Carbie Problems

[GiuliettaJewel]

Hello All,
I have been a member for some time, but just have not found the need to post about anyhting. so maybe i will start with what sort of car i am having the problem with. I own a 1985 Giulietta 2.0L Sedan, my problem is that my carbies apparently are not working properly, (i run the Del orto twin carbs) now when i accelerate around 2000rpm to 3000rpm the whole car vibrates very badly. i have been told this is something to do with the fuel getting to the engine. i have tried numerous carbie cleaners, new fuel filter (which was filthy), blowing out the pump jetts, and numerous other things. so right now any help would be great, otherwise im up for new carbies..

Thanks

[papajam]

My first thought is, is the ignition system in good order?
90% of all carb problems can be traced to something other than the carbs.

[alfa-franzz]

Check synchronisation maybe? Easy to check by looking at the progression holes. You should see the butterfly at the same location on both pairs. They are covered with a blanking screw. Checked the mechanism of the balance lever?
My guess is synchronisation, on one pair main circuit will open while the other pair is still on idle circuit. On higher revs both pairs are working on main circuit and engine works better.
Also full acceleration will work better since butterflies are fully opened.
My experience if it is the jetting, it will often be more like a "hesitation" when accelerating.

[GiuliettaJewel]

Hey Guys,
thanks for your replys,
since i dont know much about the carbies on these cars, alot of that was jibberish to me . however i did have a chat to my mechanic, who said that the factory settings had been played with and he said they are hard to get right again...

is this true? or has my leg been pulled?

Many thanks again

[alfa-franzz]

No, it is not that difficult. Only time-consuming....
First check sparkplugs and all wires for ignition and check that ignition advance is correct. When all ignition related parts and adjustments are OK start with the carbs. Without good ignition you can't properly adjust the carbs. Do the sparkplugs look good?

Check for airleaks between the carburettor and intake manifold also. Often you can here a whistling sound at idle if there is an airleak.

There is a "support-rod" for the carburettors with one end at the engine mount and the other end connected to the carbs. If this support is not good the carbs will vibrate to much and can cause strange things to happen. Can be an idea to look at the end with a rubber bushing, do you still have any bushing? Is it healthy or worn out?

Here is a good link Slection and tuning of Dellorto DHLA carburettors

You have "how to do" and a plan view of the DHLA with all necessary adjustments. I guess you don't have any Airflow meter or Carb synchroniser, but you can see the edge of the butterfly through the progression holes. Just look and see if the edge is located at the same place on both pairs. If not you are out of synch between the pairs. If needed, adjust as good as you can.
For real finetuning you need a tool like Carb synchroniser, but with eyes and ears it can be good enough.

Is it a standard engine with DHLA 40? It should be no problem. In worst case
new rubber mounts and gaskets, new main needle valve maybe.

[pathung]

Sounds like a timing problem to me; wonder if he got it sorted out?

[Alfajay]

Alfa-Franzz had written: "I guess you don't have any Airflow meter or Carb synchroniser, but you can see the edge of the butterfly through the progression holes. Just look and see if the edge is located at the same place on both pairs. If not you are out of synch between the pairs. If needed, adjust as good as you can. For real finetuning you need a tool like Carb synchroniser, but with eyes and ears it can be good enough"

I have had very good luck using a length of tubing + my ears. Sure, a meter is better, but listening for the same loudness of hissing across the intakes is a great way to get the carbs synchronized. I've never had much luck with seeing the progression holes through the little windows.