Re-jetting (or not) the DFEV

[wetminkey]

Ignition has been gone through already,...ran fine with new components previously.
Yeah,...easy to say "reinstall the old carb"! And I would do so, IF it were not a TRUE PITA! Remember, we're talking a carb AND a dual plane manifold with ALL of the emissions crap intact! Ask geospider about having to swap all of that stuff over,...!
I think I'll just keep shooting in the dark.
Have ANY of you EVER rejetted a carb before? So far, I don't think anyone has recommended an approach to sequential jet changes. Where to start, what jet(s) to change first? I assume that increasing the size of the air correction jets would be the best first step,...but both, or just the primary, first?

[18Fiatsandcounting]

I hear you about the PITA work needed to change the carb back... Meanwhile, I suggest starting with the primary jets. Install as small a jet as you have, in both primary and secondary. 110 to 120 range, as I noted earlier. Don't worry about performance at this point; all you want to do is get this puppy running better. While you're doing this, check the level of the gas in the carb float bowl right after you remove the cover. If you have more than an inch of gas, probably too much, and the float level would need to be adjusted accordingly.

I'm no expert on carbs, but my understanding is that the overall barrel diameter (32 or 34 or whatever) determines the maximum amount of air that you can reasonably pull through the carb. Bigger displacement engines pull more air in of course, and thus need bigger barrels. The barrel diameter also has an effect on how much fuel is pulled into the engine as well, but what matters perhaps even more is the diameter of the venturi in the center of the barrel (the narrowest part). This number will be stamped on the outside of the barrel, towards the throttle linkage, and these numbers on both primary and secondary barrels have a circle around them. These are usually 23 or 26 or 27 or something like that. This narrowing causes the air being sucked into the engine to speed up as it moves through the narrow opening, and faster air velocities = more vacuum and thus more fuel sucked from the secondary venturi (the wing looking thingie in the middle of the barrel). Same principle as airplane wings. Secondary venturis are usually 3.5 or 4.5, and they are usually the same in both the primary and secondary barrels. The main venturis (the narrowing) are not changeable on these models of Webers, while the secondary venturis can be changed but usually don't need to be.

Hope this helps...
-Bryan

[SteinOnkel]

Ignition has been gone through already,...ran fine with new components previously.
Yeah,...easy to say "reinstall the old carb"! And I would do so, IF it were not a TRUE PITA! Remember, we're talking a carb AND a dual plane manifold with ALL of the emissions crap intact! Ask geospider about having to swap all of that stuff over,...!
I think I'll just keep shooting in the dark.
Have ANY of you EVER rejetted a carb before? So far, I don't think anyone has recommended an approach to sequential jet changes. Where to start, what jet(s) to change first? I assume that increasing the size of the air correction jets would be the best first step,...but both, or just the primary, first?

Ooooh that's right, it's not a direct bolt on.

Have ANY of you EVER rejetted a carb before?

Sure, lots of times. I recommend getting one of these:

http://www.gunson.co.uk/tech-torque/Col ... on-chamber

And focusing on idle first. No gas pumping, nothing. Just idle. Not even close with the screw 5 turns out? Go up on the idle jet.

Then you start blipping the throttle. Adjust your pump (if possible) so it doesn't stumble. Done.

Then hold the throttle at say 2000 rpm. Is it totally lean? Go up a size on the primary jet.

That's it.

The rest is done on the street. But almost always with this approach, you don't need to do anything else.

[wetminkey]

Cool, thanks.
I've seen the "Color Tune" before,...
Idle speed screw seems to 'like' 2.5 turns out right now. I think I'll reduce my DFEV's 60 primary idle jet by 0.5mm,...one step, to 55. Secondary idle jet is a 50. This is consistent with info I've found, and my Reline High Altitude jetting kit contains a 55, so that makes sense,...
I think I'll increase air correction jets after that,...at 5000 ft, the carb needs AIR to provide the proper A/F ratio. And I think I'll jump to what I have info on,...go from 165/160 to 180/170. Those are the smallest of the air correction jets in my jet kit (meant for 5000 - 10,000 ft. I'm at 5000).
I've got 130, 135, 140, and 145 mains, but my DFEV has a 137/140, so I guess I'll swap to the 130/135.
Um,...adjust the pump,...? Mechanism?
The car is not driveable,...I can get 1500 rpm out of it, but no more - it bogs if I try to raise rpms beyond that. I can make it down the driveway and back, but I can probably run faster than this car can go right now.

[18Fiatsandcounting]

Listen to Steiny; he's your friend.

The only other advice I have at this point is not to worry about the air corrector jets or the altitude correction. The air going through the air corrector jets is totally swamped by the liters of air going through the barrels of your carb every second. They are there for fine tuning across the rpm band, and you've got much larger problems going on. As for altitude, on my cars I only notice an altitude issue once I go above 10,000 ft. You're around 5,000 ft if I recall, and at that altitude you should only need a slight correction. Perhaps more if you do Pike's Peak on a regular basis...

-Bryan

[SteinOnkel]

As a total shot in the dark: but I decided to re-jet my carb today.

I swapped the primary main jet. It was a 125 and it ran fine, but it was lacking in power and the plugs were more white than brown. So I decided to install a 130. Guess what it would not rev past 1500 rpm. It just sputtered and died. I had the colortune installed at the time and it just did not show any combustion at all when you revved it.

I thought surely I must have messed something up. So I reinstalled the 125. Car ran fine.

So I went back to the 130. Same thing again

Then I installed a 140 and bam it ran fine, pulled much much stronger than before.

Took it for a spirited test drive - pulls like a bat out of hell. Very nice.

Parked the car in the garage, tried to restart it and I only get a click from the starter. You gotta love 41 year old junk

I suspect there is something wrong with the 130 jet itself. But I couldn't tell you what. Looking at it, you can't tell a difference.

P.S: as far as the altitude is concerned, I second what Bryan is saying. A few weeks ago I took my programmable efi car up to Truckee. I live it at sea level and that place is at around 6000 feet. By about 4000' I thought hang on a second this is a great time to check out the altitude correction. A feature I dont usually use, because like I said I'm at sea level. Pulled over, hooked up the laptop and turned it on. I went on my merry way and afterwards downloaded the datalogs from the car and looked them over in the cabin. The ecu was adding no more than 2-4% fuel to compensate for this elevation. Just food for thought...

[18Fiatsandcounting]

As a total shot in the dark: but I decided to re-jet my carb today.

What, you mad, bro'....??

I suspect there is something wrong with the 130 jet itself. But I couldn't tell you what. Looking at it, you can't tell a difference.

That is weird. Usually if you hold the jets up to the light, you can visually see the difference between, say, 130 and 140, and just barely between 130 and 135. Not that I want you to take apart your carb again, but it would be interesting to see what's up with this 130 main jet. Perhaps take it to a machine shop that has a selection of 1.xx mm drill bits and see what the opening really is.

P.S: as far as the altitude is concerned, I second what Bryan is saying. A few weeks ago I took my programmable efi car up to Truckee. I live it at sea level and that place is at around 6000 feet. By about 4000' I thought hang on a second this is a great time to check out the altitude correction. A feature I dont usually use, because like I said I'm at sea level. Pulled over, hooked up the laptop and turned it on. I went on my merry way and afterwards downloaded the datalogs from the car and looked them over in the cabin. The ecu was adding no more than 2-4% fuel to compensate for this elevation. Just food for thought...

A/F mixtures tend to richen as you go up in altitude, so I'm guessing your ECU leaned out the mixture a bit as you climbed up to Truckee. The engine is still pulling in the same volume of air as it was at sea level, but there are less air (oxygen) molecules in that volume due to the air being less dense. Less air molecules + same amount of fuel molecules (its density doesn't change with altitude) = richer mixtures at altitude.

-Bryan

[wetminkey]

Bryan, the air correction jets are important to altitude correction,...I believe that you meant to say "emulsion tubes", which are only changed for very fine tuning at higher rpms.
I'd LOVE to tell you that there is SOME other reason for this car to act the way it does, BUT THERE IS NONE!
Unless new distributor, coil, and ign. module are malfunctioning. The engine has been gone through (new head gasket, timing belt, etc,...), and the fuel pump has been replaced.
I've got a good compression test. I even replaced the BRAND NEW timing belt because I thought that I'd got the replacement off a tooth, because of the way the engine acts. Carefully set it up at TDC. No change.
Rejetting seems to be a lot of shooting in the dark. Try this, warm up, test drive, try that, repeat. What a bunch of crap,...the carb should run out of the box,...Spanish made Redline Weber.
Winter is setting in, and that's NO TIME to be rejetting a carb, so I may have to park it for the cold months,...
I've got all the old crap (dual plane and ADHA) in a box, and I'm seriously considering yanking the DFEV and single plane and revert back. It at least ran with that carb/manifold,... And I'm getting NOWHERE FAST with this thread!
Have a good weekend, dudes.

[18Fiatsandcounting]

Todd, sorry I can't be of more help, and you could be right. I'll have to do some more research on air corrector jets, as I've been known to be wrong before. Based on all the symptoms over this entire thread, it does sound like you're either going way too lean or way too rich as you rev up the engine and thus it "peters out" over 2000 rpm or so. If it's too lean, the engine will start missing, and if it's too rich, it will start to surge and stumble.

I did quickly Google Weber air corrector jets, and their function seems to be twofold: 1) they mix air into the fuel which is then easier to atomize into a mist as it exits the venturi and heads into the intake manifold, and 2) they provide a "leaky straw" effect which prevents the fuel from being sucked too readily into the venturi. Look at it this way: If you suck on a straw, it's easy to pull the liquid up to your mouth. If the straw has holes in it, you have to suck harder to pull the liquid up. Same principle in the carburetor. If your air corrector jets were closed off, it would be too easy for the engine vacuum to pull fuel into the engine when you don't want it. Opening them up provides a controlled "leak" that is tuned for optimal performance.

One thing I do know: if you see fuel dripping or spraying when the engine is idling and you look down the carb throat (either barrel), there's definitely a problem. At idle, fuel should only be coming out of the idle hole which is below the butterfly valve where you can't see it (when the engine is idling). The amount of fuel coming out of that small hole is determined by the idle mixture screw (and the size of your idle jet).

-Bryan

[SteinOnkel]

Swapping in a different main jet takes all of two minutes...

I understand your frustration, but you're giving off the vibe that this is somehow our fault. My last bit of advice to you is to get a wideband, colortune spark plug or anything else to determine without a doubt whether you are rich or lean so you can finally stop guessing.

Good Luck
Steiny

[wetminkey]

No,...nobody's fault but mine!
I've probably bought, and installed, better than 10 carbs before (and nearly as many intake manifolds), and I've never had one that ran crappy right out of the box. I'm not very impressed with Redline Weber's spanish-made DFEV.
I learned how to tune carbs by ear, nearly fifty years ago. I know them pretty well, and know Weber carbs even before I got this one. But, other than beginning sequential changes in this carb, I do not understand why it has a problem.
While SCREWING AROUND with this carb, I was able to clean and tune my '68 Mustang's Holley double-pumper, and get it running great, with a full engine tune. But this Fiat has gone no more than 200 ft since I installed the DFEV.
Yes, 'stumble' describes what I call 'bogs',...! And it occurs just above 1500 rpm,...results in ZERO power. Especially with an AUTOMATIC transmission! Boy, does that suck, or what?
Two minutes to swap jets? Once the carb top is removed, perhaps.
Our temps are in the low 50's today,...snow on the way for the next three. It's what I was worried about happening,...FALL. I can't even warm, and idle, the car without pulling outside the garage. So, I don't think anything is happening real soon. Better weather forecast for next week,...
I've done enough research to know that rejetting is nothing more than guessing! But I'll get the ColorTune and use it,...I've wanted to own one for years. Just never forked over the bucks,...

[GarageRat]

Todd,
I do think that the color tune or O2 sensor is a good idea, but it almost seems like there is something wrong with the carb. As you said, I have had carburetors that were jetted all wrong and the car ran poorly but at least could be run in neutral. Is there anyone else from the forum here who lives nearby or from a local car club who could let you try another dfev or even a 32 adfa (a carb that works with single plane manifold)?

Steve

[18Fiatsandcounting]

Todd, I know you're frustrated and about ready to throw this DFEV in ye olde garbage can, but I have one more thought: It almost sounds like your main fuel circuits are never coming on. The idle circuit handles the idle, and the progression holes handle the idle speeds up to about 1500-2000 rpm, at which point the main jets kick in. It sounds like the main jets are never kicking in.

You don't by chance have the auxiliary venturis installed 180 degrees backwards, do you? Those wing like things with the round tube in the middle of the barrel. If installed backwards (very easy to do), the main fuel circuit will NEVER operate and would lead to exactly what you're seeing.

Solution? Remove the top cover, remove the auxiliary venturi on the primary barrel, and verify that the end that has the fuel opening is indeed pointed towards the center of the carb when installed. Verify secondary barrel as well.

-Bryan

[wetminkey]

There are no removable venturis in the Weber DFEV, Bryan. It's a down draft Weber,...and brand new, with no alterations.
I have a friend, up the road, who may have a Weber hidden away in his Redline boxes in his garage,...'Racer Mikey'. He may have a Weber I can easily swap to for troubleshooting purposes,...I may have to check.
Without specifics about rejetting, this thread has become a burden. It's not helping.

[18Fiatsandcounting]

Fair enough, Todd, please seek a second opinion. Meanwhile, there is indeed a removable auxiliary venturi in the DFEV series carburetor; see part #97 in: http://www.carburetion.com/diags/3236DFAVDiaginfo.asp Sometimes you have to pry it out, unless of course you have a version where it was cast or welded into place.

If the auxiliary venturi is installed 180 degrees backward (very common), the engine would behave exactly as you describe.

-Bryan