48 Dellorto blow through hesitation at transition

[Buggsy]

If your running a cam with more than 286 degrees advertised duration, and 7.6 compression, your dynamic compression is very low. You should be running 14, 16, or maybe even more initial timing. I run 20 initial with a very short mechanical advance curve, and as much ported vaccuum advance as I can get to my SVDA. Give the engine what it wants, not what you think it needs. Don't be afraid to crank the distributor around a little and see what kind of response you get. Listen for ping, of course. Could be five minutes well spent, and you can always put it back where it was.

[brookester]

I tried the ignition advance route awhile back but it didn't help.
What if I drilled another transition hole in the carbs. Might that help?

[Buggsy]

I know some guys used to drill up to three transition port holes in the old race IDAs, but they had none to begin with. I would call that a last resort. Before I did that, I would take the carbs off and make sure your not already into the transition ports at idle. The reason I say this is you mentioned earlier in the post that you went rich on the idle jets, and it helped a little but was to rich at idle. From what I understand, the idle jets are overridden by the idle fuel adjustment screws at idle, so if you can't lean the idle out appropriately with the screws, maybe your pulling fuel from the transition ports. Geesh, on something as big as 48s, I have a hard time picturing this happening, but guess it is worth a look. It would take one damn big cam to have the throttle plates open that far at idle. Let me know what you find.

[seabeebuggy]

is your hat blowing from the top down on to the carb or is it coming from the side on the hat blowing in? I had to mount a 308 bullet brass casing to my float vent to keep direct pressure from blowing to much air into the float bowl. It sounds nuts but after doing so I was able to tune much better. the direct flow of air was making the float drop down and too much fuel was pushing in.

[brookester]

It's blowing from the side. You can see a picture on the first page.
So are you saying yours was going lean or rich?

[brookester]

I had Dan drill another transition hole in the carbs but I havent had a chance to test it much. I'm dealing with another issue first.

[seabeebuggy]

I honistly don't remember what it did. It just would not tune until I added the stacks. After I had it tuned I removed the stacks and it ran like poop. So I returned them and it has lasted .

[brookester]

How did you attach the stacks to the carbs?

[Bigg Tim]

Did you figure this out, how did that extra hole work out? I am putting together a similar setup with 45 dells, looks like Randy's old setup, using the same fuel pump and regulator.

[brookester]

It didn't make any difference.
I put in 38mm venturis and put a stack on the hole that pressurizes the float bowl(like Seabeebuggy did)so it now takes in air from above the main jets. It runs decent now but it's still a little lean on tip in. Very driveable now and I didn't lose too much top end power with the smaller venturis. I tried 20lbs the other day and I can't complain about power.

[Bigg Tim]

Do you think you can snap a pic and post it the next time you're in there so I can see? 20lbs......that's nuts, how much faster and how much power is there with the dual blow throughs versus the single side draft draw through you had?

[brookester]

Yea, I can do that.

Haven't dyno'd it yet but With the draw through it made 248hp and248 tq at about 16lbs at only 5700 rpm.
I think it should be over 300hp at 6800 rpm and 20lbs.

[70turbobaja]

Hey man whats up? One quick question, which side did you put the stack on? I just finnished my turbo blowthru 1835 with single centermount dellorto 45 but im having the same issue you are. If I roll on the throttle im good but if put my foot into it it falls on its face. I have not gotten my wideband to tell the a/f ratio. My car dies idles fine. I checked my accelerator pump and it is injecting

[brookester]

The hole is between the jet stacks. It's a rectangular hole that I stuffed a rifle shell casing into [like Seabeebuggy did] and the I put a silicone tube over the top to extend it above the main jet stack. I JB Welded it in but the mains hold it in just fine. When I get a day off I will take a picture of it. It's totally reversible back to stock. You will probably need to re jet.

[70turbobaja]

Did seebeebuggy post a pic? Do you think bigger main will fix my issue?