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Fine tuning advise needed
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Brian
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PostPosted: Mon Aug 27, 2018 9:31 pm    Post subject: Fine tuning advise needed Reply with quote

Hey guys,

Would love to ask for some help on some fine tuning on a motor that I just built. Been going in a little over my head to learn as much as possible, this is my first real build and I absolutely loved doing it. Assembling the clock was stressful, but it's been super sound after the break-in. Spins up to 6k quicker than I would have thought with a stock flywheel, but has room for improvement to be a smooth runner.

Jetting took forever, used some Chinese IDFs that are actually really nice so far but could be a root to many problems. Facing a problem now with some backfiring and drive-ability. I've used 019, 010, 034 and 205zb on some builds but went with a CB Magnaspark for this one and wow.

Here's what I got:
2110
Bottom
82x90.5
5.4 rods
web163

Top
40x37.5
Floats at 14mm
Idles 45
Mains 125
Air 200
Tubes F11

Right now, I'm getting pretty bad hesitation off the line. Popping around 2,5k and not a lot of power on the top end. I'm on the default user settings and need to fine tune it. Any suggestions on where to start? Should I try modeling a stock distributor and carve down from there?

Here's where I'm at right now, looks like I idle at about 76 kpa, WOT at 100, and lowest I've seen while driving was 45 kpa.
I'm putting my rev limit at 6k, just because this motor frightens me. And is my daily.

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mcdragracer
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PostPosted: Mon Aug 27, 2018 10:07 pm    Post subject: Re: Fine tuning advise needed Reply with quote

Your small on your idle jets, should be more around 50 and 55, what size are your chokes? Your probably gonna be to small on your mains.
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Brian
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PostPosted: Mon Aug 27, 2018 10:16 pm    Post subject: Re: Fine tuning advise needed Reply with quote

50s were way too rich for me, checked with an LM1 and my afr was in the single digits. Open to going larger on the mains but I don't feel like I need to.
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74 Thing
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PostPosted: Mon Aug 27, 2018 10:52 pm    Post subject: Re: Fine tuning advise needed Reply with quote

What exhaust, what size carbs and venturi's, what compression, are the heads ported, have you verified jet sizes, have you verified fuel pressure?

Backfiring and popping can be many things: lean, rich, plugged idle jet, carb synch off, exhaust leak, intake leak...
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andreas5bmw
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PostPosted: Mon Aug 27, 2018 11:01 pm    Post subject: Re: Fine tuning advise needed Reply with quote

Your idle and main jets are to small,,,I would install a wide band o2 sensor and gauge and you will find out how lean you are running
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Brian
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PostPosted: Mon Aug 27, 2018 11:04 pm    Post subject: Re: Fine tuning advise needed Reply with quote

My next big one is exhaust leak. I haven't done a retorque on the new exhaust in about 100 miles.

Vents are 28, triple checked jet sizes as I got one of those nice drills sets from Pierce Manifolds.

Compression is something at about 8, have to refer to my notes. My deck height was crazy positive so I had to stack shims, and my heads didn't allow for a lot of chambering. Wanted to work them hard but only got 54ccs.

Exhaust ports cut to match at 1-1/2, with a CSP comp-evo. Its really nice.

So on that for popping, I think I'm at exhaust leak as I have a little bit of a run on and pop 5 seconds after shut down.



After that, smoothness of driving; I'm thinking that I'm getting too much advance too soon.
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74 Thing
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PostPosted: Tue Aug 28, 2018 7:02 am    Post subject: Re: Fine tuning advise needed Reply with quote

Have you VERIFIED fuel pressure?

Are the heads ported?
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Clatter
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PostPosted: Tue Aug 28, 2018 7:12 am    Post subject: Re: Fine tuning advise needed Reply with quote

I always really love the climb-under-there-with-the-engine-running-and-stuff-a-rag-up-the-pipe test.

It will show you right away and for real if you have any exhaust leaks.

If you donít already have exhaust leaks, and might easily in the future,
It will get them going for you, so you can suss them out now.. Wink
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Brian
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PostPosted: Tue Aug 28, 2018 8:17 am    Post subject: Re: Fine tuning advise needed Reply with quote

FP checked. Heads are ported a tad, and the manifolds match. Manifolds are the universals that will fit 48s as well.

I'll pick up some atf on my way home from work today. Do one barrel at a time and smoke the whole neighborhood.

Side note, when I checked my plugs last a week ago they looked perfect. But I'll throw a picture up after checking again.
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74 Thing
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PostPosted: Tue Aug 28, 2018 9:06 am    Post subject: Re: Fine tuning advise needed Reply with quote

I think the carbs may be a little on the small side for your engine, but you should be able to get it to work, however, this may be the root of your problem "used some Chinese IDFs"

Hopefully you can work through it though.

You can pull your main jet stack and just run on the idle jets. Warm it up and do that and see if it pops back or is good until a certain rpm. This is where your transition should occur. Remember that anytime you make a timing change or idle jet change then you have to warm it up and set the idle mixture to LBI.

If you are using a wideband LM1 you have to make sure there is no exhaust leaks and that the sensor is calibrated to fresh air.
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PostPosted: Tue Aug 28, 2018 9:26 am    Post subject: Re: Fine tuning advise needed Reply with quote

look down the throat of each barrel and make sure you don't have unmetered gas (dripping) on any carb....also cover each air horn on the carbs and see if there is one cylinder that hardly makes any changes.
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PostPosted: Mon Sep 10, 2018 2:14 am    Post subject: Re: Fine tuning advise needed Reply with quote

10mm-11.5mm for the float height. Be certain fuel pressure is no more than 3.5lb

47.5 - 50 for idle jets

190 air correctors

You could can either pig rich or super lean depending on the mixture screw/s setting with 50 idle jets, hell with any size idle jet for that matter. Just be certain you are 'Lean best idle' with them.

Are you sure your auxiliary vents are oriented correctly?
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PostPosted: Mon Sep 10, 2018 7:31 am    Post subject: Re: Fine tuning advise needed Reply with quote

The other guys did the work, I am just agreeing, sounds like too lean which will cause backfiring. Fix the exhaust leak first, get it out of list of suspects, it adds to Backfiring, or itself can be a cause.
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PostPosted: Mon Sep 10, 2018 9:06 am    Post subject: Re: Fine tuning advise needed Reply with quote

Your spark table is WAAY off. Get that fixed first. Then worry about jets.
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Brian
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PostPosted: Mon Sep 10, 2018 10:10 am    Post subject: Re: Fine tuning advise needed Reply with quote

Almost forgot about this. So yea, exhaust is good from leaks.

Any suggestions kn the timing?
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PostPosted: Tue Sep 11, 2018 11:50 am    Post subject: Re: Fine tuning advise needed Reply with quote

Brian wrote:
Almost forgot about this. So yea, exhaust is good from leaks.

Any suggestions kn the timing?


What distributor?
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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 Webers - LM-2 47.5 idles/120 mains/200 air corr./F11 tubes/28mm Vents - Float height 10.45mm/Drop 32mm
Bosch SVDA w/Pertronix module
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Brian
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PostPosted: Tue Sep 11, 2018 11:52 am    Post subject: Re: Fine tuning advise needed Reply with quote

Magnaspark II
Right now I'm on the pre-set timing map for dual carbs.
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PostPosted: Tue Sep 11, 2018 11:55 am    Post subject: Re: Fine tuning advise needed Reply with quote

28-30 degrees full advance (centrifugal) no more. At ~3200rpm's
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Headflow Masters New AMC 42x36mm heads w/Porsche swivel adjusters
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Bosch SVDA w/Pertronix module
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Brian
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PostPosted: Tue Sep 18, 2018 11:47 am    Post subject: Re: Fine tuning advise needed Reply with quote

I thought it was kind of odd that it idles at ~15 and goes max at 34. It goes up to 34 very quick.

Should I probably drop the idle down and the max all together? I'm just really lost at where to start with making a map.
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PostPosted: Tue Sep 18, 2018 12:13 pm    Post subject: Re: Fine tuning advise needed Reply with quote

Brian wrote:
I thought it was kind of odd that it idles at ~15 and goes max at 34. It goes up to 34 very quick.

Should I probably drop the idle down and the max all together? I'm just really lost at where to start with making a map.


If you've got a known good (functioning correctly) distributor 009, SVDA drop it in and time it to 30 degrees full advance at 3200rpm's and see how it runs. Also watch what the timing does (or is at) at different rpm's.

Then you'll have better luck in mapping your Mag.

You may never get rid of the occasional popping on decel with aftermarket dual carbs. High decel will account for large air draw into the exhaust from the end of the pipe.
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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 Webers - LM-2 47.5 idles/120 mains/200 air corr./F11 tubes/28mm Vents - Float height 10.45mm/Drop 32mm
Bosch SVDA w/Pertronix module
NGK B5ES - .028 gap
Pertronix Flamethrower 40K coil
S&S 4-1 w/Walker QP 17862
3 rib 002 Trans
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