Carb jets for 5280 feet (1 Viewer)

Joined
Jan 31, 2005
Messages
3,848
Location
Denver CO
Subzali, may I have an opportunity to turn you into a believer in the church of the fine tune? With any luck I'll have a set of sea level jets, a set of stock altitude jets for my year, and one extra set to dial in with the reamers, and some time to do some tuning (hopefully with some decent weather to match...) within the coming weeks. I live about 7 miles up from the stretch of road referenced above, and I'll be basing my operations between there and the aforementioned parking lots. An assistant is always a plus to operate stop watches, monitor widebands (if I can get my hands on one), work cameras (I think I might be pretty terrible at gauging what's going to be of interest for these sorts of things), etc.

We'll get a baseline with the sea level jets, then swap for the factory spec altitude jets and get a new baseline, and then see if we can make any progress from there (given that the altitude jets are for my exact engine combo and altitude, I doubt we'll be able to get too terribly much better, but I'll have a set of jets specifically for the purpose of fine tuning).

If I can get everything off of my plate (no promises) I'll be there. And then I'll show you that the problem of not being able to get up your driveway in high range isn't a jetting problem ;) :p :D :cheers:
 
Joined
Dec 22, 2011
Messages
212
Location
Coal Creek Canyon, CO
You're on! I was able to do it in a far heavier vehicle with half the drive wheels and half the power (my old '62 VW Panel Bus with half my shop in it)! Care to make a wager? (Haven't figured out smileys from my phone... So pretend there's a series of clever and applicable ones here.)
 

PabloCruise

SILVER Star
Joined
Jun 3, 2004
Messages
20,418
Location
Northern Colorado
A 78 is a very different vac secondary carb with very different jet sizes.

Got it, thanks.

TJ, it would probably be best to start with the stock jet sizes, get an O2 sensor bung welded into your exhaust pipe, and use a wide-band O2 sensor to fine-tune it. Otherwise you're just shooting in the dark.

I should be good, Jim C laid hands on my carb and dizzy a few years back. He set me up for Ft Collins (Denver) altitude.

Jim C said it well - very different. When you're ready TJ both Marco and I have the zeitronix zt-2 units. Any exhaust shop can install the bung. We can hook the unit up and you can get all the AFR details. That said, having used it on my rig the same results can be achieved using the lean drop method with a vacuum guage.

Thank you! The analytic part of me would like to gain experience with this. When I got my carb back from Jim I bolted it on, and then have gone back and set idle and advance a few times using lean drop & vacuum.

I just ordered some jetting gauges and reams as well, and can close/open whatever jets will fit the holes to work. I also have a lead on a complete set of stock jets for my stock and complete 11/73 1.5F, and I'll let you know how it pans out and pass on the info. It sounds like we're close geographically and doing the same project at the same time... I sense a group workday project.

I have a stretch of road picked out that's dead in the middle of my altitude needs for dialing. I advise having a good idea of what range of altitudes you intend to jet for (try to keep the spread around a max of 2,500'), and find yourself a low traffic stretch of road that you can really stomp a little in. I.e. I live just under 8k' and regularly drive as low as 5,200', so 6,500' is my middle ground, and there is 2 mile a stretch of 72 going west from 93 goes from about 6,400'-6,600' before it gets curvy and has parking lots at either end (a bus stop and what I think is a bike launching lot). Straight with a slight grade helps so you can get an idea for acceleration and power. That said, the wideband setup would be ideal to eliminate quite a bit of guess work.

This sounds really fun!

If I can get everything off of my plate (no promises) I'll be there. And then I'll show you that the problem of not being able to get up your driveway in high range isn't a jetting problem ;) :p :D :cheers:

You're on! I was able to do it in a far heavier vehicle with half the drive wheels and half the power (my old '62 VW Panel Bus with half my shop in it)! Care to make a wager? (Haven't figured out smileys from my phone... So pretend there's a series of clever and applicable ones here.)

Sounds like a good time to be had!
 
Joined
Jan 26, 2012
Messages
3,751
Location
Ohio, Illinois
Just to poke my .02 worth : just keep in mind that jetting results are only for a particular engine - each owner , if they choose , must tune their jetting to their engine specifically .
Sarge
 
Joined
Sep 8, 2008
Messages
3,346
Location
High and dry in the desert, dancing between hemisp
spectre6000 said:
Subzali, may I have an opportunity to turn you into a believer in the church of the fine tune? With any luck I'll have a set of sea level jets, a set of stock altitude jets for my year, and one extra set to dial in with the reamers, and some time to do some tuning (hopefully with some decent weather to match...) within the coming weeks. I live about 7 miles up from the stretch of road referenced above, and I'll be basing my operations between there and the aforementioned parking lots. An assistant is always a plus to operate stop watches, monitor widebands (if I can get my hands on one), work cameras (I think I might be pretty terrible at gauging what's going to be of interest for these sorts of things), etc.

We'll get a baseline with the sea level jets, then swap for the factory spec altitude jets and get a new baseline, and then see if we can make any progress from there (given that the altitude jets are for my exact engine combo and altitude, I doubt we'll be able to get too terribly much better, but I'll have a set of jets specifically for the purpose of fine tuning).

I'm game if you're ever in Santa Fe
 
Joined
Dec 22, 2011
Messages
212
Location
Coal Creek Canyon, CO
Just to poke my .02 worth : just keep in mind that jetting results are only for a particular engine - each owner , if they choose , must tune their jetting to their engine specifically .
Sarge

It only takes a few minutes to alter jets for anyone wanting to set up at the same altitude (out, clean, and reamed in under 20 minutes provided we can feel our fingers). I'm thinking more for instructional purposes than anything to start.
 
Joined
Sep 8, 2008
Messages
3,346
Location
High and dry in the desert, dancing between hemisp
If I could find the part number for the altitude jets for my rig I'd do it. However the dealer here doesn't think they are made anymore. I have a carb from my 83 US spec cruiser but it had smog. Does anyone know whether there was a difference between smog and non-smog jets?
 
Joined
Dec 22, 2011
Messages
212
Location
Coal Creek Canyon, CO
CDan says they're NLA. I'm chasing some down still, and as soon as I hear some positive news from some source or another, I'll share. I anticipate doing a writeup on how to plug and ream when the above discussed jetting exercise eventually takes place (within the next few weeks).
 
Joined
Sep 8, 2008
Messages
3,346
Location
High and dry in the desert, dancing between hemisp
spectre6000 said:
CDan says they're NLA. I'm chasing some down still, and as soon as I hear some positive news from some source or another, I'll share. I anticipate doing a writeup on how to plug and ream when the above discussed jetting exercise eventually takes pla (within the next few weeks).

That wouldbe great. I'm not confident about the plug and ream thing, but could be convinced.
 
Joined
Dec 22, 2011
Messages
212
Location
Coal Creek Canyon, CO
Plugging and reaming can be less than ideal if you're not careful, but it's the quickest way to dial in (20 minutes between sizes versus however long shipping takes), the cheapest way (one set versus buying a tackle box full of jets), and when jets aren't available it's the only way. It's tried and true, hot rodders have been doing it for decades, and it just works. The biggest argument against is that if you get the holes off somewhat you might mess with the way the fuel flows through the aperture... I'm not worried about clocking my spark plugs either.
 
Joined
Feb 6, 2002
Messages
15,224
Location
OC, CA
Yes. US-spec carbs are calibrated to pass an emissions test.
ROW carbs are calibrated to run well.

Different jets, air jets, emulsion tubes, yadda...

Don't forget that they had to meet the then new CAFE standards, which are also responsible for their peculiar performance.
 
Joined
Feb 6, 2002
Messages
15,224
Location
OC, CA
The truck runs rich (you can smell it) and averages 10-11 mpg pretty consistently.


Burning a rich mixture produces carbon monoxide, which is odorless, so you can't smell a rich mixture unless it is so extremely rich that it won't ignite, resulting in a misfire. You can smell misfiring.
 
Last edited:

PabloCruise

SILVER Star
Joined
Jun 3, 2004
Messages
20,418
Location
Northern Colorado
Pin_Head said:
Burning a rich mixture produces carbon monoxide, which is odorless, so you can't smell a rich mixture unless it is so extremely rich that it won't ignite, resulting in a misfire. You can smell misfiring.

But you can definitely smell a difference btwn a poorly tuned carb and one that is well tuned. What is one smelly there?
 

FJ40Jim

The Cruiser Whisperer
SILVER Star
Joined
Sep 26, 2003
Messages
11,030
Location
Lancaster, Ohio, USA
Lean tends to be more stinky to the human nose. Higher HC's due to the poorly burnt mixture.

As Pin sez, rich burns most of the HC, but burns it to CO instead of CO2.
 

Users who are viewing this thread

Top Bottom