1973 Johnson 20 hp sneezing at low idle.

[sharrison]

Bought it a month or so back but finally had a chance to get on the water with it.

Things i've checked, replaced or rebuilt prior to taking it out on the water..

Good compression 100 psi +/- on both cylinders
Good spark, It will jump 1/2" gap with no issues
New plug wires and boots
Cleaned and set points to .020"
New J4C plugs gapped at .030"
Rebuilt carb completely with a kit so the plugs were pulled to completely clean it.
Fuel lines replaced
New water pump
Armature plate doesn't wobble around
I pulled the intake and checked the reeds, All were clean and apeared to be sealing. I did not completely pull the reed plate off the motor since I did not have a new gasket for it.
Checked the throttle plate opening correctly with the marks on armature plate. It starts to open right at the 2 marks

Didn't notice any oil around the upper crankshaft seal, But I did just pull it all apart last night and cleaned it, So if it does leak hopefully it will show next time I get it on the water.

Slow speed is about 1 1/2 turns out. If I run it with the SS needle out further it doesn't seem to make much if any difference with the sneeze, But does make a difference when I go WOT. When it's turned out richer it bogs down slightly when I go WOT.

Motor starts right up with one or two pulls and seems to run good except it will sneeze at low idle. If you crack the throttle slightly it doesn't do it and will go around the lake at low speed without any issues.

It doesn't have a thermostat. Waiting on it to get here. It still sneezed even after running it for 20 minutes or so around the lake and the water was warm coming out of the housing.


Sorry for all the text, Just wanted to try and get all the info the first time..

Any thoughts? something i've over looked.

 

[ultra353]

How does the tip of of the needle look, any grooves, tip not broken off. Was the low speed packing replaced. When its running spray wd-40 around all gaskets and mating surfaces to see if there are air leaks. Rpms will increase if you have a leak.

 

[sharrison]

Needle looked good and when fully seated it sticks into the low speed cavity. Yes both seals were replaced on the low speed. The inner one was hard and came out in pieces. The keyed one was ok but was replaced as well.

I forgot to mention I did spray it while it was running and couldn't find any vacuum leaks. But i'll recheck that just to be sure..

Thanks for the suggestions..

 

[Pappy]

Is it sneezing from the carburetor throat? If not you should be able to locate the area that the sneeze is occuring from. Very often it is located where the crankcase halves meet so take a strong light and shine in that area while it is occurring. Another area is the intake by-pass covers. Check there as well.
If it is sneezing from the carb throat then make sure the throttle blade is closed at idle. There are marks on the pick up cam that will align with the roller on the carb to start the throttle blade opening. They should not be open until that point and the engine should be able to idle on proper timing and mixture adjustment under that point.

 

[sharrison]

It's popping through the exhaust. Sounds and acts pretty much like this one does I found on Youtube.https://www.youtube.com/watch?v=IozvLtLN3Jg

I did adjust the throttle plate using the marks on the armature plate so it's closed until the roller gets to the marks. So when it's in neutral it never opens the throttle plate.

I'm going to try and test it tomorrow if the weather holds out, I'll video it and post it up if I do.

Thanks again guys. Great suggestions and i'll try them all.

 

[sharrison]

Didn't get to test it today due to the bad weather we've been having lately. I did put the Thermostat in it so we'll see if that makes any difference.

 

[sharrison]

Got it back on the water today for an hour or so and it ran pretty good. Still had the sneeze from time to time in no wake zones, But seemed alot better then before, Maybe the thermostat helped?
With all my fishing gear, 6 gallons gas, 2 batteries,ect. GPS showed 23 mph. The boat isn't light so i'm happy with that.

I pulled the flywheel off when I got home and there was no oil coming from the top crank seal. But I think just for my own sanity i'm going to replace every seal and gasket on the motor. It's not expensive for the kit and i'll know it's good to go then.. I've did almost everything else beside that so why not.

 

[sharrison]

Still having some issues with this motor. I am 98% sure it's not a vacuum leak anywhere, I did order all new gaskets but hate to tear into it that far unless it's needed. I've tested every gasket and seal while it was running and it made no change.
I took it out this morning and it started right up but didn't want to stay running at first unless I gave it some throttle. It never shut off on me but you could tell something wasn't right. It felt really weak and was alot slower then the last time I had it on the water. I got it home and pulled the plugs and both were wet, I retested the spark and the top coil seems to lose fire at times now. The bottom coil will still jump a 1/2" gap with blue spark no problem but the top one will not. It will jump a 1/4" gap but sometimes it seems the fire is weak. I swapped the coil pack harness wiring to see if it could be the points or condensers and it still did the same thing, The top coil was always weaker then the bottom one. So that pretty much points to the coil correct?

I'm tired of throwing money at this thing, But I want it right. What should I do? Buy 2 new coils and try that?

Also on a different note, When I rebuilt the carb I couldn't get the bottom orifice plug out of the carb bowl. Is there a trick to doing that? I did make sure it wasn't clogged, But would like to be able to pull it out at a later date if need be.

Thanks

 

[ultra353]

If you have an ohm meter try testing the coil thats giving you trouble. I believe it should be between 3-8k ohms to work right. I would check your plug wire as well on both ends for corrosion/breaks ect. Make sure the points are clean( no finger prints, residue. I always spray them off will elec contact cleaner when i`m done ) and use your meter on the points. Is your float installed correctly with the proper adjustments. Welch plugs on carb completely sealing- try some sealer around the plugs?
Pull your fuel pump and make sure its not leaking thru the pulse hole, with pump off squeeze the bulb and look for fuel coming out the back. Another possibility is the lower crank seal

 

[sharrison]

If you have an ohm meter try testing the coil thats giving you trouble. I believe it should be between 3-8k ohms to work right. I would check your plug wire as well on both ends for corrosion/breaks ect. Make sure the points are clean( no finger prints, residue. I always spray them off will elec contact cleaner when i`m done ) and use your meter on the points. Is your float installed correctly with the proper adjustments. Welch plugs on carb completely sealing- try some sealer around the plugs?
Pull your fuel pump and make sure its not leaking thru the pulse hole, with pump off squeeze the bulb and look for fuel coming out the back. Another possibility is the lower crank seal

Great suggestions.. Brand new plugs,wires,boots on the old coils. I'm like you and always clean the points with electrical cleaner before putting the flywheel back on. Float is adjusted by the OMC instructions. I sealed the welch plugs when I did the rebuild. Fuel pump is rebuilt and I did check it before I put it on to make sure it didn't leak and the check valve/spring inside was in correctly and you could only suck through it one way.. I did order a new lower and upper crank seal, So worse case I do have them as well as all the rest of the gaskets ready to go

Now what I did find...

Rechecked the top coil the other day and the primary side is bad. Only acts up some times, Sometimes it reads 6K ohms, other times it doesn't read at all. I even pulled the plug wire out of the coil to make sure that wasn't the issue. Weird it reads fine sometimes and then bad others. Most times they are either good or bad (at least on auto type coils) So I'm going to get some new coils and that should fix that issue. Then we'll see if the low speed miss goes away..

Thanks again for the great suggestions.