Jetting help

[RustyBuckets]

So i have a 79 350 bored .040 over that ive recently built but are not sure how to jet properly.
The mods are:
vortec heads
1.5 roller rockers
xe268 cam
edelbrock 1406 600cfm

I think it is running rich but im not sure how to check any suggestions on tuning or jetting?

 

[scottybaccus]

You need to begin with the main jets. The best way is by reading the plugs, but it's hard to get a good reading. To do so, you need a place where you can sustain wide open throttle for 30 seconds or so. Naturally, a chassis dyno and wideband O2 are safest, but a long stretch of highway can be useful. You need to sustain high throttle and rpm, so 2nd gear is a better idea. Just avoid over revving. As you finish the run, don't lift the throttle, cut the ignition. Then coast off. (getting the idea how hazardous this can be?) Now pull a couple of plugs and check the color. Make changes by two or three sizes at a time.
Most of these carbs will not require a change in main jet. The smartest money you can spend is for the Edelbrock calibration kit. Tuning the midrange and low end will open up remarkable improvements. Order the kit, follow the instructions, and don't be afraid to experiment. You can change every part of the tune with the carb installed, and wet.

 

[rich weyand]

Easiest is to get a good broadband A/FR meter. That's what I did, and was able to tune the mixture to dead on the numbers.

The Edelbrock standard tune is way rich, except on the cruise circuit of the "mileage" carb, which is the 1406. That's actually lean at cruise.

First thing to do is check the float levels. They do not come set to spec from the factory; usually they are overfull, with an impact on mixture and mileage.

Second, what tune is in it (jets and rods)? The stock one?

 

[rich weyand]

You might want to try this tune. It's what I am running, set with a good broad-band A/FR meter. My setup isn't exactly the same as yours, but this tune has worked on a couple different setups.

Primaries: jets .092 (#1425), rods .062 x .052 (#1441); secondaries: stock; step-up springs: 8# (comes with #1464). You will also need to replace the airhorn gasket (qty 5 is #1499) when you change the primary jets. Adjust the float bowls while you are in there, as they will be wrong.

 

[RustyBuckets]

money

I looked up a could afr gauges and they are over 100$ is there a cheaper device to help me jet the carb? Or a specific kit that will have all the jets i could try?

 

[rich weyand]

You're too far away or we could work on it here.

Try the tune I posted above. Maybe $40 in parts. It should be real close. May have to change the rods a bit, but that tune was spot on for several different 350 SBC setups I went through.

 

[RustyBuckets]

All right ive got it ordered. Thanks

 

[firebane]

I would focus on getting the idle set correctly and then vacuum gauge the carb and get your idle mixture screws set first before tweaking anything else.

 

[RustyBuckets]

i dont have vacuum gauge

 

[Skweegle89]

I picked one up at Napa the other day for like $10 or $12. It will last you forever and you will use it all the time.


Sent from an old rotary telephone.

 

[rich weyand]

A vacuum gauge is good for setting the idle mixture. It won't help with the cruise and power circuits, but if you copy my tune you should be real close on those. Then use the vacuum gauge to set the idle mixture. Also, the pop-up springs should be half of the idle vacuum, so for example if you read 16" of vacuum at idle, you should use the 8" pop-up springs. I think the Edelbrock comes stock with the 5" pop-up springs installed, which is way late for the power circuit to kick in on one of these engines.