DHLA40 Jetting / Setup help!

[MarkMk1Golf]

Hi

Dont know any VW forum with carbs, so ill give it ago on here.

My problem is that someone has "DIY" drilled some of my jets so i have to start over.

Engine is running, and can idle and rev without any problems.

My problem is "part throttle driving" and full gas from low rpm while driving, the engine stutteres/shakes/nosedive until i reach abit higher rpms. Same problem for part throttle driving, if i want to slighty increase my speed in 5th gear, the engine stutteres/shakes/nosedive.

Info on my engine:

2.0L
10.8:1 compression
16v
DHLA40
Chokes / Venturis : 32
Sport Camcat cams 283/279

What would you recommend for main jets, air correctors, idle jets, idle jet holders etc ?

Really hope someone can help

Thanks

[Pumaracing]

You're wasting your time trying to jet carbs by guesswork from a vague engine spec. However I can tell you for nowt those are very small chokes for a 2 litre 16v engine with a bit of cam.

https://web.archive.org/web/20110809041756/http://...

You don't say if the head has been ported but even without you should be looking at 170 bhp plus. That means 36mm chokes as a minimum and then every bit of jetting you've already got will go straight out of the window. 40mm carbs are also far too small for such an engine. You want 45s for up to 200 bhp and 48s for over that. 40s are only good for about 150 bhp, maybe 160 bhp tops. Those carbs have probably come off an 8v engine with about 130 bhp so you're pissing in the wind trying to get them set up properly.

I also hope you're not using a VW 16v Mangoletsi inlet manifold which will destroy any chance you think you have of getting decent power.

[MarkMk1Golf]

Hey Pumaracing

First off, thanks for the reply - Any help is appreciated.

Im not doing this engine swap for the bhp, only for the sound of carbs, and it looks much nicer in the enginebay, compared to a 1.8 8v which i had before.

Its a standard 2.0L 9A bottom with a standard PL head. The inlet manifold is a Redline one, which should be OK.

Ive already had it on a dyno and it made 160.2 bhp, so you´re right about the 150-160 range The guy doing the dyno test should have fixed my part throttle problems, but he couldnt :/ (Lack of knowledge)

Could these part throttle problems have anything to do with 32mm chokes ?

I can do my carb specs as they are right now.

Chokes : 32
Main Jets : 142
Air Corrector : 210
Emulssion : .6
Idle Jet : 0.7 (Used to be 0.52)
Idle Jet holder : 4x 150 (Used to be a 7850.1)
Acc Pump jet: 0.45 (Used to be 0.4)

Looking forward to hearing from you.

Thanks

[Pumaracing]

Even in the days when carbs were the norm there were never many people in the UK who could set up Dellortos properly or even understand their bizarre jet numbering system and I'm not one of them. You always stood a much better chance with DCOEs.

However if you read my tuning article it should already be apparent that your mains are rather big for that choke size and consequently the need for huge air correctors to lean things back out at the top end. I suspect it's going rich and bogging down at mid rpm until the air correctors start to kick in. This should all have been abundantly clear on the rollers to anyone even vaguely competent but the guy probably spent most of his time on the top end and the idle and had little clue how to get the mid range driveability right. Find someone else.

[MarkMk1Golf]

Back again

Followed your guide somewhat, but still having issues when opening the throttle slighty. Its more or less the same "Part throttle / midrange" problem i had before, now its just more serious. Before the change it was at cruising speed, now its also in very slowly acceleration.

Chokes : 36
Main jets: 142
Air corrector : 210
Idle jets : 0.5
Idle jet holder : .2
Pump jets : 0.45

Can you give any advice on what to do next ?

[X8Matt]

Based on my experience of messing around with Holley carbs, you need to either fit a larger idle fuel jet, or a smaller idle air bleed.

This website should give you some pointers....

http://www.aircoolednut.com/erkson/ttt/engine/carb...

[PeterBurgess]

May I suggest you buy and fit an afr monitor so you can measure what is happening with regard to fuelling rather than guessing?
We have found the NGK Powerdex AFX fast and reliable, it is no longer available but Ballenger Motorsports make a replacement to better than the oe specs.

http://www.bmotorsports.com/shop/product_info.php/...

Ignition timing has an effect on the afr as well so you need to optimise that also.

Peter

[MarkMk1Golf]

Alright - I got some 0.7 idle jets from the last setup, i will try these with the new chokes + idle jet holders.

[Pumaracing]

MarkMk1Golf said:

Back again

Followed your guide somewhat,

No you haven't. I make it clear in the article that once the desired chokes are within 7mm of the carb size you need to move to a bigger carb. Airflow through 40mm carbs peaks at 33m choke size. Anything bigger is a waste of time. It just reduces the signal to the jets without increasing power potential.

Either fit 45mm carbs and 36mm chokes or leave the chokes at 32mm in the 40mm carbs. You have a vanishingly small chance of getting it running correctly by guesswork.

[DVandrews]

There is a short article about Dellorto jetting off my old personal website at www.dvandrews.co.uk, follow the link and see if it helps?

Dave

[MarkMk1Golf]

Thanks Dave, i will have a look at it.

Though i got it running perfectly yesterday with the old chokes.