Carb help, Holley 390 or 470TA

[Jaya]

Hi Gutthans,

I have managed to install the .031 squirter correctly and also .049 jets and it was great, performance and MPG are very good.

From a dead stop, the jeep can now take off very strong .. quick and it was a crisp launch. This makes me wanted to try the .025 squirter ...

I did gap the spark plug to 0.047 in. Any suggestion on the spark plug to use ... I currently using Autolite but are planning to try champion (I forgot the P/N).
I feel a big performance difference between standard plug gap and the .047 gap ... makes me want to back to a CD ignition ...

However, I still haven't had the chance to tune the secondary springs as I got the spring kit already and measure the exact MPG.

Thanks.

 

[gutthans]

Whatever you try next, TRUST ME...do one thing at a time and road test the result before moving on to the next 'improvement'. If your change doesn't work better, then put it back the way it was immediately before the change...THEN, and only then, do something else different.

Autolite 985 is a typically good plug to start with. You can find the cross-index online to convert to the same plug in a different brand. Whichever brand you prefer...find the factory heat range chart (online) and note the next plug up (hotter) and down (colder) from the one you have. With Champions, an RJ12YC would be hotter than an RJ9YC for instance, but Autolite codes differently so you'll need the range chart.

Check the plugs after a week of driving...dry soot will mean either too rich or too cold adjust either the jets or install a 'hotter' plug. If the plug is too white then you're either too lean or too hot and you would adjust either the plugs or jets in the opposite direction.

Basically, a rule of thumb is that Daily Driving mostly under 2000 rpm needs to be leaner and hotter than if you freeway drive 2500-3000 where you want a colder plug with a slightly richer mixture.

Oh, and stay away from 5th gear under 40 mph...that will cause the power valve to open too often around town and you actually get better mileage in while in 4th gear instead.