page loaded in 0.062 seconds
| | Site Map | Back Page Art | Back Issues | Privacy and Security | Terms of Use | |
| Home | Features | Articles | Daily Drives | Rear View | Driveway | Directory | Showcase | Classifieds | Store | Games |
by Tim Cerami
Copyright (c), 2003, Tim Cerami -- All Rights Reserved I am the proud owner of a 1975 Pymouth Valiant Brougham 2-door, one of only about 5700 ever made. After throwing down a mere $400 for this 318 powered "beauty" with a known oil pump issue, I found myself faced with performing a complete engine rebuild. After spending the spring months rebuilding the engine and getting it back in the bay, it was time to fire her for the first time. After some complications with the transmission linkage, the V8 came to life with a roar. After a couple hours of tinkering around with the timing and carburetor settings, I had her running pretty smooth. My expectations were high considering I just spent many, many hours tediously laboring over every nut and bolt during the rebuild. With the engine running well, it was time to take the car to pass the emissions testing where I live in Idaho. For those wondering, some counties in Idaho do require emissions inspections and testing and we aren't just about growing potatoes. (ha, ha) Feeling extremely confident, I pulled my car to the testing station and let her idle. After the tester attached a line to my #1 spark plug wire and jammed the sensor into the tailpipe, I hopped out to watch my car pass with flying colors. After all, I had basically a brand new engine, a rebuilt Carter 2bbl carburetor, new plugs, new wires and an otherwise solid ignition system. After about a minute, the tester indicated that the prognosis was not good and failure was forthcoming. Another minute later I was holding a report that showed my failed results in both the idle and high speed test. I was perplexed, along with $13.00 poorer! For a 1975 vehicle, the Idaho test requires the car to remain under a 3.00 CO level at idle and high-speed, around 2500 RPM. My car pushed levels of 4.5 and 4.7 respectively. 
Driven to pass this test, I got my hands on a screwdriver and attacked the idle mixture screws.
I leaned out the mixture pretty far, causing the engine to stumble and miss at idle. The next
day I returned to the test station for test #2, which is free if I don't pass.I was nervous as test #2 started, wondering what I would do if the car didn't pass this time. I sweated under the hot Idaho sun as I watched the computer screen for a huge sign that said, "Congratulations, you passed!" Unfortunately, no such indication was given as I was again handed a report with discouraging results. For test #2, I passed the idle speed test at 2.75 but again failed the high-speed test. As I studied the report, I asked some questions to the tester. What adjustments can I make to pass the high-speed test? His response... "Smaller jets." With report in hand, I ran over to a recommended repair shop to ask more questions. Again, re-jetting the carburetor was mentioned, along with about $200 in expenses to get this all worked out. $200..???? I could go through the test over 30 more times at that expense! I decided I was going to figure this out one way or another myself! With some new information and still several days before I needed to pass the test, I started asking my friends and fellow car enthusiast for their opinions. I put my thinking cap on and considered EVERY possibility. Were these the stock jets? How could the jets get worn to the point that they allow too much fuel? Did the previous owner install different jets? The questions went on and on. I pulled out some spark plugs and found them to be very carbon fouled. So I picked up a new set, gapped and installed them. I then started thinking back to when I first bought the car. The previous owner installed an Accel coil and spark plugs that were one heat range too hot. Why...??? What problem was he trying to solve…??? It had to be this very problem!  A couple days later I received an e-mail from my friend Pete that contained scanned images of his 1974 Plymouth service manual. He focused in on the pages concerning the Carter 2bbl. I studied the pictures carefully and focused my attention on the assembly that holds the metering rods. Was there a way to get the metering rods to sit deeper in the jets, allowing less fuel to flow through them? The answer to this question was my next mission! I pulled the entire carburetor off the car and began a complete tear down. This will be the 3rd time I have done this, so it was like tying a shoe at this point. When I got back to refitting the metering rod assembly, I noticed a small hex head screw at the top of it. With it almost completely assembled, I marked the height of the assembly. I then grabbed an allen wrench and started to spin this screw down. Doing so lowered the metering rods down into the jets by almost ¼" based on my previous markings. Now this was starting to make some sense. With my adjustments made, I placed the carburetor back on the manifold and mentally prepared for emissions test #3. The next day, and in weather that did not favor passing a test (too hot), I took the car in for its third test. Unlike test #2, I was feeling pretty confident that my adjustments would result in a passing grade. After all, I had already passed the idle test during test #2. 
With the car hooked up, I leaned on the door and watched the computer screen. The high-speed test
ran first, which I passed at 2.75. Next was the idle test. FAILED! But not just your typicall fail.
This failed badly, pushing a 7.05 CO level out the pipe at idle. I felt both shock and anger rush
over me. This could not be. I already passed the idle test before. What the hell happened? Was there
any way I could pass both tests at the same time? I was irate!Now what was my plan? I felt like I could do no more to adjust this carburetor, but I knew it had the capability of passing this test. I drove around, thinking about my next move. More adjustments…?? Give in and take it to a shop…??? Grrrrrr!!! Saturday morning I rose with a clear head. Since my next test was free, I decided to attack the mixture screws again as my internal adjustments may have "upset" the previously successful idle speed test. This time I decided to pull out a vacuum gauge to do the test. After attaching the gauge to vacuum, I verified how many turns out each mixture screw was set at. About 2.5 turns out. Seemed excessive. I started the engine and watched the gauge rise and settle. I turned the screws in to 2.0 turns out. No change in vacuum. I then turned them to 1.5 turns out. Again, no change in the vacuum level. I went in to 1.25 turns out and vacuum started to drop. I found the mixture screw sweet spot at 1.375 turns out. Below that I lost vacuum while above that I didn't gain vacuum. Now I felt I had it completely tuned. After stopping at the donut shop for a bear claw, I headed to the testing station for test #4. My thoughts drifted between confidence and nervousness as they hooked back up to my engine and tailpipe. I was at my technical limit this time. There would be little to proceed with if I failed again. To put an end to this frustrating experience, the engine finally passed both tests with the following results: 
Idle test: 2.05 High-Speed test: 0.25 Victory was finally mine, along with the full function of my brain, which was constantly spending cycles trying to solve this problem. In all, I learned a lot, saved some money and got her to pass the test. What could be better for a car nut? With this accomplished, I could start thinking about fun things like tires, wheels, new exhaust and more. I hope this writing may help many out there with similar carburetors and emissions issues. Don't give up until you know you have exhausted every source of help and information. Many thanks go to those who offered their assistance in any way! 
page loaded in 0.062 seconds
|