Jettings suggestions - 79 special with 80-81 carbs

[JTNWEvo]

Hi All,

I recently acquired a 79 Special "project". The carbs were in pieces and I have determined that they are 80-81 style. Most jets are missing or destroyed.

The bike has some kind of aftermarket 4-2 exhaust and the airbox has been drilled.

Could anyone suggest what size main, pilot, etc jets I should purchase to use on this bike with this configuration?

In case it is not clear here are the specifics:

79 Special
80-81 Carbs
Aftermarket 4-2 exhaust
drilled airbox

Thanks!

JT

[DGXSER]

With the 80-81 carbs stock jetting would be 110-120 main jets depending if they are 81 or 80 repsectively, For your 79 I would go with 120s. 42.5 pilot jets. The idle air jets (in the inlet bell) should be 180 IIRC.

4-2 aftermarket shoudl not change the jetting and the drilled air box would also not typically change the jetting.

[81xsproject]

WHAT? NO!! I don't know how no one caught this.

For 70's carbs, stock Main in 137.5. For your setup I would start at 140 mains and stock 42.5 pilots.

[bikerphil]

Could anyone suggest what size main, pilot, etc jets I should purchase to use on this bike with this configuration?

79 Special
80-81 Carbs
Aftermarket 4-2 exhaust
drilled airbox

My suggestion would be 115 mains and 42.5 pilots, they should be fine with 80-81 carbs and your particular setup. The 4/2 exhaust and drilled air box won't require much larger jets, maybe one size up from stock, JMHO

[conquest87tsi]

Jetting

The man has 80-81 carbs in a '79 bike. So I think 140's would be super rich.

I am running the same set up since I damaged my #3 carb when trying to remove a broken mixture screw tip. I actually purchased a parts bike basically just for the carbs. Took them apart to clean them and someone had installed 110 jets all the way around. It was running quite lean, whiteish gray plugs after about 50 miles. So I raised (lowered when adjusting) to 21mm just to get by until my 120 jets arrived. I have the jets, but it's running great right now so I don't really want to tear into her again. Maye once the season is over.

Oh, and I have aftermarket 4-2 exhuast and pod filters. Can't remember what pilots I'm running.

I guess the question I would have is: When I install the 120 main jets in the '80 carbs, should I try returning the float height to 23mm? It runs great at 21mm, and the mains should primarily change the top end. I kind of like having my floats a little higher as i can't adjust the needle jet on these carbs.

Not trying to steal your thread, but since we're running the same type of setup.....

[fredintoon]

- - - The carbs were in pieces and I have determined that they are 80-81 style. Most jets are missing or destroyed.
The bike has some kind of aftermarket 4-2 exhaust and the airbox has been drilled.
Could anyone suggest what size main, pilot, etc jets I should purchase to use on this bike with this configuration? - - -

Hi Jamie,
many posts on the subject all agree that the jets should match the year of the carbs, not the year of the bike.
The carbs neither know nor care what year of bike they are on.
Look in the modifications forum for recommended jet sizes for '81 carbs on a bike with aftermarket pipes and a drilled airbox.

[natemoen]

WHAT? NO!! I don't know how no one caught this.

For 70's carbs, stock Main in 137.5. For your setup I would start at 140 mains and stock 42.5 pilots.

Jessie, your slipping, he says he has 80-81 carbs!

[JTNWEvo]

Thanks for all the input guys! I will give 120s a try.