I've had my 75 Brick for twenty years. When I first got it I was worried about the backfiring on overrun so I consulted numerous sources. And was told mostly they will all do it to some extent some more some less. And that you could reduce it by not having the throttle partially open on overrun, correctly adjusting your TPS, fix and air leaks, fix exhaust leaks, and have your mixture adjusted correctly.
This has generally worked with only the occasional backfire overrun mainly after giving it a bit of stick. However due to a persistent leak between the muffler and the headers the back fire comes back. I was quoted $50.00 Au for the disintegrating fairy dust gasket ( I recently found out that you can get them for $20.00 Au. I tried various solutions all of which worked for a short period then the leak came back, and the backfiring came back. At the moment I am waiting on the hopefully final solution one of Bocutter Eds collet gaskets. Thanks Ed.
In the meantime due to a sooty tailpipe and higher fuel consumption I decided to have a play with my injectors. I built a test rig to observe spray patterns suspecting I had clogged injectors. I had previously had them cleaned professionally twice and recently I have used an Aldi ultrasonic jewelry cleaner every couple of years as well as running Techron once a year. Even then the Brick still occasionally backfired.
After finding dirty injectors I cleaned them by flushing them forwards backwards, and ultrasonic bathing. Finally got two with the correct pattern, and one with an improved but still bad pattern. I ran out of time so I threw the injectors back in and took it for a run and ran it up to temperature. Using a laser temperature gun showed one was significantly hotter than the other two. I decide to run it only occasionally until I sourced stronger cleaner and a sequencer to pulse the injectors. I was also unsure of the correct colour pintle caps, I had tried to get what I believed was the correct yellow but they were not available. I ended up with green, blue and orange, I had green on originally which I replaced with blue.
To try to find out about the correct colour pintle I decided to go over to a mates place and have a look at a totalled engine he had and check it. Before I left I removed the belly pan in order to get a better shot with the temperature gun. I gave it a bit of stick after it had warmed up, and found that it had ceased to backfire. I tried to get it backfire by leaving the throttle partially open on overrun, no matter what I tried it would not backfire. At my mates place I hit the headers with the temperature gun and they were all pretty much even. I have since tried to get it to backfire by leaving the fast idle open and it still won't backfire. and the exhast is still leaking. I pulled the spark plugs on getting home and they are all the correct grey tan.
At the moment I am waiting for correct pintle caps and the sequencer. The mates son who knows a bit about injection is away for another week.
He is building, not sure if it is finished a multi injector tester cleaner with graduated vessels, and is using a much stronger cleaning solution. once I get the parts I'll pull the injectors and see what sort of pattern I get. At the moment I am stunned that maybe when they cleaned them they did not check the patterns. :dunno
Regards Martin.
