Hi all,
Just found this forum. Wish there would have been something like it when I started restoring my 73 2 liter back in 1980. Anyhow still have, and love the car! Here is my question , why is my car backfiring when shutting the engine off?Is there something going on with the carb conversion (dual 40 IDF's) that I did many many years ago. Checked timing, plugs, carb balance etc.. I don't have any gaskets where the manifolds come in contact with the heads, only on the top where the carb meets the manifold. Could this backfires indicate an air leak of some sort, and if so what is the best material or sealant to eliminate it.
Any suggestions would be helpful.

You can cut some gaskets from sheet material from your local FLAPS. Put gasket material on manifold end and lightly tap around the edges with a ball peen hammer then cut with a razor.

You will have a significant increase in idle speed and you will need to ajust the throttle plates. If I recall there should only be like a few thousandths between the butterfly and the bore wall. Back fires should stop too.

Does it also backfire during decel down a hill or rolling to a stop while in gear? Exhaust leak.....

Welcome to the club.

Joe R, thanks for the tip, I will try the gaskets, kinda thought it was an air intake leak, hopefully they will help.
Mikez, never thought about the exhaust, will tighten as well.
Thanks for the quick responses.
RWD

make sure you dont over tighten it and break an exhaust stud. I think the spec torque is like 15 to 18 lbs

Chris, yea I will be careful. I also have to make sure the exhaust sits correctly on the copper gaskets, because I shaved out the center diameter of the gaskets to match my larger exhaust ports when I had the heads ported at Competition Engineering many years ago.

i used new, stock, isolator plates for the both of the intakes. they come with gasket material on both sides. do you experience any "sneezing" or "poping" back trough the carbs? while the engine is running, block the exhaust pipe with your foot, (while wearing a shoe ). if the exhaust system is leaking you will hear it. if it is sealed nicely the engine will labor and nearly die. get 10 replies in and post some pictures.

kevin

When you pull the intake manifolds, check to make sure they are flat where they bolt to the head, both of mine had warped over the years. How old is the carb rebuild? If more than a couple of years then you might consider a rebuild to clean things out. How are the valve clearances? If they tighten up, especially intakes you can get backfiring. Finally, how loose are the throttle shafts? If they have worn too much they can cause a big air leak. Good luck.

Did any one suggest a switch to FI?

FI ?????

If ya can't get carbs to work what makes you think FI would be as easy and inexpensive as a couple of gaskets?

There's always one isn't it

Rdauenhauer, reason i originally switched from FI was because I was sitting at a traffic light one day and someone pulled up next to me and was nice enough to tell me that my radiator was leaking. Can we all say "raw gas on hot exhaust manifolds". Thank God I didn't burn up. I told myself that was it, and ripped out all of my cloth covered german hoses and went to carbs after I rebuit the motor with bigger pistons and cylinders a hotter cam and ported and polished heads.

if it IS an exhaust leak... don't play around... get it fixed, that's how I ended up with a burnt valve... my 1.7 was doing the exact thing you are describing... I would gun it, and when I let off... it would backfire... or after driving on the highway, if I slowed down for a parking lot(or 75) it would continually backfire... then I developed a "miss" that didn't sound right.. and had low compression <_<