vibrating_cake

im having problems ajusting my carbs right (so its goo enough to drive to the professional tuning guy)

car:::: 2.0 pinto with twin dellorto DHLA carbs on std dizzy with vac advance fr32 cam
the problem is on idle and acceleration the centre 2 carbs spit out as if they are underfuelling, with a loud noise similar to the sound of an exhaust manifold thats unseated itsself....but the outer two run perfectly fine (or so it seems)
am i right in thinking that it is the float chambers that are set wrong? as the single left hand barrel runs fine and the single right hand barrel runs fine.
i have also tried ajusting the idle jets to richen the fuel on the 2 centre barrels that are spitting, and this seems to be doing nothing???

any ideas?? i dont want to be running it so lean and so noisy for 45mins to get it to the carb centre to get it set up correctly?????

tabetha

Firstly, take OFF the vac advance, as you cannot run with this, the pulses from the venturi will be kicking the ignition back and forth, I used to run these barbs on my celica RA28, with Yamaha engine.
The floats feed both the venturi's on each carb, are you using MISAB on the carbs, these suffer terribly from vibration upsetting the mixture with fuel frothing very common, they MUST ABSOLUTELY NOT BE AFFIXED BY NORMAL NUTS TO THE INLET manifold, they need a spring cups arrangement, so you should be able to grab them and move them up and down a good 2".
tabetha

vibrating_cake

yepyep got them on rubber gaskets which are about 3mm thick rubber rings on either side of a gasket kinda thing, n then they have the brass cups with rubber bits in middle arrangement tightened down so theres ~1mm between cups on all cups

900ss

They shouldn't be rigid true, but surely 2" is way ott

If it ran fine before you fitted the carbs then its them at fault. Spitting back? to me says running weak so check ALL the jets?
Just a thought, have you checked all the jets are the same and not mismatched sizes?

tabetha

2" a firm tug should see a deflection up of 1" or close to it and the same down, measured at the extremity of the carb, sure that's what I used to use, with a 3mm gap.
tabetha

vibrating_cake

not yet haha, just unscrew them out all the way and check if the numbers match??
n if they match what else could it be?
they look to be fuelling somewhat, just spitting it back out

Turbosystems

iTrader: (5)

you have your answer here

vibrating_cake

the answer to that is yes i have misab plates with all the rubber bits n bats, n tried it with vac advance off and its still spitting

vibrating_cake

oh yea and are jets on dhla 40's interchangeable with the ones on 45's (as i have a full set of jets that ran fine on the 40's... just for a try if the jets on the 45's are too weak or mismatcheD?

Turbosystems

iTrader: (5)

you will need a modified dissy i would say your ignition timing curve is wrong for these carbs

vibrating_cake

ive had the car running fine on twin 40's idle-7k
swapped the carbs for 45's and its spitting through the ignition on tickover (only tried up to about 3k as i dont wanna push it with the noise it makes!
so does the dizzy have to be changed when changing carbs between 40's and 45's?

Turbosystems

iTrader: (5)

you need the correct ignition curves a standard dissy curve is no good
ring your professional tuning guy and ask him he should be able to sell you a modified dissy for your set up if he still does carb tuning

vibrating_cake

and where can i get these modified dizzys approximate prices etc?

Turbosystems

iTrader: (5)

as above it has been 15 years since I did this sort of work

Rod-Tarry

Twin Dellorttos that takes me back, I used to take mine to a little old guy who always wore a flat cap (Fred Dibnah lookalike) I swear he was at least 90 at the time. He would fiddle about, adjust , listen, fiddle somemore & they would be perfect, a real expert who could not retire because he was still in demand. Great carbs but nasty to get just right.

Turbosystems

iTrader: (5)

was he your younger brother Rod

ian sibbert

We have use H & H for perfromance dizzy's in the past, good service and very helpful...

http://www.h-h-ignitionsolutions.co.uk/index.htm

In respect of the carbs, well the fault could be difficult to pinpoint over the net, you ideally need to ensure they are specced correctly for your motor. The fault could be incorrect sized idle jets, worn or incorrectly sized chokes, air leaks et etc.....

Have you tried the car under any load?

Have you used a synchroniser?

Check that any of the jets havn't been soldered up and re-drilled....

A good base setting for the idle mixture is to screw them fully home and back them off 2.5 turns.....

The float height IIRC is 25mm from the large end of the float to the underside of the casting....

I'd doubt the floats are your problem though....more than likely to have a split MISAB or its drawing air in or some old tired carbs that need an overhaul.....use some WD or similar sprayed around the seals, if the engine note changes as you spray, you have a leak....strip the carbs and publish the sizes of the idle and main jets, choke sizes etc might give us more of an idea...



Or tow it to the carb centre....

vibrating_cake

ive swapped over all 4 jets for the ones i used in the twin 40's and the centre 2 carbs are still spitting back out (now with vid)
where should i be squirting the WD around which seals?? the seals to the manifold are brand new and ive cleaned up both faces before sealing these.

erm the carbs spit and make the noise like exhaust manifold bust. but when i cover the 2nd carb from the bottom this stops (on idle) but anything over idle the 3rd from bottom spits and makes the noise too
but when i cover this one it quietens down on tickover aswel.

vibrating_cake

riight

jettinggs for the 45's

35mm chokes
130 Main jets
7772.5 Emulsion tubes
110 Air corrector
4.5/45 pump jets?
7850.6 Idle jets
and i dont know where the aux vents are....

they should be ok if... the main jet assembly (from top to bottom) goes
air corrector,
emulsion tube,
main jet

and on the old 40's i used to use

30mm chokes
105 Main jets
7772.5 Emulsion tubes
180 Air corrector
4.5/45 pump jets?
7850.1 Idle jets.


if im in need of re-jetting would it be a good idea (while im there) to replace the 35mm chokes with 38mm chokes, or wouldnt this make much difference... at all for the cost?

ian sibbert

36 - 38 mm chokes
1.45mm main jets
350-475cc emulsions
180 air correctors
40 pump jets
.50mm idle jets
4.5 aux choke

That would have been my estimate, dependant on the amount of head work you've had done....but 35mm mains should still be ok..

My experience is mainly in weber's though, not dellortos but they are largely the same.

I still think it's drawing air in.....is the linkage setup ok, is it operating on the right carb first, not on the balanced one....

Squirt the WD round the MISAB seals and i'd try round the spindle's as these might be worn, do you know the history of the carbs?

The main chokes might be slightly shy, but they are better that, a higher air speed will promote better atomisation....too big and only mild modification could cause you more problems....

vibrating_cake

not much headwork has been done, nothing too major atm
the linkage setup is all worked in and theres a slight tension on the opposite set of carbs to the set with the idle screw (so the opposite set opens approx the same degree as the other ones on the main spindle) and the carbs have just come off a 2.0 and been cleaned up well. not got any new gaskets on but the ones on it (bar one aux jet/choke i had to replace cause i ran it along the threads when i took it out)
erm i think i give up, just tow it to the carb centre lol!
thanx for ur help.

p.s. how much is the dizzy going to help? once its jetted etc and running on the std dizzy, is it just a case of swapping for a new mechanical advance dizzy (maybe a piper item) with no vaccum advance and just setting the timing up with a strobe to make it run as good as it did again... just with better timing all the way up the rev range?

900ss

imo to get it running so its usable it isnt.
Unless your dizzy is fooked or you have an ignition prob a pukka dizzy isnt going to cure your 2 cylinder misfire.
I run that setup on 40's and a fast road cam + std points dizzy, then a std sierra dizzy and was able to get it to idle n be drivable.
Even if it that isnt the perfect answer your engine should be able to idle n rev ok with what you've got!

900ss

Just watched your vid again
You sure you ant got those HT leads around the wrong way

EIL132

Would check ignition, had this mk2 S running splits and it was similar. Turned out to be the leads! Sounded a bag of nails and misfiring like you wouldn't believe, smoking, fouling on different plugs, spitting carbs, etc.

vibrating_cake

it was the headgasket between cylinders 2 and 3 bout a 2hr job so not as bad as i expected.
really does make sence after thinking about it

thanks for ur help guys

vibrating_cake

woo

900ss

And 3 n 4 by the looks of that
Glad you sorted it