Carbs from hell

[Alstrup]

In theory you can. However I have found the signal to be uneven at rpms. The flow is apparently doing something to the vacum right there. Move the orifice away just 1/4" and it all clears up.
Wrt the dual carb timing map. If you are running a low compression engine, 15 degrees at idle is fine and will help the engine to be more powerfull off the line. On an engine with good dcr it is often too much because the idle will be too high. I have found that the sweet spot generally seems to be about 12 degrees. With the BB I typically set it for 10 -11 degrees at perfect idle speed and then make a line 100-150 rpms below with 1-2 degrees more and then of course the starting timing in the first line. This helps tremendeously in stabilizing the idle especially when cold, but also coming up to a traffic light and similar.

[Johndecarlo]

On another note, 1 question, running the cb crank trigger, can i get rid of the vacuum plates and just use the vac /air bleed take off on each barrel that are on drlas? I figure its both vaccume from under the butterflies so why not? Right?

[Johndecarlo]

Well so o think i may have figured out the answer to my own question, for reference in case anyone is ever searching for the same issue; i believe the culprit was a loose aux vent, somehow causing random and unmetered air to get in and cause a lean condition. I haven't verified this for certain yet since after taking yhe carbs apart again and cleaning and giving them a going over, i now have a vacuum leak at the manifold, almost certainly because of reusing an old gasket that got reused 1 too many times, however even with the obvious vacuum leak, the carbs are performing noticeably "different" i might even say better, but only in certain areas, but ill update after the weekend when i go back and fix my oversight.

[Johndecarlo]

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after changing the timing, did you re-tune the idle speed and idle mixture on the carbs? You need to.
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[Johndecarlo]

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you have way too much timing, at both full advance and at idle. That's not helping. Go back to 28-30 total, 8-10 at idle. Then re-tune the carbs.
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[67 Sunroof]

What gauges are you using for your a/f ratio readings?
Just curious...

[modok]

[Johndecarlo]

[Alstrup]

Idle timing is too high. Reduce to 12.
Reduce Idle jet size to 0,58.
135 mains (?) venturi size?

Dependant on which model Dellorto you have, there are a set of bypass srews beside the mixture screws. They may need to be set into action to close the butterfly enough with that much displacement. BGut do the top 2 things first.

T

[Johndecarlo]

[Johndecarlo]

Okay so drove it tonight and paid close attention to a few things, leans out based on throttle position, not rpm, in other words i can engine break, without it leaning out, and once im driving, i can get it upto say 80mph in 4th, and let off the pedal a bit but keep the rpms above 2500 or even 3k and it doesn't lean out, but as soon as i hit the pedal a bit and pass this invisible mystery point, it instantly leans out. Also tells me its def not an accelerator pump issue cuz if im driving with the pedal mashed and its leaning out and then let off the pedal some, mixture richens up/ goes back tj where it should be. Other than that, the lean condition stays through WOT. One last peculiarity, as i was driving and starting to push the engine, at about WOT and holding it there, the engine suddenly made what i can only ralate to a big backfire, but just one, one big loud solid BANG, and my car jerked back and forward some, and then kept on going just fine like nothing happened. This was rhe only backfire or anything of the sort. Not since i first built tje engine has anything even similar happened, it was pretty strange tho, didn't feel like the usual lean backfire, more like pressure had been building up in a tank or something and then snap crackle pop, it went bang. Got pretty nervous for a second something serious happened, but as i said drove on just fine, cyl head temp stayed around 350, oil around 180. Any help here is really appreciated

[modok]

alfa1750, he knows carbs, does not know VW's tho

This guy was funny, https://www.thesamba.com/vw/forum/viewtopic.php?t=717707&highlight=transfer+port+size
He tried everything else except what I recommended.
lead a horse to water?..... or, more like dragging a mule backward by the tail....politely?

But he sure tried every other idea and found what didn't worked, and kinda worked, so I guess it's worth it.

[Johndecarlo]

Thanks for all the input guys, fuel psi is 3 on the dot, even shelled out the big bucks a while back on a precision analog gauge that only reads from 0-5psi, so confident on that, havnt checked float since i first got the carbs a few months ago, but they were fine last i checked, carbs came to me very clean from some ebay guy, alfasomethingorother, good reviews and talked to him a bunch, seemed to know his stuff and honest guy, cleaned them when forst got em and a few times since, including a few days ago trying to solve this. Car drives alright, tbh would only really be able to tell its running lean from the afr gauge, no spitting or anything. But its been like that since i got thr carbs, only now looking into it since i installed a crank trigger with magnaspark and so running more advance and worried about detonation. Built the motor about a year ago, lean condition came with the carbs for sure. Not sure how slightly i can expose the bottom prog hole, any pics would be awesome

[modok]

Two key bits of information missing
the venturi size
transfer port sizes, are the top holes 1.4 or 1.8mm?

The first transfer port is only covered when the throttle is 100% closed, so, if you want to idle with the throttles closed you will probably have to drill out the idle mix seat for more fuel and adjust the idle speed with the bypass valves. Or, not, because, WTF

also WHY are you running #3 tubes? is that what came with them or a deliberate choice.

[HBRag]

Lean transition is highly affected by float level. Make sure pressure is 3 PSI +\- .25 and set for 5mm close. I ended up with .3 emulsion for 45s on a 2276, which helped the transition. I still increased the air correction to 200, and tuned for lean cruise (MagnaSpark Digital). With that my transition still climbs from 16.0:1 to the 17.5:1 range, but the car runs fine. Without the floats at 5 mm, the lean hole rises to 20:1 and results in a misfire about 3800.

If you measure down the main jet hole for fuel level, and index the depth on the stack, the fuel level should be just below the first row for four large holes, and above the step.

Short if messing with the progression holes, I think this is the nature of the beast. I didn’t go there because with a lean progression tune, I’m is the safe zone for EGT/Head Temp. With a rich progression tune, the leaning might but you right in the danger zone at cruise.

[j-dub]

Exposing the bottom progression hole just slightly is normal for DRLAs.

Leaning out at half throttle sounds like it is not getting on to the main circuit soon enough. What size vents are you running? Are you running the "update" kits by chance? I would also check your float height, if they are too low that will delay the mains.

What happens at wide open throttle? Do the mains work properly then? 0.8-0.9 lambda?

It might also help to mention if this used to run great then there was a sudden change, a change over time or it always had this problem.
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[67rustavenger]

Do you have a set of .2 emulsion tubes?
The .3's are a compromise between .1 and .2.
What's likely happening is that at medium engine speeds. The carbs are running rich once you have opened the throttle half way.

I run a 2180 with Dellorto 45's. My idle jets are .50 (just verified last night) and run a little rich. .60's on a 2110 are likely very rich.

Good Luck.
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[nextgen]

John, when were the carbs last rebuilt. I had a back fire that I tried everyting to get rid of, nothing worked, had the carbs rebuilt and my bug runs great.

I rebuilt carbs but after seeing photos of all the parts and it done by a pro. I knew I as not even close.

Ok also could be fuel pressure, Timing but at $120 per carb, there is a world of a difference. Try the other things first.

Flames were coming out from back fires. Now nothing . Photobucket shut me down, because I will not pay for my free photos they gave me an and now want money to use.

IF you want some photos PM me and I will send them to you. Never though a rebuild would get rid of the back fire 90% of the guys said exhaust leak.
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