Is there a Dellorto guru in the house?

[elansprint71]

For some reason I can't put my hand on my Dellorto manual and I can't find an answer in the archives to a recent problem which has manifest itself.

I'm experiencing a slight juddering when in the cruise, from approximately 1500 rpm to 3500 rpm, I suspect that a progression hole might be blocked, it almost feels like it's running on 3 cylinders, or, more accurately 3.5 cylinders. As soon as the acceleration pump comes into play we're back to normal.

Can someone point me to which jet is the most likely culprit, before I pull them all out? It's so long since I needed to tinker that I've forgotten what does what on the Dellortos.

[Lotus fan]

El Pres.

According to the Des Hamill book :-

Low to mid range RPM.

If the main jet is too small the engine will not produce good power anywhare in the range.
An excessively lean overall mixture will see the engine missing and backfiring through the carb chokes under load.
Continue to increase the main jet size as long as the power keeps going up.
For 'flat spots' or hesitation check the accelerator pump jet sizes.
Firstly, increase the pump jet by up to 5 and see isthis improves the situation.
If this works to a very small degree and the misfire or hesitation is still present but now slightly higher up the rpm range,
the problem is not with the accelerator pump jet, so go back to the original size.
What is happening in this scenario is that the accelerator pump is masking the real problem.
Next change the emulsion tube for a richer one.
If the emulsion tube is wrong for the engine it will show up during acceleration.
With the engine in top gear, accelerate the engine slowly from 3500rpm (or from the rev range the engine comes 'on cam'),
slowly so that the engine does not get a fulll shot of fuel from the accelerator pumps.
If the emulsion tube is wrong then the engine will 'stumble' then clear as the revs rise.
This 'stumble' is caused by acceleration phase leanness and a richer mixture can be provided by changing to an emusion tube
that will supply a richer air/fuel mixture.

Or put simply........... shite in your emulsion tube



P.S. completed engine and gearbox now back in chassis


Ian F.

[elansprint71]

Thanks Ian... so which is the emulsion tube? Actually I've just found some supplementary pages in the Lotus manual which give an exploded diagram of Dellortos, I didn't know that was there. Tomorrow I'll pop the Colortune in and see if one cylinder is burning a different colour. Faiuling that.... I'll pull all the gizmos out and clean them.

So; your engine is back in, will we see the car at Gawsworth?

[Lotus fan]

maybe Gawsworth 2013
need electrics, build body and furtle around with other bits !!!
but I do see the light at the end of the tunnel.
my new job helps 'cos I can work on the car in the week too

[elancoupe]

I would suggest sending a PM to Esprit2, he is extremely sharp on Dellortos.