Weber 34 ADF Tuning

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friedman
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Re: Weber 34 ADF Tuning

Post by friedman » Sat Dec 02, 2017 8:16 am

I was building the superlight version of a street X so who needs all the heater stuff....when it's 99 degrees out. I thought I would just skip winter driving but I find letting a Fiat sit for five months is not a good idea, especially if you enjoy driving it.
Carl in Virginia
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covesurfer
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Re: Weber 34 ADF Tuning

Post by covesurfer » Sat Dec 02, 2017 12:45 pm

Ok, so I spent some time fixing vacuum leaks and de-smogging. Now I am about to put the carb back on, and before I make any other changes wanted to note what my current jetting situation looks like. You'll recall the baseline numbers I posted earlier; the blue reflects what are in the carb now:

Main venturis 24/26
Aux Venturi 4.5/4.5
Main jets 120/140 --> 125/140
Emulsion tubes F11/F75
Air Correctors 140/180 --> 145/180
Idle jet 47/90 --> 50/90
Pump Jet 40 --> 40
Float Valve 1.75 --> 1.75

Before I start it back up and try tuning, is there anything that looks wildly out of place? I'll report back on how the idling situation turned out...
Daniel
Frisco, TX
1977 124 Spider
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Re: Weber 34 ADF Tuning

Post by covesurfer » Sun Dec 03, 2017 6:51 pm

Today was a good day. I put the carb back on and made a couple of changes - lost the solenoid holder and took the main idle down to 47. Happy to say it started up and I was able to get it idling in the normal range. Driving was a blast - very spirited acceleration, and the jerking/starvation symptoms happened at much higher speed / load. A few things I noticed:

- Solenoid doesn't appear to be working. I am not sure if removing it had more effect than changing the jet size.
- Hesitation is gone, but comes back if I put the solenoid with the 50 jet back. If I could pry the 47 out of the holder I would give the 50 a try again, but it was stuck and I was tired
- I didn't have the rising/falling rpm symptom of vacuum leak before, but I do now. I sprayed some carb cleaner around the base, and looks like it is coming from where there are gaskets and a spacer at the intake mount. I will replace those and hope for the best.
- I noticed both a time when I removed the fuel cap and there was suction, and when there was pressure built up. I the process of plugging the smog stuff, I plugged both the top and side ports on the charcoal canister. Would keeping one of those open help with regulating pressure in the tank?
- For the jerking/starvation symptoms...could that come from a bad fuel pump, if the filter is fairly new? I blew out the lines and they seem clear. For now that is my last issue before I can be worry-free.

Any thoughts / advice would be appreciated! Thanks!
Daniel
Frisco, TX
1977 124 Spider
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sunracer
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Re: Weber 34 ADF Tuning

Post by sunracer » Sun Dec 03, 2017 10:54 pm

try it again with the cap loose. Seems your tank isn't venting. Vacuum won't help your fuel pump at high rpm. Pressure could overwhelm the needle and seat. Have you checked the float level?
Pierre
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Re: Weber 34 ADF Tuning

Post by sunracer » Sun Dec 03, 2017 11:02 pm

try it again with the cap loose. Seems your tank isn't venting. Vacuum won't help your fuel pump at high rpm. Pressure could overwhelm the needle and seat. Have you checked the float level?
Pierre
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Re: Weber 34 ADF Tuning

Post by covesurfer » Mon Dec 04, 2017 7:07 am

Thanks and I'll give it a try with the cap loose. Float level is at 6mm min, 13mm max.
Daniel
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friedman
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Re: Weber 34 ADF Tuning

Post by friedman » Mon Dec 04, 2017 8:26 am

I'm a bit confused on your statements about the idle jet solenoid. Does this carb use an idle solenoid or an old style idle jet holder? With an idle solenoid you can remove the spring and plunger and it will function as a normal idle jet without having to plug in a 12v source. As for the idle circuit, you should see little to no difference between a 47 and 50 idle jet, however it will affect transition.

You really need to solve all your vacuum leaks and gas tank venting before you attempt to fine tune the jetting.
Carl in Virginia
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Re: Weber 34 ADF Tuning

Post by covesurfer » Tue Dec 05, 2017 10:11 am

Sorry for the confusion. I replaced a 32 ADFA, which had the idle stop solenoid. The 34 ADF has a old style holder. I just put the solenoid in to see what would happen, and the hesitation at low RPMs came back, so I think there is an issue there. I am working on the other issues and will report back; I was thinking it would be nice to use the solenoid to stop any dieseling, but will stick with the old style holder while I take care of the vacuum leaks and gas tank venting.
Daniel
Frisco, TX
1977 124 Spider
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Re: Weber 34 ADF Tuning

Post by friedman » Tue Dec 05, 2017 12:42 pm

Since my first Fiat in 1967, I have never had a Fiat diesel, do not try to fit an idle stop solenoid assembly into a carb that didn't come with it.
Carl in Virginia
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Re: Weber 34 ADF Tuning

Post by covesurfer » Tue Jan 30, 2018 8:51 pm

I thought I would pop in to update the thread. As you may recall I was trying to address rough idling and some fuel starvation symptoms. I received some professional help and here is what I found out:

- The stop screw on the secondary throttle was mis-adjusted so the secondary was open too far, which was messing up all my tuning. Things are good now.
- My fuel pump was going bad, which was the source of the starvation symptoms at higher rpm. New facet cube and all is well.

Thanks as always for all the great advice and support!
Daniel
Frisco, TX
1977 124 Spider
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