Help with '59 Johnson 10hp - Carb rebuild and seafoam

[Beefer]

I tend to be a bit long-winded, but it gives you the whole picture, so bear with me....

I have a '59 Johnson QD-20 10hp on my tinny. The first few times I took it out, she cruised right along, with a max of 21mph. Problem was, she would die at idle, and the needle valve wouldn't adjust anything. I figured I need a cleaning/rebuild. On Wednesday, I wanted to go out, and I threw a full can of seafom into about 5 gals (6gal tank). Well, (I'm guessing) this caused a loss of power because of the high ratio of seafoam to gas, and I could no longer get up on plane (6-8mph WOT), but the low end was running a bit better (still wouldn't hold idle). So I succumbed to the fact I need to do it right, and actually tear the carb down, clean, and rebuild. Last night (Thursday) I did this, and got a decent amount of crud out. Today, I re-assemble everything, and add 4 gals of fresh gas to the remaining seafoam mix (about 1.5 - 2 gals). First thing I noticed was it wouldn't start in anything but full throttle (I attributed that to the carbs needing adjustment).

So now I have her running in WOT, trying to lower the rpms, but she keeps stalling out if I come off full. In the high speed needle seat I have 3 packing washers, and also 3 in the low speed. I originally only put in 2 in each. Now there are changes when I turn them, but I still can't come off full throttle without dying.

So my first question is - could the seafoam mix be affecting the runabilty that much?
Secondly, if it's not the seafoam, where should I be looking?

Unfortunately, I only have one gas tank to run off of, otherwise I'd try fuel without seafoam.

 

[Johny25]

Well seafoam does not burn as well as gas so that could be an issue if you have added a high concentrate. Second, seafoam is meant to break up and dislodge all sorts of gunk, and this is all suspended and floating around in you fuel lines, filter, carb.....etc now. So you probably need to get it running and try to keep it running until you know you are running clean fuel. Then I would suggest another carb inspection (teardown). Is there any way you can flush your fuel lines up to the carb? Seafoam will dislodge junk out of your gas tank and line going to your engine also. Feeding into your motor.

 

[cajuncook1]

Seafoam is great fuel additive that helps decarb your motor and not your carburetor. A carburetor has to be manually disassembled and cleaned.

Chances are that when you put all the Seafoam in the gas ( which is ok ) you didn't harm your motor, you gunked up your spark plugs. Your plugs need to be removed and cleaned and make sure they are gaped at .030 inch with a feeler gauge.

Here is a link with some very good information about your motor. The author is creditable.

https://www.sschapterpsa.com/ramblings/johnson_QD.htm

 

[Beefer]

cajuncook1 - You are da man!

Between the time I posted the thread, and the time you responded, I rebuilt the carb again, checking to see if I missed something, or put it together wrong. Nope, everything was done correctly the first time.

Saw your post, and sure enough, there was a tiny piece of gunk in the top plug!

Just tried her out, and WOOHOO! Running like a champ! Thanks ever so much!