1960 40 hp Johnson backfires, won't start

[willinokc]

First posting but have received a lot of useful info from this site. Thank you for that.

Have a 1960 40 hp johnson, don't know the history of this engine. Person I bought from said it had run "a while" back, but wasn't sure when. Electric start, thank goodness. Changed points, condenser, coils and spark plug wires to fix no spark issue. Finally found they had wired the kill wires to ground, not sure why. Took me a while to find, my inexperience working against me there.

I'm going to check compression, now that I know I should have done that first, before putting any more money into it but right now I have spark but it smokes and backfires (sounds like a shotgun going off) but will not run.

Flywheel key not sheered, flywheel nut torque to 105. Fuel mix 40:1. Will probably go to 24:1 if I can get running. Gapped points at .20, plugs at .32. I know now I have the wrong plugs but would that cause that much of a problem?

Any ideas where I go next?

 

[jbjennings]

Re: 1960 40 hp Johnson backfires, won't start

Spark plug wires backward reversed?

If not, it MIGHT do that if it were really lean. You might try spraying some premixed fuel into the carb throat or, in case there's other problems, maybe even a little dab in the cylinders.
JBJ

 

[Daviet]

Re: 1960 40 hp Johnson backfires, won't start

Wrong plugs can cause a problem, you didn't say what you had. You didn't say anything about the carb. I bet is in dire need of a serious overhaul.

 

[willinokc]

Re: 1960 40 hp Johnson backfires, won't start

Will reverse wires tomorrow and see if that works. Not sure on plugs but they are way off from what was in there, Autozone found what they said would work. Now I know better. Will get the correct plugs after I do a compression test to make sure engine is worth it.

Have not rebuilt carb yet, going to do a compression test before shelling out more $$$.

Just trying to get an idea of what to trouble shoot next if that comes out ok.

btw, have ordered repair manual but found out after the fact that who I ordered it from (ebay vender) is out of town for another month so I'm up a creek for now. Trying to help myself but it's been one of those weeks.

Thanks again for any advice offered.

 

[Daviet]

Re: 1960 40 hp Johnson backfires, won't start

Just keep askin questions, lots of people here to help you out.

 

[tmcalavy]

Re: 1960 40 hp Johnson backfires, won't start

If if backfires loud like a shotgun, not just a sneeze and jerk, it may blown a hole in the gasket under the powerhead. Got one in the shop that did that...don't know the cure however, except a new gasket, or what causes it.

 

[willinokc]

Re: 1960 40 hp Johnson backfires, won't start

She's alive!...kinda. Compression check is 110 both cylinders. Changed plugs back to original, J8Js I believe. Still backfiring, not kicking over. Then I remembered the suggestion to check plug wires, switched them around and it smoked a LOT less and actually tried to run, had it going for 5-10 seconds at a time. NO BACKFIRES! I know I kept the wires on the same plugs as when I got the engine which means the guy I got it from probably know less about motors than me, SCARY! Tomorrow it's a trip to get some new plugs and I'm thinking next step is a carb rebuild kit probably. I'll be reading up on the site about doing that.

Couple more questions. I'm missing a rod that goes from the High Speed adjust know to I believe the bottom lever. See attached pic. Am I correct in thinking there should be a rod there and can anyone tell me how long it should be, I'm thinking I can probably fashion one w/ a coat hanger. Would a carb rebuild kit come w/ one????

Also, I've heard about taking the bowl apart to see if it's gunked up (technical term), is that the thing on the left of the carb?

 

[Elbo]

Re: 1960 40 hp Johnson backfires, won't start

On the slow speed rod length.What I have done is set the needle about 1.5 turns out.Set the outside of cover ,manuel adjuster.all the way up so when you close the needle on top it will turn it in .Once you have the needle at ruff adjustment most likely you will have to close the needle.Form your rod from the manual knob up to where the needle is at rough setting.If that is not in range you my have set your rough setting again until you get in range of the closest setting.

 

[Willyclay]

Re: 1960 40 hp Johnson backfires, won't start

I scanned and saved a non-factory service manual that covers your motor. If you would like a free copy, send me a Private Message with your email address and I will reply with the manual attached. Good luck!