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Dellorto Cough  Rate Topic 
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 Posted: 02-15-2022 06:40 pm
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Paulreese1
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Installed fuel regulator set to 2.5 psi. Float weights are 10 gram set at 16.75mm. Measured fuel levels. Front carb, front jet well came in at 25.3mm, rear carb, front jet well was 25.4mm. No smoke or gas out of exhaust during hard rev. Running out of carb things to check so thinking looking at timing. Have a new 43D distributor.

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 Posted: 02-16-2022 04:08 pm
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discogodfather
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When I measure fuel pressure I have two small gauges sitting at the carbs they measure 2.5psi. A few feet away at my fuel pressure regulator they single line measures at 4 psi (I have a cockpit mounted electric gauge to see that pressure).

I think that depending on the regulator, measuring at the carbs is the correct way to measure fuel pressure, and that there is a significant drop across the regulator. Not sure what you setup is like.

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 Posted: 02-16-2022 05:24 pm
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Jh092
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Paul,
The carbs are the last things to adjust. Yes, you have to make sure they are set up properly and don’t leak fuel and have the right jets, and the floats are set, etc., but if there is an ignition problem, you’ll never dial in the carbs and make the car run correctly. All ignition components should be good and without problems. The points and timing should have been set correctly when the new distributor was installed. What about plug wires, plugs, cap, rotor, coil?

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 Posted: 02-26-2022 10:53 pm
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Paulreese1
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Thanks all for inputs. New distributor (it came with electronic ignition), plugs, wires, coil and timing light not coming on. Light works fine on another car. Getting 9.9V with resister wire. Coil measures 1.4ohms. Thinking about bypassing resister wire and tryimg 3 ohm coil when I can get back to the car in a couple days.

Last edited on 02-26-2022 11:16 pm by Paulreese1

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 Posted: 04-13-2022 11:29 pm
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Paulreese1
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Finally! Venturi were upside down. Will definitely give you a flat spot. Thanks for all the inputs.

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 Posted: 05-02-2023 12:00 am
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jensendriver123
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Hi Guys, Just now getting my car on the road after 3 and a half years (https://www.youtube.com/shorts/zHaHKprByuI ). But, I think I'm having the same problem with my delortos. It seems to run very nicely but not until I open the idle screws up to 6+ turns. I live in reno and the carbs are supposed to have been correctly jetted for 5500 feet of elevation. But, I'm guessing they probably aren't quite right and are going to need some tweeking. Do the jets have any markings that indicate what sizes the are? I'm guessing my first step is to determine what I'm currently running.

Also, is there any information, online, detailing the carb, how it works and what the various jets, etc., are? I'm guessing I need to understand, a bit better, the ins and outs of these carbs.

Thanks.

Richard

Last edited on 05-02-2023 12:07 am by jensendriver123

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 Posted: 05-02-2023 03:21 pm
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DonBurns
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The jets have numbers stamped on them. There is a book "How to Build and Power Tune Weber & Dellorto" by Des Hammill. It does a good job covering how the carbs work and lists all of the available parts. I read it 3 times but still can't figure out how to tune a Dellorto, but I keep trying. I have added an O2 meter, which I think is pretty important if you are not a "carb whisperer" ;) Very small changes to the mixture screws which don't seem to do anything to idle speed or audible engine running affect the mixture big time. You see it on the o2 meter. Of course there are mechanical issues in the carb that can cause problems also. The book goes over all that as well.

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 Posted: 05-02-2023 05:59 pm
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jensendriver123
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Thank you DonBurns. I'll look for that book. Can you tell me what type of CO meter you purchased? Thanks much. Richard

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 Posted: 05-02-2023 10:11 pm
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DonBurns
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I started with an Innovate Motorsports LM-2 A/F meter, which is a hand held meter. It was giving me some issues with freezing during a run (should be able to record multiple channels of data. A/F mixture and RPM at least. I ended up replacing with a AEM in dash gauge, which I have placed where ashtray should be. Of course you need the sensor, and have to get a muffler shop to weld a bung on the exhaust.

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 Posted: 05-09-2023 02:21 am
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jensendriver123
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Thank you Don,

Yes, that was my understanding, that I have to get a muffler shop to weld it into the exhaust.

Interesting. could you post a picture of how it looks in the console?

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 Posted: 05-09-2023 04:34 pm
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DonBurns
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Someday will probably rework center console to make it look more finished.

Attachment: O2 meter 500.jpg (Downloaded 27 times)

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 Posted: 05-11-2023 08:09 pm
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Esprit2
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Be careful about using an O2 sensor/ AF meter to tune carbs. Those tools will lead you to a chemist's version of perfect combustion, a stoichiometrically correct air/fuel ratio. Perfect combustion... depending upon whose definition of 'perfect' you use.

Neither the 907 nor Dellorto carbs ever studied chemistry in Grad School, and neither gives a darn about a stoichiometrically correct mixture. If you wish, use it as a starting point, and tune from there toward a better mixture, then go for it. But don't get your hopes up that a 'by-the-book' stoich mixture "end goal" is going to make your 907 run well... regardless of which brand of carbs are installed.

As a kid, did your Mom ever try to give you a medicine that some doctor said was good for you, but it tasted like rancid crap and you fought her every inch of the way? Okay, now you're Mom, using an O2 sensor/ AF meter instead of a spoon to force a stoichiometrically correct mixture down your kid's... er, down your engine's throats that it does not like.

Be conservative about how you use an O2 sensor with carbs. There is no 'intelligent' ECU between the sensor and the engine, moderating the O2 sensor's signal into an "appropriate for the engine" carb setting. And your engine won't be happy with stoichiometrically correct, 'cuz it "tastes like crap".

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 Posted: 05-11-2023 09:00 pm
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jensendriver123
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Esprit2, Thanks for that. Yeah, I'm getting that the best way to go about it is do lots of 'tweek/road dyno test' iteratoins.

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