600 CFM vs 750 CFM...

Guys,

I think I have reached the limit of my tuning. A quick summary. I wanted at 1406, for the economy tune it comes with, but purchased a 1405 to retain the simplicity of a manual choke. The first thing I did was change the jets and rods to the stock 1406 settings.

Upon driving, that was too rich during cruise, and too lean during acceleration (not WOT). What I have tuned to now is at the limit of what I’m going to get without sanding metering rods.

Here’s what I did last night, all in about an hour, taking my time. I pulled the top off the carb and swapped the primary and secondary main jets. The primaries were 0.098” and the secondaries were 0.095”. That is now reversed. Primaries 0.095”, secondaries 0.098. The reason for that move was 2 fold. 1) I needed to go to 0.095 primaries but had no other 0.095’s except what were in the secondaries. And, 2) when at WOT on this previous set-up, the AFR’s were perfect. It would start off in the 12.5 AFR zone and approach 12.2 AFR. And it felt stronger than I had ever felt it before. So, swapping the jets should produce the exact same AFR’s at WOT.

The next thing I did was to put the top back on the carb and swap metering rods to 75/37’s. In effect, this put me at #14 in the 1406 calibration chart. Richer than the stock setting of a 1406 for acceleration, but leaner on cruise. Next I swapped the vacuum back to full advance, turned the idle mixture screw in about a half turn each, then put it all back together, and set the pump shot to the middle setting. I didn’t get to crank it as it was getting late, and the rain from Irma was moving in. All in all, I’m happy with the Edelbrock carb. No leaking, quick and easy to tune, and runs good in every condition except the 1.5 second lean spike (which I will continue to try to figure out). I suspect it will run and drive well, but may still not be lean enough under cruise. The only thing I have left (aside from sanding metering rods) is to change springs. I’m on the strongest spring, so going down in springs should allow the vacuum to hold the metering rod down in the jet more and more, as the spring sizes are reduced.

I’ve made a spreadsheet that tabulates richer/leaner characteristics with all the main jets and rods that I have accessible to me. This set up I am on now, is as lean as I can go on cruise, without going any leaner while accelerating. And I do NOT want to be any leaner while accelerating. I’ll report back on this thread about how it drives. And I’m going to run my fuel mileage test route again and see where it is at.

Question: In the 1405, there are these metal plates that are press fit into the bowls nearly on top of the secondary main jets. They had to be pulled out to remove the secondary main jet. It looks like a baffle. I can only guess it prevents too much fuel from flowing away from the front under acceleration. Does anyone know what the purpose of those metal plates are?


7milesout