Dellorto DRLA 40 modifications

[Wreck]

[Don Cichocki]

36mm Dells, 6 progression holes or 5? Did EMPI modify the original 36 when they made their copy and add another hole? That's one of the questions I had when I started this thread.

[j-dub]

Don,
I just looked at 3 36 Dells I have here and they all have 5 progression ports.
They all seem to be the CB style with 100-160-160-180-180 ports.

Curious if you had the CB style Dells to swap back and fourth what change that would make to the tuning compared to your 100-140-140-140-140.

Jeremy
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[Don Cichocki]

Thanks Jeremy!
Wonder why EMPI went to 6 holes?
I already opened my top hole to 150. Too much going on to know if it did anything. I think once I have the A/F for the rest of the range in the ballpark I might go further with the progression holes … big gamble if I screw up!
Another thing I find interesting is that a Dellorto #55 idle jet is .51mm (.0201") and a #57 Dell is .53mm (.0209"). That's only .0008" bigger in diameter! Amazing how much that small amount makes in the A/F ratio.

[Alstrup]

One explanation to the 6 progression holes in the Empi D´s could be that the throttle shaft sits too low in relation to the progression holes, and they noticed that drilling nr 6 progression hole could actually mnake the carb work reasonable. - I say this because from the sound of it the Empi D 36 is the best working of the lot. Both the 40´s and the 45´s are downright awfull.

[Don Cichocki]

Makes sense.

[AlteWagen]

I know update kits are not well liked for traditional builds but in this case would it be a benefit since you could recurve the fuel delivery
with different progression and main tube hole sizes?
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[AlteWagen]

[Alstrup]

No, only second hand reports on the 36és. Personally I have no need for aftermarket 36és. There are still plenty of those around.
On the 40´s & 45´s. Yes the progression ports are placed too high. I´m not sure it can be remedied by adding another progression port, but I have asked my local tool maker to make an attempt on drilling one extra in a set of 40´s. When I get them back I will make some tests on a "known" engine and see how and if it works. Don´t get your hopes up too high though.

[Don Cichocki]

Update:
I figured that with all the bizaar combinations I've tried why not try adding a 6th hole to possibly extend the idle circuit and help the transition (my logic). Currently my carb has 100-140-140-140-140 progression ports. I have a rich spike just as the throttle plate opens and a lean condition at transition that remains at a steady throttle. I JB Welded the first 3 holes closed and re-drilled them to 100-120-130. In an attempt to richen the lean transition I drilled the 5th hole to 150. I then added a 6th hole of 120 just as a start to see what would happen. So now I have 100-120-130-140-150-120. I now have a slight lean spot at the 2nd hole and the transition goes from 14.2-15 during acceleration but levels off at low 13's during steady cruise at 60-80 mph. Not bad. I decided to open the 2nd and 6th holes to 130 to richen up the lean spots. Well, the 130 2nd hole cured that lean spot but the 130 6th hole screwed up the rest of the A/F ratio. I'm wondering if it's acting as an air-bleed on the rest of the ports? I then JB Welded the 6th hole closed and re-drilled it to 110. It now acts much like the 120, possibly better. I'm now at 100-130-130-140-150-110. The car drives pretty nice, runs cool. I'm thinking of trying Modoc's suggestion of opening the holes some more to see the results.

[modok]

Very interesting.
It is quite complicated with... so many holes.
And yes you can hardly change one.
Change one it shifts the whole curve, so enlarging the top hole or adding one, now the middle holes are too small.

So both adding a top hole, AND reducing the size of the others was certain to be an over-correction, but....now you found the other size for sure.

The only way to find the limits....is to find the limits!

Overall it's good news, where you are (at the moment) is certainly a more GRADUAL progression, as compared to the BIG dellorto pattern, and apparently a lot closer to right than the original pattern.


Looking forwards to your continued adventures. You can't stop now!
The service life of epoxy in modern gasoline is not forever.

[Don Cichocki]

Modoc,
It certainly has been a learning experience! I think I'll put the A/F gauge away and just enjoy the car for a while, it's running very nice.
I'll put the gauge on it once in a while to see if the JB Weld is eroding, I can always redo the ports.
Wonder why the photos aren't showing up, they did when I first posted?

[Don Cichocki]

[Zed999]

Pure gold.
I was originally hoping that you would cure your lean hole via the emulsions but this is far better I think. At least it's easier to understand...I think!

And I also think if I did similar I could go up a venturi size which would be fantastic for my engine. Win, win. Thanks again.

[Don Cichocki]

Zed,
I still may open up the ports to: 100-130-140-150-160-110 to see what happens ... someone has to try it!
I must say that Alstrup's idea of raising the float level was probably the biggest improvement and led to all other modifications working.