olddragger

iTrader: (3)

well i just did a home vacumn test on the car --used lower intake port---and got a reading of about 15.8. engine has 45K--no pre mix---5/30 oil. Looks like I will be going to the dealer for a compression check?
olddragger

MazdaManiac

iTrader: (3)

That is low-ish, but not tragic.
On my high compression motor (830kpa across the board, idle vacuum is only 59 to 63 kPa (17.4 to 18.6).
I don't think they will fail you on a vacuum test until it drops below 45kPa (13.2 in/Hg).
What was the idle speed at that vacuum?

mysql101

my vacuum reading changes if the ac and radiator fans kick on (part of the int-x and the stalling issue I'm sure). Usually neg 18-19 at idle, can be as high as -15 when it's got the rough idle (intx and radiator fans + cooling mod). During engine braking it's even further down to -21 to -22 range.

Do the engine brake and see what numbers you get

olddragger

iTrader: (3)

normal idle speed--825 or so-850 on a good day.
I do have some rpm drop at idle at times , the old stumble thing. drops to 500 for a sec then goes back to regular. I really cant say i have a lost of power. maybe a tad on top end. no problems when drove for a long distance.
Could it be a carbon thing? Do I need to do steam cleaning?
MM, were you running pre mix when you took your readings?
OD

MazdaManiac

iTrader: (3)

I always pre-mix. 8oz to 14 gal. I don't think I get readings much lower without, though. Maybe 2 to 4 kPa.

With the A/C on (compressor engaged) the vac will drop at least 10kPa (3 in/Hg). Fans on will do another 3 to 5 kPa (0.8 - 1.5 in/Hg).
Decel will be 70 to 83 kPa (20.6 - 24.5 in/Hg). Engine braking doesn't tell you anything.

Idle stumble should never drop below 690 RPM. 680 and down under normal idle load (everything off) gets you a new engine.

Steam clean can't hurt. Just do it the way Pineapple Racing indicates.
http://www.rx7club.com/showthread.php?t=42318