8hp '90 Johnson carb flooding after multiple rebuilds

1990 Johnson 8hp J8RESR

here is the more complete backstory in one of my previous posts: http://www.marineengine.com/boat-fo...0-8hp-Johnson-idles-but-no-wide-open-throttle

I have rebuilt this carb at least 3 times and also had a couple of guys that are pretty solid with outboards rebuild it once. Stripped it down completely, cleaned all of the orifices, replaced everything in the rebuild kit including float every time. Each time, it starts out running pretty good, but it doesn't last. I can't get WOT, then it won't idle well, and then it's just a mess of flooding (gas pouring out the carb throat). I would certainly seem to lean toward float stuck or needle valve not closing, right? What would cause the same thing to keep happening, though?

The thing I haven't replaced is the idle mixture screw. Should that need to be replaced?

Other notes of interest:
- i've replaced the coils, wires, plugs, fuel pump, hoses, impeller. Done a compression test. added an inline fuel filter. Fresh gas mix a bunch of times.
- the tank I have is a regular 6 gal outboard tank, but I don't think it's vented (not sure if it's supposed to be). The old tank I had would never swell like this one does in the heat of the day. Is that supposed to happen? I have to open the cap to release the pressure. Could that be causing too much pressure in the system and blowing out the little valves and such?
- the inline fuel filter is clear. When the system is primed, the filter is never "full." Is it supposed to fill up completely to flow fuel correctly or not?

Do I bother rebuilding this carb again? Something I should do or try differently? Is it possible that I just need to replace the carb entirely? Problems that I can't address? Anyone have one they'd part with or a good 3rd party source?

Thanks all for any guidance on this before I kick it off the back of the boat and be done with it once and for all.

Look to see if the primer is leaking.

If the carburetor floods, it should flood when you pump up the fuel primer bulb to the firm point. Does it?

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(Carburetor Float Setting)
(J. Reeves)

With the carburetor body held upside down, the float being viewed from the side, adjust the float so that the free end of the float (the end opposite the hinge pin) is ever so slightly higher (just ever so slightly off level) than the other end. And when viewed from the end, make sure it is not cocked.
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The primer bulb itself isn't leaking, but if I pump it to firm I can cause the carb to flood by continuing to squeeze the bulb firmly. At some point, though, regardless of the correct function of the needle valve, enough pressure will force fuel by it, no? That's why I was wondering if the tank not venting was part of the problem.

I appreciate the replies!

Not the primer bulb the primer on the motor itself. Do you know how to use the primer on the motor? I would disconnect the small primer line from the carb. Now pump the primer bulb on the fuel line. With the primer on the motor pushed in all the way fuel should not come out. If it does your primer is leaking by. If no fuel comes out and the carb still floods you have a float or needle issue.

flyingscott said:

Not the primer bulb the primer on the motor itself. Do you know how to use the primer on the motor? I would disconnect the small primer line from the carb. Now pump the primer bulb on the fuel line. With the primer on the motor pushed in all the way fuel should not come out. If it does your primer is leaking by. If no fuel comes out and the carb still floods you have a float or needle issue.

Click to expand...

Are you talking about the choke? The only fuel line connected to the carb is the primary fuel line to the bowl. There is no "small primer line." What am I missing?

This motor uses a choke plate.------It does not use a manual primer pump.----------Only the primer bulb / manual pump on the hose.---------Take a good look at the float valve / float.-----Did you install a new float ?

racerone said:

This motor uses a choke plate.------It does not use a manual primer pump.----------Only the primer bulb / manual pump on the hose.

Click to expand...

Ok, good, I hought I was going crazy. LOL
Yes, installed a new float along with the most recent rebuild kit (gaskets, needle, etc).

The original issue was extreme "bogging" when WOT out of the blue. Like one day we were out running around (motor was running great) and then it just "broke." All of a sudden I couldn't open it up. I chased it through both electrical (looked for misfire, compression) and fuel (new pump, carb build, etc).

So am I back to pulling the carb again and starting over with another rebuild or is there something that might be just bad/broken about this carb? Something permanent that a clean and build cant fix and I'll just be wasting more time and money?

I've been reading about the swelling, non-vented tank. I'm going to add a fuel demand valve to it and see if that doesn't help. Sounds like a lot of people have similar pressurized flooding issues.

Make sure that the wee hose inside the float bowl does not interfere with the float.

If post reply #3 doesn't cure the carburetor flooding... either the float needle valve needs replacing (should be replaced anyhow) OR the vent leading from the float chamber to the atmosphere is clogged. NOTE that vent is damn hard to locate at times (hidden passage) BUT it must be clear!

joereeves said:

If post reply #3 doesn't cure the carburetor flooding... either the float needle valve needs replacing (should be replaced anyhow) OR the vent leading from the float chamber to the atmosphere is clogged. NOTE that vent is damn hard to locate at times (hidden passage) BUT it must be clear!

Click to expand...

I've replaced the float needle valve and seat with each rebuild. I thought I had the float adjusted correctly, but when I take it off this weekend, I'll verify.

Now, the atmosphere vent - that's the first I've heard that one. ANY idea where it is on this carb, how to find it, clean it, etc? This carb has a port on the side of the bowl with a screen on it that I get gas out of when it floods. That's not it is it? Does it require more than a good soak and blow to clear it typically?

Once again, thank you!!

bcontento said:

(1) - I thought I had the float adjusted correctly, but I'll verify.

(2) - The vent...where it is on this carb, how to find it, clean it? This carb, port side, has a screen. Gas exits when it floods. is that it? Does it require more than soaking, blowing to clear it?

Click to expand...

1 - The float... Make sure that it is NOT upside down (it happens) The small flange on the back of the hinge tab should be facing the needle valve seat. Adjust the level as I mentioned in reply post #3.

2 - The air vent from the float chamber to the outside?... yeah, that gets by quite a few techs with years experience. You won't find it in any service manual... more of a experience, go nuts, and finally come across it thing. When it clogs, air can't get out so as to let the fuel in properly, so the fuel takes any route it can find... and floods!

One time, a few years back, fellow with a old 2 barrel V4 downdraft carb couldn't find that clogged vent... shipped me the carb. The vent was indeed clogged...made him a happy camper.

Anyhow... vent location... float chamber and float removed... look very closely at the underside of the carburetor's top body aluminum assembly for a open hole. If you can blow air into it and feel it exiting the carburetor's exterior, the vent is okay.

If it's clogged, normally it takes a piece of wire and careful prodding to bust that stuff up. Solvent and air pressure alone just doesn't do it.

The thing about dismantling a carburetor time and time again, going through the same moves, same actions, etc, and expecting different results. Einstein had a theory about that which I'll leave unsaid. However, if you don't find a error in your 2nd dismantling attempt, there's a move/procedure you're overlooking.

Excellent. Thanks Joe. I'll tear into it this weekend and let you know what I find.

I recently rebuilt the carbs on my 90 HP Johnson, and one carb flooded like crazy.
In the end, it turned out to be a defective needle and seat assembly.
Put another one in, and all was well.
One would think that once you have rebuilt the carbs, it's done.
No...
Pull them out again and do them again, because the parts were junk.
Lol.
And these were genuine Johnson Evinrude parts, brand new in the box.
Replaced with a Sierra kit.
Lol.

CarMech1969

CarMech1969 said:

I recently rebuilt the carbs on my 90 HP Johnson, and one carb flooded like crazy.
In the end, it turned out to be a defective needle and seat assembly. Put another one in, and all was well.

Click to expand...

Yeah... That can also happen (faulty new component)... few & far between fortunately... but it'll drive'ya nuts!

Usually it's a piece of deteriorating fuel hose (or something) that gained entrance to that valve at the last minute as the supply hose was connected to the carburetor. That'll drive'ya nuts too!

I got the carb cleaned, rebuilt, and reinstalled last night. I also installed a fuel demand valve inline to help make sure that the bloated tank pressure wasn't part of the problem. I made sure that the float was moving freely (rotating the carb I could hear it and blowing gently into the fuel inlet, the air would get shut off when the float closed the needle valve). I still have to reinstall the rewind starter this evening (got too dark too fast last night).

I still struggle a bit with the adjustments/settings for the cam roller, idle adjustment screw, and the mixture needle valve setting. I've seen and read the following (with questions). Maybe someone can clarify some of this for me? Is this the proper order of things to do? Let's assume that all three of these screws/settings are way off at this point and start fresh.

- cam roller should be set to just barely touch the flywheel with the throttle completely closed. Yes?
- the mixture screw should be "seated gently" then backed out n turns (I've read everything from 1.5-5). I understand that this will vary based on your interpretation of "seated gently" and how the motor responds. What does seated gently mean, truly? With the spring on there, it picks up tension pretty quickly, well before it's completed seated. How do I get this one right?
- the idle speed screw (once the mixture is set pretty closely), back this one off until the motor idles low and smooth.

bcontento said:

I still struggle a bit with the adjustments/settings for the cam roller, idle adjustment screw, and the mixture needle valve setting.

1 - Cam roller should be set to just barely touch the flywheel with the throttle completely closed. Yes?

2 - The mixture screw should be "seated gently" then backed out x turns. I understand this is based on the meaning of "seated gently" and how the motor responds. What does seated gently mean?

Click to expand...

1990 8hp Johnson:

Manuals can be confusing at times. Hopefully the following helps.

1 - You DO NOT want anything touching the flywheel. The roller touches only the cam. There is normally a scribe mark on the cam. The throttle butterfly should just start to open when that scribe mark is dead center with the roller... not before or after!

2 - Gently means that you have a feeling as you are turning the needle valve in... and when it stops "That's It"! Do not increase the pressure, trying to force it further.

If needed, remove the spring and carefully turn the needle valve in "with your fingers" until it stops... notice the angle of the screwdriver slot... and measure the distance between the carburetor and the outside portion of the needle valve head, making a note of it.

Now, with the spring installed, you have a good idea of when/where that needle valve is seated regardless of the spring back pressure. Adjust the carburetor as follows.

(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.
--------------------------------------------------
That should do it... Let us know how things go for you.

Thanks again, Joe. Great info.

I didn't mean that the roller touched the flywheel itself...just the cam. Misspoke.

- So, I'll get the roller adjusted right (I do know there is a mark on the cam)
- Then, I'll set the needle valve "gently" to 1.5 turns. Then, start the engine. So far so good?
- With the engine running, adjust the idle speed screw on the throttle linkage do that it just stays running. Is that with the throttle backed all the way off or at the point the cam makes contact?
- Then, use the needle valve to smooth things out.

and pray. Somewhere in there, lots of praying! I'm at my whit's end with this thing.

bcontento said:

I'll get the roller adjusted right (I do know there is a mark on the cam)

Click to expand...

- Okay, Once set, ignore it as you do the following

bcontento said:

Then, I'll set the needle valve "gently" to 1.5 turns. Then, start the engine. So far so good?

Click to expand...

- Seat. then back out 1.5 turns

bcontento said:

With the engine running, adjust the idle speed screw on the throttle linkage do that it just stays running. Is that with the throttle backed all the way off or at the point the cam makes contact?

Click to expand...

- As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running. Ignore the cam setting.

Eventually, as you slowly turn that needle valve in, 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 no more than 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

joereeves said:

- As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running. Ignore the cam setting.

Click to expand...

But at what throttle position (all the way throttled back, throttled up to where the roller touches the cam, more than that?) do I adjust the idle here? If the throttle is open a bit, that'll effect the point at this the "engine will just stay running", no?

On most motors the throttle plate is closed at idle.------There are holes in the plate to allow in the correct amount of air / fuel / oil mixture once all is adjusted properly.------It appears to be a difficult concept to grasp , based on many owners and many posts !

racerone said:

On most motors the throttle plate is closed at idle.------There are holes in the plate to allow in the correct amount of air / fuel / oil mixture once all is adjusted properly.------It appears to be a difficult concept to grasp , based on many owners and many posts !

Click to expand...

OK, that makes sense. "Idle" doesn't universally mean throttle plate fully closed. Some, your truly included, assume it means motor running in neutral at low RPMs. Sometimes, on some motors (cars I've worked on plenty), it requires a bit of throttle plate opening, especially with a loppy or long duration cam.

Appreciate the replies all. I'll see what tonight holds for me and let you know.

I suppose it needs to be made clearer.-----On most older 2 stroke outboards the throttle plate is CLOSED when adjusting idle mixture screw.

bcontento said:

But at what throttle position (all the way throttled back, throttled up to where the roller touches the cam, more than that?) do I adjust the idle here? If the throttle is open a bit, that'll effect the point at this the "engine will just stay running", no?

Click to expand...

You continue to overthink the situation..... You've already, if you followed my instructions, adjusted those areas. All you are interested in now is keeping the engine running at its lower rpm when slowly adjusting that S/S needle valve.

Pretend the hood is on that engine and the needle valve is sticking thru the hood somewhere... and as you turn the needle valve in 1/8 of a turn, the rpm increases slightly... so you had to lower the rpms once more with the throttle control... just enough whereas the engine would continue to run.

Eventually you'll hit the point where the engine is going to either spit back or start to die out... and that is the point where you would back the needle valve out to a smooth idle somewhere in that 1/4 backwards turn.

Got the rewind starter back together, made sure the cam roller was in the right position and adjusted the mixture needle to 1 and 1/2 turns out. Primed the line and that baby fired right up. with a throttle backed off all the way it was still idling too fast so I adjusted the idle speed screw until it was a little stumbly and then turned in the mixture screw a bit to smooth things out. Got it purring pretty nicely. Honestly I really didn't do anything differently in this carb rebuild versus the last couple. The single biggest change was the fuel demand valve.

I feel like it's a little short on power compared to where it was before this all started. Not sure how to address it or if I even want to. I would much rather have a reliable smooth-running motor that is a tad short on horsepower then one that I'm fighting with constantly.

Getting thanks to all who pitched in here! I really appreciate the time it takes. Hopefully I can help y'all out someday

Hi, I've read through the post a couple times and I really think your problem was excessive fuel tank pressure. As was mentioned, the sqeeze bulb can supply enough pressure to push fuel past the needle and seat. A big fat puffed up plastic tank is the "red flag" here for me. I cannot understand why anyone would allow a non vented tank out in the sunlight, it is not only unsafe, but foolish. I'm not saying, in any way, that you are at fault, but for someone to manufacture a non vented fuel tank for an outboard motor, (other than the pre 1960 OMC's), is ridiculous.

timguy said:

Hi, I've read through the post a couple times and I really think your problem was excessive fuel tank pressure. As was mentioned, the sqeeze bulb can supply enough pressure to push fuel past the needle and seat. A big fat puffed up plastic tank is the "red flag" here for me. I cannot understand why anyone would allow a non vented tank out in the sunlight, it is not only unsafe, but foolish. I'm not saying, in any way, that you are at fault, but for someone to manufacture a non vented fuel tank for an outboard motor, (other than the pre 1960 OMC's), is ridiculous.

Click to expand...

I agree on all counts! I really think that was the genesis of the flooding. The EPA rules for these tanks prohibits them from being vented to the atmosphere now, right? The "vented" caps only vent IN keeping them from collapsing, but who care if they expand. They are designed to bloat safely. Hogwash!!

EPA is a group of " desk sitters " that makes up rules and guide lines.-----The little man can not spill any oil into the environment.----Yet Wallmart can cover acres of land with yet an other oil residue ashphalt spill and call it a parking lot !!

Right on, Racer. I could tell you about these "scrubbers" on the big ore ships that wash down the exhaust......its full of oil, from these old Pielstiks engines.......you will never guess what they do with the collected slurry. I know, 'cause I used to work on them....retired from that job now. You do what they say, right or wrong.......well.....after 12 years, I got......"dismissed". I can't force myself to do what is wrong.....for money. In the Philippines they call it a "puti".......yup, a "whore".

And....just like that, I can't get it to idle anymore. Nothing has changed except elapsed time. C'mon man! It'll fire up with a little bit of choke, but won't stay running without manually throttling it up and down (pumping it). If I back off the throttle to try and let it idle and low RPMs, it dies. If I kick it into gear while the RPMs are up a bit, it'll run and stay running, but as soon as I back off the throttle and the RPMs drop, it dies. So, am I looking at too much air (too lean) or too much fuel (too rich)? If it NEEDS choke to turn over, then to me it sounds like it's too lean, right?

For my own clarification, turning the mixture needle IN reduces the fuel flow making it leaner, right? AND, using the idle speed screw opens or closes the throttle plate either making it leaner (more open - more air) or richer (more closed - less air).

An interesting side note: the carb build kits always come with a metal port cap. My carb doesn't seem to have a place for that thing nor has it had one in the past that I can remember. The only place that it might fit is where the screen vent port is on the side of the carb, so I've never used it. Just for kicks, I put my finger over the vent screen while I was trying to keep it running and it seems like that helped. Didn't solve the issue, but seemed to extend how long it would remain running at lower RPM. I might be just imagining it though. Not sure if this helps decipher this or not.