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  View original topic: dellorto idle jet sizing
GARRICK.CLARK Mon Aug 11, 2014 12:02 pm

Hi guys.
I'm trying to tune my 40 dells on a 1911 motor I have.
First issue I have is the idle jetting.
I'm using a 60 idle jet.
I have the mixture screws adjusted for best idle speed on the 4 cylinders.
It runs nice and smooth.
Thing is on other engines I have built, ON start up with dells I always get the carbs spitting and coughing till the motor warms up , this is what the motor should do is it not, due to the dells not having electric chokes, well on my current motor when I start it from cold it just run's at an 800 ish revs. no spitting/coughing 1000 rev once hot

Are the idles too big

Thanks G

P.S
There
40 dells
34 vents
60 idle
148 main
.2's
50 pump
180 air

jfats808 Mon Aug 11, 2014 12:22 pm

I suggest pulling the plugs and reading it. If the car pulls nice and you find no issues with performance, monitor mpg for the tank and compare to what you were getting before. You can experiment with a smaller jet and go from there imo. I dont care if the others say plug reading cant be accomplished accurately. I do it and it works for me.

74 Thing Mon Aug 11, 2014 1:10 pm

I would say both your idles and mains are way too big.

You need to verify that the sizes on the jets are the actual sizes-you cannot trust the markings.

To test your idle just remove the main air/emulsion/main jets from the carbs and drive on the idle jets only. Drive around the block a few times and see how it responds. If ok, then go down a size. Each time you make an idle jet change you have to re-adjust the mixture screws on a warm engine. Then drive around again. You will get to a size and it will pop and hesitate and not run correctly. When this happens go back up a half size and you are done with the idle.

I am betting your idles will be around 55s and mains should be around 135 to 140s.

[email protected] Mon Aug 11, 2014 1:15 pm

Your idles will be in the 52-55 range when done; main around 140. I'd try a 55 and 140 next.

GARRICK.CLARK Tue Aug 12, 2014 9:45 am

Ok thanks guys.
I will remove the main stack and check the tach to see were if falls flat. There is a small flat spot too in the 2300k area.
I'll order some 55's tomorrow. I do have some spare 140's so i'll try those.

[email protected] Tue Aug 12, 2014 10:11 am

The idle jet you wind up with will depend on the distributor you are using, and you didn't mention this.

GARRICK.CLARK Tue Aug 12, 2014 10:32 am

Hi John.
I'm using an svda.
I have modified this as the total was over 44 at 3000. So the initial now is 12 btdc and total is 32 at 3000 . There is no pinking under load with the engine at running temp. There was when using the unmodified distributor.

[email protected] Tue Aug 12, 2014 11:55 am

32 total is not enough. There is nothing wrong with 44 total under light loads.

GARRICK.CLARK Tue Aug 12, 2014 1:35 pm

Ok. All I have to do is remove a spot weld to get it back to full advance. What benefit will it make to the way it runs. Should It reach the full 44 then reduce as the revs climb. Am I loosing some power/drivability.

Thanks G

[email protected] Tue Aug 12, 2014 1:43 pm

for initial setup go for 8 at idle, 28 total (hose off), and 40-44 total (hose on).

GARRICK.CLARK Tue Aug 12, 2014 2:12 pm

Ok i'll do that tomorrow and report back.

Thanks John

GARRICK.CLARK Fri Aug 15, 2014 12:57 pm

Ok a little update.
I've re set the timing as per Johns instructions.
Got the 55 idles today. those are now in.
On start up there is no noticeable difference in how it runs when cold.
No spitting/popping from the stacks.

So drove the bug to get it up to temp.
I ran the motor in the 1000 to 2300 range so still on the idle circuit and it ran well no hint of spitting out the carbs.


Pulled over and adjusted the mixtures to get the best lean idle plus a half turn. What I then had to do was readjust the throttle stops as the idle speed had gone up from 1000 to 1200 revs.

Revs now at a stable 1000 revs

So does the fact that the motor runs on the idle circuit without issues mean that I've not found the smallest idle jet yet.

If I go too small on the idle jets what symptoms am I going to get.

Thanks G

[email protected] Fri Aug 15, 2014 7:04 pm

it sounds to me like you can go smaller on the idles. Next try 53s

GARRICK.CLARK Sat Aug 16, 2014 12:10 am

Ok I will put some 53's in next week. It does feel a bit crisper/smoother.
When I find the correct idle jet the next step from what I've read on the wideband thread is to remove the entire main jet stack.. which is the .2 tube/180 air and the main jet. Then run it on the street and note down on paper what rev number it starts to goes flat.

Am i going to have to get the innovate AFR gauge kit to finish the rest of the jetting.

Thanks G

GARRICK.CLARK Mon Aug 18, 2014 12:54 pm

Did some more tuning today.
I put a vac gauge on the number 4 vac port and there was a bit of vac present. So I backed off the throttle stop till I got no reading on the gauge. I put the snail on number 2 stack and adjusted it to match number 4 stack. Number 2, 3 and 4 stack read the same with the snail but number 1 stack does pull a little bit more.

I also backed off the pumps as I think they were adjusted too much.(lots of threads showing after the nut).

Still waiting for the 53 idles to arrive.

Idle is now 750
Put the strobe on it and the degree numbers are a bit erratic , maybe it needs one of those anti pulse valves.



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