[DeTomaso] Why would an engine idle faster after valve adjustment?

Larry - Ohio Time Larry at OhioTimeCorp.com
Sun Dec 11 10:04:22 EST 2016


Jim,

You need to make sure you know if the valve lash spec is for a cold or warm
motor.

Why would the RPM go up....well if you have opened up the intake valve
more/longer you are allowing more air/fuel into the combustion chamber so it
is going to run faster.

I would disconect the carb linkage to maks sure that the carb is not being
held up from closing more.


Larry - Cleveland



-----Original Message-----
From: DeTomaso [mailto:detomaso-bounces at server.detomasolist.com] On Behalf
Of Pantdino via DeTomaso
Sent: Sunday, December 11, 2016 2:31 AM
To: detomaso at detomasolist.com
Subject: [DeTomaso] Why would an engine idle faster after valve adjustment?

My Fiat Abarth has an Autobianchi A112 A2 1050cc pushrod 4 cylinder engine,
10.5:1 CR, fairly aggressive aftermarket cam per previous owner, who used
the car in vintage racing in Germany.
 
I checked the tappet clearances set by the previous owner and found them to
be 6-8 thou, which is what a stock Fiat 4 cylinder engine of similar type
called for, and the engine idled at about 1000 rpm
 
I found the correct specs for this engine with stock cam, which are 10
intake, 12 exhaust
 
But I looked up the specs for CatCams cams for the A112 A2 motor on their
website and even their most mild "sport" cam calls for 0.35mm (0.014") "lash
ramp".  So I adjusted the tappets to 14 thou.
 
Now the car idles at 2000 rpm with the idle screw completely out, even after
I downsized the idle jet one size.
 
Compression testing shows 195 - 198 - 198 - 190 psi with a cold engine,
which is higher than the 175-195-190-175 with a warm engine I had gotten
with the 6-8 thou clearances.
 
Power is very subjective, but I would say the car runs better now.
 
How can adjusting the valves make a car idle so much faster, and can too
much lash cause a problem other than loss of power?
 
Thanks,
 
Jim Oddie
 
 
 
 


Sent from AOL Mobile Mail



More information about the DeTomaso mailing list