Re-jetting (or not) the DFEV

[wetminkey]

From my latest thread:
"Car ran well before the DFEV. That is until it's old ADHA would warm up, then idle was poor,...but car drove OK - to Ft Collins and back, for new exhaust at Ken's,...it's only problem then was just the poor seal on the head gasket. And the crappy ADHA/emissions garbage that no longer worked right, and cannot be rebuilt,...
I swapped for the DFEV/single plane, and then replaced the head gasket without making the car driveable beforehand. Too many changes at once to make Dx easy,...
I've armed myself with a tremendous amount of jetting knowledge just this morning. Thanks for the links, tima01864! I also found a couple of good ones:
Standard jetting table https://www.carbparts.eu/jetting_table
A pictorial with some guide-points https://toyotaminis.com/forum/threads/w ... hers.5834/
And I learned a couple of good guidelines. Weber secondaries are smaller than primaries, a common combination is 140/135 (1.4 mm/1.35 mm) main with 50/45 (0.5 mm/0.45 mm) idle jets, and the jet 'pairs' are usually +/- 5 (0.5 mm).
Redline has a jetting kit for about $60, I believe."
I'll just start this thread with that post,...time to un-cap the Weber and find out what jets lurk underneath,..I wonder if knowing what secondary main jet my old 28/32 ADHA has, might help with an size idea for the primary main jet of the 32/36 DFEV? Guess I'll look, if for no more than reference,...
Like I said a whole new adventure, for me,...so I'll take you all along right here. Please post-up if you know anything about this stuff,...! Thanks!
Todd.

[focodave]

Todd,

I run a Weber 32/36 DGV downdraft on my 1970 MGB GT.
1.8 Litre w/free-flow exhaust.
The car runs great, but the Weber did need some jet changes to make it perform properly.
I can drive it up to 12,000 feet elevation with no problems. Sure, it runs slightly rich at that high an elevation, but it still performs admirably for a car that goes from 4900 feet elevation to 12,000 feet elevation and everything in between.

The downdraft Webers are very similar to one another in as far as the main jet configuration, emulsion tubes, air correction jets, etc.

We need to know what size jets (both air correction and main) you currently have in there to be able to opine with any degree of helpfulness.

In general, you typically don't want to change out the emulsion tubes unless you absolutely have to. The air correction jets will allow you to change the amount of air introduced to the engine by increasing the size of those jets. That may sound counterintuitive, but those jets are regulating the amount of air, so they need to be bigger for higher altitude (in very general terms).
The main jets, of course, should be downsized in order to lean out the mixture, as they regulate the amount of fuel.

Dave

[wetminkey]

Naw. Makes perfect sense to me, Dave. I'm a boomer from the mid-50's, so I learned to tune 4bbl carbs by ear when I was 17 (in Ft Collins!).
After some reading about re-jetting Webers this morning, I think I'm prepared to tackle re-jetting this DFEV, as necessary.
First of all, NO WONDER carbs confuse people nowadays,...the diagrams are all WRONG!
I find that exploded diagrams of the 28/32 ADHA are missing the primary air correction jet and emulsion tube, and one of the main jets! Here's an example, check it out:
https://www.piercemanifolds.com/category_s/226.htm
Anyway, I was able to get past the diagramatic discrepancies and completely rebuild my ADHA awhile back. So I'm familiar with the Weber internals, and have the jet sizes recorded.
I find the same problem with the 32 ADFA (which I assume, must also have primary and secondary circuits) exploded diagrams, which is what the ADHA rebuild kits used to come with.
I did find a nice (CORRECT) diagram of the DFEV,...

The items I'm interested in are 5 and 5a, primary and secondary air correction jets,...80 and 80a, primary and secondary main jets,...and 14 and 14a, primary and secondary idle jets. My idle seems fine, so I'll just record their sizes, and work on the mains, primary first. But I'll record the sizes of all jets first, and store any removed parts carefully,...
More soon.

[focodave]

Message received and duly noted.
I meant no offense regarding your capabilities and/or knowledge -- sounds like you are on top of it and you know what to do.
So many of my "car buddies" seem to be paranoid to open up a carb, I am used to having to educate them rather than simply associate with them.
We'll be curious to see what you find, and what the final solution turns out to be.

[wetminkey]

OMGosh, Dave I took no offense at all! Please forgive me if I gave you that idea,...I must've stated something stupidly! I'm kinda old and can do that sometimes,...I apologize profusely.
Anyway, ALL IS GOOD, and I only hope to provide some valid information as I get this Spider going. It's been neglected/abused about as much as any Spider could have been, way back when. I was able to do a lot back in the early 2000s, but a lot was either not available, or affordable, at that time. Times have changed, and I'm finally getting back to this car, after so many years.
I've solved all of the problems with the transmission/suspension/brakes/chassis/electrical, but have yet to sort out the engine's difficulties. Lower engine is very low miles/new rebuilt and seems perfect in about every way. I have encouraging notes from valve shim selection/adjustment, but I have not checked valve clearances in this decade.
So, anyway,...time to record and compare what jets and emulsion tubes I have in this DFEV,...manyana.

[SteinOnkel]

Hello,

I am interested in this information as well. Please keep us updated to the progress you have made. I might be looking into a DFEV conversion here shortly, because my 32ADFA simply will not play ball at idle.

[wetminkey]

My good friend, focodave, mentioned that the Weber Redline, straight out of the box, might not be properly jetted for the Fiat Spider. He is absolutely correct, and I wanted to emphasize that, since my DFEV is intended to replace a 5200 Holley,...check the applications! I'm not driving a Ford truck,...
Start and idle are very nice (idle might be lean, 3 turns out), but I must need to reduce my main primary jet, and I'll have to tune further from there. Tomorrow I'll record present DFEV jet sizes,...
Just FYI, old 28/32 ADHA jets: air jets 175/160, mains 120/115, emulsion tubes F84/F7 (not easy to read). All is in mm and provided just for reference,...but this is original, factory, made in Italy, Weber. No modifications.
Again, mas manyana.

[wetminkey]

So,...
This chart is absolutely correct (at least, for the DFEV):
https://www.carbparts.eu/jetting_table
I found my DFEV to have:
Air Correction 165/160, Emulsion tubes F66/F50, Main jets 137/140, and Idle jets 60/50
I would assume that the other information in the chart is also correct.
I've considered focodave's recommendation about ignition, and have decided that a replacement distributor is probably just good insurance, if nothing else. My 40 year old distributor has a number of new parts, and seems to be doing well. But it's 40, and it could determine if the engine runs well, or not. A new replacement did not break the bank,...it's on the way.

[SteinOnkel]

I e-mailed one of the "leading" carburetor dealers on ebay who sells the DGEV in a Kit "for Fiat Spider". I asked what jets were in it and I got the answer "they are stock jets" - and that was it. I then asked him to specify, pointing out that I would expect a carburetor retailer to understand the importance in jetting for different engines.

Time for the next recession, these clowns are due for a humbling experience I think.

[wetminkey]

The 'jetting table' lists the DGEV, and lists all of the jet sizes.
If buying, Weber Redline is best,...but I'm betting that any carb purchased in this day/age needs to have float level checked, and fasteners torqued properly. I don't think that this can be trusted to the manufacturer anymore,...
I find some interesting variations between my old ADHA jet sizes, and the DFEV jet sizes. How is it that the DFEV primary main is smaller than the secondary? I thought that was a rule I learned,...this violates it.
Much larger main jets in the DFEV.
And big change in emulsion tube sizes,...smaller,...doesn't that mean richer, since this is an air circuit?
I'm rechecking/resetting my float level again,...just in case. Re-tightened my intake manifold bolts/nuts, also.
Next will be to ask for guidance from my racer-neighbor, who raced Webers, and cars this size, for years! He's got the 'how-to' Weber jetting book!
Idle is first, and when I tuned yesterday, I set the A/F mix at about 3 turns out,...that's a lean carb. It should be no more than about 2 turns. I'll discuss that first with my friend, 'racer Mike'.
Then should be getting the primary side correct, then the secondary,...
More soon, Todd.

[focodave]

OMGosh, Dave I took no offense at all! Please forgive me if I gave you that idea,...I must've stated something stupidly! I'm kinda old and can do that sometimes,...I apologize profusely.

Hey Todd -- you should not be apologizing to me.
I am the one who thought I should apologize -- I re-read my posts and I figured I may have been sounding slightly condescending or patronizing -- I certainly did not mean for it to sound that way. It's tough, on the web, to know the background and experience of the folks you are communicating with if you don't know them personally. I am still young enough (not young by any means, though) to be in the working world, and I guess I am conditioned to be super sensitive to hurting peoples' feelings when typing messages to them.

Sounds like you have gone down the Weber rabbit hole and you will surely come out of it just fine. The beauty of the Webers, of course, is that they are very tunable for any engine in the 1.5 to 4.0 litre engine size(s).
SteinOnkel, we can't be too upset with the suppliers of these carbs not supplying them fully tuned to work on each of our engines. The Webers are used on so many different applications that I think we all realistically have to expect to change jets and settings to suit our individual engines.

Curious to see how this all pans out...

Dave

[18Fiatsandcounting]

I'm not an expert on jetting, but here are a few thoughts based on my experiences:

1) Emulsion tube numbers (as far as I can tell) do not correlate to anything. Bigger numbers doesn't mean more holes, more gas, more air, or anything like that. It's simply a part number in essence. Emulsion tube numbers are shaped differently to introduce air into the fuel at different points and rates as the fuel flows past the emulsion tube, but anything beyond that is way beyond my pay grade.
2) The importance of the various jets (for the main fuel circuit, not idle or accelerator or enrichment) is: Main fuel jet >> air corrector jet >emulsion tube. Emulsion tube selections are for very fine tuning across the rpm band, and I doubt you would notice much difference in changing them from stock. Air corrector jets make some difference in mixture, but the amount of air entering that tiny 1.70 or so hole is miniscule compared to the air entering through the primary and secondary bores. Air corrector jets help create the right "air fuel emulsion mist" that is sprayed from the venturis, but shouldn't be used to adjust the mixture very much. On the other hand, the main fuel jets do control the amount of fuel entering the engine and thus are the ones to adjust for the right mixture.
3) I usually pull out the spark plugs after an hour of moderate to spirited driving, and if the color looks right (grey or tan), I consider the mixture to be fine. If it looks sooty, it's running too rich and I decrease the size of the main jets a step or two.
4) I usually don't worry about where the idle mixture screw is set, unless you're nearly all the way in or all the way out. If either of those are the case, you likely need to go one size up or down in the idle jet.
5) If the engine stumbles going between idle and the main fuel jets (and it's the carb that's at fault), a likely solution is to increase the idle jet size one or two steps. So, if you have a 50, try a 55 or 60.
6) Getting the mixture exactly right depends on engine size, cam timing, intake manifold design, type of fuel you're using, altitude, engine age, ignition timing, condition of intake valves, carbon buildup, compression ratio, rpm, engine load, air temperature & humidity, who's in the playoffs, and probably a host of other factors. The bad news is that every engine is going to be different, but the good news is that you can be pretty far from optimal and the engine will still operate just fine. I don't try to get it exactly right, but strive for a good idle, no stumbles on acceleration, and no sags or misses as you accelerate through the rpm range.

Hope this helps, and I too am curious to hear the conclusion of this story!
-Bryan

[focodave]

Bryan,

Well-said.

Yeah, the air correction jet sizes seem to be a little more critical in the mid to high RPM range.
The main jets seem to be a little more important in the low to mid RPM range.
But, again and as you point out, it all depends on so many variables between different engines that you simply cannot go by what the other guy did to make his Weber work. You need to figure it out for your individual engine.

Dave

[wetminkey]

This will be fun, figuring out how this DFEV should be jetted for the Spider. The DGV and DFV series Webers are some of the most common, and they are nearly identical mirror-images, so the results will be applicable to a lot of folks.
Right now, the engine cannot be reved above about 2500 - 3000 rpm, and cannot be driven, especially with an auto tranny. Plugs are dry and carbon-blackened after idling through two fan cycles and some attempts at revving.
Sure seems to me like this DFEV will deliver a RIVER of fuel when the primaries open as the throttle linkage is opened up! And I'm used to working on four barrel carbs!
The DFEV is meant to replace a Holley 5200, and that accommodates a Ford truck 6-cylinder engine!
So, perhaps it could use some further investigation.
Cool to know that the jetting table is correct in it's Weber carb detail!

[SteinOnkel]

OMGosh, Dave I took no offense at all! Please forgive me if I gave you that idea,...I must've stated something stupidly! I'm kinda old and can do that sometimes,...I apologize profusely.

Sounds like you have gone down the Weber rabbit hole and you will surely come out of it just fine. The beauty of the Webers, of course, is that they are very tunable for any engine in the 1.5 to 4.0 litre engine size(s).
SteinOnkel, we can't be too upset with the suppliers of these carbs not supplying them fully tuned to work on each of our engines. The Webers are used on so many different applications that I think we all realistically have to expect to change jets and settings to suit our individual engines.

Curious to see how this all pans out...

Dave

Hey Dave,

I was not expecting them to have everything jetted perfectly for every engine. Yet while we're on the subject of politeness, their response irked me immensely. I work with clients directly, many of whom ask for my expertise (if you can call it that) on a regular basis. I would never send them brisk one-liners with vague responses. I digress...

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@wetminkey

I'm not sure if you've posted this before, but what is your fuel delivery system setup like? If you can't pass 3.000rpm, it might be because the float bowl runs dry. Perhaps your pump is on the fritz or the float is set incorrectly.

Also, correct me if I'm wrong, but wouldn't 3 turns on the mixture screw make for a rich mixture rather than a lean one? That would align with your carbon buildup on the plugs.