transition from idle to rpm

[SGKent]

Someone asked about a flat spot. The 009 issue comes up all the time too. I found this image at weber to show how a carb is designed to go from idle to rpm. If you are already at B at idle, or the hole is plugged with carbon, or worn closed from the butterfly pressing on it, then there is no transisiton and a big flat spot results. Flat spots also result when distributor weights are sticky, the vacuum advance leaks or the idle mixture is way off. Notice in image A how the butterfly just covers the transisiton (some call progression) port.

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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Lettuce]

neat picture, explains why extra accelerator pump fuel helps, too.

[Hertzogg]

Thanks

[aceman137]

I just rebuilt the weber carb on my 2056cc bus engine.

The float was raised and the flat spot wasn't as noticable.

Float level is now correct, and experiencing the notorious weber progressive flat spot...

Jetting is

Idle circuit
60 primary
50 secondary

Mains
137 primary
140 secondary

Air corrector
180 primary
170 secondary

f6 emulsion tubes

I hope to achieve eliminating the flat spot from 1500rpms-2500rpms
your suggestions are greatly appreciated...
thanks,
ace

[SGKent]

lube the weights in your distributor and if you have one make sure the vacuum advance holds a vacuum, and that the plate moves freely. Sounds like the advance is late coming in. Does the idle hang coming down?
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[808OvalGreasemonkey]

I had a flat spot on my Kadrons,I drilled out the idle jet with a jet drill and it was a 90% improvement.

[SGKent]

fyi - keep in mind it is winter and as a single weber - do you have manifold heat on that bus?
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[aceman137]

It doesn't have manifold heat pancake style.
I'll try the suggestion about lubing the weights in the distributor...because it's lazy returning back to idle too.

[aceman137]

maybe...jet drilling? what size, on what circuit? depends on the suggestions I get...
thanks,
ace

[Wildthings]

[RatCamper]

Ahhh! Carburettors!!! Had enough of them for one day.

Don't drill the jets. Get replacements as was suggested.

Regarding the flat spot, why are people mashing the pedal anyway? it doesn't really help things move along any faster.
I've found with a lot of lower power cars that after a certain point pushing the pedal further just makes it louder and not much else.
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Vehicle: 1975 Special order delivery walkthrough panel based pop-top camper (LCA / Sunliner). Motor: Nippon 1.8L Single port Wasserboxer, Transmission: 3 rib 002.

[SGKent]

on a progressive, some have mechanical linkages on the secondaries and some have a vacuum device that locks out the secondary until a certain level of demand signal is present. Those vacuum diaphrams have long ago rotted if that is the model one has.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[aceman137]

I've got the mechanical linkage secondary. I won't be jet drilling... Considering the flat spot, from being fully stopped to acceleration, it wants to buck and hesitate, sometimes stalling between 1500rpm-2500rpm's, not mashing the pedal...feathering the pedal works well for me. Not trying to obtain land speed records here... just trying to improve drivability.

Thanks,
ace

[Wildthings]

[WI sportmobile]

I have a 32/36 DFEV Weber on my 73 and have my carb off the bus right now for cleaning/rebuild. What port on the primary barrel are you guys reffering to for idle to RPM transition? I know one goes to the acc pump and one to the vac (which I'm not using, have the 009) and the mix port is below the throttle plate. I'm not sure what the other port is. Is this the "proggresive port"? I'm just looking for a good idle starting point when I put the carb back on this weekend. Any help would be great


thankyou, Martin
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73 VW T2 Sportsmobile T4 1800 dual webber ICT's
06 TOY Tacoma TRD

Don't mess with the DNR.
"Bargain hunter becomes the bargain hunted."

[Wildthings]

The progression (transition, off idle) ports are internal to the carburetor, not external. The progression port is shown as Item #2 on SGKent's Drawing "A". Some carburetors have multiple progression ports and others have weirdly shaped progression ports.

Don't mistake "progression" with "progressive", they are two different things entirely.

[WI sportmobile]

Thankyou for the response. That's what I want to know what port does what. Where do they come from and what do they do? I'll try and get to the hp book store and get a good book on the subject. Any recommendations?
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73 VW T2 Sportsmobile T4 1800 dual webber ICT's
06 TOY Tacoma TRD

Don't mess with the DNR.
"Bargain hunter becomes the bargain hunted."

[Wildthings]

Since you are running a Weber, it would make sense to get a Weber book. The Holley book covers the DFEV/DFAV pretty well as that is the Weber they cloned.

[SGKent]

Hold the throttle plate up to light and make sure that the light is fairly even coming around the throttle plates. You don't want the butterflies slid to one side or the other where they are gouging the side of the carb and there is a big gap on the other side.

Using a thin piece of carbon paper or something thin and firm like it, set the stops that allow the butterflies to close so the paper can just be pulled without tearing. This keeps the butterflies from digging into the side of the throttle body when they are closed but makes sure the butterflies are closed enough not to affect idle.

There are two or more small holes in the side of the carb about the height of the throttle butterfly like the images above in the thread. One is for rhe idle mixture. It will be below the primary butterfly when it is closed. The second, third etc holes are above the butterfly. Make 100% sure that the transisition holes are either covered by the butterfly or above the butterfly at idle. If they are below the butterfly at idle then you probably didn't do the carbon paper test well or the butterfly is bent. If the second hole (remember the bottom is for the idle mixture), is way above the butterfly, you will probably need to move the idle stop screw until the butterfly is slightly below and/or covering the first transistion hole.

As you barely begin to open the throttle, and I mean barely crack it, the first transisition hole should become exposed. What this does is let additional fuel flow as soon as you step on the throttle but not at idle.

Make sure all your jets are blown out with compressed air and that all ball bearings are in the right spot. Sometimes I will use an old ball bearing and very lightly - like I was tapping my finger on a desk - tap it with a steel or brass rod to be sure it seats well. Sometimes they get a little corrosion under them and that reforms the seats as they are soft pot metal don't hit it hard. Then use the new ball bearing as the old one now has a itsy bitsy flat spot on the side you tapped.

Make sure you match gaskets 100%. If you have removeable venturi, make sure the venturi seat in the bores well and are not too loose. If they are loose they may suck air instead of fuel. Don't forget to blow air through the accelerator passages and make sure the accelerator nozzles seat properly as many are held on with a screw. Do not overtighten anything - no gorilla tweaks as pot metal bends easily over time.

Set your idle mixture to 2 to 2 1/2 turns open. Many of these carbs have an idle air bypass on them. Use that to set idle speed. NEVER touch the stops again if your carb has an idle air speed screw or you will mess up the transistion hole alignment you just spent time getting right.

Once the bus is warm. set the idle mixture by slowly leaning it until it begins to stumble then open it back up to where it runs best. Turn in a tad leaner. Cup your hands and bring them closer to the top of the carb. If the engine speeds up as your hands get closer then it is too lean. If the idle slows it is too rich. When it is right you should be able to get right in on it without a change in idle speed. You are tuning a sewing machine so you need to be very gentle and keep your ears open and your tach connected. Be careful of moving belts etc.

Also as I indicated make sure the weights in the dist and the wick have a drop of oil as anything that causes the weights to stick will make the engine act poorly. Check your timing after you put a few drops of oil on the dist weights in case it changes. I have expereinced sticky wieghts and it causes the bus to have flat spots, idle hangs up sometimes - and even no power at times so be sure to do this maintenance too before you spend lots of time trying to tune the carb when it is the distributor at fault.

Last - if you have black foam floats in the carb replace them. Brass hollow are Ok if there is no fuel when they are shaken and/or no bubbles come out of them when they are heated in water. The black hard foam ones can have a life of as short as a year or two.

Once you have performed these adjustments, be sure to also set any unloaders and the choke etc to specs given in the charts. Basically the unloader will force open the choke a set distance when the throttle is at a certain amount if the choke is still closed. Also set the other cold idle settings etc. Sometimes the measurement is in say like 3/32 inch etc. Convert that to a fraction and use a drill bit that size as your tool to measure the gap. When you get done you should have pretty well running carb. Once the idle is set, get it out and put an wide band air to fuel meter on it or learn to read plugs. Most likely you will find it is very close to what is needed unless the PO really tweaked the jets.

Remember this - if it runs worse say after 3 minutes than 10 minutes it is probably too lean. If it runs better cold than warm it is probably too rich. If it burbles and has black smoke tyring to get up to RPM you are way too rich and if it backfires and flat spots you are way too lean. (or the timing is messed up.)
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[aceman137]

Excellent write up!!

After reading many different threads as suggested, and utilizing a few. I am almost content w/ the work in progress pertaining the complete engine and weber progressive rebuild.

Maybe, I'll experiment w/ a couple of idle circuit jets to improve drivability...

The information that keeps us all going is greatly appreciated.

Thankyou,
Ace

If Jimi Hendrix were giving you an interview, his question would certainly be "Are you Experienced?"