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nextgen Samba Member
Joined: August 19, 2004 Posts: 6008 Location: CONGERS, N.Y.
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Posted: Sat Jul 24, 2021 6:59 pm Post subject: Interesting how a turn on mixture screw can make increase temps. |
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My bug has had an bit more of the smell of exhaust fumes, so I did some test backing off on the mixture screws.
Actually backed off all 4 of my screws and the fumes did decrease but also noticed my oil temp increased.
Not bad, was taking a while to get to 170 f, car ran fine but did smell bad. Now it hangs out at between 180 and 190 f on 90 -95f air temp days doing 65 mph and some bumper to bumper traffic..
Smell is much less, not bad at all. I don't like over 210f
No difference in power. _________________ email: [email protected]
The TYPE IV UPRIGHT CONVERSION MANUAL
BEETLE MAGNETIC DEFLECTOR SHIELDS
LETS TALK DUBS https://www.youtube.com/results?search_query=joe+cali+ghia https://letstalkdubs.libsyn.com/ep-200-joe-cali-ty...qI3xJTCzjs |
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simon varley Samba Member
Joined: March 12, 2020 Posts: 175 Location: Geelong Australia
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Posted: Sat Jul 24, 2021 8:39 pm Post subject: Re: Interesting how a turn on mixture screw can make increase temps. |
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if you run leaner, you will run hotter. that's how engine combustion works all else being equal |
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Wreck Samba Member
Joined: July 19, 2014 Posts: 1211 Location: Brisbane
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Posted: Sat Jul 24, 2021 11:09 pm Post subject: Re: Interesting how a turn on mixture screw can make increase temps. |
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I've a 4 channel CHT gauge , it is amazing how much difference 1/2 a turn will make to CHT's (over 10C )and how balanced they are . here's a graph of temperature verses mixture .
The middle of the graph is Stoich 14.7 to 1 on petrol , peak EGT ,peak power is to the rich side normally around high 12's .with lower CHT's. That is why you don't want and air-cooled head running under load around the middle of the graph .
https://www.thesamba.com/vw/gallery/pix/435515.jpg |
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Wreck Samba Member
Joined: July 19, 2014 Posts: 1211 Location: Brisbane
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Posted: Sat Jul 24, 2021 11:27 pm Post subject: Re: Interesting how a turn on mixture screw can make increase temps. |
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simon varley wrote: |
if you run leaner, you will run hotter. that's how engine combustion works all else being equal |
Thats not quite right , you can run lean at cruise as long as you have a vacuum advance type dissy or programmable ignition . It's covered a lot in the Wideband thread .
I run around 16 - 17 to 1 and 42degrees advance at cruise , cool CHT's . good fuel economy . I just got 8.3/100km highway at 110km/3400rpm . 2600cc with 48mm dellortos in a Ghia . pretty stoked with that economy considering the cam is rather large . |
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simon varley Samba Member
Joined: March 12, 2020 Posts: 175 Location: Geelong Australia
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Posted: Sat Jul 24, 2021 11:58 pm Post subject: Re: Interesting how a turn on mixture screw can make increase temps. |
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Wreck wrote: |
simon varley wrote: |
if you run leaner, you will run hotter. that's how engine combustion works all else being equal |
Thats not quite right , you can run lean at cruise as long as you have a vacuum advance type dissy or programmable ignition . It's covered a lot in the Wideband thread .
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yup, like I said "all else being equal" which is what the OP did by just adjusting the mixture. Timing changes are a whole other discussion as you point out.
that's why there are whole textbooks, theses and industrial research projects devoted to the subject |
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nextgen Samba Member
Joined: August 19, 2004 Posts: 6008 Location: CONGERS, N.Y.
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Ellis' Bug Samba Member
Joined: November 15, 2006 Posts: 650 Location: Phoenix
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Posted: Sun Jul 25, 2021 10:18 am Post subject: Re: Interesting how a turn on mixture screw can make increase temps. |
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I was under the impression the mixture screws only mattered to idle. _________________ 74 Super drag car
63 Bus, work in progress
65 Bug project
63/64 Ragtop
2006 Beck 356 |
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j-dub Samba Member
Joined: November 09, 2003 Posts: 865 Location: Phoenix, AZ
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Posted: Sun Jul 25, 2021 11:18 am Post subject: Re: Interesting how a turn on mixture screw can make increase temps. |
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Ellis' Bug wrote: |
I was under the impression the mixture screws only mattered to idle. |
That is correct _________________ 1957 Oval rag
"POLICE STATION TOILET STOLEN ... Cops have nothing to go on." |
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FreeBug Samba Member
Joined: March 12, 2012 Posts: 4278 Location: deepest, darkest Switzerland
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Posted: Sun Jul 25, 2021 12:05 pm Post subject: Re: Interesting how a turn on mixture screw can make increase temps. |
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simon varley wrote: |
Wreck wrote: |
simon varley wrote: |
if you run leaner, you will run hotter. that's how engine combustion works all else being equal |
Thats not quite right , you can run lean at cruise as long as you have a vacuum advance type dissy or programmable ignition . It's covered a lot in the Wideband thread .
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yup, like I said "all else being equal" which is what the OP did by just adjusting the mixture. Timing changes are a whole other discussion as you point out.
that's why there are whole textbooks, theses and industrial research projects devoted to the subject |
You're both wrong. You're also both right, too.
Max heat is at stoichio, as mentioned, 14.7:1. That's what the science says.
"Lean out the mixture, and you overheat" is also true in the context of stock cars of the pre-emission era. So?
Leaning out a '50s engine meant going from 11:1 to something CLOSER to the 14.7 point of maximum heat..
If you're running at stoichio, 14.7:1, closer to what a modern car does, and you lean out the mixture, it will just get cooler as it gets leaner.
Peace out. |
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oprn Samba Member
Joined: November 13, 2016 Posts: 12632 Location: Western Canada
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Posted: Sun Jul 25, 2021 12:31 pm Post subject: Re: Interesting how a turn on mixture screw can make increase temps. |
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A light car with a larger engine, and multiple carbs is still going to be running on the idle and transition phase of the carbs. Mine doesn't really start pulling through the main jets until 70 mph or more. So yes part of the fuel mix is still coming from the idle port and part from the transition ports. _________________ We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age) |
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Wreck Samba Member
Joined: July 19, 2014 Posts: 1211 Location: Brisbane
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Posted: Sun Jul 25, 2021 2:36 pm Post subject: Re: Interesting how a turn on mixture screw can make increase temps. |
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the mixture screws also affect the progression phase before the main jet starts working . |
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nextgen Samba Member
Joined: August 19, 2004 Posts: 6008 Location: CONGERS, N.Y.
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beetlenut Samba Member
Joined: May 27, 2009 Posts: 2980 Location: RI
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Posted: Sun Jul 25, 2021 4:49 pm Post subject: Re: Interesting how a turn on mixture screw can make increase temps. |
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Wreck wrote: |
the mixture screws also affect the progression phase before the main jet starts working . |
Following this thread, so does anyone have a better procedure for dialing in the volume control screw than the usual highest rpm less 20-30 rpm? Can't quite get rid of a slight bog in the progression phase. _________________ scrapyards are for quitters
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Wetstuff wrote: |
... I spend more time shaking it than directing it?! I get a pretty decent blast for 8sec. then have to shake it again. |
- Words to live by right there!
My 74 Super rebuild thread: http://www.thesamba.com/vw/forum/viewtopic.php?p=6507104#6507104 |
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Wreck Samba Member
Joined: July 19, 2014 Posts: 1211 Location: Brisbane
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Posted: Sun Jul 25, 2021 5:19 pm Post subject: Re: Interesting how a turn on mixture screw can make increase temps. |
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beetlenut wrote: |
Wreck wrote: |
the mixture screws also affect the progression phase before the main jet starts working . |
Following this thread, so does anyone have a better procedure for dialing in the volume control screw than the usual highest rpm less 20-30 rpm? Can't quite get rid of a slight bog in the progression phase. |
There is a lot of info on the Wideband thread , what carburettors etc ? |
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Multi69s Samba Member
Joined: January 24, 2006 Posts: 5360 Location: Lefty, CA
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beetlenut Samba Member
Joined: May 27, 2009 Posts: 2980 Location: RI
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Posted: Sun Jul 25, 2021 6:49 pm Post subject: Re: Interesting how a turn on mixture screw can make increase temps. |
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Wreck wrote: |
beetlenut wrote: |
Wreck wrote: |
the mixture screws also affect the progression phase before the main jet starts working . |
Following this thread, so does anyone have a better procedure for dialing in the volume control screw than the usual highest rpm less 20-30 rpm? Can't quite get rid of a slight bog in the progression phase. |
There is a lot of info on the Wideband thread , what carburettors etc ? |
It's a 34 PICT 3, but I don't want to open up another discussion on tuning or hijack this thread, I was just wondering if someone had a more precise way to dial in the VC screw. _________________ scrapyards are for quitters
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Wetstuff wrote: |
... I spend more time shaking it than directing it?! I get a pretty decent blast for 8sec. then have to shake it again. |
- Words to live by right there!
My 74 Super rebuild thread: http://www.thesamba.com/vw/forum/viewtopic.php?p=6507104#6507104 |
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Ohio Tom Samba Member
Joined: February 09, 2006 Posts: 1657 Location: Marshallville Ohio
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Posted: Mon Jul 26, 2021 8:05 am Post subject: Re: Interesting how a turn on mixture screw can make increase temps. |
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So much wrong here, I'm not sure where to start...
idle mixture screws affect idle mixture. Not much else.
once you open past the first progression hole, fuel is metered by the idle jet size.
Mixture screws are way beyond affecting anything once you start the transition to mains.
My method for setting the screws. Dial it IN until that cyl drops out. Back it out slowly until it comes back. Add an 1/8 turn to 1/4 turn. Done.
Nothing magic about that.
Most effective if you have your idle rpm nice and low.
Many times folks think there is a problem with screws not working because they have the idle speed screws so fast, the throttle plates are above the first progression hole.
They have the speed screws cranked up because the base idle spark advance is at 5deg BTDC. So they have to turn up the speed screws to get it to idle. So much so, they are into the first progression hole.
This consumes lots of fuel for no dang reason. It's still burning on the way out the exhaust and will light exh valves on fire.
I modify most every distributor so that it idles at least 12deg BTDC. This speeds up the idle all by itself. thus allowing the butterflys to be more closed and mixture screws more responsive. Things fall into place real fast when you have 15deg base timing at idle.
This all I'm going to say on this subject.
Folks have their own ideas and opinions.
Mine come from setting up more IDF, HPMX, DRLA, IDA, DCNF's than I care to count. |
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nextgen Samba Member
Joined: August 19, 2004 Posts: 6008 Location: CONGERS, N.Y.
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FreeBug Samba Member
Joined: March 12, 2012 Posts: 4278 Location: deepest, darkest Switzerland
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Posted: Fri Jul 30, 2021 1:02 pm Post subject: Re: Interesting how a turn on mixture screw can make increase temps. |
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Ohio Tom wrote: |
So much wrong here, I'm not sure where to start...
idle mixture screws affect idle mixture. Not much else.
once you open past the first progression hole, fuel is metered by the idle jet size.
Mixture screws are way beyond affecting anything once you start the transition to mains.
My method for setting the screws. Dial it IN until that cyl drops out. Back it out slowly until it comes back. Add an 1/8 turn to 1/4 turn. Done.
Nothing magic about that.
Most effective if you have your idle rpm nice and low.
Many times folks think there is a problem with screws not working because they have the idle speed screws so fast, the throttle plates are above the first progression hole.
They have the speed screws cranked up because the base idle spark advance is at 5deg BTDC. So they have to turn up the speed screws to get it to idle. So much so, they are into the first progression hole.
This consumes lots of fuel for no dang reason. It's still burning on the way out the exhaust and will light exh valves on fire.
I modify most every distributor so that it idles at least 12deg BTDC. This speeds up the idle all by itself. thus allowing the butterflys to be more closed and mixture screws more responsive. Things fall into place real fast when you have 15deg base timing at idle.
This all I'm going to say on this subject.
Folks have their own ideas and opinions.
Mine come from setting up more IDF, HPMX, DRLA, IDA, DCNF's than I care to count. |
x 1000. BINGO! |
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FreeBug Samba Member
Joined: March 12, 2012 Posts: 4278 Location: deepest, darkest Switzerland
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Posted: Fri Jul 30, 2021 1:03 pm Post subject: Re: Interesting how a turn on mixture screw can make increase temps. |
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Ohio Tom wrote: |
So much wrong here, I'm not sure where to start...
idle mixture screws affect idle mixture. Not much else.
once you open past the first progression hole, fuel is metered by the idle jet size.
Mixture screws are way beyond affecting anything once you start the transition to mains.
My method for setting the screws. Dial it IN until that cyl drops out. Back it out slowly until it comes back. Add an 1/8 turn to 1/4 turn. Done.
Nothing magic about that.
Most effective if you have your idle rpm nice and low.
Many times folks think there is a problem with screws not working because they have the idle speed screws so fast, the throttle plates are above the first progression hole.
They have the speed screws cranked up because the base idle spark advance is at 5deg BTDC. So they have to turn up the speed screws to get it to idle. So much so, they are into the first progression hole.
This consumes lots of fuel for no dang reason. It's still burning on the way out the exhaust and will light exh valves on fire.
I modify most every distributor so that it idles at least 12deg BTDC. This speeds up the idle all by itself. thus allowing the butterflys to be more closed and mixture screws more responsive. Things fall into place real fast when you have 15deg base timing at idle.
This all I'm going to say on this subject.
Folks have their own ideas and opinions.
Mine come from setting up more IDF, HPMX, DRLA, IDA, DCNF's than I care to count. |
x 1000. BINGO! |
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