Hi Everyone-
I've been posting here before about my Datsun's problems for a little while- My car runs decent until it warms up, then it starts missing and coughing fuel back through the carburettors.
I did a compression test today and I found 155psi on all of the pistons. I added a little oil to the pistons and the figure jumped up to 195psi.
My question is- does this mean that my rings are definately bad? Also, how do I make sure that I install them correctly? I don't want this to happen again! The engine has probably under 1000 miles since I rebuilt it!

-Will

After doing bit of reading it seems that my compression being lower than the specification in the manual might be because of excess fuel washing the oil off of the cylinder walls.
How should I go about lessening the amount of fuel going through my carburettors (Hitachi SU's.)

Will

195 PSI!!!! that's tight!

it might be flooding from too much fuel - "extinguishing the spark" so to speak.

i have no idea about how to tune SUs or what to do, so a search may reveal a few answers.

In my manual for the '78 Datsun F10(that's where the engine was originally installed) it says that the compression should be 192 (standard) or at least 178 (minimum.)
It sounds really high to me also, but that's what the manual says!

Will

Quote: At that mileage the lower compression would be due more to the rings being not yet bedded in, rather than worn out.
Even at 155psi of compression pressure, as long as they are within about 10% of each other, i wouldn't be worying about rings just yet. Make sure that the tappets are correctly set with the engine at full operating temperature. Setting the tappets when cold is just so that you can get it started, you gotta set them when hot once you get it running.

Once this is confirmed, then check the electrics, particularly the coil. If you are running a 12V coil through a resistor, then the reduced voltage to the coil through a warmed up resistor will cause problems, as will a faulty coil, which may perform well when cold, but,... well you get the idea.
If you use a resistor, then the coil should be marked 12V-R,.. in other words, it should be a coil designed to go with a resistor.

Let us know the outcome of these tests. Good luck.

195 psi??? that can't be right can it? i thought 155 psi accross the board in my CA was poifect? i 'm with dodgeman, as long as they are not differing by 10% or more between cylinders and they're running 150psi it sounds fine!

Thanks for the information!
When I swapped the A10 for the A14, I kept the stock coil, but upgraded to a breakerless ignition and a MSD ignition box... maybe the old coil just isn't keeping up! I'll replace it Saturday morning and let you know the results.

Will