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[email protected] Samba Member
Joined: August 03, 2002 Posts: 12785 Location: Salt Lake City, Utah
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Posted: Wed May 25, 2016 4:00 pm Post subject: Re: HPMX Jetting? Again - Sorry. |
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also understand that the idle circuit tune is completely different for engines with SVDA, and engines with cent only timing. So the idle jet used for each is DIFFERENT. _________________ It's just advice, do whatever you want with it!
Please do NOT send me Private Messages through the Samba PM System (I will not see them). Send me an e-mail to john at aircooled dot net
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XR6T Samba Member
Joined: July 12, 2014 Posts: 96 Location: Hobart, Australia
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Posted: Wed May 25, 2016 4:12 pm Post subject: Re: HPMX Jetting? Again - Sorry. |
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Thanks John,
I am going to pull the main stacks and try 55's even though I was told that for my small capacity engine they would be too big.
Am I correct in thinking that I should not concentrate on the readings but on how it drives?
I don't want to mask a problem with an overly rich mixture. |
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[email protected] Samba Member
Joined: August 03, 2002 Posts: 12785 Location: Salt Lake City, Utah
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Posted: Wed May 25, 2016 4:15 pm Post subject: Re: HPMX Jetting? Again - Sorry. |
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You have to be concerned with the idle mixture, because only if you are doing that will you know that the circuits are behaving properly.
If you have a cracked casting which is leaking fuel into the idle circuit, you will never know that if "11:1 idle A/F" is "acceptable". It's not, it's a sign that something is jacked up (either the tune, or the carb(s)).
You need to leave the main stacks out, and get the idle and progression circuits handled first.
The second red flag is the seeming lack of a response with the idle jet changes. That means the fuel is coming from somewhere ELSE. So, where and why?
"Lean" A/F can be triggered by ignition problems, or exhaust leaks, in addition to carb issues. But RICH A/F are always fuel problems, ALWAYS.
XR6T wrote: |
Hi John, I am aware of what the idle mixture screw does and am not too concerned with the idle mixture, but the other readings appear too rich in what I like to call the cruising circuit (what the size of the jets control) and the huge flat spot that has developed by going leaner. |
_________________ It's just advice, do whatever you want with it!
Please do NOT send me Private Messages through the Samba PM System (I will not see them). Send me an e-mail to john at aircooled dot net
"Like" our Facebook page at
http://www.facebook.com/vwpartsaircoolednet
and get a 5% off code for use on one order for VW Parts ON OUR PARTS STORE WEBSITE, vwparts.aircooled.net |
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XR6T Samba Member
Joined: July 12, 2014 Posts: 96 Location: Hobart, Australia
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Posted: Wed May 25, 2016 4:34 pm Post subject: Re: HPMX Jetting? Again - Sorry. |
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Thanks again, more head scratching coming up. |
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XR6T Samba Member
Joined: July 12, 2014 Posts: 96 Location: Hobart, Australia
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Posted: Wed May 25, 2016 6:25 pm Post subject: Re: HPMX Jetting? Again - Sorry. |
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55 Idles
205 Air
120 Main
Not concerned with the slightly rich readings 12.3 as the improvement is huge.
Followed the remove main jets and run on idles, we have a short driveway of about 25metres and a 3:1 slope. Car went up driveway with no hesitation, first time ever.
Ever so slight hesitation sometimes on acceleration, will now wait for some F7 Emulsion tubes. |
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[email protected] Samba Member
Joined: August 03, 2002 Posts: 12785 Location: Salt Lake City, Utah
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Posted: Wed May 25, 2016 7:59 pm Post subject: Re: HPMX Jetting? Again - Sorry. |
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keep the main stacks out and drive it for a week. Also, idle jet changes should be done in increments of "2.5". 55s are far too big for 40s, FWIW.
If that engine needs 55s to get out of it's own way, I think you'll find the engine has mechanical problems resulting in low compression, OR the engine was poorly designed and has low CR out of the box. Low vacuum means you need over-sized idle jets. _________________ It's just advice, do whatever you want with it!
Please do NOT send me Private Messages through the Samba PM System (I will not see them). Send me an e-mail to john at aircooled dot net
"Like" our Facebook page at
http://www.facebook.com/vwpartsaircoolednet
and get a 5% off code for use on one order for VW Parts ON OUR PARTS STORE WEBSITE, vwparts.aircooled.net |
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XR6T Samba Member
Joined: July 12, 2014 Posts: 96 Location: Hobart, Australia
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Posted: Wed May 25, 2016 8:45 pm Post subject: Re: HPMX Jetting? Again - Sorry. |
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Drove it about twenty miles this afternoon and it drives well. Down low and idle it is a little rich, but jogging along between 40-65mph (2500-3200rpm) the fuel reading are certainly in the ballpark. (12.5>15.0)
I think you are correct in the low compression comment. I initially seem to remember being informed that it was 7.5:1 then when asked again told it was 8:1.
I should check the vacuum readings.
I could not imagine it using anything below the original 52.5's will go back to them again for comparison.
Thanks for the help, it has been very encouraging. |
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porkchop-rob Samba Member
Joined: April 28, 2015 Posts: 440
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Posted: Thu May 26, 2016 1:13 pm Post subject: Re: HPMX Jetting? Again - Sorry. |
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A week? _________________ 1965 Beetle
1968 Beetle Baja (Son's First Car)
1976 Bus with Subaru (Wife's Riviera Camper) |
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TinCanFab Samba Member
Joined: April 04, 2006 Posts: 2743 Location: Waterford, California
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TinCanFab Samba Member
Joined: April 04, 2006 Posts: 2743 Location: Waterford, California
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Posted: Thu May 26, 2016 1:23 pm Post subject: Re: HPMX Jetting? Again - Sorry. |
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XR6T wrote: |
Drove it about twenty miles this afternoon and it drives well. Down low and idle it is a little rich, but jogging along between 40-65mph (2500-3200rpm) the fuel reading are certainly in the ballpark. (12.5>15.0)
I think you are correct in the low compression comment. I initially seem to remember being informed that it was 7.5:1 then when asked again told it was 8:1.
I should check the vacuum readings.
I could not imagine it using anything below the original 52.5's will go back to them again for comparison.
Thanks for the help, it has been very encouraging. |
Are you doing all this with the jet stacks out? If not you are wasting your time _________________ Check out my truck brought back from the dead... http://www.thesamba.com/vw/forum/viewtopic.php?t=420762&highlight=sprayed+blood
They're never really ever finished 58 rag build...
http://www.thesamba.com/vw/forum/viewtopic.php?t=658092 |
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[email protected] Samba Member
Joined: August 03, 2002 Posts: 12785 Location: Salt Lake City, Utah
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Posted: Thu May 26, 2016 2:28 pm Post subject: Re: HPMX Jetting? Again - Sorry. |
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Yes. While doing this play around with idle jet sizing, go as small as you can while retaining "manners". A little laziness is ok, because if you want more power you hit the pedal more (with main circuit operational).
A couple hundred miles will give you a good feel for the idle and progression circuit, and then you don't have to re-visit the idle jet sizing issue at all, you can focus 100% on the main and air.
porkchop-rob wrote: |
A week? |
_________________ It's just advice, do whatever you want with it!
Please do NOT send me Private Messages through the Samba PM System (I will not see them). Send me an e-mail to john at aircooled dot net
"Like" our Facebook page at
http://www.facebook.com/vwpartsaircoolednet
and get a 5% off code for use on one order for VW Parts ON OUR PARTS STORE WEBSITE, vwparts.aircooled.net |
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XR6T Samba Member
Joined: July 12, 2014 Posts: 96 Location: Hobart, Australia
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Posted: Thu May 26, 2016 2:47 pm Post subject: Re: HPMX Jetting? Again - Sorry. |
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It may "just be advice, etc."but it damn good advice. Thanks
From the many miles with the 52.5's and 50's I have a feeling that I may end up with the 52.5's or awash in the 55's. Here in Tasmania were we live, we call any straight road a mile long a freeway. It is mountainous and windy, a sports/performance car or motorbike mecca.
Now the question becomes IF I resort to the 55's to combat the low compression engine, is there any risk?
The 52.5's were almost liveable apart from the stumble, which was more annoying than anything else. Could that stumble, which was caused by a lean mixture from lack of air (vacuum) on hard acceleration at low rpm, be overcome by increasing the amount of fuel given by the acc. pump? If so this would be the way to go. |
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[email protected] Samba Member
Joined: August 03, 2002 Posts: 12785 Location: Salt Lake City, Utah
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Posted: Thu May 26, 2016 2:51 pm Post subject: Re: HPMX Jetting? Again - Sorry. |
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you just have to give it the proper amount of fuel. It that means a 42.5 idle, or a 55 or 57.5 idle, so be it.
Your same carbs on your same engine at 9.5:1 compression would want much smaller idle jets, to deliver the same amount of fuel through the idle and progression circuit. This fact confuses a lot of guys, wondering why a jetting "table" doesn't work well.
The main circuit doesn't get affected by vacuum (compression) like the idles do.
Just see which idle jets YOURS wants. But don't rush it. _________________ It's just advice, do whatever you want with it!
Please do NOT send me Private Messages through the Samba PM System (I will not see them). Send me an e-mail to john at aircooled dot net
"Like" our Facebook page at
http://www.facebook.com/vwpartsaircoolednet
and get a 5% off code for use on one order for VW Parts ON OUR PARTS STORE WEBSITE, vwparts.aircooled.net |
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XR6T Samba Member
Joined: July 12, 2014 Posts: 96 Location: Hobart, Australia
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Posted: Thu May 26, 2016 3:20 pm Post subject: Re: HPMX Jetting? Again - Sorry. |
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Thanks John and to others who have helped me start to understand a big thank you.
Will take my time and put a few miles up experimenting to get the best set up. |
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XR6T Samba Member
Joined: July 12, 2014 Posts: 96 Location: Hobart, Australia
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Posted: Sat Jun 11, 2016 6:11 pm Post subject: Re: HPMX Jetting? Again - Sorry. |
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OK, done the miles and done the testing.
Jonh's comments on give it what it wants at idle regardless of size, hit the spot.
The air fuel ration gauge has been a God send, allowing me to see what was really happening when I depressed the accelerator in real time.
The end result is:-
Vents 28
Idle 55
Air 200
Main 115
Em. F7
The accelerator pump 3 turns in.
Timing 30 degrees max advance at 2800RPM
Car runs like a dream, no flat spots and am able to accelerate from 1500RPM under load using top gear.
THanks to those that responded and a special thanks to John for his words of wisdom, no doubt gained over many head scratching sessions and time. |
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