Author Topic: Dellorto Tuning Questions (Read 1685 times)

Chris · « **on:** July 19, 2006, 09:05:46 PM »

Ok I am running a set of 48MM DRLA's and well I have read the book, rebuilt the carbs, or at least I hope so and now I need to get this car running smooth!

Here is what I have so far

190 MAIN AIR
155 MAIN JETS
55 IDLES
36 VENTURIS
#2 EMULSION TUBES

My engine combo is

1914cc

9.75 to 1 Compression
1.4 to 1 Rockers
40 x 35.5 Heads ported by KROC
Webcam 86b (i think its that or an 86c but im leaning towards the B )

What else do you need to know?

So far its definitely running lean on idle, it does tend to build up RPM after a while but I am running approx 2.5 PSI on Fuel Pressure. I am just in the process of replacing the manifold gaskets and making sure that the manifold seats are nice and flat.

First question, what is the appropriate setting for the bypass screw, I cant seem to find any info on this.

Second question, will taller velocity stacks really improve performance?

Third, why?

James Buchan · « **Reply #1 on:** July 19, 2006, 09:26:03 PM »

Not sure if it relates to Dell's but when I went from a 37 Vent to a 40 Vent in my IDA's it picked up .3 tenth at the track and seemed happier overall.

dannyboy · « **Reply #2 on:** July 19, 2006, 10:25:26 PM »

but you also have bigger valves there bucko, you can give it a shot but somehow i dont think it would run very well with 40mm vent and 40mm valves
just my opinion...

Bruce · « **Reply #3 on:** July 19, 2006, 10:29:35 PM »

Quote

First question, what is the appropriate setting for the bypass screw, I cant seem to find any info on this.

Second question, will taller velocity stacks really improve performance?

1) In theory, the idle air bypass screws will start all shut. Then when you are finished adjusting your carbs, you can open up the screw on the cylinder that is flowing the lesser amount on each carb. This means that when you are done, only 2 are open.
I have seen no difference in idle quality or smoothness before or after equalizing the flow this way. So if you don't touch them, don't fret it.

2) If you had a dyno, you might be able to measure the difference, but it will be small. The difference between no stacks and some stacks is much more significant.

My suggestion is to start with a 60 idle jet. Most guys will tell you to run a 70, but I've never seen a DRLA that ever needed one. Years ago when Darren ran 48 DRLAs, he would drive around with 65s then swap in some 60s to pass aircare. It still ran good with the 60s, but we didn't have wide band O2 sensors back then to verify the A/F ratio.

GMB · « **Reply #4 on:** July 20, 2006, 10:56:35 AM »

Hey Chris do you have an O2 bung in your exhaust? I know a guy up the hill from you who has an LM1.
Gary.

Chris · « **Reply #5 on:** July 20, 2006, 03:15:13 PM »

I have a LC-1 already, thanks. But theres always room for people to help me out!

jim martin · « **Reply #6 on:** July 20, 2006, 03:42:40 PM »

you can only adjust the idle air bypass screws correctly if you have a 4 pipe mecury colum vaccum set such as i have as well you need to have the hook up on the carbs for individual vaccum hook up.
if not leave all 4 closed and balance the carbs at 2500 rpm then set the balance at idle
i would run 40mm vents /170 /170 main & air combo , a 65 idle jet and 50 pump jets .depending on the needle and seat type /size i would run 3.5 psi fuel pressure and drop the float level close to 7mm.
if you are stuck or need more explination /tips on dellorto setup phone me tomorrow as i will be in the garage from 10.30 till 2.30
604 327 5118