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Unread 04-05-2012, 06:18 PM   #376
uptillnow
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[QUOTE=I6CJ7;13364522]Here's a pic of the choke when I pump the pedal once and start up, it was about 68 out. The second pic is after I nailed the pedal, revving it, to knock the choke off.
QUOTE]

How long was 12 volts applied to the choke, when you took this picture?

I ask this because the choke is a bi-metal strip that straightens out and re-coils from the amount of “time” voltage is applied. (13.4 volts like a toaster coil) It depends mainly on the “heat” the voltage applied creates on the bi-metal strip. One metal expands faster than the other and straightens out, when no voltage and the bi-metal strip cools it recoils, therefore closing the choke.

The typical “time” is about 4 minutes. (closed to open)
What we do as technicians is to adjust this “time” of choking to the time it takes the engine to come to operating temperature. In the winter in Alaska we would probably need a little tighter wind on the bi-metal strip therefore increasing the choking time. Death Valley in the summer time would need less wind on the bi-metal strip for a quicker start and warm up time. When the winding is too tight, we have too much or extended enrichening after the engine has come to operating temperature, too loose and it runs lean for a short time until the engine reaches operating temperature.

If you sit in your Jeep, with the ignition on, listening to the radio etc., the choke will have had voltage applied and the choke will be open. Conversely, if you don’t have enough voltage, or bad ground etc. the coils will take longer than the typical 4 minutes to open.
UTN

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Unread 04-05-2012, 07:15 PM   #377
I6CJ7
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Hah Radio? What's that fancy thing? Ive had one in my tuffy console for 4 years.... hooked to nothing!

I would say it takes about 4-1/2 minutes or less to warm up. Its starts at 900, and climbs to about 1300. But its stumbling as its warming up and almost sounds like its missing... so maybe I need a tad tighter wind on it? The missing would be an indication of too lean correct?

I need to get my ignition in order first!
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Unread 04-06-2012, 03:44 AM   #378
Matt1981CJ7
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I6,

If I were you, I'd put about 1/4-turn more on the speed screw and leave the spring tension alone. Mine had the same lean stumble as yours, when I tried to cold start at 1000 RPM. When I kicked the speed screw up to start around 1500, she purred like a kitten.

I think it's a matter of matching the starting throttle position to the starting pull-off position. If you'd prefer to start at a lower RPM, you'll probably have to adjust the pull-off to close a little more than it currently is. This should richen up the starting mixture and allow for a lower start RPM.

You'll know when you hit the choke settings your engine prefers. She should fire on the first crank and run just as smoothly cold as she does when she's warm.

Good luck, and keep us posted.

Matt
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Unread 04-06-2012, 07:19 AM   #379
Matt1981CJ7
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Hey guys,

I like coming to this thread with my half-baked theories, because I know I'll get knowledgable responses.

I found an interesting article here.

Within it, the author discusses the notion that there really isn't much difference between manifold and ported vacuum in load conditions, only at idle. He confirms this by including a chart (below) where he hooked up a couple MAP sensors and a throttle position sensor to a data logger and recorded them while driving.

As you can see, the ported and manifold vacuum lines follow the same path in almost all throttle positions except idle. This is consistent with my observations when I've watched my vacuum gauge hooked up to either source.

He goes on to say this, "As you can see, there is a direct relationship between throttle position and vacuum. When the throttle is closed vacuum is high, when the throttle is open vacuum is low, and ported vacuum is the same as manifold except when the throttle is closed. So which one do you want to hook it to? I prefer manifold vacuum. This pulls in more timing at idle which is good since there is virtually no load. Your motor will idle smoother and cooler with the extra timing.

In my feeble mind, this renders many of the debates we've seen here at JF rather pointless, since the only real difference is whether the timing is advanced at idle, or not. Since it's beneficial to have a little advance in no-load situations, the clear choice seems to be manifold.

Thoughts?

Matt
vacuum_chart.jpg  
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Unread 04-06-2012, 09:27 AM   #380
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Quote:
Originally Posted by Matt1981CJ7 View Post
In my feeble mind, this renders many of the debates we've seen here at JF rather pointless, since the only real difference is whether the timing is advanced at idle, or not. Since it's beneficial to have a little advance in no-load situations, the clear choice seems to be manifold.

Thoughts?

Matt
Yeah, probably some pointless blood loss over that stuff

I checked the ported vacuum on the old BBD and then the Weber 38 and there was a pretty big difference in the ported signal between the two carbs.

The 38 is probably the closest I've seen to the manifold vacuum signal but still off quite a bit. At least at part-throttle cruise and Sunday driving

Thanks for the link

Edit: That guy has some interesting stuff on his website. I like his idea of sizing the carb to a desired WOT manifold vacuum, although I don't fully understand his calculation.
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Unread 04-06-2012, 11:30 AM   #381
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I wish he said what carb he was using.the Carter YF has vastly different vacuum curves between manifold and ported vacuum. Possibly because of the placement of the ports. The BBD is even more interesting as there are a bunch of different ports on the same carb. The one located right at the narrowest part of the throat is interesting.

Who has a picture of the Weber port locations? When I run Manifold vacuum it's on the manifold, not a port on the carb.

Must be a young guy, everyone one knows you drill a hole in your throttle plate to keep your throttle closed properly with a big cam. That way your transfer port still work. Although if you drag race, it probably doesn't matter.


Hmm.. Go fast-for-less, gives some formula for sizing carb then tells you to try a bunch of different setups until you find one that works. :/ Go figure. I'll have to read the rest of his stuff someday.
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Unread 04-06-2012, 11:54 AM   #382
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Quote:
Originally Posted by John Strenk View Post
Who has a picture of the Weber port locations? When I run Manifold vacuum it's on the manifold, not a port on the carb.
Here's a fuzzy one. Is this the shot you were looking for? You can also see the end of the black vacuum cap just to the right of the mixture screw.

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Unread 04-06-2012, 02:35 PM   #383
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Thanks guys, I will try tomorrow and let you know.
Right now its starts with one pedal pump, and a touch of the key! Since I messed with that spring tension accidentally on the rebuild, I will try alittle tighter, then softer tension to see what happens. From there ill mess with the speed screw.
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Unread 04-06-2012, 03:06 PM   #384
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I6CJ7,
On an initial choke set-up on a Weber…

I like to start by:
1. Close the choke butterfly by hand.
2. Holding the choke closed, open the throttle plates. (step on the gas) Release the gas pedal, let go of the butterfly and you will notice you are on “high” idle. (engine off of course) The throttle lever should be ” away from the idle speed screw or the idle stop screw. This is adjusted with the screw behind the choke housing.
3. Next, loosen the three basil screws around the plastic choke element.
Close the butterfly by rotating the plastic element, releasing the tension and reclose the butterfly. There should be ever so slight tension by touch to the choke butterfly opening and spring back to close.

This is a starting place, so you know where you are and then where you are going as far as adding choking by tightening or less choking by loosening the plastic element.
Good Luck
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Unread 04-06-2012, 07:38 PM   #385
I6CJ7
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Good stuff, makes more and more sense. Im a real visual learner and sometimes have to read things a few times unless its explained a certain way
I'll let you all know tomorrow.

The wealth of knowledge between all of you guys is nothing short of amazing!
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Unread 04-06-2012, 08:12 PM   #386
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Quote:
Originally Posted by I6CJ7 View Post
Good stuff, makes more and more sense. Im a real visual learner and sometimes have to read things a few times unless its explained a certain way
I'll let you all know tomorrow.

The wealth of knowledge between all of you guys is nothing short of amazing!
Let us know when your goodies show up


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Unread 04-07-2012, 09:31 PM   #387
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Finally, my experiment with the 32/36 begins. As some of you know I've got an 89 4.2 as my DD from altitude 8800 to 5700. My BBD is tuned pretty tight with ~20mpg and adequate 5th gear power (mostly) on the uphill run. It's fully emissions compliant with Pulse Air, SolVac, etc. It isn't nuttered as I've an MSD6A wired to the dizzy which overrides the MCU, in fact the MCU isn't even connected to the dizzy but Pulse Air and Solvac still operate as designed.

I'm starting the 32/36 rebuild now with a typical gasket/diaphram kit, and ordered an adapter for $20 so I can use the factory air cleaner assembly to take advantage of the OEM TAC system:

http://www.webercarbsdirect.com/Sear...show=20&page=1

I also ordered a jet kit for $50 which seems to provide an adequate spread of jets for what I'll need for my "experiment":

http://www.lceperformance.com/Weber-...-p/1035002.htm

Considering the carb came baselined with pair or 145 mains, 170/160 air correctors, and 75/60 idles this should provide a good selection for testing. The E-tubes are both F50 and I'll relegate them to the back burner pending road testing.

I'm pretty excited about this project as I really want to know if the Weber is better than the BBD overall considering both power and economy. I'd really like to have a bit more throttle when required without sacrificing economy so we will see. A long summer ahead providing plenty of time for tweaking. There's an HP/Torque chart for Weber/Carter (click on the graphs to expand) which I'll supposedly experience -

http://www.clutchkitcenter.com/media...weber/Jeep.gif

I'll keep you posted, especially about where it finally settles in. Mindset=Analytical
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Unread 04-07-2012, 10:09 PM   #388
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Take some measurements with the current set up.

Unless you got a chassis dyno, record some times like time to get from 10 to 30 mph and time to get from 50 to 60 mph. Make a change and repeat the test and record the figures.
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Unread 04-07-2012, 10:09 PM   #389
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Double post
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Unread 04-08-2012, 03:33 AM   #390
Matt1981CJ7
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Unfocused,

I'm looking forward to your experiment, as well. It will be interesting to see how your final jetting compares to mine.

I'm not sure I'm buying the charts, however. If I'm reading them correctly, they're claiming almost a 20% improvement in horsepower at 3500 RPM, for both the 32/36 and the 38 over stock. I don't think there is that much. In fact, I think you'll find the BBD may outperform the 32/36.

Of course, I never re-jetted my 32/36, so perhaps you'll realize better results with it than I did.

Let me know if you want to get together and tell some lies, sometime.

Matt
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