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Title: Dellortos 48 drla leaning at the transition Post by: pnikas on February 21, 2021, 10:47:42 am Hello everybody, I have a 2533 type 4 with Dellorto 48drla carbs
They have 40mm venturi I put them on the engine and using a O2 sensor I am trying to tune it . It was rich on the idle circuit, ok at high rpms and it gets lean at a about 3000rpm, specialy when pressing just a bit the throttle . I tried reducing air size 200->190 Increasing pump jet 55->60 Increasing main jets. 180->190 Used 9164.3 emulsion tubes instead of 9163.2(that helped a lot ) Still gets lean at around 3000 rpm Title: Re: Dellortos 48 drla leaning at the transition Post by: Phil West on February 21, 2021, 19:18:50 pm Your problem is the idle air. I had the same issue. You need a smaller idle air jet. As we found on the Dyno, it’s a critical tuning area.
In the end we used the tall idle air holder from the cb update kit and drilled it out very big. Like 3mm. Then we used Weber air jets that just fit nicely inside the tall holder. This allowed us to change jets for the idle air. After years of living with a lean out at transition I finally got it sorted on my drla’s. Cheers Phil Title: Re: Dellortos 48 drla leaning at the transition Post by: pnikas on February 22, 2021, 03:45:31 am Your problem is the idle air. I had the same issue. You need a smaller idle air jet. As we found on the Dyno, it’s a critical tuning area. In the end we used the tall idle air holder from the cb update kit and drilled it out very big. Like 3mm. Then we used Weber air jets that just fit nicely inside the tall holder. This allowed us to change jets for the idle air. After years of living with a lean out at transition I finally got it sorted on my drla’s. Cheers Phil Thanks a lot for your answer Phil . You might jut be on to something because I had the dumb idea to use the idle jet holders from my 40 drla carbs that had fresh o-rings on them , are the jet holders marked ? Where from do they pick the air?.DHLA carbs have many options in idle jet holders . Title: Re: Dellortos 48 drla leaning at the transition Post by: Phil West on February 23, 2021, 08:45:48 am Fundamental weakness of the DRLA design - these idle air holders do not allow tuning i.e. they don't come in a whole range of sizes. I found it was one of the most important areas for tuning. For most of my motorway driving I am at the top of the idle circuit. Main jets not so relevant.
Title: Re: Dellortos 48 drla leaning at the transition Post by: Phil West on February 23, 2021, 08:51:28 am I'm sure there's many ways folk have got round the problem. My solution was pretty basic. Just fit weber airs into the top of the idle air holders in this kit. You need to spread the base of the jets a bit to fit snugly. Then you can swap airs at will. Worked at treat.
Cheers Phil Title: Re: Dellortos 48 drla leaning at the transition Post by: volkskris on February 23, 2021, 10:46:29 am Are these (or similar) idle jet holders available separately somewhere? I have 36's so no use for most of the parts that come with the update kit.
Title: Re: Dellortos 48 drla leaning at the transition Post by: Phil West on February 23, 2021, 20:18:41 pm Not that I am aware. I also am not using the other bits.
Title: Re: Dellortos 48 drla leaning at the transition Post by: JIMP on February 23, 2021, 22:12:02 pm Hello
cb has the "7348 Jet Doctor Kit" so you can get only the tall holders needed for small price Friendly Dimitrios Title: Re: Dellortos 48 drla leaning at the transition Post by: volkskris on February 23, 2021, 23:09:26 pm Hello Sweet thanks!cb has the "7348 Jet Doctor Kit" so you can get only the tall holders needed for small price Friendly Dimitrios Anyone have any idea what size air jet I can start out with on a 1600 with 36 drla's? Title: Re: Dellortos 48 drla leaning at the transition Post by: cel on February 24, 2021, 19:26:56 pm Fundamental weakness of the DRLA design - these idle air holders do not allow tuning i.e. they don't come in a whole range of sizes. I found it was one of the most important areas for tuning. For most of my motorway driving I am at the top of the idle circuit. Main jets not so relevant. I dont know but maybe the idle jet holders from the older (pre emmision) dhla carbs will fit? They are "emulsion type" and have air calibration holes. https://www.dellortoshop.com/contents/en-us/p632_(12)-Idle-Jet-Holder-Emulsion-Tube-for-Dellorto-DHLA-carburetors-7850.html |