Well all the the leaks are fixed, suspension rebuilt, brakes, tires,etc.
I have an annoying back fire when I shift gears and tromp down on the loud pedal...one time each time and can't seem to find out why.
Any ideas what I'm missing?
I'll bet Pete would know...
78 911SC Targa..Euro.

 

Talk about pressure! Seriously, does your car still have a functional smog pump?

Pete

 

Pete: it's my pop's 911 (yeah he has one too).. and no, no smog pump on it..

 

Rob: Just to be sure, the backfire, out the tailpipe, happens when you open the throttle, not when you're in decel mode... correct?
Pete

 

Pete, the decel backfire/popping was MY issue..dad's got the ACCELERATION issue..we're a pair I tell ya!

 

Rob: You're driving me nuts here! Was any camshaft related work done? Cam timing, etc... Exhaust backfire is normally one of two things (1) Unburned fuel in the exhaust that gets ignited by the heat/flame from a different cylinder, or (2) Oxygen entering somewhere that can detonate hydrocarbons. As you press on the gas pedal the throttle butterfly opens, the sensor plate lifts, the fuel distributor plunger reaches orifices which monitor fuel to the injectors, and spark detonates fuel/air at the appropriate time. Are you positive that the car is running on 6 cylinders? Are you sure that the distributor cap doesn't have a carbon track between two firing pins, or that the rotor is correct and in good condition. Are you sure that the CO% is in factory spec, and you're using good copper core spark plugs? Just some thoughts...
Pete

 

Pete, I am gonna let dad take over his thread! But on that note, what's the no-no on the platinium core plugs? I have them in mine! No local parts shops had copper plugs for my car!

 

Oh boy, platinum plugs are JUNK. They're the only plugs that I've ever taken out of a new, sealed package that was defective. There is a huge difference between the "platinum" plugs that you can buy for your car, and W3DPO platinum plugs that are made for Turbos. They just don't work correctly. You should order a couple of sets from Pelican - W8DC for '78/79, and W5DC for '80-83. OK, turn the thread over to dad...
Pete

 

Ok Pete...Dad here:
My backfire is just that...back through the intake not an afterburn out the tail pipe.
It occurs when upshifting and planting the accelerator to the floor...one "pop" and zoom you're off. in 2nd, 3rd, or fourth...haven't noticed it in 5th.
All ignition components are new...(Platinum plugs, will be changed shortly.) Scopes shows all good, timing is correct and advance curve is not erratic. Co setting is per factory spec for U.S. cars...this is a euro.
Thanks for your patience and help.
Bob

 

Thanks for the heads up on the plat. plugs..I'll order today.. Pop's will post momentarily I suspect..his 911 is a white '78 Euro version Targa and mine is the red one you see as my avatar..it's been a learning experience to say the least..

 

Rob,
I have an offer of $500.00 on that slow-motion red car...I think we can squeeze him up to $700.00.
Sr.

 

P.S. I don't have platinums in my car...Rob has 'em in the red car.

 

OK dad, now we have a whole new deal! I've been trying to process an exhaust backfire - not intake! An intake pop is generally related to a lean mixture, or something that can cause the mixture to momentarily lean out. (1) Do you have a factory manual? (2) Do you know how to check/adjust the sensor plate height?

I need more info: (1) Does the car have a catalytic converter? If yes, does it have a nipple from which a CO machine can take an exhaust sample? (2) You're positive that the ignition distributor advance is working properly - not sticking and then releasing quickly. (3) How many revs is the engine turning after you shift, and when you floor the throttle and get the intake pop?
Pete

 

Ignore my Pop's, he's just jealous mine's red and his isn't.

 

This is funniest thread I have read in a while.. Pete you gotta headache yet ?