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Setting up DHLA carbs?
pajsh - 31/3/08 at 09:17 PM

Having got my 2.0 pinto installed and running I need a bit of advice from anyone that knows about setting up DHLA's.

Running at a constant 2000 or so it's puffing back through the carbs ever 30 secs or so and simlarly backfiring through the exhaust.

I thought it might be timing so I hooked up my laptop but altering the advance seems to make no difference. So far I've not run it under load.

The carbs I have are DHLA 40H which I asked to be set up for a 2.0 pinto and they have

34mm main venturi's
148 main jets
7772.11 emulsion tubes
195 Air correctors
55 idle jets
Kent RL21 cam

I've read Des Hammill's book and Dave Andrews notes and Dave's notes say for 34mm venturi's

136 main jets
7772.5 emulsion tubes
186 Air correctors
50/55 idle jets

I've booked it in for a rolling road session in a couple of weeks but if anyone has any ideas then I might be able to get it a bit closer first.

Any advice gratefully received.

caber - 31/3/08 at 09:53 PM

Both those set ups are guesses, wait until you get it on the rolling road to fine tune it.

Caber

lotustwincam - 31/3/08 at 10:07 PM

Let me start of by saying that I am not an expert.

My experience is that when talking about the 40H's you can throw Des Hamill's book out the window.

The DHLA 40 H are a different beast from the earlier, non emissions carb. (The idle circuit is fed from the well and not from the float chamber).

My notes, gleaned off the net show that for a fast road cam, 2L pinto your existing jetting can't be too far off.
32mm chokes
148 main jets,
58 idle jets,
tubes 7772.11,
air correctors 210

Personally, I'd play around with the idle jets 1st, but don't ever expect perfection with these carbs and a long duration cam.

matt_claydon - 31/3/08 at 11:58 PM

Doesn't seem any point worrying if you've got it booked in, they will sort it out for you far better than you could ever do with guesswork. If you buy different jets now they will still almost certainly get changed at the RR so you will end up paying twice.

02GF74 - 1/4/08 at 08:52 AM

you've checked there is no air leaks on the inlet side? and that the thackery washers are done up correctly?

pajsh - 1/4/08 at 09:30 AM

quote:
Originally posted by 02GF74
you've checked there is no air leaks on the inlet side? and that the thackery washers are done up correctly?


I've got the rubber grommet types but I'm going to wind them up at the weekend. Following DH book I left about 1.5mm between the washers but I think they can go some more.

DH seems to contradict himself alot in the book. In one sentance he suggests a 2000 will need 45's with 38 venturis and then he says 40's with 34's will suit most road applications.

He says stear clear of emmision type carbs but then later says they will be OK on larger (2000) engines.

The guy (italian dellorto dealer) who set mine up thinks DH is wrong to dismiss the emission carbs.

cliftyhanger - 2/4/08 at 04:48 PM

The idle jets need to be bigger, at least 60, maybe 62 or so.
Also check the obvious, the vac takeoff is blanked off, and it doesnt have the little "nipples" attached for balancing the carbs.
Found the morgan carbtune to be excellent for balancing BTW, the RR couldn't believe how accurate it was when I took it in. Well worth begging one if poss.

Clive

pajsh - 2/4/08 at 09:08 PM

quote:
Originally posted by cliftyhanger
The idle jets need to be bigger, at least 60, maybe 62 or so.
Also check the obvious, the vac takeoff is blanked off, and it doesnt have the little "nipples" attached for balancing the carbs.
Found the morgan carbtune to be excellent for balancing BTW, the RR couldn't believe how accurate it was when I took it in. Well worth begging one if poss.

Clive


Thanks Clive,

Yes have blanked off the vac tubes but will bear the idle jets in mind.

Have studies the RL21 carb a bit more and it's pretty wild. Very early opening and late closing with a wide overlap. I guess I'm probably expecting a bit much given the long durations.