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weber carburetor troubleshooting


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#1 mechanik1959

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Posted 11 November 2012 - 12:28 PM

I recently installed a weber conversion carb kit on my 87 honda crx-model DX. after completing and dialing everything in. I went for a test drive and noticed there was a lack of power when I excellerated. . went back and checked adjustments and discovered I wasen't getting any vacuum from the port line that connects to distributor advance diapham. so the issue I'm having is my timing isen't advancing when I try to excellerate. I am not sure what I need to do to correct this problem. it seems to me that there should be some sort of vacuum frome vacuum advance port on carb. I'm not seeing any vacuum at any of the three ports. I have good vacuum reading on vehicle. it idles great. so if there's anyone out there that has a suggestion what to do or where to go from here I would love your help, thank you, Dave...........

#2 datzenmike

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Posted 11 November 2012 - 03:23 PM

Vacuum advance only applies to part throttle. Full throttle acceleration will have almost no vacuum advance.

How did you determine that you have no vacuum advance??? No carb made after the late '60s has vacuum advance at idle. It's only when the throttle is opened that vacuum is applied to the vacuum advance on the distributor.

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#3 ggzilla

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Posted 11 November 2012 - 11:48 PM

Yes, and more specifically, vacuum advance doesn't cause timing to advance when acclerating.

So your problem is something else. Have you asked in a Honda forum?
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#4 mklotz70

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Posted 12 November 2012 - 05:46 AM

Don't some hondas have constant vac from the intake mani to the dizzy at idle and the loss of vac on accel causes the advance? It actually seem like a better way to do it since the loss of vac stays around under full throttle.

The vac advance signal from the carb is to create an advance in timing as the throttle is opened. On a weber, if you hit the pedal too fast, the vac signal is too quick or non-existent and the dizzy doesn't have time to react. The webers are a bit tricky to adjust. You want the butterfly closed as much as possible when you do the tuning. There should be no vac signal at idle, but as you crack the throttle, you will see it jump up close to manifold vac. When you tune the weber, just keep in mind that having the butterflies closed as much as possible is your primary goal and tune around that.
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#5 ggzilla

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Posted 12 November 2012 - 12:28 PM

Loss of vacuum causes the vacuum advance to stop working. So you get no advance. The vac advance signal from the carb is to create an advance in timing as the throttle is partially open, down to almost closed. Vac advance signal from manifold is to create an advance in timing as the throttle is partially open, down to almost closed -- and including closed (which is the only difference). I believe you still set initial timing on a Honda like on other cars, with the advance line disconnected and plugged. Check with the Honda boys to verify.

yes, adjusting idle-mixture must be done with throttle butterflies 100% closed. And choke butterfly 100% open. Just like any carburetor.
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