Compresion test help

[nashwinter123]

Hi,
Im doing a compresion test on my 40 hp 1964 johnson. Both cylinders read 60 psi. This is in nutreal and the power is off obviously. It is an electramatic. I dont know if that makes any difference but i tryed the test with the lever all the way down too because i herd that it could make a difference. First of all is the throtle placement true? Sencond I know its not supposed to be 60 psi. 125 or 135 is right, right? I have not been able to adjust the carb correctly yet because of this odd behavior. No matter what it is throwing out LOTS of white smoke. Im thinking the head gaskets dead and water getting in. Any other suggestions

 

[nwcove]

Re: Compresion test help

some say test at wot., others say it doesnt matter. i test with the throttle closed. jmo...but for the price of a head gasket, its definitely worth doing....and check the head for warpage and do the diy fix if it is. pulling the head will also let you have a look at the cyl walls.

 

[Sixmark]

Re: Compresion test help

General rule of thumb is for the cylinders to be within 10% of each other, but seeing how you are only at 60 psi that's low no matter how you slice it.

 

[HighTrim]

Re: Compresion test help

That is too for that motor. I have had many of them, all were in the 110 to 145 range. Doesnt matter where the throttle is, if you dont believe me try it, it will be the same.

Pull the head, dress it by taping a piece of emory cloth to glass panel or a mirror or something perfectly flat and doing figure 8s with the head. Install new head gasket and torque to spec. Then re test. Hopefully that solves your problem.

 

[nashwinter123]

Re: Compresion test help

Could it explain why i cant get my carb adjusted right? And the white smoke?

 

[HighTrim]

Re: Compresion test help

If that white smoke is actually steam, that is not good. Do not run that motor again until you investigate what is going on. I would start by pulling the head

 

[F_R]

Re: Compresion test help

It is SUPPOSED to smoke!!! That's what happens in a two-stroke where you mix oil with the gas.

As for the compression, remove the bypass covers from the side of the powerhead and poke at the rings to see if they are stuck in the grooves. You can do the other side too, if you feel like it.

 

[nashwinter123]

Re: Compresion test help

This smoke isnt normally 2 stroke smoke. Its THICk

 

[twocyclemania]

Re: Compresion test help

Could it explain why i cant get my carb adjusted right? And the white smoke?

It may well be why you can't adjust the carb! Just had a similar problem with my 53 Firestone 5. It has been a previously well running motor but on a recent tests I could not get it to idle. I had the carb off three times and was about to give up when I realized how easy the pull start was (no resistance). Checked the compression and it wasn't there. Head gasket time. Sounds a lot like yours. Good luck!

 

[boobie]

Re: Compresion test help

You could also try a different compression gauge and see what you get.