1980 Spada 36mm Carb Upgrade

I am considering changing the standard 30mm carbs on my Spada for 36mm pumpers from a Lemans. I suspect it makes them harder on fuel. One of the things I like about my Spada is the excellent fuel economy, I can get up to high 50s MPG on normal riding (ie for me usually 60 - 70mph) Has anyone got info on how much the larger carbs affect fuel economy relative to standard carbs.

Many Thanks


ONE THING I NOTICED WAS IT WAS NOT VERY GOOD AT LOWER REVS and i felt even when giving it a lot of right throttle i did not notice any differance in performance as you are restricted on the spada valve sizes and diameter of inlet ports etc used to pop and fart a lot as well took them off and fitted standard 30 again much more enjoyable

Thanks for that Ex smokingbiker. I once got a spin on a stock Spada with the 36mm carbs fitted and was impressed by the performance, so was hoping to get the same result with my bike?? Obviously impressions can be deceptive especially over time and I don’t want to spend a load of money and time etc fitting them if they are no benefit.



Only my impression will be costly as the carbs are dear i let mine go a month or so ago for £150 and that was cheap i have seen them go on ebay for well over double that figure you would need the bigger inlets and some 8mm to 6 mm studs to fix them on with regards ray

 I did the exact opposite in 1989.    Swapped carbs on my 850 LM1 engine to the VHB30 flat/square-slides type.    Reason, I'd just gone self employed and money was tight, I think also there'd just been a price hike at the pumps.     The year before I'd done a week's touring in Cornwall with a pillion and it was 30 mpg. Must have been due to all the narrow twisty roads and holiday traffic. I thought that was rediculous for a bike, hence the carb swap.   Fortunately I just happened to have 3 VHB's in the shed to play with, AND a pair of new unused K&N's for them, so only needed the corresponding inlet stubs.    Got a whole round extra 10 mpg, went from 40 mpg to 50 mpg (average).    So I would say not worth it, IMHO.   HTH    PS (edit):  you probably won't get more power just doing that either, will probably need the LM style less restrictive silencers as well. So lotsa money involved, and will it be worth it in the end?  

Mike H2014-08-30 14:26:12

Yes I remember that too, and initially I was very surprised, it being 948cc and all. I also seem to remember frequently ringing its neck like a 2-stroke to make it 'go' ...

Mike H, Thanks very much, very useful information!! I will have to consider very carefully before going ahead with the big carbs!


Agree with Ray, have had both…aint worth it…

You could try a pair of 32mm mikuni’s, the improved carburation will make it feel smoother (and faster?) but not effect mpg