Dancing Dellortos

[ken1967]

My brother has just put my engine back together on my Alfetta GTV after fitting new pistons/liners/gaskets.I bought a pair of overhauled Dellorto 40 DHLA carbs from Italy to replace the original Solex.With these fitted we started the engine for the first time since rebuild.The car started quickly but the engine is jumping around more than Mick Jagger and some fuel is leaking on top of the carbs,from the fuel banjos we think( the guy in Italy says to check the banjos for any dirt or dents).As far as I know, all the carb gaskets would have been replaced.We have still to check the banjos out.My brother is wishing he had fitted the original Solex carbs to the car so he would know that the engine was fine.I am going to buy the Carbtune Pro from Morgan Carbtune in the UK to try and tune the carbs.Neither I or my brother have ever tuned carbs so I hope the Carbtune is easy to use.My brother had read somewhere on the site about people having to advance timing on an engine to get it to work properly with the carbs.Is this something that has to be done? or will the 4 column synchronizer be enough to do the tune? I have read it is a great product.One other point,when you increased the throttle the engine shook less and I drove the car at 70mph yesterday but with the Sprint airfilter(also new addition) fitted it sounded more like a VW Beetle at lower speeds.

[alfa-franzz]

Have a look at this page!
Slection and tuning of Dellorto DHLA carburettors

[Alfajay]

ken1967:

Your fuel leak, and your shaking around at idle are most likely two separate problems.

The fuel leak is just plumbing. Yea, there may be dirt or a nick in one of the brass washers that the banjo fitting mounts with. Disassemble, inspect, replace, retighten, ... This stuff isn't rocket science, especially once you narrow down WHERE it is leaking from

The shaking at idle is probably incorrect synchronization between the two carbs. As your engine idles, it has two cylinders with the throttle 5% open, and two with it 10% (or whatever) - naturally it runs erraticly. I don't know what a Carbtune Pro is, but just placing a 1m length of 8mm tubing in the carb inlet, with the other end near your ear, and listening to the loudness of each intake will tell you which one is open too far. That article that alfa-franzz referred to describes how to do this.

You said that the Dellortos were rebuilt, but didn't say if they were jetted appropriately for your engine. Again, the article talks about calculating jet sizes. EuroCarb there in the UK is a Dellorto specialist, and can supply different jets if you need them.

[1,6 HF]

Jay's right--there are 2 problems, and the shaking is almost certainly a synchronization problem. For synchronization, I tend to come down in between a complicated device like the Carbtune Pro, and 'wet finger--stick in air' approach of a length of hose. I'd suggest a simple airflow meter, as mentioned in the excellent article that alfa-franzz recommended.

[ken1967]

Thanks guys,I have saved the article refered to by Alfa-Franzz.I know about Eurocarb in the UK.The Dellortos came from the seller Alfa1750 on Ebay and I had a choice of venturis and opted for 34mm.Do not have a clue what the other jets and emulsion tubes are on these carbs,but he knew it was for the 2ltr twin cam engine.Just bought a colourtune combustion tester,which screws into the spark plug socket and allows you to see the flame colour so you can adjust the carbs by flame colour for best mixture.

[alfa-franzz]

Maybe you need this file. Rename it jetting.exe.
Gives you the size of jets and emulsion tubes.
(First time I attached a file, hope it works)

[Ennio]

I would break in the engine with the solex, then install the Dellortos. You shoudl first adjust timing, then balance carbs (by ear, carbtune, synchrometer) and then adjust mixture (with colortune).

You may look at this thread:
Synchrometer type

[Jahirul]

Can Dellorto 40 DHLAs be bored out to 45s and would all the chokes and stuff from a 45 fit on the 40s if I bore them out.

I have previously had my Solex units bored out to 45 and they worked fabtastic.

[PSk]

Before putting carbs on any engine you should manually ensure that all adjustable parts are set exactly the same. Again not rocket science, but to just put them on assuming they are set the same is not a good idea.

Then it simply becomes a process of making EXACTLY the same adjustment to each setting to get the engine to run right ... because you started with a balanced set of carbs. Yeah sure, use the fancy tools but if the carbs (and engine) are rebuilt then they should run well with pretty much with the same settings.

Most people make a complete mess of balancing carbs because they are all over the place with adjustments ... should be quarter of a turn on first choke, and then quarter of a turn on the other 3 ... let the motor settle, and try again if necessary. Always keeping adjustments the same on all 4 chokes.
Pete
ps: Also if you have not confirmed that your ignition and camshaft timing settings are right ... please do that before touching the carbs again!!