TheSamba.com :: View topic

Fri May 02, 2014 8:52 pm

First and foremost, I am a new member but have been reading through posts for a while now.

Here's what's going on. I bought a sand rail with a 1915 turbo. I don't have a lot of experience with VW air cooled engines, and even less with this Dellorto carb that's in there. The car ran good when I drove it in Pheonix, once I got I back to my home town I started going through the car more and found the turbo piping clamps all loose. After I tightened it down the motor didn't want to run right. I initially raised the idle to keep it from stalling, but knew that wasn't the right way to do it.

The carb is a Dellorto DRLA 40. It currently has 34 Venturis, 120 Main jets, 185 Air corrector jets, 70 Pump jets, 9164.2 emulsion tubes, 65 idle jets. With this setup I had to have the idle air screws out 5 1/2 turns to idle properly @ 1000rpms.

The car starts fine, every time. But once it's started, any sort acceleration off of idle causes the motor to bog badly, and as soon as I let off throte the motor runs well again. If I VERY GENTLY ease on the throttle it revs up okay. I have checked the plugs and they seem black, as is the tail pipe... Which to me says rich. However, most everything I've seen about thing these carbs tells me that 5 1/2 turns out on the air idle screw means I'm lean?? Also once the car is warmed up, at higher RPMs there seems to be white or blue smoke from the tail pipe. I'm thinking oil?? I'm running 15w50.

I know there is a lot of information here, hoping somebody can point me I. The right direction. I have pretty much googled my heart out this past two weeks and if I do any more I'm going to find the end if the internet. Thanks for ANY help !

Fri May 02, 2014 9:17 pm

I bet the mains are drilled, it should take 145-150 mains to make it work with the 34 venturis.

What's the fuel pressure? Does it have an electric pump and regulator?

Fri May 02, 2014 9:33 pm

modok wrote: I bet the mains are drilled, it should take 145-150 mains to make it work with the 34 venturis.

What's the fuel pressure? Does it have an electric pump and regulator?

Yes, it has an electric fuel pump and regulator. Regulator is set around 2.5psi.

One of my buddies had mentioned the same thing... I just put new mains on there, they are 130's now. Same effect.

Fri May 02, 2014 9:44 pm

Why 130? the right size won't be less than 145
Could also drop the venturi down to 30mm, then 130 may be ok, and may be better off overall.

The 65 idles should be fine. If you need larger then that's indicating problems elsewhere, like the manifold it too big or too cold, so fuel is just building up in there.

Sat May 03, 2014 7:07 am

Why do you say 145? I'm in no way arguing... I'm just trying to absorb as much info as possible. Do you think 70 is too big for the pump jets?

Sat May 03, 2014 8:11 am

s13_marine wrote: Why do you say 145? I'm in no way arguing... I'm just trying to absorb as much info as possible. Do you think 70 is too big for the pump jets?
-------------------------------------------------------------
It's possible that your accelerator pump lever is not adjusted properly by the sounds of it. Is this a "pull through" or a "blow through" application? If you use very much boost you will need more fuel and less advance on the distributor or the engine will lean out and over heat with pre-ignition.

Sat May 03, 2014 8:17 am

Are you sure this is a DRLA and not a DHLA CARB?. DHLA is a SIDE DRAFT carb usually used on a turbo application.
Just checking. :)

Sat May 03, 2014 10:00 am

s13_marine wrote: Why do you say 145? I'm in no way arguing... I'm just trying to absorb as much info as possible. Do you think 70 is too big for the pump jets?

main jet size is normally 4.1 times venturi, using the carbs as intended.
Since you have a single, it will require more in the range of 4.2X. Moving the carb father from head loses sitgnal, that is why I am reccomending smaller venturi and 4.2X jet size.

70 may be ok, or rather, even if it is too big it won't hurt.
The gasoline takes so long to get through the manifold it probably isn't critical.

Sat May 03, 2014 10:32 am

Quote:
It's possible that your accelerator pump lever is not adjusted properly by the sounds of it. Is this a "pull through" or a "blow through" application? If you use very much boost you will need more fuel and less advance on the distributor or the engine will lean out and over heat with pre-ignition.

This is a blow through, I am 100% sure that the carb is a DRLA 40. I was reading about removing the carb and testing how much fuel is pumped from the pump jets. Question... To adjust it, would tightening the nut introduce MORE or LESS fuel? To me it seems the less the diaphragm moves the less fuel that would be pushed????

Sat May 03, 2014 12:25 pm

If the engine is at idle and I blip the throttle, the motor stalls out. If Ease on the throttle the RPMs will steadily rise until around 3000-3500 RPMs, then it will stall out as well. If I hold the throttle open after the stall, the RPMs drop rapidly and the engine will die.

Sat May 03, 2014 1:25 pm

What diameter tubes on the manifold?
Read this:
http://www.thesamba.com/vw/forum/viewtopic.php?t=3...mp;start=0

Sat May 03, 2014 1:49 pm

modok wrote: What diameter tubes on the manifold?
Read this:
http://www.thesamba.com/vw/forum/viewtopic.php?t=3...mp;start=0

I'm not sure. Are you talking about inner diameter of the center manifold, or the long metal tubes that go horizontally out if it? The carb is still mounted on the manifold and the manifold is still on the engine

Sat May 03, 2014 1:51 pm

modok wrote:
Read this:
http://www.thesamba.com/vw/forum/viewtopic.php?t=3...mp;start=0

Good read, so if the manifold is too large, or if the centuries are too big it will cause the fuel to not travel or atomize quick enough?

Sat May 03, 2014 3:02 pm

Post a pic of your carb, turbo and intake so we can see what it looks like.

On my blow through Bocar I had to increase the main from 130 to 155 in order to get any driveability out of it let alone boosting it.
When I extended the bowl vent into the top hat it changed everything though.

Sat May 03, 2014 3:07 pm

modok wrote:
Read this:
http://www.thesamba.com/vw/forum/viewtopic.php?t=3...mp;start=0

Good read, so if the manifold is too large, or if the centuries are too big it will cause the fuel to not travel or atomize quick enough?

Sat May 03, 2014 3:34 pm

Sat May 03, 2014 4:57 pm

can't even see it! but from how it's sitting probably the CB one, which is one of the better ones.

Fix the jetting and it should work!

Sat May 03, 2014 5:08 pm

Sat May 03, 2014 5:19 pm

Not the CB one, if it was it'd have plugs on top for the heat riser.
Doesn't look to big from the top tho.

the tubes that connect to the end castings is what we were talking about. You have calipers to measure OD of those?

Sat May 03, 2014 5:21 pm

The nice thing about a blow through turbo is you are getting warm air from the turbo so you don't have the icing problems like a draw through or for that matter a N/A single carb that has no carb heat.
Also your fuel travel is the same as a stocker.
that carb should be fairly easy to tune.

Make sure your accel pump is squirting as soon as the throttle is moved. if not adjust the play out so you get fuel with the slightest movement.
My guess is with those larger Venturis you are losing some velocity when the throttle is opened and it leans out a bunch.
Pump more fuel or smaller Venturis.....