Re-jetting (or not) the DFEV

[SteinOnkel]

I did, I saw what others have said about the vac advance being not needed or noticeable. I do not agree with those statements. I have the 22 deg the 34 deg vac advance electronic distributors, and currently run the MarelliPlex type that does not have the vac advance. There are huge rev differences and performance curves between the three. If you run the 22 deg unit without the vac advance, your rev's will top out early.

I can confirm that this is not the case.

But just for you when my new carburettor gets here (34 ADF) I'll drill it out to have ported vacuum

Or do you guys just connect them to manifold vacuum?

[wetminkey]

The Weber 32/36 DFEV has a port for distributor vacuum,...that's what I'm using. A distributor should receive ported vacuum so that it does not advance at idle,...
If ya want info on your carb, buy a DCOE, or similar,...lots of info on jetting side-draft Webers! Not so much on down-draft types, like the DFV/DGV series Webers.
I did find a nice Redline high altitude jet kit for just under sixty bucks,...looks like it may come with some instructions.
And I found a number of sources for re-jetting guidance on the internet. Any that I find useful, I'll post here.
Ahhh! Shims are in, and my gaps are more like what they should be,...#1 - #4 Exhaust: 0.018, 0.018, 0.018, 0.019
#1 - #4 Intake: 0.016, 0.016, 0.015, 0.016 I like those numbers!
Doesn't seem like there is any way to contact Redline Weber. Email is rejected, phone message goes unanswered so far,...
That's encouraging,...

[wetminkey]

Oh, I forgot. Those gaps,...
Just look at the shiny spot that the cam lobes leave on each one of the valve shims, and you will see that they are intended to be the wear point in this type of valve train, thus increasing the gap over time.

[wetminkey]

Belay m' last!!
Chris, at Redline Weber, finally returned my call.
And advised that I purchase the Weber high altitude jetting kit for the DFEV that I purchased from them earlier today! I'm encouraged again,...
And all is right with the world,...

[dinghyguy]

Hi Todd,
Looks like you are doing all the odds and ends while you wait for parts. I have read you thread with interest and do really think the issue is the carb, not to say that replacing your distributor and doing all the other crital items like fixing the door handles will not make the car run better!
So in the usual manner of suggesting work for others.....might as well replace the oil in the diff, touchup the undercoating and install fog lights while you are waiting. I would have said lube your brakes and adjust your handbrake but i don't want to remind you of other trials and tribulations.

If it makes you feel any better, after rebuilding the 32 adf and installing on my most recent car (which turns out to be the oldest CS2 in the spider registry), it idles perfectly, pulls well, but, and you knew there would be a but, it burbles significantly on deceleration, and i don't have the choke setting on the steps right yet. It idles too fast until it is warm.

Carry on and keep reporting, we are all learning something....
cheers
dinghyguy

[wetminkey]

Ah ha! He lives! I was not sure how long you were supposed to be gone, and was about to muster up the coast guards of BOTH countries to look for the two of you! Lost at sea,...
Glad you made it back OK!
The car is sure to run better after I got both windows to operate so smoothly! Ya know, I just checked that differential, the brakes are all BRAND NEW (and freshly adjusted), and I just recently cleaned up the filthy undercoating while I was replacing the driveshaft! I'll have to look into that fog light installation,...THAT would make it run better, for sure!
Sounds like you've got some minor issues with the 32 ADF, but nothing that can't be troubleshot. Maybe I'll stumble across something that will help you with your carb's deceleration business,...you'll get the choke adjustment fixed easily.
Welcome back! Hope ya had fun!! Cheers, my friend!

[wetminkey]

A couple of things have slowed progress a bit, but I've done my studing up, and here's one of the best items I've found, pertaining to high altitude jetting:

Tuning Weber Carbs for High Altitude
This is a question we get asked all the time. There is no magic answer or formula to altitude jetting Sidedraft or Downdraft Weber carbs. Here are the steps you need to take in order to Re-Jet your carb for High Altitude operation. This applies to both Single and Dual Sidedraft Carbs and Single and Dual Downdraft Carbs. Bear in mind that there is nothing you can do to stop the power loss you experience at high altitude. That is just a function of the lack of Air to mix with fuel for combustion. Jetting the carb properly to get the correct fuel mixture is the key to maximizing the available power.
Step-1: Find out what is in the carb now! Do not guess and think that you have the jetting that supposedly came from the Weber factory. Find out what Main Jets, Air Jets and Idle jets you have in your carb. If it is a progressive carb make a note of what jets were in the Primary and what jets were in the secondary. The Primary is the barrel that opens first. If you have Sidedrafts or Downdrafts with removable venturis then find out what size venturis are in your carb(s). This is CRITICAL. You cannot tune a carb without knowing what you are starting with.
Idle Jets: You will normally need to drop 1 Idle jet size (Meaning a step of 5. 50 to 45) for every 2000 feet above 3000 feet of altitude. This assumes the car ran properly at seal level. If you have No Sea Level Reference then you just have to get a range of jets smaller than your starting point.
Main Jets: You will normally need to drop 1 main jet size (Meaning a step of 5. 150 to 145) for every 1000 feet above 3000 feet of altitude. This assumes the car ran properly at seal level. If you have No Sea Level Reference then you just have to get a range of jets smaller than your starting point.
Air Jets: You will normally need to Increase 2 Air jet sizes (Meaning a step of 10. 150 to 160) for every 1000 feet above 3000 feet of altitude. This assumes the car ran properly at seal level. If you have No Sea Level Reference then you just have to get a range of jets Larger than your starting point.
Flat Levels and Fuel Pressure: No changes to these for High Altitude operation.
There are no shortcut or magic formulas. You just have to work through it. The guidelines above are starting points based on correct seal level operation. You will just need to invest in a range of jets to properly tune the engine at the altitude you are operating at.
Note...From Sea Level to 2500 Feet there will be very little change.

I reset my car's timing to add just a little more initial advance. Re-tuned, I find that my A/F mixture screw is now at two turns out, with my idle speed screw engaged about 0.5 turn. That sets my idle at about proper setting for an auto tranny, about 1000 rpm in park.
I recorded all of my DFEV's jet sizes previously, compared them with of my old ADHA jet sizes, and I've planned some jet changes, based on the jetting recommendations above. The Weber jetting kit is intended for 5000 - 10000 ft, so I'm planning very mild jet changes for our 5000 ft altitude.
A tidbit that I had to call Redline Weber to get the answer to: Idle jets,...there's two, so how to properly re-jet? To make incremental changes, small idle changes are made by changing the secondary,...large changes are made by changing the primary. I did not find that in all of the literature that I reviewed.
It might be a few days before I'm able to make the changes and test run the car, but I'll sure get on it ASAP.
Todd.

[GarageRat]

I read through this entire thread and it seems like everything has been covered but wanted to throw out one more thing that you probably already checked. I had a similar issue when sorting out my carb issues and it turned out to be a partially clogged electric fuel pump (surface rust in tank!). I even checked fuel flow with a cup and graduated cylinder and it seemed to flow enough, but clearly wasn't keeping up. Once I changed that, the problem disappeared. Of course I still had jetting issues...but refusal to rev went away

[Turbofiat124]

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

I have a 1977 MGB with the same setup!

This may or may not be the rule of thumb but I found the colder (and denser) the air is outside, the worse a car will run if not jetted correctly.

When I set my Yugo up for a 1500 engine and a turbo, I used the original 28/28 DFTA and I rejected the secondary (150 I think) and the idle jet (due to more than 1.5 turns or something according to the manual) but never bothered to rejet the primary. I didn't think I needed to, I'm not sure why. Even though I was going from an 1100 to a 1500 engine.

If it was in the 90s, the car would run fine but the cooler it got outside the crappier it would run. At 60F, it would start bucking under cruise. Around freezing it would backfire. Full throttle it ran perfectly fine even with the turbo wound up.

So I put out a questionnaire asking what size jets people with 1500 Fiat SOHC engines were using in the carburetors. I got replies anywhere from 120 to 130. So I aimed in the middle.

I stepped up from a 100 primary to a 125 and now it runs fine whether it's freezing or 90 degrees.

So I suppose the best time of year to tune a carburetor is in the winter when the air is denser. It seems an engine can deal better with a mixture that is richer than it can with a mixture that is too lean. If that makes sense.

[wetminkey]

First of all,...sorry, I've been 'out' for a short period, but back at it again (pretty much)!
Secondly, specs:
I find the DFEV to have:,................................................................................and my old ADHA to have:

Air correction jets 165/160,...........................................................................................................175/160
Main jets 137/140,...........................................................................................................120/115
Idle jets 60/50,...............................................................................................................60/55
(and emulsion tubes, that should not be changed: F66/F50,......................................................................F84/F70)
Interesting differences,...especially considering that the DFEV's primary is 32mm, and the ADHA's secondary is 32mm,...

And third,...since I'm at 5000 feet, I'm relying on "Tuning Webers for High Altitude":
http://www.lcengineering.com/LCTechPage ... titude.pdf
The article agrees with all of my other on-line research,...
If my Weber was tuned for sea level, the carb needs -5 idle jets, -10 main jets, and +20 air jets from what it has in it to run well at 5000 ft.
My Weber High Altitude jet kit has a range of jets to use for 5000 - 10000 ft, so I've decided from within their assortment.

Largest changes are in the air correction jets, so I'll make a leap there, and change the 165/160 to 180/170 and see how it does. That's +15/+10 in the air jets. Changes in the mains should be from the existing 137/140 to the available 130/135 jets (-7/-5 from existing) in the jet kit.
My idle is good with A/F mix screw at two turns out,...exactly what Weber recommends. I'll not make changes there, unless indicated later. According to the high altitude instructions, I should be able to reduce the idle jets from 60/50 to 55/45,...
But, again, the kit is meant for 5K to 10K, and I'm at the lowest altitude of the range,...
I'll still have to make incremental changes afterward, but I want to 'leap' to the big air jets, and see if that speeds the re-jetting process.
Wish me luck!
More soon,
Todd.

[SteinOnkel]

But how does it run with the current setup? Still no revs passed 3k?

[18Fiatsandcounting]

One other thought (very general):

Sputtering, "surging", or feeling like the engine is choking at higher revs = too rich or an ignition problem.
Missing = too lean or an ignition problem.

-Bryan

[wetminkey]

It falls flat on it's face at about 2500 rpm. And 'fuzzy blackens' plugs trying to do so. Idles fine.
Ignition is perfect. No missing or surging.
We've been through the entire troubleshooting process, guys,...it's time to move on to re-jetting for altitude. Pretty obvious.
I've got a fuel pressure gauge coming Friday, that I'll install in the Weber's input. I'll KNOW what my input pressure is for sure, even with the return line. If I need to regulate it, I can do it in the return line,...
Then it's time to pop the Weber's top, check float level again, and change some air jets. That is the biggest high altitude change, and I hope it will get me in the ballpark. Not enough air up here, at 5000+ feet. Not for a progressive, sea-level tuned carb.
I'll post as soon as I get a change done, with my results.
Anyone with re-jetting experience can sure post up at any time! I can do this, but I haven't before. But, that has never stopped me in the past,...
Again, wish me luck!

[18Fiatsandcounting]

It falls flat on it's face at about 2500 rpm. And 'fuzzy blackens' plugs trying to do so. Idles fine.

Again, wish me luck!

Good luck! And just checking here, and maybe you've done this: Sure sounds like the engine is running way too rich at rpms other than idle. Just for grins, could you put in the main jets from your old ADHA and see how it runs?

-Bryan

[wetminkey]

I'll keep my nicely cleaned and rebuilt ADHA stored away (I'm not quite exactly sure why,...). But you've come across the same idea that I had,...32mm is 32mm,...ADHA, or DFEV. Shouldn't the air/fuel ratio be gained in a similar manner? The jets sizes that I posted above are OBSERVED sizes, so I know exactly what is in both carbs. Makes it easy to make changes, or go back,...
If I need 'em, jets can be purchased individually,...but I think that this kit probably contains what I need for 5000 ft,...I don't have to tune a racing engine to this altitude!
Thanks! I'll need the good luck. Hopefully, it will reduce the number of times I need to make internal changes to the DFEV!