'90 Johnson 8hp idles but no wide open throttle

[bcontento]

I have posted threads related to this issue on other forums and gotten some good advice, but have not been able to track down this issue yet. I need a fresh set of eyes on it. Frankly, I'm at the end of my rope with this thing. I'm going to write a novella here, so sorry for the length, but hoping being thorough will help.


1990 Johnson 8hp J8RESR on a 12' Jon Boat


backstory:
over a year ago, the motor was running great at all speeds. One day, we're out flying around in the Jon Boat with it wide open and all of a sudden, it sputters pretty hard and stumbles and will no longer hit wide open throttle in gear. It was running fine and then it wasn't. It wasn't a gradual deterioration. It would idle and run in low/mid speed range, but with the throttle wide open, it would stumble and shake a bit. In neutral, it'll throttle up perfectly, but not under load. To me, it felt like I lost spark on one of the cylinders. I messed with the motor for some time back then, trying to get it right, but never could. And then it sat. Fast forward a year (this summer), and it was time to "get that dang boat running again," so I attacked it.


Current Status: same issue - idles but no WOT. Bad stumble/bogging


I started by rebuilding the carb and replacing the fuel pump. Checked for spark, and compression. All seemed good. I put it back together and had the same issue. I ended up giving it to a buddy at work that is fairly proficient with outboards. He and his buddy tore it apart again. Rebuilt the carb, changed the impeller and some odds and ends cleanup. They got it running and idling nicely and they THOUGHT running right. What might be an important note here: the only way it would idle is with the mixture screw turned out like 7-8 turns. He thought that was odd because everything calls for 1.5-3 turns.


I took it back, hung it on the transom and out I went, or so I planned. I couldn't get the stupid thing to turn over and idle and it did just hours before that. I gave it back to them. He said they took that carb apart again and thinks the float got stuck. Gave it back to me, and out I went. It idled nicely. But STILL no WOT.


So, back to the bench. I pulled the carb AGAIN. Thought maybe the float needed setting or the needle was sticking. I noticed that the nozzle well (plastic riser in the center of the float) would slide down out of place when the carb was hanging. It actually seemed to interfere with the float moving, like it rubbed on it. Thought that might be it. I re-secured it in place, cleaned everything up again, put it all back together. This time, I set the idle speed and mixture screws to spec. The cam roller right at the mark on the flywheel and the mixture screw to 2 turns out. Got it to idle nicely at these settings. First time, so i thought maybe I had it.


At first, it did the same thing, but then...fired it back up and went for another run and at first it started acting the same way but after a minute it sort of got itself together and throttled up perfectly. I was able to run it at wide open throttle for a few minutes! When I backed off the throttle slowly it stalled. Then, I couldn't get it to idle at all without manually feathering the choke off and on. I ended up backing the mixture screw out to 7+ and turning the idle speed screw up a bit to get it to idle again.


Pulled the flywheel and the key is fine. Put it back together. No change.


I decided to turn my attention to spark. I decided to just replace rather than test/guess. New plugs, wires, and coils. No change. I ran it around my Lake a bunch and couldn't get it wide open just like before. Unlike last time when it finally did kick itself over it didn't do that this time totally. However it almost did and I might have a telltale indicator. I could feel it start to throttle up strongly but at the same time I could hear a distinct clicking. To me it almost sounded like what you hear when a spark plug arcs. The click definitely coincided with a throttle change. Again, I thought maybe I had it figured out. Now just had to find the arc. I ran it at night thinking I'd see it, but of course, now it won't do it. I decided to pull plug wires and see what I felt. I pulled the top plug wire and started it. It idled noticeably worse. I put that one back and pulled the bottom plug wire and started it. I immediately heard arcing. The retaining clip that I believe attaches the ground leads on the bottom coil we're arcing. I think that not having the plug wire attached forced the spark to try to find an exit. I thought I may have figured it out - again! I adjusted that retainer to be farther from the spot it was arcing, reattached the plug wire and fired it up. No change.


So, that's kind of where I'm at. Some thoughts:
- While it was bogging (WOT), I squirted some fuel mist into the carb throat and it got worse. To me that indicates it's already getting too much fuel. Yes? Would being WAY to rich cause this behavior?
- could it be something else with the ignition system based on these symptoms? Power pack, charge coil, rectifier, etc
- I read a post somewhere that a guy had similar issues and it was plugged up exhaust system. Is that worth looking into?


Are there some other tests I can do to help ELIMINATE possible culprits? I'd love to be able to narrow it down to definitely ignition, or fuel, or mechanical, or whatever.


It goes without saying, I really appreciate the time to read through this mess and any help offered! I'm buying a round for the group that gets this thing right!

[Joe Reeves]

The spark & compression...... What is the psi compression of the individual cylinders?... The spark with all spark plugs removed, should jump a 7/16" air gap (air gap testers available at any auto parts store) with a strong blue lightning like flame... a real SNAP! Does it?

Check for piston play:
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(Piston Play Check)
(J. Reeves)

This procedure will tell you if there is any wear or play in the Wrist Pin, Wrist Pin Bearing, or Connecting Rod to Crankshaft area.

Remove the spark plugs. Insert a screwdriver, dowel, punch, or some object of your choice through the s/plug hole and into the cylinder/piston area. Hold the tool lightly against the top of the piston. Turn the flywheel by hand, bringing the piston up to top dead center, then continue turning the flywheel to pull the piston down about a inch..... all the while holding the tool lightly against the piston top.

Now, at the point whereas the piston has been dropped down about a inch, grab the flywheel and hold it firmly. Now, push that tool solidly and firmly against the piston top.

If the piston moves without moving the flywheel, there is a problem (wear, play, clearance, etc) somewhere with the items mention in the first sentence. Be sure to check all of the pistons/cylinders.
********************
Does the carburetor on that model also have a adjustable high speed needle valve or is it a regular high speed jet?

The coil arcing out to ground when the HT lead is pulled from the spark plug indicates a cracked coil... Check It! That could very well be the "clicking" you hear which coincides with the throttle variation.

(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)

Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

--------------------------------------------------
(Carburetor Adjustments - Two Adjustable N/Vs)
(J. Reeves)

Initial settings are: Bottom high speed = seat gently, then open 1 turn out. Top slow speed = seat gently, then open 1-1/2 turns.

Setting the high and low needle valves properly:

NOTE: For engines that DO NOT have a shift selection, obviously there is no NEUTRAL position. Simply lower the rpms to the lowest setting to obtain the low speed needle valve adjustment.

(High Speed) Start engine (it will run pretty rough), shift into forward gear, take up to full throttle. In segments of 1/8 turn, waiting for the engine to respond between turns, start turning in the bottom high speed needle valve. You'll reach a point whereas the engine will either start to die out or spit back (sounds like a mild backfire). At that point, back out the needle valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest setting.

(Low Speed) Slow the engine down to where it just stays running. Shift into neutral. Again in segments of 1/8 turns, start to turn the top needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running. Eventually you'll hit the point where the engine wants to die out or it will spit back. Again, at that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

When you have finished the above adjustments, you will have no reason `to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

Let us know what you find.

[bcontento]

AWESOME INFO! New stuff to try. Really appreciate it. I'll check the piston play next. I believe compression on both cylinders was around 105psi, but I'll recheck that as well

- the coils are brand new, so no crack. The arc was coming from the metal retainer to the small electrical boot/terminal (what I guess is the "in" side of the coil - not the side out to the plug). The metal tab was bent and angled out really close to that boot. The arcing/clicking I was hearing coincided with IMPROVED operation, not degraded. That seems kind of backwards doesn't it? If the spark was arcing out of the normal circuit, wouldn't expect it to operate worse like a misfire?

- I will invest in an air-gap tester to more precisely check the spark

- the carb has a single mixture needle with a spring on it. The spec says 1.5 turns out from "lightly seated." How do you determine lightly seated? the pressure from the spring makes it difficult for the untrained screwdriver operator to know the difference.

- for setting the initial idle, I was told to set the accelerator pump screw (the one that connects to the cam roller and the throttle lever) so that the cam roller makes contact right where the mark is on the flywheel. Then, lightly seat the mixture needle and back out 1.5 turns. I did that as best I could and was able to get the motor to idle there fine. However, once the motor kicked in on that one test run and was a WOT, I could no longer get the motor to idle at that setting and had to revert to backing the mixture needle way out and increasing the idle speed screw. To me, that would mean that something changed when it fired over that caused the fuel flow to become a problem. That leads to having to back the mixture out (richer) to compensate and that also requires more air (higher idle speed setting). Does that make sense?

[Joe Reeves]

The arc was coming from the metal retainer to the small electrical boot/terminal (what I guess is the "in" side of the coil - not the side out to the plug). (1) - The metal tab was bent and angled out really close to that boot. The arcing/clicking I was hearing coincided with IMPROVED operation, not degraded. That seems kind of backwards doesn't it? If the spark was arcing out of the normal circuit, wouldn't expect it to operate worse like a misfire?

- I will invest in an air-gap tester to more precisely check the spark

- the carb has a single mixture needle with a spring on it. The spec says 1.5 turns out from "lightly seated." How do you determine lightly seated? the pressure from the spring makes it difficult for the untrained screwdriver operator to know the difference.

- for setting the initial idle, I was told to set the accelerator pump screw (the one that connects to the cam roller and the throttle lever) so that the cam roller makes contact right where the mark is on the flywheel. Then, lightly seat the mixture needle and back out 1.5 turns. I did that as best I could and was able to get the motor to idle there fine. However, (2) - once the motor kicked in on that one test run and was a WOT, I could no longer get the motor to idle at that setting and had to revert to backing the mixture needle way out and increasing the idle speed screw. To me, that would mean that something changed when it fired over that caused the fuel flow to become a problem. That leads to having to back the mixture out (richer) to compensate and that also requires more air (higher idle speed setting). Does that make sense?

1 - Metal Tab??..... There's supposed to be a wound spring like connector (identical) on both the primary coil connection you describe and also one to connect at the spark plug terminal

2 - That indicates that something is amiss within the carburetor, and without being there, I know not what it is. The need to back that Slow Speed adjustable needle valve out as far as you state indicates that fuel is no longer flowing normally through the slow speed passageway.

However.... fuel must flow freely through the high speed passageway first before the fuel has access to the slow speed passageways. You're apparently (temporarily) curing that problem... BUT... on your test run, apparently something is moving out of place within that carburetor.

Oh, forgot.... Seated?... simply gently screw it in until it stops. You can temporarily remove the spring to get a idea where that is. Those new needle valves are usually steel (not soft brass), so you stand very little chance of gouging the tip taper.

[bcontento]

1 - Metal Tab??..... There's supposed to be a wound spring like connector (identical) on both the primary coil connection you describe and also one to connect at the spark plug terminal

In the photo. The circled bolt/retainer/tab/clip thingy. Technical terms, I know. It's arcing where the blue line is.

I've now taken the carb apart, cleaned and rebuilt it like 4 or 5 times (including what the other guys did). I'm leaning toward stripping the entire fuel system down and starting over. Empty and flush the gas tank. New fuel lines (the one from the tank is new). Open the fuel pump and clean/rebuild if needed. Rebuild the carb...again. If I temporarily remove the spring on the needle, then just seat it gently, I can then figure out where that position is then put the spring back on, right?

https://scontent.fmia1-2.fna.fbcdn.n...78&oe=5BFB80B5

[Joe Reeves]

The arcing location.... Oh, okay, now I understand. No doubt cleaning and tightening would cure that.

[bcontento]

update:
- no play in the pistons
- removed the carb and all fuel lines and pump. Took the carb apart. The plastic nozzle well has a tube where the little rubber hose/line connects and a small orrifice (I believe that is the high speed jet, right?). The orifice/jet is clear BUT the hole where the little tube opens did seem to be plugged a bit. I couldn't see light through it. Could that be the ultimate culprit? I'm going to soak and clean the CRAP out of the carb this time. The rebuild kit will be here tomorrow. Then, all back together with new hoses, inline fuel filter, new gas.

[Joe Reeves]

I removed the carb and all fuel lines and pump.... Took the carb apart.... The plastic nozzle well has a tube where the little rubber hose/line connects and a small orifice (I believe that is the high speed jet, right?). The orifice/jet is clear BUT the hole where the little tube opens did seem to be plugged a bit. I couldn't see light through it. Could that be the ultimate culprit? I'm going to soak and clean the CRAP out of the carb this time. The rebuild kit will be here tomorrow. Then, all back together with new hoses, inline fuel filter, new gas.

Yes, any jet/orifice in that area would be a high speed jet. I believe you're on the right track as your explanation of how the engine acts describes something coming loose in the carburetor... OR... something floating loose in the float chamber that would get drawn into a fuel restrictive area (which I encountered with a V6 many years ago)... a real mind cracker!

[bcontento]

I think i've got it! New fuel lines, fresh gas, inline fuel filter and rebuilt carb after really good cleaning, soaking, using copper wire to chase the passages, blowing it out with air, new float. Got it all back together and set the mixture screw to 1.5 turns out (removed the spring to get an idea of where that was to start). I set the idle speed screw right where the cam roller makes contact with the mark.

VROOOM! I was flying around the lake again!

moral of the story: buy at least 2 carb rebuild kits because unless you are a pro, you'll need to do it again after pulling all of your hair out trying to figure out your issue.

thanks all for the help!