How to know when to jet up?

[MikeyT]

Hi all,

I know this is a silly question. I got a 496 in the charger with a 750 QFT slayer on it. It has 72 primaries and 84 secondaries I believe. This seems low for the engine. Ok, I guess how do you know the engine wants bigger jets.

Thanks.

Mikey

 

[lewtot184]

look at the plugs. big engines don't necessarily need to be jetted up. jets are restrictions and sometimes a big engine needs more restriction due it's capability to draw fuel. sometimes it's the small engines that need an up jet (less restriction). that 750 is too small.

 

[MikeyT]

A better carb would be?

 

[69 GTX]

Do you run it at the track? A chassis dyno would be the real way to find out.

 

[lewtot184]

A better carb would be?

850

 

[mentor70]

id even consider a 950 HP holley.

 

[Photon440]

You MIGHT need to jet up if:

1. your plugs are bone white
2. you have no power
3. you have double digit gas mileage.

 

[HEMI-ITIS]

Need to read the plugs properly or use an air fuel gauge.

 

[Cornpatch MO]

Back when gas had lead in it, it was fairly easy to read plugs. Accelerate hard, shut off the ignition while you push in the clutch, coast to a stop and pull out a couple spark plugs. The color of the insulator and the electrode was easy to tell rich or lean. The difference today's gas is so subtle, it is hard to tell. The soot inside your tail pipe may give you an idea if the engine is not burning oil and the carb and jets have not been changed for a while. .......................MO

 

[HEMI-ITIS]

Actually,to read the plugs,you need to be at WOT at max rpm in at least 2nd gear and click the key off and roll to a stop.Depending on your exhaust set up,be carefull NOT to burn your self.
In my pictures above yoe can see the dark plug,then after a jet change they looked MUCH better.