Dellorto Carb. Problem

[GeoffH]

I have a single side draught Dellorto 45 on my 1600 crossflow. It's been fine for the past 12 years and 65000 miles now I have an intermittent idle problem. Sometimes it idles fine, sometimes it's REALLY uneven. I discovered the problem is that in just one of the barrels, petrol drips from the progression holes thereby creating an overrich mixture on one side. But what's causing this!??!!

 

Someone told me to change the needle valve which I did and it's helped a bit but not much. I once had a fuel regulator in the line but took it off as I kept getting air locks. I have a mechanical pump.

 

I've no idea where to go next. Help!!

 

Geoff

[Griff]

I used to have an old Alfa Spider with twin Dellorto's which were a nightmare to keep in tune until I took the car to Circuit Motors at Castle Combe, which is a Dellorto dealer I believe. Can't remeber his name, but an old chap there has seen it all before and gets these well set up, rejetted and running a treat. Worth a try if you're ever down the M4 (they're about 15 mins from J17). Good Luck.

[Jez P]

Try Eurocarb in Reading (www.dellorto.co.uk) I'd be very suprised if they cant help!

[Mr Locust]

Have you checked the condition of the thackeray washers as they break and stop the springiness of the manifold / carb joint absorbing the vibration of the engine.

[CHRIS CLARK]

Dellorto's ? Bah !!!

Had the damn things on the Esprit S3. Nightmare to keep 'right on song'. Good luck!!!

[Mr Locust]

Geoff,

 

I had a problem like this on a Triumph engine fitted to my old Locust (now deceased, the car that is).

 

The engine was fitted with twin dellorto 45 dhla's which were supplied new to me only about 2000miles previously, so I was reasonably confident of the condition of the carbs.

 

The car ran fine except at idle whhich it wouldn't - it just died, but not instantly. Having gone through all the piece (at least twice) I moved onto the carb mounting arrangement.

 

The problem I had was along the lines of engine idles for a few seconds, then could be seen to start shaking (particularly the carbs) and the engine then slows and dies. The shaking of the carbs seemed to be upsetting the float valves and flooding the engine. New Misab seal plates and Thackeray washers sorted it out for less than about £15's worth of bits.

 

Observations from my experience on these capers (for what they are worth which may save time, aggravation and a nasty learning curve experience/scenario);

 

1. I Silver coloured (plated) Thackeray washers broke in less than 500miles because they were brittle. (Not properly de-embrittled if you are a metallurgist) So use the black, self-coloured variety.

2. Avoid rubber bobbin type Thackeray washer replacements - the rubber ages, goes hard and the vibration problem comes back.

3. Avoid plastic o-ring mounting sandwich plates - I found these more prone to resonant vibration problems at idle. Use the proper Misab aluminium and bonded rubber seal types.

4. It's worth balancing the carbs after you've had them off the manifold - just to get that super slinky idle. I was always able to get an engine with 285 cam, raised compression and ported head etc to idle at 800-850 rpm - smoothly! So it's worth a bit of effort. Gunson carb balancer is remarkably easy and about £15 - Halfords if nowhere else.

 

That is a relatively concise (? 😬!) idea of what to look for if you have the same problem that I had.

 

Keep us posted if you are still having grief

 

Regards

 

Ian Blakeman