70S popping at idle

[Sunbeam47]

My '70S is starting to making popping noises out of the exhaust at idle. Nothing on the over run so I don't think it's an exhaust leak. Possibly an MFI setting? Thanks in advance for any suggestions as to what to look for.
Kevin

[boxster03]

running rich - check plugs - throttle bodies worn - how is the idle ? if running above 900 now and you didn't make any changes - check plugs first then its worn throttle bodies

[Sunbeam47]

You know it does seem a little rich and idle is about 1200. Gets higher the hotter it gets. I'll check the plugs this week.

[wicks]

Search here for multiple possible causes. Could be the dwell/timing is a bit wrong, check MFI pump timing, make sure MFI pump isn't getting debris in the galleries or starving for pressure, correlate your rods, throttles on stops set exactly right. make sure your microswitch is right. How are the air bypass screws set? Fuel pressure, etc. Check warm up thermostat. But all checked, measured, adjusted in the correct order of course. Very important. Don't skip over anything or make any assumptions while doing MFI CMA. Get the timing exactly right and make sure nothing is loose in your distributor/points.

http://forums.pelicanparts.com/porsc...rce-index.html

[Sunbeam47]

Thanks Wicks for the response and the link to the PP site. Lots to check and its possibly/probably beyond my wrenching skills so I would hate to screw it up. I am in the South Bay (Redondo Beach) and I was wondering if you could recommend anyone that knows the MFI system anymore. Lomita911 was my go to place years ago but not sure if they still work on the old stuff. Is Dutch Treat still good?

[RSTarga]

I don't know why everyone immediately goes to an MFI problem. Once set up properly it is VERY reliable. If it was running well before, I would not look there first.
Timing, plugs, plug wires, valve clearance, compression, throttle body wear, distributor wear, etc. etc. etc.
MFI does not adapt to changing parameters like computer controlled systems.
I haven't touched mine in years.

[wicks]

CMA procedures are mostly simple, except for a couple of time-consuming steps like valve adjustment. The steps on top of the motor can be checked off rapidly if things are not out of adjustment. If it doesn't get used much some of the steps can only make things better. First thing I would do is check ignition (including the distributor and timing), microswitch is closing right, and measure the pump rod, clean and re-grease the fittings on all the rods and make sure correlation is right. First making sure the throttles are stopping fully closed but not binding, then close all the air bypass screws, re-open to a couple turns, see how it idles while using an air meter (cheap tool), to balance all the stacks with the air screws. Not a bad idea to pull the air screw all the way out and stick a pipe cleaner through the passage to make sure it's clear. Put each air screw back in its original hole. The idea with these engines is don't CHANGE anything. I mean unless you're intentionally changing something. Just check, measure and adjust.

I tried using mechanics when I had an impossible idling problem, but ended up having to learn the motor - which is a beautiful thing to study, a work of art - and found numerous problems that couldn't be found before. Now, being able to do the simple checks and basic tune in very little time, I always have a perfectly running motor. It's a 73 2.4 MFI with almost 70K on it, original throttles, etc., and it will idle in a state of extreme perfection anywhere I want it, from 500 RPM on up. It is at 850-950 at all operating temperatures now, where before I began she would only run high idle at 1200, or almost stalling choppy idle and nowhere in between, before I began.

A couple bits I learned in the process:

- MFI pumps don't like to sit for a long time without use because the metal will begin to corrode inside and create blockages.
- Timing does a LOT to affect the tune of these engines. Set the points exactly right with a dwell meter.
- Throttle stops need adjustment when the racks start to age. Take all the rods off, carefully arranging them on a towel to go back in exactly the same way, spray out the old grease with parts/carb cleaner, re-grease. Check each throttle body, they should be just a hair from "sticking" shut on the adjuster screw. Then reinstall the rods, making sure that none of them pushes or pulls on any of the throttle bodies when at rest. You install the pump rod first and it must be exactly 114mm I think it is (check the articles). Then installing the rest of the rods, make any adjustment necessary to achieve a snyced open on all 6 throttles. Fun and easy to do. Erector set. Legos.
- Fuel pressure must be good for the system to work right. Especially at idle speed of the MFI pump. Could also have a dirty injector.
- Try a new plug in the popping cylinder to see if any change. You can easily identify which is popping with the air cleaner off. My popping went away after I got the corrosion out of the fuel gallery in the MFI pump (I had already done everything else).

[1970 Porsche 911S]

Hi Sunbeam47. I just bought your Albert Blue 1970 911 from Naples. Would love to speak to you about the history of the car if you wouldn't mind. My email is mlampert50@optonline.net. thx.