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Discussion Starter · #1 · (Edited)
In my other thread HEI installed I discussed about a backfire I was experiencing and The Ape Man posted this.....

Quote:
Originally Posted by Sasquatch
if you abruptly remove your foot from the pedal the car decelerates and then backfires once pretty good. Now it did this even with the old dist. Don't know what the fix is or if there is one. Keep in mind this is a hearse and I'm not constantly into the pedal. I would always back off gradually before and never a backfire. Same thing now. Only happens if at high RPM's and winding it out I just pull my foot off the accelerator. Could this still be a timing issue? Timing chain worn maybe? I can live with it by just gradually coming off the gas. How often do you pull your foot completely from the pedal anyways.




Are you still running the A.I.R. pump? If so, there is a manifold vacuum operated valve connected to the pump's outlet somewhere. If this valve fails or isn't hooked directly to manifold vacuum, the engine will backfire at deceleration.

My question is I am no longer running the Q-jet but instead an Edelbrock 1411. According to the diagram I am posting from my service manual the A.I.R. pump picks up vac at the carb. So on my new carb I should run it from the manifold vac port? This port is teed already for vac. advance and tranny. Just install a threeway tee and go? Take a look and let me know what you think. I've read where people completely remove these pumps? To read in my service manual you'd think it is necessary to have this. For proper crankcase ventillation. Like I said I know there are people who have removed these. As a matter of fact I've only left mine on since it is also the belt tensioner. How do you avoid backfires if this has been removed? Thanks.



 

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The airpump is only needed for emissions control and therefore doesn't "need" to be there for proper operation of the engine. As for the trailing throttle backfires, removal of the airpump will eliminate the backfires if they are caused by "non-diverted" air from the pump. Obviously, if the backfires are due to exhaust leaks, the pump removal will have no affect.
 

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1980 FBC
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The A.I.R. pump valve is controlled my full manifold vacuum. Ported vacuum will not work. You can T it in to something else other than the PCV if there are not enough ports but if it's diaphragm fails then you will lose a lot of vacuum to other critical stuff like the vac advance. It's a good idea to hook the vac advance right to manifold vac and nowhere else if your vac advance is calabrated for that. BTW, make sure the diverter valve actually holds vacuum and is not popped.Of course you can always remove the pump but you will need a pulley setup from a later non A.I.R. equipped Cadillac such as a 77/8/9 W.O. A.I.R. or some earlier 472's. You will not notice any difference in performance without the pump in place and your alternator will spin much slower. The slower alternator usually makes little difference but if you are stuck in stop and go traffic in the rain at night with the lights, wipers and defrogger all on then you might see the lights dim at idle.
 

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Discussion Starter · #4 ·
Think I'll leave it the way it is. No REAL problems. Interesting info on the A.I.R. though.Just took the hearse to Daytona Bike Week this weekend and it ran great no problems. The bikers loved it.

 

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I just pulled on the hose going to the pump. Its now pumping air to nowhere in particular. People remove them, but if you ever had one off and turned it, it doesnt have much resistance. Not worth the fight to reroute the belts, as that is the adjustment for belt tension for the waterpump belt.
 
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