engine and drivetrain Weber running lean - air pressure - thoughts?

[danco_]

Change your emulsion tubes to F66. You'll thank me later. 

[GreenSwede]

Change your emulsion tubes to F66. You'll thank me later. 

 

Because...?

 

(I know very little about the effect of E-tube shifting.)

[GreenSwede]

Ok so it seems your fuel pump is up to the task because you can get to 12.5-13 afr with a bigger main jet.

 

Typically the air corrector doesn't have a large affect on afr until the upper range of the rpm.  However, the ac can influence when the main jets come in.  So one possibility is a small ac is causing your mains to come in too early and mixing with your idle jets which havent stopped contributing yet.  What size main and ac are in it now?

 

mains 140 and ac 165, not quite sure where I gave up for the season..

 

The ac is a very fine tuned adjustment and should be kept at stock relationship to the mains for initial tuning.  I am not familiar with 38's but for DCOE's the formula is to add about 50 to the value of the mains for the ac as a starting point.  So if you have a 135 main you's start with a 180 or 190 ac.

 

The carb came like this:

0 IDLE

135 MAINS

185 AIRS 

PUMP JET 55

E-TUBES F50

And ran very lean, cruise at around 17-18 afr and WOT above 15. Or something like that.

 

 

Next I would examine the idle jet behavior.  On DCOE's you can remove the mains and run on only the idle jets up to a point.  Once the idle jets crap out and start to pop or afr goes above your desired amount, just before this rpm is when the mains have to come in to play.  Too early, and it's rich. Too late, and it's lean.  A close overlap is what is desired.  So if possible with your carb, carefully drive on the idle jets to see when they start to crap out under slight load and no load.  Do so in a low traffic place because if you quickly step on the gas the engine will die.  Usually it's around 3k rpm under light load that they run out.  Lower rpm's the more load is put on them.

 

Will consider this! (soon, still salty roads here)

 

If you have some smaller idle jets try them with the bigger main jets to see if this helps your lower rpm and cruise afr's.  If you are cruising under light load in 2nd or 3rd gear at 3000 rpm and you start to pop/sneeze then your overlap is not correct.  Once you mash the throttle to WOT the idles are not involved and it is all main jet, this is why the mains should be set to your desired afr and the other jets tuned around it.  At least this helped my situation. 

 

Thanks!

[jireland2002]

The 2 barrel down drafts will run lean at sustained high RPM because the 2.00 needle and seat are too small leading to starvation.  This is especially true with the 38mm carb.  Install a 2.50 needle and seat.

[GreenSwede]

The 2 barrel down drafts will run lean at sustained high RPM because the 2.00 needle and seat are too small leading to starvation. This is especially true with the 38mm carb. Install a 2.50 needle and seat.

Done! No effect, sadly.

(Got that tip from you earlier, sir:))

Edited January 16, 2015 by GreenSwede

[Stevenola]

What was your original idle jet size and what is it now if you've changed?  Do the idle jets also have an air bleed or is this fixed?

[GreenSwede]

What was your original idle jet size and what is it now if you've changed?  Do the idle jets also have an air bleed or is this fixed?

 

The out-of-the-box idles were 50 (bought the carb from TEP). Right now I'm not sure (the car is until tomorrow sound asleep at storage), but if anything I went leaner on idles. As, I think, when doing mains and airs idle ended up around 10.5 afr. Now, a bit leaner, 11.5-12. I think.

[norda]

The answer is in the e-tubes do some research on them and you will find that the e tubes are how you tune afr within the rpm range. All the jetting is to be set for wot and then you get into the tubes for rpm range. There is a really good you tube lecture (couple minutes) mainly referring to Holley and edlbrock carbs but the principle is the same

[TobyB]

 

maybe I should play with E-tubes.

 

http://www.webercarburatori.com/?p=handbook&s=2

 

Christ.  I bookmarked it, but forgot... 

 

This is the best I've seen on specific e-tube stuff.  It is brilliant. 

I wish I'd seen it 12 years ago.

 

I think it will help.

 

I would, however, agree that putting a fuel pressure gauge on just to check is probably not a bad idea.

 

I will also throw this awful concept in, in hopes that it's not the problem-

at high revs, the M10 sets up some pretty fierce vibrations.

I hope it's not fuel foaming in the bowl, because that's absurdly hard to figure out.

And 'foaming' can be simply a standing wave so odd that the jets are getting uncovered...

 

As to the manometer, I found that pressure in front of the grille was much higher than pressure at the cowl.

I had a hard time with the inside of the engine bay because the air inside it gets very turbulent, and

my $15 manometer is digital and slow.  AND air seems to build up in odd places in there, and

also get pretty aggresively sucked out the bottom.  I ended that little experiment by putting the

test equipment and notes into a black plastic envelope and burying it inside turn 2 at Pacific Raceways...

 

t

[ray_]

Toby, was it in the car at the time?

 

You carb people....

 

Ola you should listen to Stevenola -- he's running more carbs at the same time than most here

 

Why no, I don't have anything constructive to add

 

Cheers,

 

 

I ended that little experiment by putting the

test equipment and notes into a black plastic envelope and burying it inside turn 2 at Pacific Raceways...

 

t

[GreenSwede]

http://www.webercarburatori.com/?p=handbook&s=2

 

Christ.  I bookmarked it, but forgot... 

 

This is the best I've seen on specific e-tube stuff.  It is brilliant. 

I wish I'd seen it 12 years ago.

 

I think it will help.

 

I would, however, agree that putting a fuel pressure gauge on just to check is probably not a bad idea.

 

I will also throw this awful concept in, in hopes that it's not the problem-

at high revs, the M10 sets up some pretty fierce vibrations.

I hope it's not fuel foaming in the bowl, because that's absurdly hard to figure out.

And 'foaming' can be simply a standing wave so odd that the jets are getting uncovered...

 

As to the manometer, I found that pressure in front of the grille was much higher than pressure at the cowl.

I had a hard time with the inside of the engine bay because the air inside it gets very turbulent, and

my $15 manometer is digital and slow.  AND air seems to build up in odd places in there, and

also get pretty aggresively sucked out the bottom.  I ended that little experiment by putting the

test equipment and notes into a black plastic envelope and burying it inside turn 2 at Pacific Raceways...

 

t

 

I'll disregard the theory about foaming fuel in bowl.. That just sounds too much:)

 

Had a quick look at the link, maybe F66 tubes aint a bad idea..

 

And, I'd need a gauge to watch while driving I guess? What kind of pressure do I want? 

 

Ola you should listen to Stevenola -- he's running more carbs at the same time than most here

 

 

I am! I gathering ideas, thoughts and knowledge to get this sorted once spring comes:)

And again, most thankful for all replies and thoughts! You guys are great:)