low compression on both cylinders 20 hp johnson. wont start

Hi, I have a 1966 20 hp johnson I recently bought that was said had not been ran in a couple of years. I have cleaned the carb, put plugs, points(set at .020) and condensers in it and it does have good spark. I can not get it to fire at all even if I spray gas or starting fluid in the carb., only a back fire. I have 60psi on the top cylinder and 58psi on the bottom. They are both pretty consistent with each other which I know is good but I am unsure if they are both too low and causing my problem. I have spoke with a few boat mechanics and have of them say it is too low and the other half say it's fine. Everyone says a little low is fine (80psi or 90psi) but no one say anything about 50 or 60. Is this the problem? Could it be something else? I do have some piston slop so I realize it does need some work but I would like to get through this summer before I bite the bullet. Please help!

Re: low compression on both cylinders 20 hp johnson. wont start

60psi is pushing and 50psi is bad JuJu time for piston and rings! Welcome to iboats.

Re: low compression on both cylinders 20 hp johnson. wont start

Try squirting some oil in the cylinders and see if the compression comes up.
The compression you have is enough to start the engine.
When you overhauled the carb, did you remove the small welsh plug on top of the carb and clean the passages inside? Where is your low speed jet set, should be 1 1/4 turn out from lightly seated.
You don't have the plug wires crossed do you?
And DO NOT use starting fluid, spraying fuel mixture into the carb is ok.

Re: low compression on both cylinders 20 hp johnson. wont start

Yes I did do a wet compression test and it really didnt improve much but maybe 1 or 2 psi. I will check for that welsh plug and the low speed jet tomorrow. I dont know which coil goes to which wire, can you help with that? This is already helpful thanks.

Re: low compression on both cylinders 20 hp johnson. wont start

Without looking it up, I beleave the front coil goes to the top plug.

Re: low compression on both cylinders 20 hp johnson. wont start

Thanks I will check those things and get back with you tomorrow.

Re: low compression on both cylinders 20 hp johnson. wont start

Pull start? If so, you're not going to get a lot more than you did. Keep checking. It should run.

Re: low compression on both cylinders 20 hp johnson. wont start

does anyone know if I can get sleeves for this engine?

Re: low compression on both cylinders 20 hp johnson. wont start

I have seen them bored, but don't think I have ever heard of anyone sleeving one.

Re: low compression on both cylinders 20 hp johnson. wont start

If it has sleeves, it's not a DIY deal.

Re: low compression on both cylinders 20 hp johnson. wont start

I don't think your compression is too low. The match is good. The only thing I know of that can make both cylinders low and still match up well is a leaky head gasket. With 60 and 58psi it should run, even if the gasket does leak.

The backfire is the major clue. Check that your plug wires are correctly connected and that your flywheel key is not sheared.

Go to the Top Secret File ^^^ and do "Outboard won't start" troubleshooting.

Let us know what you find.