[phpBB Debug] PHP Warning: in file [ROOT]/includes/bbcode.php on line 112: preg_replace(): The /e modifier is no longer supported, use preg_replace_callback instead
[phpBB Debug] PHP Warning: in file [ROOT]/includes/bbcode.php on line 112: preg_replace(): The /e modifier is no longer supported, use preg_replace_callback instead
[phpBB Debug] PHP Warning: in file [ROOT]/includes/bbcode.php on line 112: preg_replace(): The /e modifier is no longer supported, use preg_replace_callback instead
[phpBB Debug] PHP Warning: in file [ROOT]/includes/bbcode.php on line 112: preg_replace(): The /e modifier is no longer supported, use preg_replace_callback instead
[phpBB Debug] PHP Warning: in file [ROOT]/includes/bbcode.php on line 112: preg_replace(): The /e modifier is no longer supported, use preg_replace_callback instead
[phpBB Debug] PHP Warning: in file [ROOT]/includes/bbcode.php on line 112: preg_replace(): The /e modifier is no longer supported, use preg_replace_callback instead
[phpBB Debug] PHP Warning: in file [ROOT]/includes/bbcode.php on line 112: preg_replace(): The /e modifier is no longer supported, use preg_replace_callback instead
[phpBB Debug] PHP Warning: in file [ROOT]/includes/bbcode.php on line 112: preg_replace(): The /e modifier is no longer supported, use preg_replace_callback instead
[phpBB Debug] PHP Warning: in file [ROOT]/feed.php on line 173: Cannot modify header information - headers already sent by (output started at [ROOT]/includes/functions.php:3887)
[phpBB Debug] PHP Warning: in file [ROOT]/feed.php on line 174: Cannot modify header information - headers already sent by (output started at [ROOT]/includes/functions.php:3887)
Racing Fuel Systems Forum for carb guys. 2023-11-05T22:36:58+01:00 https://racingfuelsystems.com/feed.php?f=5&t=394 2023-11-05T22:36:58+01:00 2023-11-05T22:36:58+01:00 https://racingfuelsystems.com/viewtopic.php?t=394&p=2738#p2738 <![CDATA[Re: IDLE AFR QUESTION]]>
https://static.summitracing.com/global/ ... 282010.pdf


From the suggestions I read back when I noticed the stumble (over 10 years ago), I wound up putting in .025's at all 4 HSAB. Didn't have any way of logging A/F then, was just happy it stopped the stumble as the only thing I was aware at the time of maybe causing it, was the accelerator pump shot.

Statistics: Posted by kgb — Sun Nov 05, 2023 10:36 pm

]]> 2023-11-05T22:25:59+01:00 2023-11-05T22:25:59+01:00 https://racingfuelsystems.com/viewtopic.php?t=394&p=2737#p2737 <![CDATA[Re: IDLE AFR QUESTION]]> Statistics: Posted by Right hand drive — Sun Nov 05, 2023 10:25 pm

]]> 2023-11-05T12:29:18+01:00 2023-11-05T12:29:18+01:00 https://racingfuelsystems.com/viewtopic.php?t=394&p=2735#p2735 <![CDATA[Re: IDLE AFR QUESTION]]> Statistics: Posted by rgalajda — Sun Nov 05, 2023 12:29 pm

]]> 2023-11-05T05:21:11+01:00 2023-11-05T05:21:11+01:00 https://racingfuelsystems.com/viewtopic.php?t=394&p=2734#p2734 <![CDATA[Re: IDLE AFR QUESTION]]> I believe what is stated in the original Holley book, written by engineer & later VP, Mike Urich. Somebody I know, also an engineer, worked at Holley during the halcyon days, knew MU & said he was a very smart engineer.

Page 23 says this.......& it is unambiguous: " The strong signal from the discharge nozzle is bled off or reduced by the MAB so there is is less effective pressure difference to cause fuel flow. The mixture will become leaner as the size of the bleed is increased."


While it doesn't say it in so many words, it should be obvious from that statement that a smaller bleed starts the system earlier...& vice versa.

Statistics: Posted by GTO Geoff — Sun Nov 05, 2023 5:21 am

]]> 2023-11-05T01:32:00+01:00 2023-11-05T01:32:00+01:00 https://racingfuelsystems.com/viewtopic.php?t=394&p=2733#p2733 <![CDATA[Re: IDLE AFR QUESTION]]>
Re: MAB's, when I experienced the stumble from the MD750, as-installed, I read up on people having the same problem and solving it via smaller HSAB (MAB) jets. Made sense then and makes sense now, the bleed is a hole in a straw between the outlet side and supply side, the outlet side has to suck harder to overcome the hole in the straw, the sucking comes from venturi effect which increases with engine demand that pulls air through the venturi to make it all happen. Smaller hole, less suck required (lower engine draw/rpm), it activates the system sooner. That all makes sense, provided the issue is the point of transfer from idle circuit to main circuit, which seems to be the case. Problem disappeared; I have a measure of faith I'm seeing what I'm seeing but won't put money on anything having to do with carburetors.

What also makes sense is what I'm reading from RHD here, emulsion system bubbles help the fuel get sucked through the pipe easier. Something I'm not sure of, is the use of terms like "help" the fuel get moving through the main circuit. The part that rings true is, aerated fuel should lift easier. But just how much easier (and we're talking fine points of when the system initially starts to flow) do the introduced bubbles make that process? Since the emulsion holes are so much smaller, and in my mind would activate in order from the top to the bottom since the upper ones should see less resistance from the weight of fuel on the other side (and assuming the lower ones that are below bowl fuel level are submerged until fuel starts to move through the main well), any commonly used MAB is more than big enough to supply all the emulsion air required. Its effect as a direct bleed to the venturi draw through the main circuit discharge tube is what should determine initiation of the main circuit, in my mind, and making it smaller should bring that system into play earlier. I believe that's what happened with my MD750, prejudiced because I was told that's what was going on so easier for me to believe. I can't prove it, of course.

Or is it supposed to be a matter that the bleed through the main discharge, above the fuel since it's not moving yet to cut it off, is fully utilizing a smaller MAB and there is not enough to be drawn through the emulsion holes, requiring a larger MAB to serve both demands so that emulsion may begin?

I can see both sides of the theory, how do we prove it in actuality? Plug every emulsion bleed, accept a crappy, inefficient maybe even impossible to burn a/f mixture, but depict when it actually starts flowing? Backing up a bit, completely plug the main circuit first, to establish the exact point when the idle system cuts out, for a baseline. Then uncover just one emulsion at a time and find those resulting points of activation, in pairs, whatever combinations are available.  

Statistics: Posted by kgb — Sun Nov 05, 2023 1:32 am

]]> 2023-11-01T11:21:13+01:00 2023-11-01T11:21:13+01:00 https://racingfuelsystems.com/viewtopic.php?t=394&p=2729#p2729 <![CDATA[Re: IDLE AFR QUESTION]]> Statistics: Posted by rgalajda — Wed Nov 01, 2023 11:21 am

]]> 2023-11-01T05:51:58+01:00 2023-11-01T05:51:58+01:00 https://racingfuelsystems.com/viewtopic.php?t=394&p=2728#p2728 <![CDATA[Re: IDLE AFR QUESTION]]> Statistics: Posted by GTO Geoff — Wed Nov 01, 2023 5:51 am

]]> 2023-10-31T13:19:23+01:00 2023-10-31T13:19:23+01:00 https://racingfuelsystems.com/viewtopic.php?t=394&p=2727#p2727 <![CDATA[Re: IDLE AFR QUESTION]]> Statistics: Posted by rgalajda — Tue Oct 31, 2023 1:19 pm

]]> 2023-10-31T05:07:16+01:00 2023-10-31T05:07:16+01:00 https://racingfuelsystems.com/viewtopic.php?t=394&p=2725#p2725 <![CDATA[Re: IDLE AFR QUESTION]]> Statistics: Posted by GTO Geoff — Tue Oct 31, 2023 5:07 am

]]> 2023-10-30T12:24:11+01:00 2023-10-30T12:24:11+01:00 https://racingfuelsystems.com/viewtopic.php?t=394&p=2723#p2723 <![CDATA[Re: IDLE AFR QUESTION]]> The metering block used the standard .028" emulsion . PVRC was staggered .072" and .075" . The secondary metering plate was also staggered .093 and .091" jets.
Main jet was #64
IFR .039"
TSR/tube .024"
IAB .066
HSAB .027

SIAB .059
SHSAB .035

The only other change I made was to drill a .030" bypass in the vacuum pod and leave the check ball and original spring. The carb performed very good .
As for the cfm of this carb. Don't know , but definitely over 700 cfm.
This was a complete restoration that I spent a year putting back together for a friend.
The camshaft was 107LSA 227/240 duration Thumper cam.

Statistics: Posted by rgalajda — Mon Oct 30, 2023 12:24 pm

]]> 2023-10-30T05:05:53+01:00 2023-10-30T05:05:53+01:00 https://racingfuelsystems.com/viewtopic.php?t=394&p=2722#p2722 <![CDATA[Re: IDLE AFR QUESTION]]> Statistics: Posted by GTO Geoff — Mon Oct 30, 2023 5:05 am

]]> 2023-10-29T10:05:10+01:00 2023-10-29T10:05:10+01:00 https://racingfuelsystems.com/viewtopic.php?t=394&p=2721#p2721 <![CDATA[Re: IDLE AFR QUESTION]]> Statistics: Posted by rgalajda — Sun Oct 29, 2023 10:05 am

]]> 2023-10-28T23:04:08+01:00 2023-10-28T23:04:08+01:00 https://racingfuelsystems.com/viewtopic.php?t=394&p=2720#p2720 <![CDATA[Re: IDLE AFR QUESTION]]> Statistics: Posted by Right hand drive — Sat Oct 28, 2023 11:04 pm

]]> 2023-10-28T21:23:53+01:00 2023-10-28T21:23:53+01:00 https://racingfuelsystems.com/viewtopic.php?t=394&p=2719#p2719 <![CDATA[Re: IDLE AFR QUESTION]]> Statistics: Posted by GTO Geoff — Sat Oct 28, 2023 9:23 pm

]]> 2023-10-28T14:33:32+01:00 2023-10-28T14:33:32+01:00 https://racingfuelsystems.com/viewtopic.php?t=394&p=2718#p2718 <![CDATA[Re: IDLE AFR QUESTION]]> Statistics: Posted by CDN — Sat Oct 28, 2023 2:33 pm

]]>