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Author Topic: need some help with carbs... updated, no one gives a shit, in may  (Read 858 times)
MrChainsaw
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need some help with carbs... updated, no one gives a shit, in may
« on: October 29, 2007, 07:47:18 PM »

i recently picked up this rabbit that has a single dual carb on it.  it idles about right and runs pretty good except for one thing.  when you go to punch it the carb loads up and stalls for a second and then it goes.  it makes taking off a big pain in the ass.

the guy i bought it from tuned it by ear to idle and what not, but never messed with the secondary adjustments.

i've yet to get ahold of a wide band to see where my a/f is at through the rev range.  but i can tell from the smell at idle that it is def. running at least a little rich.  it also seems to pull pretty hard, but it really dies off higher in the rev range, even a bit before i think it should for a 8v.

i was wondering if anyone has any good advice on adjusting a carb.  is it something best done on a dyno or can it be taken care of pretty easily iwth a wide band?  i can get a hold of a wide band pretty easily i think, if not i was thinking of getting a kit with a gauge so i can monitor that shit from inside the car and make adjustments when needed.

i'm not sure of the jets that are in it right now.  i have the information somewhere, i just need to locate it all.  i'm sure knowing the type of carb would be nice too, which i'll have to check, but this just came up to me tonight to ask about and its dark right now and all the records for the carb are in the car right now and i'm too lazy to go outside and hunt for it in the dark...


update:  i finally got a wideband on the car.  and this is what it is doing.

idle is around 1500rpms and air fuel is at about 17 most of the time.
under throttle partial:  about 15 a/f
full throttle:  jumping on the throttle goes over 18 a/f after that its 15-16
cruise:  cruise is about 12-13.5 regardless of rpm as long as it is constant.

when i bought the car they guy had said he adjusted just the primaries and left the secondaries all the way down.  i'm assuming the secondaries are doing very little which is causing the lean mix under acceleration and then the primaries are flowing too much under cruise, causing the rich reading.  i'm thinking turning the secondaries up till i get a decent idle mixture (14ish) and then turning the primaries down so that i can get the cruise up to around 14-15 and hopefully this will get my acceleration down to the mis 13s somewhere.

the car pulls pretty hard as it is but does hesitate a little when applying throttle and the reading is definitely lean, and the rich cruise would help to explain the poorer gas milage i am seeing.
« Last Edit: May 15, 2008, 07:08:31 PM by MrChainsaw » Logged

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Re: need some help with carbs...
« Reply #1 on: October 29, 2007, 07:52:26 PM »

What kind of carb is it?  It could be the accel pump circuit not functioning correctly.
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Re: need some help with carbs...
« Reply #2 on: October 30, 2007, 11:42:27 AM »

You know, I have a Holley 5200 that does that but it was Jetted for a 2L and was sitting atop a 1.6L - I figured it was just getting to much gas...
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Re: need some help with carbs...
« Reply #3 on: October 30, 2007, 12:01:35 PM »

sound like it may be over jetted to me.
« Last Edit: October 30, 2007, 12:58:31 PM by jaydub » Logged

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Re: need some help with carbs...
« Reply #4 on: October 30, 2007, 12:52:38 PM »

sound like it may over jetted to me.

Exactly
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MrChainsaw
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Re: need some help with carbs...
« Reply #5 on: October 31, 2007, 06:41:03 PM »

the guy i got it from did mention that the jets are a little on the large side for the displacement.  i was hoping to offset this a little by adding a fairly good sized cam to it, it already has a header and a 2.25 inch exhaust with no cat.

The carb is a Dellorto side draft, i think its a 45.  i still can't find the paper work that has the jet sizes on it.

i need to get a A/F on the thing so i can figure out how off this thing is.
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Re: need some help with carbs...
« Reply #6 on: November 01, 2007, 06:35:31 AM »

Do some WOT runs with fresh plugs and then shut the motor and pull 'em.  That should tell you how rich the top end is.  If you roll into it does it run good? Or does it not matter if you roll in or slam in? 

If the main jets are sized right, it could also be the emulsion tubes being incorrect for that app.

let me know if I can help, I've got Dell 40's on my racecar.
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Re: need some help with carbs...
« Reply #7 on: November 02, 2007, 04:11:51 PM »

if you get into it with any aggresion it will start to choke and then it'll open up and go.  sometimes even rolling into the throttle will cause it to start stalling.
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Re: need some help with carbs... updated 1/30/08
« Reply #8 on: January 30, 2008, 01:19:23 PM »

updated first post with a/f readings and my assumptions.
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Re: need some help with carbs... updated 1/30/08
« Reply #9 on: May 15, 2008, 07:07:57 PM »

I need a Idle air adjustment screw for a Dellorto  DHLA 40 with the enclosed towers..   wwwweeeeeeee


And I realize no one cares or will read this.
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Re: need some help with carbs... updated 1/30/08
« Reply #10 on: May 16, 2008, 08:08:48 AM »

I need a Idle air adjustment screw for a Dellorto  DHLA 40 with the enclosed towers..   wwwweeeeeeee


And I realize no one cares or will read this.

Have you tried the normal suspects?  CB Performance, EuroCARB in the UK, or that Ebay guy in France?
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Re: need some help with carbs... updated, no one gives a shit, in may
« Reply #11 on: May 17, 2008, 08:38:05 PM »

I found one place in the UK that has them.  I couldn't find any of the fully enclosed fine thread ones on ebay, all the ones on there are the exposed screws.  I was kind of hoping that I might find some inside the US that I could get at without having to deal with international shipping.  I have one guy around here that I need to get in touch with because he hordes carbs and carb parts.
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