Re-Jetting my 40mm Dells

I've posted this for two reasons:  1. I'm selfish in that I hope to get some solid info and make these Dells much more drive-able, even if I give up some mid/high end power in the process and (2.) others may be having troubles and might learn a bit about how these (and Weber, too) carbs work and maybe can do a little simple tuning on them, too.  (Didn't one of the Todds on here just go through this??)

All I know is, whatever I have done to "improve" things for the past fifteen years has either made no change at all or made things slightly worse.  That's why I'm going back to basics to see (hopefully) what I've been doing wrong, correct it, get a pair of nice-running Dells and move on to something else I can be OCD about.

I have my first question for @Pat Downs

What was the purpose of inserting the lead plugs in the "idle circuit" (taken from a Hot VWs article).  What would happen if they were removed but I kept the Horizontal discharge tubes?

I'd increase the float height a little, should help richen the transition. I don't know how Dells are but Webers have different emulsion tubes, some richen at a lower rpm, some higher. You might try that. F11 and F7 for example richen at different places in the transition.

If none of that works, I'd be inclined to investigate your spark curve. As has been said many times 90% of carb problems are ignition problems.

While on the topic of dell 40ś I like to replace the oval filter setup and run individual stack filters--I do have the stacks inside of the filters. So--who runs this style--any issues--where do I purchase without getting robbed? Any advice is appreciated.

Gordon Nichols posted:

 

What was the purpose of inserting the lead plugs in the "idle circuit" (taken from a Hot VWs article).  What would happen if they were removed but I kept the Horizontal discharge tubes?

I don't know their purpose but I'll bet they're there for a reason, and taking them out will make it run worse, not better. Or try it and report back what you find... 

Gordon, I'm confused:  Do you have a single Dell 40 or dual Dell 40s.

Since you refer to your "Dells" in the plural, I presume you have dual Dells.  If you have duals, you probably don't have 40mm venturi (I hope).  40 mm vents come on Dell 48s and are way too 'flat sided' for anything but driving WOT to redline between shifts, even on a heavy breathing 2332.  

Remove a vent, it should have the size etched somewhere on it.  If not, measure the inside diameter at its narrowest point.  For around town drive-ability you want vents shaped somewhat like an an hourglass; narrower in the middle, more open at the top and bottom.  You didn't say what engine size you have, but if it is maybe a mildish 2110, then 30-34mm vents sound about right.  The 30mm vents should be crisper buzzing around town.

I learned the hard way, bigger is not better.  On my 2332 I have Dell 48 tri-jets (big mistake), and they originally had 40mm vents (bigger mistake).  Until I choked down to 36mm vents the engine would fall on its face with any throttle input until eventually the rpms got high enough to suck some air through those big straight sided 40mm holes.  It didn't matter how I was jetted, nothing happens with throttle input if the engine is too small to generate enough vacuum in mid-range rpms to accelerate intake air through the vents.  

As far as jetting, I liked the look of your 'by-the-book' jetting better (again, assuming we are talking dual carbs).  It sounds way too rich now, and what lead you to the 70mm accel pump?

What disty are you running, Gordon? 

DannyP posted:

 I don't know how Dells are but Webers have different emulsion tubes, some richen at a lower rpm, some higher.

Danny  --  Dellorto has a similar selection of emulsion tubes, for the same purpose.  And it could be that Gordon somehow ended up with 'specialty' emulsion tubes or tubes that have been alien modified which are causing him problems.

Ok, let’s see.....

Engine is a 2,110, 044 wedge-port heads, match-ported intake manifolds, Engle 120 cam, brand-new MagnaSpark II disti set precisely at 32° and the advance curve checked and set on a Sun Distributor bench.

The carbs are a pair of dual 40mm DRLAs 

I’ll measure the vents tomorrow to see what I’ve got.  Should be interesting, but they are slightly hourglassed.  I suspect that they’re 34’s but we’ll see.

Getting to the larger jets was a long, uneventful story.  Surprisingly, I’ve never seen any black smoke from the exhaust.

Remember, these had long ago been converted to horizontal discharge tubes so I guess they could be called “alien”, but they can certainly make gobs of power.  A little untamed, but lots of power, and I have never encountered anyone else on here or elsewhere running them.  The amount of acceleration “snap” up over 4 grand is always surprising.

What’s important is that I‘m going back to a baseline that is known to work and is drive-able in many other 2,110 engines and begin again from there.  Should be in interesting trip.  

I guess I’m getting less impressed by raw power as I get older.  

Loud mufflers just might be next!

The lead plugs block off the air inlet for the idle jets. This allows the idle jet extensions for the update kit to work properly. The theory is to raise the air inlet higher so debris doesn’t find its way into the stock air inlet creating a plugged idle jet. 

  You can always drill out the led plugs and go back to the stock idle jet holders. 

I would remove the discharge tubes and go back to the stock Venturi and booster Venturi. I see no issue leaving the lead plugs in and using the extended idle air jet. 

  If you don’t have your stock parts, I have modified the update kit allowing for a stock 34mm Venturi, keeping the discharge tube. The smaller 34mm Venturi signals the discharge tube harder, eliminating the flat spot

Pat!  Thanks for the info.

I dug in my shop attic and actually found the box of original parts from the 1990's

It pays to forever be a pack-rat, even after three house moves and three states.

I'm going to try installing the original stuff and see how that works out.  At my age, I'm willing to give up a little mid/high "grunt" for more smoothness through the range.

Thanks for the info on the plugs.  Since I've already got the extended idle jet holders (are those the same as "Jet Doctors?) I'll just leave the plugs in place.

I'll post on here how I make out, and thanks, again, for the help!

Gordon

Been too hot to be out in the shop working, but I looked closely at the original Venturiis and they are all 34's.  (You were right - they were stamped with the number).  When I found the original parts up in the attic of my shop I also found the original conversion instructions (Hoo-Ray!) and now feel confident that I can easily reverse the process and go back to stock.

As soon as it gets down below 90F in the shop.......

Hey, just thought of something:  The narrow part of the Vent is off-set to one end.  Can these vents only go in only one way or should I pay attention to which way the narrow end goes, up or down?

I've got it 'narrower to the top', and it is important.  Also, make sure the Auxiliary Venturi is installed right side up or you will never see 3000 rpm.  (Don't ask how I know.)  There is a fuel inlet port in the middle of the Aux Vent and it must face down. 

Thanks, Mark.

Boy, I've learned a LOT in just a day or two with this.  

Someday, I may even know what the heck I'm doing!

LOL, don't confuse me with those who actually do know what the heck they are doing!  I'm not in their league.  But if you have one of these, it helps:

 https://www.cbperformance.com/product-p/0101.htm

Maybe you can beg Pat Downs for an electronic copy since the hard copy seems to be out of stock.  In fact, maybe you could suggest CB offer all future reprints in an electronic format rather than restocking a publishing load of paper copy inventory.

One way or another, if you have Dells you need the CB tech book.  

I have both the Dellorto AND weber Thomlinson books.  For the most part, they get you in the ballpark and a line drive up the middle will drive in a run if you take it slowly and think about what your engine is telling you.   

Still, tuning carburetors is fast becoming a lost art in this world of commonplace electronic fuel injection.  Sometimes I feel like Doctor Zook - the dark-robed Druid from "Hagar the Horrible".

Gordon, the secondary Venturi is installed one way. If you want, give me a call at CB, I can explain everything to you.

Thanks, Pat - I think I've got it - Notches up, fuel nozzle pointing down, line up the port with the inside hole of the throat and lock 'em in with the setscrew.  

All I need is some free time and lower garage temps, but I may call just to make sure I'm doing it right when I'm ready to go.  Thanks!

Does anyone have a source for the fiber washers used on the Dellorto fuel supply banjo connections?  They are two different sizes on each connection and are showing as "no longer available" on the CB perf. website.  I assume we need to use fiber rather than rubber because the gasoline will attack the rubber.

I have a couple of carb rebuild kits on order and hope they show up in there, but would like to have a few extra sets in stock here, especially because they are often single use items that destroy themselves when you remove the fitting after they've been on there for a while.

Thanks,  Gordon