| Slant Six Forum https://slantsix.org/forum/ |
|
| High A/F ratio at idle- Weber DGV https://slantsix.org/forum/viewtopic.php?t=51100 |
Page 1 of 1 |
| Author: | SpaceFrank [ Wed Feb 13, 2013 1:01 pm ] |
| Post subject: | High A/F ratio at idle- Weber DGV |
So I installed a wideband sensor to properly tune my 32/36 Weber DGV. I disconnected the linkage between the two throttle plates so that I could tune each barrel independently. Each barrel has an idle jet, a main fuel jet, and an air corrector jet (which apparently helps to keep the mixture from getting too rich at high RPMs). I had to get creative with the meager collection of jets I have at my disposal, and the closest I could get it was still a little richer than I wanted. I was aiming for the rich side of stoichiometric just to be on the safe side. Currently, the A/F gauge reads about 14 at 1000 RPM and falls off pretty evenly to the low 12s at 3500 (which is as high as I cared to run the engine in the driveway of my teammate's nice suburban neighborhood). The issue that concerns me is that the gauge reads pretty lean at idle, even with the biggest primary idle jet installed (90); the number bounces around a lot, but the gauge tends to read between 16 and 17 at 650 RPM. The engine idles a little rough, but it's good enough for me. Is this lean idle ratio going to kill me? It doesn't get down to 15 until about 900 RPM. I'm honestly boggled as to why it stays that lean. All the other examples I've found of people running this carb with this engine, they use smaller idle jets. It's almost as if my idle circuit is clogged or something. Or is it supposed to be lean at idle? One thing to consider is that Webers apparently like electric fuel pumps at around 3 psi. I'm still using the stock mechanical pump and running the fuel through a decent regulator. Not sure if the idle would clean up with an electric pump or what, but I get a pretty consistent 3-3.5 psi across the tested RPM range. The engine runs much better with the regulator installed than it did before. Another weird thing: with the air cleaner off, if you shut off the engine, you'll see what looks like smoke filling up the primary venturi. Like there's still gas leaking into the intake somehow and vaporizing. One time when I had the cover plate off, I saw small bubbles periodically coming out of the hole that feeds the accelerator pump, so it's possible that the pump diaphragm is leaking. It's new, but I may not have installed it tightly enough. I'll check on that next time. Otherwise, aside from a little difficulty cold starting and a slightly rough idle, the car drives great now. |
|
| Author: | ceej [ Wed Feb 13, 2013 6:52 pm ] |
| Post subject: | |
You'll need to check the reading under load. In the driveway, your not going to have vacuum levels that are indicative of what the circuits are really doing when going down the road, off idle. Take a friend along to monitor what the AF ratio is doing under normal driving conditions.  A lean idle shouldn't be a big issue. Something to work on for idle quality. I wouldn't be too concerned, as EGT's should still be pretty low at low flow rates. 2¢ CJ |
|
| Author: | tlrol [ Sat Feb 16, 2013 7:03 am ] |
| Post subject: | Weber jetting |
A couple of things to consider/check for: 1. What Ceej said. You need to drive the vehicle for the best test. Best bring a friend or you will make texting on a cell phone look easy...try writing down F/A numbers on the fly. Some A/F devices will log stuff for you... 2. Carburetors are somewhat imprecise, so stick with trends and averages and don't get freaked out by statistical variations. 3. Start by tuning the idle circuit by ear, per Webers recommendation. Check that with the A/F device, and tune to stoich as needed. 4. Buy a number of jets for tuning on the road. The main and air correctors are what plays at highway speeds. 5. Check for vacuum leaks. Twice even. What ARE your vacuum levels? Damn A/F numbers can be easily confused for vacuum numbers so post the units with the numbers. My guess would be that the plates for carb adapting or the manifold itself might have a leak...start there and eliminate that as a possibility first. |
|
| Page 1 of 1 | All times are UTC-08:00 |
| Powered by phpBB® Forum Software © phpBB Limited https://www.phpbb.com/ |
|