Dellorto Part Throttle Leaning - SOLVED
Turbo Mini Forums

Folks, im going to take my blue mini for tuning next month at John Sleaths, however in the mean time id like to get the car something like as the close as! Ill get charge via the hour so I want to Save some money at the tuners!

Right Ive got a Dellorto DHLA 40H Carb on, the engine is a 998 with an MG Metro Camshaft, now it ticks over loverly, and at Full Throttle it pulls as it should. However at Part throttle to Full Throttle the engine jerks and stutters like its going lean? Now from what ive read this is called the Progression Stage? anyhoo this can normally be solved by upping the Idle Mixture, ive got the idle mixtures out to full (rich) and it makes no difference. Ive checked the size of the Idle Jets and they 58's which i presume are pretty large, the main jets are 160. Is it possible that my Chokes are just too big for the engine? Thus making the adjustment of the Mixture Pointless? Or is there more to it?

Any help would be great

Mike

Edited by MikeRace on 14th Mar, 2013.

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

Id say those jets need to be smaller,

The idle adjustment is just idle. Take it you dont know what engine the carb came off?

13.95 1/4 mile on a 2.95 fd. Carnt be that hard to beat!

No afraid not.

This is taken from a dellorto tuning site

The idle jets control the critical off-idle progression between closed throttle and the main jet circuit, it is this part throttle operation which is so important to smooth progression between closed throttle and acceleration and for part throttle driving

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

Id whack a nice fuel sipping 44 on there till u get it on the rollers.

There very awkward carbs

13.95 1/4 mile on a 2.95 fd. Carnt be that hard to beat!

mike make sure john has the correct jets for it befor you go, or if not, you may be able to take a few combinations with you

pm me when your going mike, i will come with you for the afternoon out if you wish

what chokes are in it mike ,and what cam in the engine .also what air correctors and emulsion tubes . is there any rpm point where it will respond ok when you tip in the throttle from a steady cruise ,and will it cruise steadily at all rpm ?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

if you have vizards book it tells you the correcty choke sizes required with different stages of tuning

Done now needs redoing lol

Not sure what chokes, it does it around 2000 rpm but its a lot worse at low speeds in lower gears, the cam is an mg metro

Here's a vid of it, it does it at 17 secs and around 43 secs


Check out this video on YouTube:

http://youtu.be/Y9DvjTP-mi8


At

Mike

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

ooo that sounds awful

Done now needs redoing lol

looks like either the idle jets are too small the acceleration pump circuit isnt working , or the chokes are too big . or its an emmisions carb with the small progression holes .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Right I've just been out to the car, I can't remove what I thought was the chokes but ill need to remove the whole carb so that's a job for sat, but I have a sneaking suspision that I have no chokes fitted, I undid the bolt on the side of the carb and slid out what I think is the aux Venturi about a 1/4 on an inch before it touched the bulkhead, a number said 7848.3 which is indeed the aux Venturi.

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

Get an SU on there!

If something is worth doing, it's worth doing half of.

Su's are for pansies

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

One would suit you down to the ground then.

Right then Chepattis!

Ive had the Carb off at Dinner to inspect whats what

Chokes - 32mm
Main Jets - 150 (Evidence of Soldering)
Main Air Corrector - 160
Pump Jet - 33
Idle - 58
Aux Air Jet - No Idea

Yellow Bible Recommends

Choke - 32mm
Main - 145
Air Corrector - 200
Pump Jet - 40
Idle Jet - 55
Aux Air Jet - 4.5

So the Carb isnt a million miles away, I think my next option will be to slap the AEM Gauge in it and do so proper tuning to see whats what......

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

Given that it's lean on accel I'd look to up the pump jets, that also follows true for the Vizard recommendations.

Yep thats was my initial thoughts, obviously the Lambda Will confirm this.

Ta

Mike

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

Reet Ave Fixted it!

I removed the Idle Jets and Aux Air Tubes and noticed there was a big difference between the hole. The Jet hole was tiny and the air holes were quite big, So I drilled out the Idle jets to about 0.8mm from around 0.5mm and hey presto the car drives nice and smooth now.

Ta

Mike

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

Noisy

If something is worth doing, it's worth doing half of.

You love it you slaaagggg

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

nice one

Done now needs redoing lol