Dellorto DHLA Carburettors - discuss / tune /fettle?

[anthony1956]

nice to have company 🙂

current battle is with accelerator pump dribble, which is screwing up my attempts for excellent emissions... over in my "blog" thing 

 

Edited September 8 by anthonym

[Andrew Gilbert]

love talking carbs, but I'm only Weber and SU I'm afraid and even then its rudimentary stuff for me, having just refreshed the webers on my xflow with new gaskets etc and a general clean up with copious amounts of carb cleaner to clean stuff up internally that have been standing for a few years. Am expecting a first fire up in 2 to 3 weeks then set them up and go from there.

[jbcollier]

Still haven't seen an actual question.  Here are some general comments:

The accelerator nozzles are close to the throttle plates so you won't easily see much if you pump the throttle while looking in the bell mouth.  They are best checked with the carbs off.

You have set your fuel pressure, great.  Now take off the gauge and fit a plug.  Gauges can leak and then the car burns.

I have set up many a carb and carbs from scratch.  It isn't easy and it isn't cheap as brass costs $$$.  On one set-up, I went through 4 emulsion tubes before I found the ones that worked best.  That's 16 emulsion tubes.  Best is to have a baseline that you just need to tweak for your local altitude and climate.

Get an air/fuel ratio gauge.  Even the good guys got it wrong back in the day.  An A/F-R gauge goes a long way to making it almost easy.

[anthony1956]

12 hours ago, jbcollier said:

You have set your fuel pressure, great.  Now take off the gauge and fit a plug.  Gauges can leak and then the car burns.

 

yes, just need to find the plug...

[anthony1956]

12 hours ago, jbcollier said:

Get an air/fuel ratio gauge.  Even the good guys got it wrong back in the day.  An A/F-R gauge goes a long way to making it almost easy.

celebrating today, got a consistent reading: we need CO2 >8 CO <4 HC< 4000

I had these better, lower HC several months ago before the recent several months hiatus. We have 6 plugs in, not 7s. Have wonder about using 5s.

Also wondering how to establish exactly what degrees BTDC we have given we are happy the car works at all but I can't help wonder if a bit longer to do the burn might help. As you can see 02 is under .9 so we must be running rich. 

Jets wise etc I am sticking with what we have, no changes regardless; it's been like this for nearly 40 years and I do not wish to interfere with it. Maybe when I get the hang of it all I might play with changes for altitude, but not for now.

The rpm in the image is 1035 

Edited Saturday at 15:33 by anthonym

[anthony1956]

12 hours ago, jbcollier said:

The accelerator nozzles are close to the throttle plates so you won't easily see much if you pump the throttle while looking in the bell mouth.  They are best checked with the carbs off.

Did both, including measuring cups .In thE end the problem was ballbearings located on top of the weights instead of under. Fixed that, no dribbling. e

Edited Saturday at 15:25 by anthonym

[anthony1956]

12 hours ago, jbcollier said:

Still haven't seen an actual question.  Here are some general comments:

Lots of them, but none in this thread where I was just wondering if anyone at all these days engages with carbs. I tend to put most of my stuff in the blog section https://www.caterhamlotus7.club/blogs/blog/69-anthonyms-blog/  so I don't lose it for ongoing reference. These days I tend to do both, a thread then a blog or even both at once, as blogs don't seem to get the attention. 

 

Edited Saturday at 15:29 by anthonym

[anthony1956]

3 minutes ago, anthonym said:

Here are some general comments

Thank you for even trying to engage when it seems you haven't seen much afoot. 

[Ivaan]

Hi Anthonym,

Is it possible to make adjustments for altitude whilst on the go? 
When touring in the mountains, mine struggles with power loss and miss firing. I guess the AFR gets too rich at higher altitude when set up for mainly use at sea level.

[anthony1956]

19 minutes ago, Ivaan said:

Is it possible to make adjustments for altitude whilst on the go? 

ah well now! I have bought the jets but not yet experimented. Des Hammill writes that the emulsion tubes will not need to be changed, which saves significant bucks. Buying jets etc is NOT cheap. Couple of things strike me you could try; good old guess work and lean the mixtures, given you are only passing by seems like the simplest. Beyond that are various AFR (not really sure I like that acronym as it suggests i know more than I do) so, Air Fuel Ratio, i.e. the mixture in my language, devices you could carry. 

Gas analyser (dead easy to fit), Carbtune Pro (mucking about with screws to fit), Gunson Colortune (changing spark plugs on a hot engine TWICE, did this today.. still reflecting.)

Methinks none of all those are what anyone will want to carry and learning how to lean and re-richen the mixture is the way to go. 

Anthony (is it your old sixspeed I have? goes well.)

[jbcollier]

Lots of questions now.  Increasing ignition advance for a more efficient burn.  Advancing timing also increases the amount of time for heat to soak into the pistons and head.  So, it's a balance.  I think you have a BDR?  They have a pretty good port and chamber design and run well on less ignition advance than "normal".

Whether you need to rejet for altitude depends a lot on your state of tune.  Full race engines go off song if the sun goes behind a cloud while more pedestrian engines can run the same jetting from sea level to 5K feet.

Gas analyzers are great for getting your tailpipe MOT happy.  For actual tuning, an air/fuel ratio gauge is better choice.