1986 Johnson 90 V4 idle question...

[Janniklindskov]

Hello There...

Hope you understand my english, if from Denmark so it is not the best...

I just got my old 1986 90 hp V4 Johnson started up today on the muffs.
It startede right up and It idle fine but sometimes it had like a little stumble, not acturly a misfire. I would idle and then drop in RPM and after 1 sec it will get back up again to normal idle. The funny thing is that the water peeing got hot when it had these stumbles. The peeing is realy strong.

Last summer it had these stumbles, but not the thing with the peeing gettng hot. Because of this I rebuild the carbs and cleaned them this winter - I used BPR parts.
The stumbles is only at idle, it will go through the trottle range with no problem an get my boat on plane very easy, and run great on WOT.

Well back to the problem..... - After a few mintues with this stumbling and the water getting hot, I stoped the engine and just gently hit the thermostat housing to maybe get them to open or something..... After that i started it up again and then the stumblin was a lot less, i could just see the engine sometimes just shake a little. The peeing was also not hot.

When the engine was running i noticed that the rightside(in the sailing direction) of the engine was a bit more hot then the left. Could not hold my finger on either side because it was to hot.

Here is what i have been doing this winter - fresh fuel, all new fuel lines. Rebuild carbs, new throttle cables. I know i haven't done a compression test og spark test.

I dont know what the problem is, in my opinion if it would be electric the problem would be there all the time, but this is just coming and going.

Hope that anyone can give me a clue on where to start....

Nest time i will have it on muffs i will make a video og the engine running and then it is easier to see.

Jannik

 

[DargelJohn]

Re: 1986 Johnson 90 V4 idle question...

The combination of stumbling and one bank getting hot may be a leaking head gasket. I would first try retorquing the head bolts (20 foot/pounds). Consult a manual for the torque sequence.

The tell tail stream comes from the middle area between the cylinder banks. This area should remain cool. Check for kinks in the cooling hoses that connect the cylinder banks to the thermostat housing. May need to rebuild the thermostats.

 

[emdsapmgr]

Re: 1986 Johnson 90 V4 idle question...

That engine has two thermostats in the thermostat housing. One controls the temp to each head. If one head is running hotter, at idle, you probably have a bad thermostat. I'd consider pulling that housing apart and replace both stats. Also-in the thermostat valve body, there are either a pair of very small holes in the valve body, or (on later models) a single oval hole in the valve body. Make sure these are open. The early models with the dual holes tend to plug with debris with age. If these holes plug up, the engine can overheat at idle on one or both sides. If you have an occasional miss at idle, possible that it is a "lean sneeze." This is not an ignition problem but is a lean condition in the carbs. Likely the small, dedicated idle passages in the carb bodys are slightly restricted-perhaps with dried fuel from last year. You should pull the carbs completely apart and spray some type of aerosol carb cleaner (like a Gumout product) through those passages, and note the spray coming out of the other holes. Compare the spray flow from one passage on one carb with the same flow from the same passage from other carb. Pull all the jets out and visually inspect them.

 

[Janniklindskov]

Re: 1986 Johnson 90 V4 idle question...

Hello again

Thanks for the quick replyes...

Today i tried to get the thermostat housing off but i can get to the bolts, and they are pretty rusty to. Then i tried to get the aluminium plate off that is under the engine, got 3 bolts off and the fourth snaped so i had to drill it out. When the 4 bolts were gone i still could not get the aluminium plate off..... what am i missing???
I would really like to chech my thermostats but i don't want to break the bolts with the aluminium plate on because then i can't get them drilled out.
I also tried to pour in some hot water to see if there where any passage though the thermostats, and on both small hoses the water passed and poured out in the small holes in the leg.
Regarding the carbs, everything that you mention "emdsapmgr" i did this winter. I also took out the small plugs where there are alot of small holes under. Sprayed everything with this cleaner and then with compressed air. I put in fresh fuel when i started it up the first time.

 

[emdsapmgr]

Re: 1986 Johnson 90 V4 idle question...

On some of the early (1979 vintage) flatback V4 engines, you can remove the 4 bolts that hold the lower pan. When removed, you can slightly move that pan, and it's a big help. With the later models that have the VRO, seems to be a different story. When those 4 bolts are removed that pan doesn't give much, as you found out. Technically, on those flatback models, you should be able to access the stat housing without moving the pan. You may find a 1/4" drive socket set with a movable knuckle may be of help. You can have misfires if the timing is too far advanced at idle. If you disconnect the spark advance rod between the timer base and the spark advance lever, does your timer base move smoothly through it's normal range? Not unusual for the grease to dry out and restrict/slow the movement of the timer base.

 

[Janniklindskov]

Re: 1986 Johnson 90 V4 idle question...

Because of the state that the bolt on the housing is in it think i will leave them and hope for the best. The thermostats are open and water are getting though hence my test with the hot water floating though.
I haven't tryed to move the spark advance rod disconneted but i will tomorrow. Am i right that the rod you are refering to is the one witch is advancing the ignition when you are giving the engine some gas?? I did not think of that thing so it is defently worth a try, and i think the grease there is hard and dry, because there has not been done a lot of work on this engine.
I will keep you posted on the development....
Thanks for the tips on where to start my trouble shooting.
Jannik

 

[emdsapmgr]

Re: 1986 Johnson 90 V4 idle question...

Yes, that rod should have a ball and socket on the timer base arm end. If the timer base is stiff, you'll have to pull the flywheel to get at the timer base. Clean it and relube with some white lithium type grease. Get your hands on a laser temp gun. If you can't borrow one, you may be able to rent one from a local auto parts store. That engine should idle between 143 and 155 degrees. When you get on plane, the pressure relief valves open, and the crankcase gets flooded with add'l water and will decrease powerhead temps dramatically. Overheat horn goes off at 212 and silences when the powerhead temps get back down to 175, which is still much to hot. Is this a saltwater engine by any chance?

 

[Janniklindskov]

Re: 1986 Johnson 90 V4 idle question...

I am on the right track then, it was the same part that i had in mind. I will try to put the flywheel off then do clean it and lube it with new grease so that i done and i don't have to think about that anymore. I don't have the 1' 5/16 socket but will get it from a friend, will havein the next couple of days....
Next time on the water or on muffs i will try to measure the temp on the powerhead and see what it reads.
I think the previous owner used it mostly in saltwater and i don't know if they flushed it after every time on the sea. I have had it for almost 3 years and before that it had been sitting in a barn for 3 years. I mostly use it in lakes and sometimes in the saltwater, but i always flush it after it has been in saltwater.
I will keep you posted on how everything works - i'm rebuilding my new house so i may be a couple of days
Thanks, Jannik

 

[emdsapmgr]

Re: 1986 Johnson 90 V4 idle question...

Saltwater engines may eventually have water flow problems internally, which can cause cooling problems, and variances in head temps. I'd be inclined to do a fairly easy check. You can pull the head covers off the heads. (don't pull the heads off the block-only the covers.) Check inside for buildup of material which will restrict water flow. Whatever you find inside the heads, will also be inside the block between the cylinder liners and the outside of the block. If you find a lot of sediment buildup that requires cleaning, then I'd probabaly pull the heads and check around the cyliners and esp the 4 rubber water diverters.

 

[Janniklindskov]

Re: 1986 Johnson 90 V4 idle question...

Maybe that is the cause of the difference in the temp of the two sides of the block, and the way you are saying is an easy way of inspecting the inside of the channels in the block. I will try it.....
Today i tried to pull of the link to the ignition of the main trottle assembly and i could move it forward and backward quiet easy with no hard places on the stroke. I don't know how easy it is surposed to be but maybe it is a good idear to take the flywheel of and manuely inspect it???
Jannik

 

[emdsapmgr]

Re: 1986 Johnson 90 V4 idle question...

If the timer base moves easily throughout it's full range, I would leave it alone.

 

[Janniklindskov]

Re: 1986 Johnson 90 V4 idle question...

Ok I will leave it then.
I will try and address the cooling issue later this week.....
Thanks for your time and help-
Jannik