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VDub Campers Ltd
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Joined: September 16, 2008
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 Posted: Fri Jan 27, 2023 12:37 am Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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| Wildthings wrote: |
| SGKent wrote: |
| Wildthings wrote: |
| SGKent wrote: |
Mike - aren't the power valves in Holley progressive carbs and not Webers? |
I think they are in most, if not all of the 32/36, both DFE* and DGE*, but there have been a lot of variants of these carbs made over the year with lots of thing added and lots deleted. The float with a split in the middle is there to work with the power valve, the two barrel Webers without a power valve have a simpler single cell float. |
The ones we had did not have a split float or a power valve. But yes, there are many variant. My understanding is that the Holley built ones had the power valve. |
DGV diagram:
DFV diagram:
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Wildthings. The lower diagram is the closest to what I have. All the the carbs used for Aircooled VW seem to be DFEV. Which is closest to that lower diagram. But DFEV has an electric choke instead of a hot coolant triggered choke.
Can you point me the location/number of this power valve you spoke of please?
Thanks.
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VDub Campers Ltd
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| Posted: Fri Jan 27, 2023 12:42 am Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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Is the part you call power valve parts 51-46? Because I thought that was something entirely different. I thought that was just to hold the choke open a touch at idle.
Or…is it part 10?
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SGKent 
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| Posted: Fri Jan 27, 2023 1:15 am Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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| VDub Campers Ltd wrote: |
Is the part you call power valve parts 51-46? Because I thought that was something entirely different. I thought that was just to hold the choke open a touch at idle.
Or…is it part 10? |
93 on the top image, 10 on the bottom. The stuff on the side of the choke is usually part of the choke unloader circuit. Both models that are shown are for water cooled engines. Some progressive carbs have electric chokes and no power valve. They work really well when set up right.
power valve image from carburetion.com
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VDub Campers Ltd
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| Posted: Fri Jan 27, 2023 1:21 am Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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That’s great thanks.
So you advise blocking the vacuum hole that feeds this diaphragm unit, because you have a device that can provide live readings of combustion gases. And this device has shown that at times, such as wide open throttle, when this valve opens up, it is over enriching the overall mixture.
Is summary this accurate?
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Wildthings
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| Posted: Fri Jan 27, 2023 4:30 am Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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| VDub Campers Ltd wrote: |
That’s great thanks.
So you advise blocking the vacuum hole that feeds this diaphragm unit, because you have a device that can provide live readings of combustion gases. And this device has shown that at times, such as wide open throttle, when this valve opens up, it is over enriching the overall mixture.
Is summary this accurate? |
In the bottom diagram the power valve is Item #82 and the plunger which operates it is Item #10. When you REMOVE the plunger the power valve itself will remain in the closed position as there is nothing to cause it to open any more. Yes you need to block the vacuum passage in the lid of the carburetor where the plunger bolts on, you do NOT reinstall the plunger just leave it out. As mentioned before, you are going to need to enrich the mixture a few jet sizes. |
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W1K1
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| Posted: Fri Jan 27, 2023 8:35 am Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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| VDub Campers Ltd wrote: |
That’s great thanks.
So you advise blocking the vacuum hole that feeds this diaphragm unit, because you have a device that can provide live readings of combustion gases. And this device has shown that at times, such as wide open throttle, when this valve opens up, it is over enriching the overall mixture.
Is summary this accurate? |
an O2 sensor in the exhaust will read your AFR, something like the LM2
https://www.innovatemotorsports.com/shop-all.html?p=2
you can log the information and play it back, or download it into the laptop and graph it , it helps a lot when you are making jetting, or vent changes to see what's going on.
a couple examples:
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mikedjames
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| Posted: Fri Jan 27, 2023 1:46 pm Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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| SGKent wrote: |
| Wildthings wrote: |
What happens on these carbs is that at idle because of the high vacuum the power valve is closed, and as you open the throttle it takes a quarter of a second or so for the power valve to open causing a lag. Then at cruise because you have a tiny engine pushing a big box down the road you have low vacuum and thus the power valve is open causing a rich condition. The long runners also likely cause air to pass both ways through the carb also adding to the engine running rich at cruise, I believe this is why most carbs sold for both Type 1 and Type 2 engine so not have power valve as the mixture naturally enriches due to the fluctuation when near full throttle.
Everyone always screams that the problems with these carbs is caused by icing, which I myself believed likely 35 years ago when I first bought a Type 4 with a progressive on it, so I added both an intake air preheat and a heated manifold setup and saw close to zero change in how the engine ran. I tolerated a minor lag coming off idle for years, even with the two forms of heat and then once I got a wide spectrum A/F analyzer I began to see what was actually happening and ditched the power valve and rejetted, leaving a smooth running rig once the engine warms at all. At sea level my AFR runs about 15:1 at light cruise and about 12:1 at full throttle.
As for the effects of the throttle valve size on these engines a 32mm throttle bore is pretty small for a 1700-2000cc engine, so needing some bypass air at idle is not unexpected.
IIRC I am running either a 50 or 55 idle jet. The idle AFR is about 12:1 as well. |
Mike - aren't the power valves in Holley progressive carbs and not Webers? |
I have owned two Weber European manufactured progressives, both have power valves.
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Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
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mikedjames
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| Posted: Sat Jan 28, 2023 10:26 am Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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And as an addendum, the AFR from these carburettors is all over the place ... steady state at WOT might be OK, but the dips and peaks in AFR as you accelerate and one of the six jets takes over or another. .
4 normal jets, one accelerator squirter and one power valve ..
Makes me drift towards EFI...
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Ancient vehicles and vessels
1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.
1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy |
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Wildthings
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| Posted: Sat Jan 28, 2023 11:58 am Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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| mikedjames wrote: |
And as an addendum, the AFR from these carburettors is all over the place ... steady state at WOT might be OK, but the dips and peaks in AFR as you accelerate and one of the six jets takes over or another. .
4 normal jets, one accelerator squirter and one power valve ..
Makes me drift towards EFI... |
Getting rid of the power valve and the high speed enrichment on the secondaries makes jetting the carbs muc more straight forward and gives much smoother transitions. The Holley carb does go rich on full decel, which is where a 34PICT3 style bypass idle circuit would be nice, never tested the Weber on this point. |
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VDub Campers Ltd
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| Posted: Sat Jan 28, 2023 12:31 pm Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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Ok this is interesting. I will give it a try and see how it feels. This is certainly not something I’d usually do without viewing published data. But seeing as you have witnessed improved live readings via LM2, il take your advice and give it a go.
Thanks for sharing.
Interestingly I’ve had a new customers bus come in, with same carb on a 1776. He’s reporting occasional pinging on hills. Timing is all correct, and distributor is in good condition. So I’ll look at the jetting and maybe this power valve, could be a contributing factor. Maybe it’s over rich and causing detonation.
I’m still waiting for small idle jets to arrive to fine tune the idle on this 1600. Another curious thing, to experiment with.
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SGKent
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| Posted: Sat Jan 28, 2023 2:56 pm Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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| VDub Campers Ltd wrote: |
Ok this is interesting. I will give it a try and see how it feels. This is certainly not something I’d usually do without viewing published data. But seeing as you have witnessed improved live readings via LM2, il take your advice and give it a go.
Thanks for sharing.
Interestingly I’ve had a new customers bus come in, with same carb on a 1776. He’s reporting occasional pinging on hills. Timing is all correct, and distributor is in good condition. So I’ll look at the jetting and maybe this power valve, could be a contributing factor. Maybe it’s over rich and causing detonation.
I’m still waiting for small idle jets to arrive to fine tune the idle on this 1600. Another curious thing, to experiment with. |
too much compression and a dead on to lean mixture would be the cause of detonation. Also if the engine is not new, carbon built up on the pistons could cause it. Too rich would make it less prone to pinging. 28 BTDC full in with any advance hoses disconnected at full RPM (3500+) would be the safest timing on a bus like that.
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69BahamaYellow
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| Posted: Wed Feb 01, 2023 6:38 am Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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| Very interesting insight on the power valve in these progressive carbs, Wildthings. I used to run Weber progressives on both buses and 914's in the '80s and '90's. The lighter 914's used to ping a lot in the summertime, when you were at cruise RPM and needed to accelerate. The heavier busses would rarely ping in this same scenario, but I'm guessing that's because at cruise, the throttle is already open further, so perhaps the power valve was already operating to provide enrichment. Engine compression ratio differences contributed to that problem a lot also, but I had never considered the possibility of the power valve being a contributor until reading your posts. Always good stuff to learn here! |
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VDub Campers Ltd
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| Posted: Wed Feb 01, 2023 7:09 am Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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Well….I’ve overcome the original running issues with this carb related to vacuum etc and idling without ported vacuum.
But. I have plugged the vacuum hole behind the power valve diaphragm and went out for a test drive.
Could’nt get over 50 mph.
So at the moment I’m skeptical about the power valve disconnect.
Am going to change the jetting and try again.
1600cc currently jetted:
Prim Idle 50
Sec Idle 60
Prim Main 140
Prim Air 170
Sec Main 150
Sec Air 160
F6 emulsions.
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VDub Campers Ltd
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| Posted: Wed Feb 01, 2023 8:29 am Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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Ok. Changed jetting to:
Prim idle 60 (Weber recommended setting)
Sec idle 50 (Weber recommended setting)
Primary Main 140
Secondary main 160
Prim air 170
Secondary air 180
Idle is awful with that. Definitely not right. Will change back to 50 primary
Other than that felt slight improved but low to midrange is lacking power.
Will now reject again and change primary main up to 150 and primary air up to 170 or 175.
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VDub Campers Ltd
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| Posted: Wed Feb 01, 2023 9:16 am Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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Test drive result with jetting:
Prim idle 50
Sec idle 60
Prim main 150
Prim air 170
Sec main 160
Sec air 180
Moving in the right direction. Improved midrange. But still think more is possible.
Top end is still lacking. Still not achieving much over 50mm on a 1/2 mile straight.
Will quickly try Changing secondary idle up to 70 just to see what that does before jetting up again.
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VDub Campers Ltd
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| Posted: Wed Feb 01, 2023 9:32 am Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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Test drive result with jetting setting:
Prim idle 50
Sec idle 70
Prim main 150
Prim air 170
Sec main 160
Sec air 180
Going in right direction.
Throttle response is improved.
But still top end ceiling height of 55mph over 1/2 mile straight.
Will go up to 80 on secondary idle see what happens. Then will size up sec main, and air.
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VDub Campers Ltd
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| Posted: Wed Feb 01, 2023 9:54 am Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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Drilled 80 sec idle jet had negligible positive impact. Possible negative overall.
Put 70 sec idle back in.
Removed spark plug as a guide. Electrode and ceramic very lightly sooty.
Possibly from secondary idle? We will check again after further adjustments.
Will now reject mains and airs upward. See what happens.
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Wildthings
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| Posted: Wed Feb 01, 2023 10:45 am Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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| VDub Campers Ltd wrote: |
Drilled 80 sec idle jet had negligible positive impact. Possible negative overall.
Put 70 sec idle back in.
Removed spark plug as a guide. Electrode and ceramic very lightly sooty.
Possibly from secondary idle? We will check again after further adjustments.
Will now reject mains and airs upward. See what happens. |
Don't go upwards on the air correction jets, if anything go down. If it seems to run well at light cruise but lacks power as you open the throttle more you might want to increase the size of the secondary main jet, again leaving the air correction jet alone.
As a rough guess if you started at 140 (primary main) and didn't change the air correction jet, you are going to want to be somewhere around 155 (primary main). You want the main jet to handle the mixture from off idle to light cruise and then let the secondaries enrich the mixture upwards as you add more throttle above light cruise.
If the 50 idle jet was working before it should still work now.
I would give you my jetting, but the Holley's have a double booster venturi versus the Weber single booster, so have different jetting requirements, plus I don't have my log book with me and would probably blow it trying to give it from memory.
You need to pull the plunger, not just block off the vacuum. |
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Wildthings
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| Posted: Wed Feb 01, 2023 10:58 am Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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Maybe try:
Prim Idle 50
Sec Idle 60
Prim Main 155
Prim Air 170
Sec Main 170
Sec Air 160
F6 emulsions. |
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VDub Campers Ltd
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| Posted: Thu Feb 02, 2023 5:52 am Post subject: Re: Weber DFEV carb vacuum signal at idle. |
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The saga continues……
As I get further along, I am starting to feel that this removal of the power valve is not a good idea. I have not been able to achieve more than 50mph since doing these test runs.
However. There is another point of uncertainty potentially at play. The problems with idling have come back. She now will not idle again. I’m certain this is nothing to do with jetting but to do with either intermittent valves issue, or spark plugs again.
I say this for two reasons.
1/ I’m running a vacuum gauge in the engine bay still, left over from when I was fine tuning the idle speed screw to achieve no ported vacuum at idle. When I’m revving the engine at WOT I am seeing the needle flicking violently, sometimes.
2/ previously during setup tuning we went through 7 spark plugs before we got consistent spark firing without fail.
Regarding point one above. I can’t know if the vacuum gauge flicking is due to misfire due to poor mixture, or valves intermittently not sealing. I need to test further to know these things. This engine is driving me nuts. Taking so much time. Time I’m not gonna end up billing for.
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