[DMCForum] cold start tube explanation doesn't apply
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[DMCForum] cold start tube explanation doesn't apply



Well, you must have a very small path to your intake somewhere and 
it's going to be highly sensitive to a solvent like that but not to 
air. In the stock configuration the path is simply to small to matter 
except to volatile solvents. 

>>Has always bothered me that PRV has no obvious way to vent passenger
side of engine. Guess it's supposed to pass through timing chain 
cover.<<<

Thats exactly how it supposed to work.

>Simple fact remains: many PRV gaskets and O rings, if not tight, 
allow test solvents inside combustion chambers. You'll see and smell 
it in exhaust, so obviously getting in there.<<

I don't doubt that for a minute but air and volatile solvents are 
apples and oranges in their effects.

>>Have spent most of my ownership in quest for perfect idle. Has 
driven me fair to crazy.<<

Mine was a mess also but was easily straightened out. Idles perfectly 
now, hot or cold. And it does so with the valve cover off or the 
breather removed. (Makes a mess with the cover off though, I wouldn't 
do it.)

All I'm saying is there is a very limited path into the induction 
system from the rocker covers and therefore, the timing cover. Using 
carb cleaner to chase leaks will lead you down a false path. Sure, 
you'll find the leaks and mabe even fix them and thats a good thing 
but it'll have little or no bearing engine performance, especially at 
WOT where the delta P is small. In other words, you've been "suck 
into" believing these leaks are bad by the volatility of the carb 
cleaner. Now a direct leak into the induction system from say, an 
intake gasket, is much more of an issue.

Technically, any air drawn in is not good but there is not vacuum as 
you're used to dealing with it under these covers. Even my Turbo 
Toyota Supra's service manual makes it clear these areas should be 
leaktight but only for proper crankcase and rocker scavenging, ie; 
PCV operation since the PCV system does port into the intake. If you 
want to know for sure how these cover "leaks" affect idle performance 
the only real test is to port a gas anaylzer into the exhaust stream 
and see if the mixture changes when they're present. It will change 
for sure when you spray carb cleaner around the covers as long as 
some finds that small path to the induction system, even though that 
same leak as air would have little or no effect. If there were a path 
large enough to upset the idle it would certainly happen when the oil 
breather is removed.

When dealing with any vacuum system you must always consider where 
the high and low pressures are and try to visualize the direction the 
gases will flow and under what conditions. You must also be cognizant 
of the flow rate and volume involved, not just the pressure. 
(Although pressure and flow are related to a point.) 









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