So I've been noticing a LOT of backfiring lately on deceleration with my teener. Timing is good, all excess vacuum ports blocked, what gives?

A can of carb cleaner and a few sprays around the intakes... bam -- intake leaks.

I took off the #3/#4 side and it's brittle, some small cracks. That's all it takes! Cleaned the mating area with brake cleaner and cloth rags on both sides of the engine. Took off the intake runners and sanded them a bit. On the new gaskets I used a permatex semi-hardening compound. Says resistant to everything but laquer thinner, we'll see how it works over the next few months.

I also took the time to remove my cracking intake boot and replace it with a cherry one salvaged from one of the junk engines at Ron's shop. I blocked the large side port that would normally go to the vacuum diaphram that controls EGR stuff and also the other large port on the passenger's side of the intake manifold. I'll save that one for later if/when I install air conditioning and need an auxilary air valve to keep the idle higher. I then removed the large rail that goes across from the intake to the EGR diaphram. This removes the oil breather from the intake system. I installed an early-style oil filler and vented out of the engine bay. I figure if oil is puking up that far while in the high RPMs, i'll be moving so what's the biggie.

I've noticed a bit of an increase in fuel economy, even with smal tires. Somewhere in the neighborhood of 24-26mpg when I was getting 20ish with all that smog crap hooked up. I did have to re-adjust my Air Flow Sensor twice now that it is accurately measuring the air going into the engine. I also noticed when taking the old equipment off a LOT of oil in the intake boot, going to the manifold, etc. Oil does not burn very well so I might pick up a little power and some fuel economy there. Also taking the oil-breather off of the intake may avert the previous 'leaning out' issue at higher RPMs, like 4500-5000.

Now all that's left is to patch the hole in the exhaust and weld in a bung for an O2 sensor and use a wideband O2 in prep for the new engine. And of course, work to be done on the 2056 waiting on it's stand.

On a small tangent... I have obtained a Speed/Reference sensor that I'll be adapting to the L-Jet system. Later variations used a TDC sensor and I plan to do the same to make the injection system independant of the ignition system. I'll probably use a small wheel on the impeller side or look into putting a small magnetic pole on the flywheel. If this goes as planned, it should make the tach and injection timing a bit more accurate. And 'floating points' won't be an issue... for the FI and Tach.

Hmmm... I've been noticing a fair amount of "burbling" sorts of backfires on my 914/6 when it's warm while holding a steady speed or decelerating. Air leak you say? Might I have the same sort of problem? An air leak would suggest too lean a mixture, which is then combusting in the exhaust system somewhere?

Thx,

Skip

Any pics of these areas for a newbie? My 74 1.8 has some popping on deceleration as well. Thanks

Paul

Paul - I'll take some pics when I get home from work. You have a '74 so you'll have a different intake boot and oil filler neck than a '75. Yours should already have the oil breather system not attached to the intake. Can you take a picture of your engine bay as well? It will be easier to make comparisons that way.

I've already covered the car up for the week (that's how it is around here in northern MI). I do have a few pics I can post, though, thanks!

Paul

Are you using the MSD 6 on the 1.8 ?

Yessir Jim, the Hyfire VI. havving issues with the coil takin a poo below 3k RPMS, I'll be getting the same coil as Aaron soon, I hope.

OK, here goes:







Truth is, I've never done any engine work more than replacing the clutch (more times than I care to remember), tuneups, starter motor. To me it looks like a hopeless jumble of hoses and wires.

Paul

Wow... if the Cap'n saw that he'd probly blow a load. Looks like it just came out of the factory.

You're right, it is a jumble of hoses -- to a degree. Back when it was built it conformed to smog regulations of California.

I have a feeling our engine bays will look a tad bit different. New batteries in the camera tomorro!w