Where's the flame arrestor?

autobonrun · autobonrun's Garage

My Clymer's manual states that the crankcase emissions vents to the oil tank then through a flame arrestor before going to the air box. I see nothing from the oil tank to the air box but a hose. Are flame arrestors used and should my 79SC have one?

RarlyL8 · RarlyL8's Garage

The "flame arrestor" is a small metal weave band in the hose. This is part of the reason that the idle becomes erratic when you take the cap off of a CIS car vs a carbed 3.0L (modified, of course).

RoninLB · 01-12-2002, 07:56 PM

Rarly.. I remember reading about the eradic idle when oil cap is removed. Do you remember the rest of the story?? I have a '77 CIS and never noticed any idle change.

autobonrun · autobonrun's Garage

Quote:

Originally posted by RarlyL8
The "flame arrestor" is a small metal weave band in the hose. This is part of the reason that the idle becomes erratic when you take the cap off of a CIS car vs a carbed 3.0L (modified, of course).

Should it be visible and if not should I just assume it's inside? Is there a danger if it is not?

Early_S_Man · 01-12-2002, 09:05 PM

The same flame arrestor pn is used for all carbed, MFI, and CIS applications, and it is always a slip-fit into the air filter/box end of the barb fitting for the 25 mm vent line to the oil tank. If you remove the vent line, then the air filter housing or air box ... look directly into the end of the fitting for the vent hose and you should see a perforated brass object, assuming it wasn't removed and accidentally left out after cleaning, etc.

RarlyL8 · RarlyL8's Garage

I have'nt done any research on the specifics of the idle drop when the oil cap is removed. My '78SC with CIS drops the idle because the pressure of the dry sump system changes when you open the closed system to the atmosphere.
My '73T with Weber carbs did not change idle because the system was adjusted at ambient pressure with a K&N oil breather filter placed on the oil box in place of the line that would normally have gone to the air box for the MFI. The fitting at the air box is blocked off, eliminating the Vacuum leak caused when the oil cap is removed.
If your CIS car does not drop idle when the cap is removed the system must not be receiving the change in presure, or has been adjusted to accomodate it somehow.

RoninLB · 01-13-2002, 09:04 PM

RarlyL8...good info, gives me some thing to work with. Not sure I under stand it all. I remember this subject but never followed up on it. May be a '77 US CIS is some how different, may be not. No idle drop before rebuild and none after. No one has ever touched eng but me since I have owned it, which was before rebuild. My brother owned it since '79 and always took it to high end Los Angeles Posche only shop. The vent into air box is clear. "Adjusting to accomodate it somehow " I never did any thing special when setting up eng. after rebuild. I guess the little fuel burner between my ears has some thing to do now. Thanks for feed back.