I bought second hand IDF's three years ago and fitted them to my bus. Then, last year had a rolling road test which seemed to verify everything was about right altho in all honesty the guy didn't have much in the way of venturis or jets to try different set-ups so I was a bit suspicious! The bus runs pretty well but with that little hesitation and with a little spit back in carbs especially when cold - these things seem to be very common. The fuel consumption is not great at only about 20mpg and I have noticed variations between my set up and those which seem to be recommended by the experts. In particular the venturi size on mine is 32mm, mains 140, air corr 220 and idles 45 whereas most experts recommend 28 venturi, 130 mains, 200 airs and 55 idles. I guess that with a biggger venturi then it makes sense to have bigger mains to keep the air-petrol mix the same but do bigger venturis also affect the idles? I suppose that as the idle circuit is the one in use most of the time (?) it is these jets which are more critical? Are there any advantages in having bigger venturis (and consequently bigger mains) in the first place and do larger venturis and mains affect fuel consumption? I was thinking of trying out the smaller venturis and reverting to the above recommended set-up but would I gain anything from doing this?
My understanding is that smaller vents results in higher bottom end torque, better response on pick up at the expense of reduced mid range acceleration and lower top speed! But someone who actually knows will be along soon. I was advise 34 vents for my dells, bought em and now im probably going to go for 30s
not too sure wether the jet sizes are a direct comparison from webbers to dells , ive 28 on my 1700 and i know a few who have 30 vents on 2litres , i started off with 30 but had a flatspot , changed to 28 and gradually increased main jet (now 124) and shes good ,
Steve,Hi. Are you saying that your flatspot was caused by too small a main jet or do you think it was the mix of venturi and mains? What sort of fuel consumption do you get overall - I've seen some people claiming 30 mpg but I suspect this is optimistic or not measured properly!! Interesting that your 1700 venturis are specced the same as a 2l but the mains jet is somewhat smaller - to be expected perhaps on slightly smaller engine? What idles do you have, 55's?
when you think of the vent size on a 2 l with twin solex its smaller than 28 and there is only one per head , usual rule of thumb with dells is your main jet is x4 your vent size + 1 size so 28 vent = 114 main jet 30 vent = 122 etc i started with 28 vent and 114 main and increased this till No hesitation or flat spot and ended up with 124 main ..... The dell superformance book states 180 airs 55 idle for all air cooled and .2 emulsions . I `ve not measured MPG if it was me i`d go 30 vent ... isn`t there a webber tuning book or web info ? So any sujestions as to what to fit in my supercharged dell 40`s ?
This says it all... go somewhere else, and talk to them before spending your cash!! Most rolling road places won't mind you airing your concerns before they do the work!! A mate of mine had his but RR'ed a year ago... said awesome job, then started grumping at me about it not running right... he took it somewhere else, and it turns out the guy had drilled out his idle jets (big no no) and not had any to swaps on the shelf to do the job properly!! 2nd place sorted him out, and now he's running a treat!! Engine size?
