1984 JOHNSON, 90HP runs rich trimmed dn

[sterl]

84 Johnson, 90 hp on 16 ft 84 stratos with tilt trim. Boat new to me & motor
runs rich trimed down & fine trimed up to where "tilt" takes over, whether in water or on trailer with water hook-up. Example, with engine on idle and
trim up max (where tilt starts), runs good: start trimming down and engines
begins to struggle, smokes excessively and will die in 10-15 seconds after full trim down.

Other problems that may or may not be related: Tack doesn't work; tilt & trim
Gauge doesn't work. (tilt & trim operating fine)

Attempts to solve problem: new needles & seats; lowed floats to minimum
per shop manual and VRO disconnected. Proper fuel mix has been adhered to
with some 10 hr operations since attemps were made.

 

[HighTrim]

Re: 1984 JOHNSON, 90HP runs rich trimmed dn

How did you set the carb floats?

The trim sender back on the engine is a variable resistance thing. You set your multi meter to measure resistance (ohms). Then, you put the multimeter probes on the two sender wires and measure the ohms when the sender is in the full up vs. full down position.

Various outboard makes have differing specs for this - some are high resistance "up", low (or zero) "down"; some are opposite. The gauge needs to be matched to this spec, whatever it happens to be for your outboard's sender. Check the link posted below for your measurements.

"http://ww2.tflx.com/pdf/trimsy~1.pdf"

It could be that your gauge is mis-matched, that the sender is bad or the wiring between the sender and gauge is faulty.

Concerning the tach, check for 12-volt power and proper ground first. A volt-ohmmeter or 12-volt test light are great tools for this procedure. Simply ground the meter or light, turn the key on and touch the positive probe to the purple wire on the back of the tach. You should see 12 volts indicated on the meter, or if you’re using a test light, its bulb should illuminate. Reverse the leads to check for proper ground, or use the ground wire on the tach to ground your meter or test light.

If either the power circuit or ground is the culprit, you can repair the problem and the tach should work fine. In a no-power situation, see if your tach has an inline fuse. These often blow due to constant vibration. After inspecting for power and ground, if it still doesn’t work, it’s time to check the signal-input source, or the tach itself.

A simple way to determine if the tach is bad is to use another tach. Some shops will have a tach ready with alligator clips just for this, ask them and see if they will let you borrow it, or borrow one off a buddy.

In the event you don’t have access to a shop tach, you’ll have to refer to the manual to check the signal source. The signal is a pulse-positive output that’s provided directly from the stator assembly through the rectifier. A peak-reading voltmeter set to “positive” and the lowest volt scale will enable you to read any voltage output (on this circuit) from the stator.

Check the procedure and specifications for your engine, since the inspection point, procedure and wiring are not the same for all outboards. In addition, your ohmmeter can be used to check the continuity of the stator windings, as well as the integrity of the rectifier diodes.

If everything still checks out, you will need to test your rectifier/regulator as per your manual.

"http://ww2.tflx.com/pdf/obtach~1.pdf"

 

[walleyehed]

Re: 1984 JOHNSON, 90HP runs rich trimmed dn

sterl, did this boat come from the same altitude that you operate at?
You may have a/some recirc valves plugged....best to have a manual to show how to check them....and by all means BE CAREFUL lowering the float....you can cause a lean condition that may burn a hole in a piston.
Another thought, which would also require a manual, yet is a common problem, is doing a link-N-sync on the carbs/timing arms. If this is not right, they don't idle well.
If the reg/rect is out, you may have tach problems that turn into stator problems...

 

[rodbolt]

Re: 1984 JOHNSON, 90HP runs rich trimmed dn

check the floats and the gasket for the fuel bowl, as you tilt up the fuel in the bowl goes fwd effectivly making the float go up even higher.
if you have carbs with the black plastic bowls carefully check the bowl surfaces for warpage.

 

[emdsapmgr]

Re: 1984 JOHNSON, 90HP runs rich trimmed dn

It is possible that you may have raw fuel accumulating in the bottom of the airbox. When you tilt the engine down, it may be sucking this fuel/oil mix into the bottom cylinder, causing the engine to smoke, slow down and eventually die. Take the airbox cover off, then rerun the engine then trim down and see what is going on. You have gotten some good advice on the check valves and the carb floats.

 

[Dhadley]

Re: 1984 JOHNSON, 90HP runs rich trimmed dn

Good advise about being careful with the float level. There's another factor that's easily overlooked.

On a relatively small boat with a V4 cf it probably sits pretty far down in the back when in the water. This creates a lot of backpressure in the exhaust. The further you tilt it down (under) the worse it gets. Tilting up relieves some backpressure and the motor idles better.

Once you've verified all the things the guys have mentioned you might want to play with the backpressure deal. Move to the front to see if that picks up idle, things like that. You can't operate like that but you can see if that's what the issue is.

That's why you see a lot of performance boats with their jackplates up when idleing around. Then as they start to plane off they'll drop the plate. Once you move fast enough (couple mph) to pull water away from the midsection it should be fine.

 

[sterl]

Re: 1984 JOHNSON, 90HP runs rich trimmed dn

Thanks for responses...all considered and in progress applying suggestions.

I'm concerned about cautions of me lowering carb floats...wondering if in any
event I should restore setting to original. Let me expound:

Due to rich operation, I checked Johnson outboard manual for this engine and
specs were for the float settings to be between 7/8" to 1 1/8".

I found setting to be near 1 1/8" and lowered to near 7/8".

Should I go back to the 1 1/8" setting to be safe on burning reeds or piston??

Engine is 84, 90 HP Johnson #J90TLCRD

 

[HighTrim]

Re: 1984 JOHNSON, 90HP runs rich trimmed dn

You are referring to the drop.

I believe the main issue is that when turning the carb body upside down, the float should be parallel to the gasket surface and away by the spec as per your manual.

Although I would not want to lower the drop quite that much. Keeping it in the middle at about an inch should be sufficient.

 

[ezeke]

Re: 1984 JOHNSON, 90HP runs rich trimmed dn

Actually, the drop setting is 1" with an allowable +/- 1/8". The important setting is as HighTrim stated.

 

[HighTrim]

Re: 1984 JOHNSON, 90HP runs rich trimmed dn

Actually, the drop setting is 1" with an allowable +/- 1/8".

Isnt that what he said?