 Dual carb question, Dellorto 40s on a 1.8L to be exact |
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| terrymason |
 Jul 14 2007, 07:00 PM
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#1
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Member  Group: Members Posts: 346 Joined: 23-November 05 From: Virginia Beach Member No.: 5,174  |
The problem - The car will go very lean around 2500 rpm, as if the pump jets were too small.
History: New fuel pump (3.5 PSI to each carb) 55 idle jets 55 pump jets 140 main jets 175 air correctors These carbs are new to the car, and I'm trying to dial them in. The car is lean when I first start it (16 / 17 on my air / fuel gauge), but then levels out to a nice 14.7 idle when warmed up. While driving, I can give the car 20% or so of the pedal, and drive up to highway speeds nicely, but when I goose it, it will go very lean (18-22 on my gauge) followed by a series of backfires and loss of power. I started off with 35 pump jets, and have moved up to 55s, which appear to be the most popular around here. I've also adjusted the pump jet linkage, from the nut fully loosened, and moved it in as far as it would go before affecting the main throttle shaft (like 60 turns or something). What do you guys think, do I need 75 pump jets? |
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| BxtrBill |
Jul 14 2007, 11:22 PM
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Newbie Group: Members Posts: 23 Joined: 31-December 05 From: Arcadia, CA Member No.: 5,342 |
40 Dells were usually equipped with 34mm venturis from the factory (hence the urban legend that 40 Dells flowed like 44 Webers which were also equipped with 34mm vents, but I digress)
The pump jets you have, being 55s, are probably enough to flat drown a 1.8 if you blip the throttle real quick a couple times. Just for reference, I've got 40 Dells on a 2056 with 30mm vents, 125 mains, 60 idles (CA gas, may it reek) and *40* pump jets. I could probably do with 35s just fine, but the 40s work, so they're staying. Your problem, whatever it is, is NOT due to the the size of the pump jets....the pump jets' function is to meter fuel when the accelerator pumps pump. They have nothing at all to do with steady-state running. If I had that problem, I'd probably be looking at the idle jets first. Good rule of thumb is, most engines will run on the idles up to about 3000-3500 RPM or so. A plugged idle jet can make lean conditions, and the Dellorto design has them located where they can pick up any crap that makes it through/past the air cleaners. HTH |
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Posts in this topic
terrymason Dual carb question Jul 14 2007, 07:00 PM
Grelber Send JR91472 a PM. He has a 1.8 w/ dual dell... Jul 14 2007, 08:37 PM terrymason I've tried quite a few idle jets from 46 to 60... Jul 15 2007, 12:44 AM Blood red 914-6gt The problem is that dellortos suck. Sorry if you l... Jul 15 2007, 01:12 AM
Paul Illick
The problem is that dellortos suck. Sorry if you ... Jul 15 2007, 05:23 AM type11969 Terry-
You shouldn't be running that lean at ... Jul 15 2007, 07:18 AM terrymason OK, I have made some big headway on this. I pulle... Jul 15 2007, 05:26 PM BxtrBill
Ok...you got me on that one. The pump jets sit i... Jul 15 2007, 08:12 PM terrymason
Ok...you got me on that one. The pump jets sit ... Jul 15 2007, 09:15 PM type11969 Did you ever check out the vent size?
You should ... Jul 15 2007, 08:48 PM BxtrBill [/quote]The smallest vents CB had as of a month ag... Jul 15 2007, 09:12 PM terrymason
Oh..almost forgot.....if you look down the carb t... Jul 15 2007, 09:18 PM BxtrBill
Hm..hadn't considered someone might put them... Jul 16 2007, 09:47 PM terrymason
Did you ever check out the vent size?
You should... Jul 15 2007, 09:25 PM type11969 You gotta try to adjust the linkage such that the ... Jul 16 2007, 07:00 AM 904svo Sounds like your venturis are too big for a smooth... Jul 15 2007, 06:48 PM type11969 .1, .2, .3, .4
Jul 16 2007, 07:02 AM 9146986 Going lean at 2500 probably isn't a function o... Jul 16 2007, 07:41 AM rhodyguy i disagree with the "you should not be adjust... Jul 16 2007, 09:02 AM type11969 This is what I mean. Linkage disconnected, pull ou... Jul 16 2007, 09:31 AM rhodyguy the linkage ABOSOLUTELY comes into play when the ... Jul 16 2007, 10:04 AM type11969 Wait, if both idle speed adjusting screws are rest... Jul 16 2007, 10:22 AM rhodyguy ok. linkage off. flow set the same side to side wi... Jul 16 2007, 10:39 AM type11969 Well, if one rod is longer than the other and it f... Jul 16 2007, 11:29 AM Joe Ricard So what are we betting here?
What Kevin is saying... Jul 16 2007, 12:10 PM rhodyguy i'm glad you see what i'm getting at joe. ... Jul 16 2007, 12:28 PM type11969 The bet was if you sync the carbs with the linkage... Jul 16 2007, 12:34 PM terrymason I'm working in Seattle all this week, so won... Jul 17 2007, 12:48 AM terrymason You can actually see the aux venturi below Aug 2 2007, 02:40 PM terrymason etubes Jul 17 2007, 12:51 AM type11969 Looks like at least that one etube had one of the ... Jul 17 2007, 07:22 AM Joe Ricard Them aren't webers are they.
At least they loo... Jul 17 2007, 04:13 PM BxtrBill Here's a pic of the venturi out of the carb...... Jul 17 2007, 10:04 PM terrymason So, there's a blunt end, and a tapered end? T... Jul 17 2007, 11:29 PM Twystd1 I just went through this with some other 914 breth... Jul 18 2007, 03:06 AM Joe Ricard That' odd having the blunt end of the Venturi ... Jul 18 2007, 06:00 AM type11969 I'm pretty sure that is reversed, I'm almo... Jul 18 2007, 07:03 AM BxtrBill
I'm pretty sure that is reversed, I'm alm... Jul 18 2007, 11:14 PM terrymason I'm back in town, and had some time to look at... Jul 22 2007, 09:33 PM BxtrBill
You might want to order some smaller main jets w... Jul 23 2007, 09:48 PM rhodyguy i think your car is going to perform vastly better... Jul 22 2007, 09:51 PM Joe Ricard Agreed, it "should" pull better down low... Jul 23 2007, 08:42 AM jr91472 Clayton is spot on regarding the dizzy. Go stock ... Jul 23 2007, 08:48 AM rhodyguy your next decission is which intakes to run. i pos... Jul 23 2007, 08:53 AM jr91472 Yes please. I want to hear how the 30 vents work.... Jul 23 2007, 08:57 AM mike373 Hey rhodyguy. I think you may have the manifold i... Jul 23 2007, 11:03 PM terrymason well, I've made alot of progress! I have ... Aug 2 2007, 12:23 PM eric914 Not to hijack but I have 40 IDF's with an 009 ... Aug 2 2007, 03:01 PM BxtrBill
Well, seein' as how the hijacking has alread... Aug 6 2007, 09:19 PM 9146986 I remember hearing that the best stock dist to run... Aug 2 2007, 07:03 PM Twystd1 If you choose to use a factory vacuum advance 914 ... Aug 6 2007, 10:08 PM terrymason I'm ready to pull my hair out over this thing.... Aug 7 2007, 09:07 AM type11969
I'm ready to pull my hair out over this thing... Aug 7 2007, 11:41 AM 9146986 Sounds like trash in the fuel is clogging the jets... Aug 7 2007, 09:36 AM rhcb914 That to me sounds like a plugged idle jet. It... Aug 7 2007, 09:39 AM terrymason OK, I can deal with that. I'll go home and pu... Aug 7 2007, 12:12 PM Joe Ricard Yes I run one before the pump. and one after the p... Aug 7 2007, 12:28 PM terrymason OK,
New fuel filter after the fuel pump (2 now)
I... Aug 7 2007, 07:44 PM terrymason and another
Aug 7 2007, 07:45 PM terrymason another
Aug 7 2007, 07:46 PM terrymason and the last one
Aug 7 2007, 07:47 PM Twystd1 intake leak i sniff.
Is that an open vacuum port ... Aug 8 2007, 03:16 AM type11969 Those should seal when screwed in all the way . . ... Aug 8 2007, 07:15 AM terrymason Success!!!
Problem 1 - I think that s... Aug 9 2007, 03:13 PM Twystd1 It will still run MUCH better if you toss that diz... Aug 9 2007, 07:22 PM bjinright So, Now what do you have running? I also have a 7... Apr 24 2008, 11:00 AM type11969 33 pumps seem awfully small. Verify that they are ... Apr 24 2008, 12:18 PM terrymason do you have a wide band o2 sensor? It made it ALO... Apr 24 2008, 01:38 PM bjinright
do you have a wide band o2 sensor? It made it AL... Apr 25 2008, 09:27 AM type11969 Its tough to find the right etubes, and they are e... Apr 25 2008, 10:05 AM bjinright If I wasn't absolutely positive that I would s... Apr 25 2008, 10:52 AM type11969 Yeah, the reamer sets are simple, just take your t... Apr 25 2008, 11:09 AM bjinright
Yeah, the reamer sets are simple, just take your ... May 6 2008, 07:53 AM bjinright Finnally looked at my emo tubes. They looked sad ... Apr 28 2008, 09:29 AM type11969 Going back to the first page of this post it looks... May 6 2008, 08:24 AM rhodyguy remember, when you make a change to the idle jets ... May 6 2008, 08:28 AM bjinright
remember, when you make a change to the idle jets... May 6 2008, 12:11 PM type11969 .2ccs per two throttle pulls I think, its in the d... May 6 2008, 12:16 PM rhodyguy how low of an egine speed are we talking about whe... May 6 2008, 04:03 PM bjinright
how low of an egine speed are we talking about wh... May 6 2008, 04:28 PM rhodyguy 7k, do you hate your car? :blink: how old is the r... May 6 2008, 04:35 PM bjinright
7k, do you hate your car? :blink: how old is the ... May 6 2008, 04:59 PM |
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