8hp Johnson carb tuning float adjust help needed

[bcontento]

I have a 8 horsepower Johnson that needed a carb rebuild after sitting. Rebuilt with no with issues but still having some trouble on the boat. I'm able to get it to idle nicely and run up a little bit but at anything more than half throttle it bogs really badly. I've got good compression on both cylinders and good spark. I figured that when we put the carb back together that maybe the float adjustment was bad and it was flooding badly at wot. I had a buddy of mine that is better at this than I am helping. When we put it back on the motor and went to dial it in he was surprised at how far out we had to turn the mixture screw. He said it's typically two or three turns and we were out like 7 or 8. Not sure if that matters at this point.

I have the carb back off. Can someone point me to the correct way to set the float level? I know I have to bend the little metal Tang but I need a measurement or visual guide. Some of the things I've seen online don't come with any level of accuracy.

Also where thethe little fuel Inlet tube attaches to the plastic Riser are appears to be a tiny little set screw next to it. Does that do anything? Do I need to do anything with it? It's in the the photo below.

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[RCO]

The float should be level with the carb body when the carb is flipped upside down. From what you are describing, I don't think the float level is your issue. At 7-8 turns on the low speed mixture to get it to idle, something in the carb isn't right.

 

[racerone]

Could be a hole in fuel pump diaphragm.-----Does spark jump a gap of 3/8" or more , yes or no ?----I do not believe it is a " float level " issue.----The little " set screw " may well be the high speed jet and it needs to be clean.

 

[bcontento]

thanks guys. Forgot to include that the fuel pump is new as well. Not to say it couldn't be a hole. Not sure on the spark jump, but I'll test it and post results.

So if that set screw is in fact a high speed jet and it's out of adjustment, that would make sense with my symptoms, yes?

 

[racerone]

It is a jet but it is not adjustable.---It has a calibrated hole to let the correct amount of fuel through.----You installed a new pump instead of repairing with a $4.00 diaphragm ?----Any pictures of that " set screw " and is there a wee hole in it ?---Checked the flywheel key ?

 

[oldboat1]

Post a model number.

 

[bcontento]

ok, some clarification.
- the set-screw/jet in the plastic center piece is like racerone just a jet. not adjustable. I took it out and there is no adjustment of any kind
- fuel pump was rebuild, not replaced. mispoke
- the motor model number is J8RESR
- don't know how to check the flywheel key

In checking the float adjustment, I noticed that the center plastic riser does not stay in place against the metal base in the throttle body. It has play in it up and down so when the carb is flipped right side up, it slides down a bit (1/8"-1/4") and interferes with the float a bit. I don't see a way to afix that plastic piece. there is no screw or hold down to keep it in place? If it was keeping the float from rising correctly, that would certainly keep the needle valve from closing causing severe flooding, yes?

One more note: the motor winds up to full throttle in neutral no problem. The stumble is only under load.

thanks again all! Trying to get the boat running for my boy to fish in.

 

[bcontento]

found the diagram finally.
"plastic thingy" = nozzle well
set screw = high speed orifice
idle mixture screw that is 7 turns out = slow speed needle

https://www.boats.net/catalog/johnson/outboard-by-year/1990/j8resr/carburetor

 

[oldboat1]

The plastic nozzle well in your '90 has a gasket on the top and the bottom. Run a very small piece of wire or piece of monofilament through the orifice in the little plug.

 

[oldboat1]

Initial idle screw setting is likely 1 1/2 open from lightly seated. Adjust from there when running.

[Edit. will work for cross reference here: http://ww2.iboats.com/Carburetor/dm/cart_id.618333994--session_id.075394392--view_id.1536636]

 

[racerone]

The motor will run fast in neutral on just 1 cylinder so that test / statement means nothing here.

 

[bcontento]

The high speed corifice is clear The gaskets don't keep the nozzle well from moving. I feel like it should be seated more tightly somehow.

I used a stand of wire to clear all ports again and blew air through everything.

How should the screw (in the photo) that controls the throttle be set at initial setting? The butterfly inside the throttle body. Should it be cracked open just a hair?

 

[oldboat1]

After assembly, the roller on top needs to contact a cam on the mag plate under the flywheel. It opens the throttle, and needs to be adjusted to contact the cam precisely on the mark (on the cam). The nozzle should be held properly in place when the carb bowl is reattached, after the float is in place.

Beyond that, I don't know what you are describing.

 

[bcontento]

all makes good sense! I appreciate the help in the clarification. I need to figure out how to keep that nozzle well in place because it definitely moves

 

[bcontento]

Update:
put the carb all back together and reinstalled. I set the cam follower throttle screws at the roller makes contact right at the Mark and I set the slow idle mixture needle to one and a half turns out. It's difficult to tell where lightly seated is with that spring on there but I did my best. After a little dialing I was able to get the motor to idle nicely at a low speed. I had to turn the slow speed needle out about one more turn and mess with the cam follower speed screw a little but not much. I think previously that adjustment was way off requiring the low-speed needle to be letting much more fuel in.

Put it in gear and headed out for a test run and unfortunately experienced to the same issue. shut the motor off and pulled one of the plug wires and started it back up and it ran very similarly (idle but no real throttle) leading me to think maybe the other plug or cylinder wasn't firing. I shut it back off and pulled the other plug wire replacing the first one and again it ran about the same. I put both plug wires back on and fiddled with where they connect to the coils. 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. Now I can't seem to get it to start or idle without excessive choking and Feathering on the throttle but once I do get it started and in gear it flies. Not sure if that will last. I'm kind of stumped. I'm going to start with new plugs. Any other suggestions?
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[oldboat1]

Progress, it seems. Try adjusting the needle slightly richer for starting (c.clockwise). Also, measure the spark to test ignition health -- should see about 7/16":

 

[bcontento]

Tested spark. Jumps across a good sized Gap (screwdriver to plug). I don't have a real gauge for testing spark. Of course, that's just at start, not throttled up. Something happened during my first test. I went from idling nicely with the nearly correct screw settings but no WOT to it finally kicking into WOT but no it won't idle. Only way to keep it running is to manually feather the choke off and on.

Don't know where to turn next. :mad-new:

 

[bcontento]

Any other suggestions would be greatly appreciated. I'm stuck

 

[oldboat1]

There are spring clips in the coil boots. You might make sure that they have solid contact with the wires. From your description, it sounds like there may be a coil connection issue.

 

[bcontento]

Thx. I'll check that tomorrow. Can I buy plug wires for this motor at Auto parts store or are they special wires?