Dual carb question, Dellorto 40s on a 1.8L to be exact Options

[Joe Ricard]

Agreed, it "should" pull better down low.

And you will probably not run out of power all the way to 5800 RPM.

Above that and you need lots of internal engine work anyway.

[jr91472]

Clayton is spot on regarding the dizzy. Go stock with the vac advance connected. I also upgraded it with the Crane Fireball ignition system.

I have hardly touched the carbs since....

[rhodyguy]

your next decission is which intakes to run. i posed the ? re short vs tall for a f.i 2.0 engine and 40idf. len hoffman said to go with the talls for better top end performance. better power down low with the short intakes. my car is more of a highway runner. i went with the talls. keep us updated with your results. too often, we never hear the end of the story.

k

[jr91472]

Yes please. I want to hear how the 30 vents work. I went with 32s on my 1.8L / Dell combo. Runs really really well, but if 30' are better (IMG:style_emoticons/default/idea.gif)

keep us updated with your results. too often, we never hear the end of the story.

k

[BxtrBill]

I'm still waiting on my new 30 venturis. and will report back when I get them

You might want to order some smaller main jets while you're at it....those 140s are gonna be way on the rich side, especially with the 175 airs. Rule-of-thumb says 120s should work...125s may be better. Too lean typically ain't good.

[mike373]

Hey rhodyguy. I think you may have the manifold info backwards. I heard tall manifolds for low and midrange performance. Creates more port velocity.

Mike

[terrymason]

well, I've made alot of progress! I have installed new 30 venturis, and re-adjusted the linkage (one side was about vertical, while the other was a an angle). The car no longer backfires, and runs much better, but it does still go lean when switching from idle to main circuit.

I noticed that the auxiliary venturi (the tube over top of the main venturi) don't all match. 3 of them have the number 2 stamped on them, while one has the number 1 on it. I'm assuming that this is a measurement of some sort right? What size should I want? Any idea what this would cause?


Thanks guys! It's great to have my car running again!

[terrymason]

You can actually see the aux venturi below

[eric914]

Not to hijack but I have 40 IDF's with an 009 dist. If I put the factory dist back on where do I port the vacuum from. Can I use one of the ports at the base of the carb? Do I need to connect the ports from both carbs together to keep the flow through them the same? I am also having some backfire issues and the motor seems flat when accelerated hard in the 3500+rpm range.

[IronHillRestorations]

I remember hearing that the best stock dist to run is the 1.8 with the vacuum pot connected. Can anyone back this up?

You are getting good advice here. You have made double sure that the drop links for both sides are dead nuts the same length right? Both sides have the same angle and hit full open throttle at the same time, as well as both resting on the idle stops? There's some pretty schlockey linkages out there, and Joe's dead on with how important the linkage set up is.

I don't know Dells, but I'd try just larger idles, or just larger mains first, but probably not both at the same time.

Where are your mixture screws set at? If you have to set the mixture less than 1 1/2 turns out then I'd try larger main jets, and smaller mains if you've got to go more than 3 1/2 turns out.

[BxtrBill]

[quote][quote name='eric914' date='Aug 2 2007, 02:01 PM' post='930974']
Not to hijack but I have 40 IDF's with an 009 dist. If I put the factory dist back on where do I port the vacuum from. Can I use one of the ports at the base of the carb? Do I need to connect the ports from both carbs together to keep the flow through them the same? I am also having some backfire issues and the motor seems flat when accelerated hard in the 3500+rpm range.
[/quote]

Well, seein' as how the hijacking has already been done (and also seein' as how other folks might want to know), vacuum for the distributor advance is always taken from a point ABOVE the throttle plates. If you have the later version of 40IDFs (hecho en Espana, I believe?), they will have one port on each carburetor that you can use for this, Seems to me the earlier (Italian) versions have none, but I could be wrong....been a while. In any event, do not use any port that is below the level of the throttle plates unless you need to feed a vacuum retard can.

You can parallel the vac ports on the two carbs and I do, when I have two to use.
Lots of Dellorto pairs have only one vac port on one carb and I'll be danged if I can tell the difference.

I've used the stock 1.8 dizzy and I think it's a good choice for a carbed car. That said, I like the -205 distributors from early Jettas/Rabbits/whatnot, though they do require a bit of lathe time to make them work. A distributor from a later Bus will work too, and slips right into the hole in the case. The neat thing about these options is the bulletproof FACTORY electronic ignition that comes as part of the package. I fiddle with the advance curve some, set the timing and pretty much never look at them again. If you go this route, be sure to get the so-called Fairchild module, the special coil and the wiring harness to connect everything together.

[Twystd1]

If you choose to use a factory vacuum advance 914 Bosch dizzy on carbed engines.

NOTE: You can run a pertronix or Crane electronic setup in any of these dizzys. And thats a good thing IMnonHO.

You have a couple of choices.

!) Get your ported vacuum above the throttle plates. On some carbs there is already a vacuum port for this. On some there isn't. In that case you have to drill the carb body and install one. It's pretty dam easy to do. Then you epoxy a brass fitting in and VOILA.. Insta vacuum port.

At that point you will need to have BOTH carbs ported to vacuum. ONE carb doesn't work well.
Why you might ask...?????
Because of venturi fluctuations of the valves closing and opening. That will pulse the dizzy vacuum diaphragm and create all kinds of timing fluctuations. And thats bad....... Ya can't tune around it.

So what ya do... is is get 2 matching ID sized rubber hoses to each vacuum port on each carb. Then each hose to a Plastic or Brass "T". (Combined signal of both carbs)
Now comes the fun part. Go to your nearest parts house or even better.. A Vee Dub shop. And get one of those little plastic fuel filters that you have seen on every old Vee Dub engine you ever looked at. They are like a buck or two. Put that filter inline with the last hose that comes from the "T" to the Dizzy vacuum pot.

This will help dampen out the vacuum pulses that occur at lower RPMs and keep the points palte via the vacuum pot from over reacting to the pulses.

DONE....!!!!!

2) Don't run vacuum advance on your stock type IV distributor..
And leave the dizzy port OPEN. Else the vacuum pot will create resistance on the points plate and prevent it from clocking (turning) at the proper rate according to engine rpm.

3) Buy a Mallory "Non Vacuum Advance" electronic dizzy. Thats the best of the dizzys. No vacuum pot... No problems.

4) Buy a SVDA dizzy for a type IV engine from John Connely at www.aircooled.net
That is a very good vacuum dizzy that is curved for a type IV engine.
Note you must have vacuum fittings for this carb.

Lastly. Vacuum advance helps on fuel mileage and constant RPMs efficiency. Like a freeway or any long steady state speed driving.

If'n this engine is for having fun and hauling ass on turns. Auto X or simply occasional driving. I don't think the advance setup is worth the trouble in your case.

Anyway... thats what I think.

Now go make it work......!!!!!!!!

And I am glad you are tossing that piece of crap 009 dizzy. Those little critters have screwed up more Carbed type IV engines that anything I know. Period.

Cheers,
Clayton

[terrymason]

I'm ready to pull my hair out over this thing. I got it tuned ok 3 days ago, idling around 11:1, and going alittle lean when driving, but no backfiring. I get in today, and try to drive - it's idling at 14:1, and going crazy lean - completely undrivable. I don't know what changed to make it drive so differently!

So my question: Could this be something else, other than carbs?

i.e - maybe my valves need adjusting? I'm trying to step back and think of the whole picture.

[IronHillRestorations]

Sounds like trash in the fuel is clogging the jets.

[rhcb914]

That to me sounds like a plugged idle jet. It's happened to me, quite frequently until I completely cleaned out the tank, changed the lines and replace the fuel filter and rebuilt the carbs.

[type11969]

I'm ready to pull my hair out over this thing. I got it tuned ok 3 days ago, idling around 11:1, and going alittle lean when driving, but no backfiring. I get in today, and try to drive - it's idling at 14:1, and going crazy lean - completely undrivable. I don't know what changed to make it drive so differently!

So my question: Could this be something else, other than carbs?

i.e - maybe my valves need adjusting? I'm trying to step back and think of the whole picture.

Definitely plugged idles . . .

[terrymason]

OK, I can deal with that. I'll go home and pull them all and check.

Do you guys see any value in me running 2 fuel filters? I've currently got the one that came with my new fuel pump sitting in front of the pump itself, but nothing between the pump and my carbs.

[Joe Ricard]

Yes I run one before the pump. and one after the pump. Fuel injection grade cans.
I made the most improvement against plugged jets with better filters.

[terrymason]

OK,
New fuel filter after the fuel pump (2 now)
I"ve pulled all the old idles and put in new 60s
one pump jet looked clogged, so I pulled it and blew it out.
I"ve also readjusted the linkage, so that they seem to be pretty well in sync.

I'm now getting backfire from the exhaust at low speed, and backfire out the carbs during accelleration.

Does anything look crazy wrong with my linkage to you guys?

If not, then tomorrow I may just pull one carb and begin tearing it apart and cleaning it out.

[terrymason]

and another