression tester and see what going on...

 

[rob711]

Re: 84' 90hp johnson

ok about 120psi on all four....what now..hmmm

 

[reeldutch]

Re: 84' 90hp johnson

sometimes the connectors from the primaiy wires make bad contact from the pp to the coil.

also make shure that coil is grounding realy good.
those motors are known to get dirty grounds on the coils.

if that doesnt help you should get a multi meter and peak voltage adapter a good manual.
we will then trouble shoot the pp output and trigger output.

good luck.

 

[rob711]

Re: 84' 90hp johnson

i just switched coils from left side to right...the problem stayed on the same side...so if changing the coils did not change any thing i'm guessing its the power pack...any other ideas before i order a new one...oh and the iboats store does not have a power back for this year/hp?

 

[Walker]

Re: 84' 90hp johnson

Sounds like a fuel problem at that cylinder. Pull the carbs and tear them down. Give them a good soaking in carb cleaner, like over night. And then blow them out with compressed air making darn sure all jets, orifices, and passageways are crystal clean and open.

 

[jtexas]

Re: 84' 90hp johnson

rob, since you have spark, the coil, powerpack and stator are functioning. Since you also have compression, all that's left is fuel. Order yourself a couple carb kits follow Walker's instructions.

good luck.

 

[rob711]

Re: 84' 90hp johnson

thanks for the info fellas...i'll order that tonight...i quess its hard to say but would a fuel problem be so intermitent...when i was on the water after it died the first time it was difficult to start so just for the hell of it i turned up the idle...but when i was starting it up today it idles a bit high even though the one cylinder was not affecting how it ran...could i switch power packs...from the other side to see if there is a difference...thanks for every ones help

 

[jtexas]

Re: 84' 90hp johnson

There is the possibility of getting a weak spark outside the cylinder that fails under compression. A spark test at 1/2" (without the plug) would rule that out. Or swap the powerpacks. Or inspect the spark plug after idling - dry plug = no fuel; wet plug = either no spark, or too much fuel.

As you can see, your motor will idle beautifully on 3 cylinders, maybe even 2 if you up the idle enough.

But note that, if any cylinders are starved for fuel, they are also not getting any lubrication, so best not to run it like that except as needed for troubleshooting.

All you need for combustion is compression, spark and fuel - if you have compression & spark that leaves fuel. If she's hitting on 3 cylinders, that rules out the fuel system upstream of the carbs.

good luck and keep us posted.