Jets. Jets, Jets

[usmcsgt1968]

Trying to find out what the jets size for the Festiva Aisan Carb are. So I can put the right size in my Weber 32-36. does anyone have any Idea what they are?

[Otorres1129]

Any luck

[ccreddell]

Yeah, I'm looking too.

[ccreddell]

Yeah, I'm looking too.

[ricko1966]

Anytime I did a Weber swap I had to drive the car,read my plugs,feel the car and jet accordingly.

[ricko1966]

First jet is Idle jet if you have to use the throttle stop screw to make it idke,not the Idle volume screw then the Idle jet is too small,turning the throttle stop screw in robs fuel from the transition circuit to idle,so when you step on it,it goes lean and stumbles because you used your transition fuel at idle. After you have Idle dialed in play with your primary jet look a plug reading a little lighter than a cardboard box,if it surges you are too lean. Secondary main go FAT then start jetting down. Find 2 land marks 100 yards or so apart,accelerate hard, check speed at the second marker. Speed! not time. Start jetting down until your speed quits increasing then go back up 1 jet size. This is assuming your vacuum advance and timing are set and setup correctly,you can't dial in a carb if the ignition isn't right.

[theastronaut]

Trying to find out what the jets size for the Festiva Aisan Carb are. So I can put the right size in my Weber 32-36. does anyone have any Idea what they are?

You cannot use the same jet sizes from the original carb in the Weber carb. Jets sizes aren't universal, they're carb specific. A 60 Dellorto jet will not flow the same as a 60 Weber jet, or a Mikuni jet, or an Aisin jet.


Reading the plugs only works on drag cars that run at WOT only. They make a run, shut the car off immediately after the traps, then read the plug. You're only able to read the plug for WOT condition; driving around you're using the idle mixture circuit, primary idle jet, primary main jet, secondary idle jet, and secondary main jet. They all function together and there are times when multiple jets are in use at the same time, overlapping so you'll never get a reading for just a certain jet to know if that certain jet needed to be increased or decreased in size.


The easiest and fasted way to jet a carb is to install a wideband air/fuel ratio gauge, you can watch the gauge while you're driving to see exactly when and exactly what the jets are doing. This takes out the guesswork.

[theastronaut]

This website has good articles on carb jetting theory. Keep in mind I'm posting this as "theory" info, disregard the jet sizes listed since that's for an aircooled VW but the principles outlined are sound and apply to a Weber or Escort carb on a Festiva. Both the Weber and the Escort carbs are versions of Weber's two barrel progressive design. The Escort carb is a Weber DFTA which uses different series of jets compared to a DFE/DGE series Weber.

https://www.aircooled.net/vw-carburetors-jetting-102/

https://www.aircooled.net/making-weber-progressive-dfev-work-aircooled-vw-engine/

[ricko1966]

You cannot use the same jet sizes from the original carb in the Weber carb. Jets sizes aren't universal, they're carb specific. A 60 Dellorto jet will not flow the same as a 60 Weber jet, or a Mikuni jet, or an Aisin jet.


Reading the plugs only works on drag cars that run at WOT only. They make a run, shut the car off immediately after the traps, then read the plug. You're only able to read the plug for WOT condition; driving around you're using the idle mixture circuit, primary idle jet, primary main jet, secondary idle jet, and secondary main jet. They all function together and there are times when multiple jets are in use at the same time, overlapping so you'll never get a reading for just a certain jet to know if that certain jet needed to be increased or decreased in size.


The easiest and fasted way to jet a carb is to install a wideband air/fuel ratio gauge, you can watch the gauge while you're driving to see exactly when and exactly what the jets are doing. This takes out the guesswork.

I've been jetting street cars and motorcycles since early 1980s by reading plugs and feeling the vehicle. We didn't use to have wide band O2 sensors. That may be an easier method IDK. But you can jet a street car reading plugs. How do you think we did it 40 years ago?

[theastronaut]

You can, but on a street car that is constantly using a mixture of all the jets under varying condition the plugs will only tell you an average of all the jets. You can jet each circuit/jet precisely with an AFR gauge without guessing.


The first few pages of this thread have excellent info on sorting out the jetting with a wideband AFR guage, and the process you should use to tune each circuit. The posts by john@aircooled dot net are extremely informative, he's an expert on tuning carbs.

https://www.thesamba.com/vw/forum/viewtopic.php?t=293837&highlight=wideband+results