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jesus_chrysler Samba Member
Joined: March 04, 2009 Posts: 425 Location: Wisconsin
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Posted: Sat Oct 10, 2020 9:57 am Post subject: 1915 stumble |
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I was running my new 1915 with dual IDF 40 carbs with 28 vents and it ran great but plateaued like I expected. So I went to 32 vents and now I can't get it to transition without stumbling. I know people run much bigger carbs than this on 1915's so I don't think that is the problem. Moved the main up to 140 and it runs great once it gets to the main circuit. Moved my idles up to 55 then 60 and it got less and less stumble each time but still does it. Carbs are synced, fuel pressure 3.5psi, floats set at 10mm. Any suggestions would be appreciated. Im hesitant on adding more idle jet. Yes, my air bypass screws are turned all the way in.
1915
W120
40mm valve heads
1.25 rockers
9.0 compression
32 vents
60 idle
140 main
F11 emuls _________________ My collection:
58 beetle rag top
63 Single cab
67 11 Window
70 Charger 440
76 Kawasaki H1 triple 2stroke
71 Yamaha R5
06 Chopped HD |
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jesus_chrysler Samba Member
Joined: March 04, 2009 Posts: 425 Location: Wisconsin
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Posted: Sat Oct 10, 2020 10:41 am Post subject: Re: 1915 stumble |
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And Im at 1000 ft elevation. _________________ My collection:
58 beetle rag top
63 Single cab
67 11 Window
70 Charger 440
76 Kawasaki H1 triple 2stroke
71 Yamaha R5
06 Chopped HD |
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UK Luke 72 Samba Member
Joined: September 07, 2011 Posts: 2867 Location: Little Britain
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jesus_chrysler Samba Member
Joined: March 04, 2009 Posts: 425 Location: Wisconsin
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Posted: Sat Oct 10, 2020 11:40 am Post subject: Re: 1915 stumble |
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Pertronix SVDA. I tried with and without vacuum advance. Timing set at 34 total. _________________ My collection:
58 beetle rag top
63 Single cab
67 11 Window
70 Charger 440
76 Kawasaki H1 triple 2stroke
71 Yamaha R5
06 Chopped HD |
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j-dub Samba Member
Joined: November 09, 2003 Posts: 865 Location: Phoenix, AZ
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Posted: Sat Oct 10, 2020 12:25 pm Post subject: Re: 1915 stumble |
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Maybe try 30 vents next _________________ 1957 Oval rag
"POLICE STATION TOILET STOLEN ... Cops have nothing to go on." |
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jesus_chrysler Samba Member
Joined: March 04, 2009 Posts: 425 Location: Wisconsin
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Posted: Sat Oct 10, 2020 12:41 pm Post subject: Re: 1915 stumble |
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I was thinking about running 30 vents but I don't see why the 32 would be a problem. I see guys running IDA's on 1915's. As soon as it gets into the main it runs amazing. It also idles smooth as glass. _________________ My collection:
58 beetle rag top
63 Single cab
67 11 Window
70 Charger 440
76 Kawasaki H1 triple 2stroke
71 Yamaha R5
06 Chopped HD |
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Alstrup Samba Member
Joined: July 12, 2007 Posts: 7177 Location: Videbaek Denmark
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jesus_chrysler Samba Member
Joined: March 04, 2009 Posts: 425 Location: Wisconsin
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Posted: Sat Oct 10, 2020 2:37 pm Post subject: Re: 1915 stumble |
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Dual IDF 40's. 34 degrees total without vacuum advance. _________________ My collection:
58 beetle rag top
63 Single cab
67 11 Window
70 Charger 440
76 Kawasaki H1 triple 2stroke
71 Yamaha R5
06 Chopped HD |
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Alstrup Samba Member
Joined: July 12, 2007 Posts: 7177 Location: Videbaek Denmark
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jesus_chrysler Samba Member
Joined: March 04, 2009 Posts: 425 Location: Wisconsin
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Posted: Sat Oct 10, 2020 4:22 pm Post subject: Re: 1915 stumble |
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They are the HPMX 40's and 043 40x35 heads with cleaned up ports. CB offset intake and linkage kit. _________________ My collection:
58 beetle rag top
63 Single cab
67 11 Window
70 Charger 440
76 Kawasaki H1 triple 2stroke
71 Yamaha R5
06 Chopped HD |
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Lingwendil Samba Member
Joined: February 25, 2009 Posts: 3987 Location: Antioch, California, a block from the hood
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Alstrup Samba Member
Joined: July 12, 2007 Posts: 7177 Location: Videbaek Denmark
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Posted: Sat Oct 10, 2020 6:54 pm Post subject: Re: 1915 stumble |
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OK. Now we are getting somewhere.
Ignition timing @ idle 10-12 degrees. 30-32 max advance. 37-40 at full vacum. - But I doubt you can pull that with non modded HPMXés. I could be wrong since I have not had a set of those in my hands for the last 2-2½ years.
Float height 11,5-12 mm
Idle jet 50-55.
F11 E tubes.
Most likely 200 main air
130-135 main jet. _________________ https://www.thesamba.com/vw/forum/viewtopic.php?t=435993 |
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jesus_chrysler Samba Member
Joined: March 04, 2009 Posts: 425 Location: Wisconsin
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Posted: Sat Oct 10, 2020 7:30 pm Post subject: Re: 1915 stumble |
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I will try taking some timing out. _________________ My collection:
58 beetle rag top
63 Single cab
67 11 Window
70 Charger 440
76 Kawasaki H1 triple 2stroke
71 Yamaha R5
06 Chopped HD |
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j-dub Samba Member
Joined: November 09, 2003 Posts: 865 Location: Phoenix, AZ
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Posted: Sat Oct 10, 2020 9:45 pm Post subject: Re: 1915 stumble |
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As I understand it you went up in size on the vents and now have a delay between the progression phase and the main circuit.
The main ways that you can tune when the main circuit starts are vent size, float height, air jet size and e-tube.
As you already stated you can extend the progression circuit with a larger idle jet at the expense of running excessively rich on cruise as you go larger.
People are asking for more specifics on your set up to help provide the correct guidance on the next step. _________________ 1957 Oval rag
"POLICE STATION TOILET STOLEN ... Cops have nothing to go on." |
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Alstrup Samba Member
Joined: July 12, 2007 Posts: 7177 Location: Videbaek Denmark
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Posted: Sun Oct 11, 2020 3:35 am Post subject: Re: 1915 stumble |
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On second thought I would remove the 1,25´s as they are most likely "part of the problem" to why you need so large idles and have poor transition. They also probably don´t do much good apart from making the engine wanna rev high _________________ https://www.thesamba.com/vw/forum/viewtopic.php?t=435993 |
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air-h2o-air Samba Member
Joined: January 25, 2015 Posts: 579
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Posted: Sun Oct 11, 2020 4:51 am Post subject: Re: 1915 stumble |
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Smaller air jet, to quicken the transition from idle to mains |
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Zed999 Samba Member
Joined: March 04, 2018 Posts: 1240 Location: UK
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Posted: Sun Oct 11, 2020 8:38 am Post subject: Re: 1915 stumble |
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What vehicle? 32 vents might be too much for a bus. |
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udidwht Samba Member
Joined: March 06, 2005 Posts: 3777 Location: Seattle, WA./ HB, Ca./ Shizuoka, Japan
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Posted: Sun Oct 11, 2020 11:58 pm Post subject: Re: 1915 stumble |
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Down on the vent size...start with 28mm, 45.7 idles, 120 main, 200 air corr., F-11 tubes. Redo LBI keep timing down for now. @28*BTDC full advance @3200+ rpm. Idle 850-900rpms
Float height 10-11mm gasket in place ball NOT depressed. Float drop 28-32mm
Fuel pressure 3-3.5psi max
No dial regulators of any kind. _________________ 1972 Westy Hardtop/Type-4 2056cc
96mm Biral AA P/C's~7.8:1CR
Headflow Masters New AMC 42x36mm heads w/Porsche swivel adjusters
71mm Stroke
73 Web Cam w/Web solids
Dual 40mm IDF Webers - LM-2 - 47.5 idles/125 mains/190 air corr./F11 tubes/28mm Vents - Float height 10.45mm/Drop 32mm
Bosch SVDA w/Pertronix module (7.5 initial 28 total @ 3400rpm)
Bosch W8CC plugs
Pertronix Flamethrower 40K coil
S&S 4-1 w/Walker QP 17862
3 rib 002 Trans
185R14 Hankook tires |
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Alstrup Samba Member
Joined: July 12, 2007 Posts: 7177 Location: Videbaek Denmark
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Ohio Tom Samba Member
Joined: February 09, 2006 Posts: 1657 Location: Marshallville Ohio
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Posted: Mon Oct 12, 2020 5:22 am Post subject: Re: 1915 stumble |
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How about addressing the problem directly..
Turn up the accel pump shot...
Do this by turning the 6mm nuts "in" so you have about 3/8" of thread showing.
That will give more volume when you stab the throttle and help bridge that gap.
If it ran good with 28's then it's not anything else wrong here.. |
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