Technical 650 Carburation ?

Currently reading:
Technical 650 Carburation ?

SPA

Member
Joined
Jan 8, 2017
Messages
38
Points
63
Hello. Hoping for some advice! We have a 500 with a 650 engine fitted with a 30S2H carburettor.
Firstly - is this a good set-up or one to change?
What is a recommended alternative carb?
Do we have a standard surface on the head to attach to or has there been any modification?
I know nothing about the internals of the engine, but no reason to suspect anything but standard.
And final question - anything else we should be aware of with regard to carburation?!
TIA
 

Attachments

  • IMG_3010.JPG
    IMG_3010.JPG
    157.2 KB · Views: 80
  • IMG_3011.JPG
    IMG_3011.JPG
    143.3 KB · Views: 24
  • IMG_3012.JPG
    IMG_3012.JPG
    143.3 KB · Views: 30
  • IMG_3013.JPG
    IMG_3013.JPG
    118.2 KB · Views: 32
As far as I can see from the photo, no modification has been carried out on the cylinder head in order to fit this carb. It does however, seem to be a big carb for that engine. Did it come with the engine? If it did, there is an evens chance that the jetting is correct. If it has come as a 'to be bolted on' modification, I would suggest that you find out what engine it came off in order that you can find out what jets etc. are fitted vis-a-vie what you will need for the 650 engine.
Alternative carburettors?----strewth, where do I start? This can be quite a contentious subject! Personally, and from my own experience, I think that the best alternative carb for the 650 engine is the Dellorto FZD--30/24 or 30/26 for a standard engine, 32/28 for a tuned engine---single, simple, fairly light and stay in tune. The downside is that they are now getting rare although if you are prepared to spend some time trolling through the Italian sites, they are still available. A word of warning--there is a 'Chinese' copy on the market, discernible by the lack of the word "DELLORTO" cast onto it---do NOT buy one of these under ANY circumstances--you WILL have problems! Alternative carbs include the Keihin and Mikuni bike carbs (manifolds available 'over the counter') and the Dellorto OVC 34/30D (must be the 'D' variant)--a sort of side-draught FZD, and still available NEW! If a 'twin-choke side-draught' carb floats your boat Weber, Dellorto and Solex all make versions for which inlet manifolds are on the market. The Dellorto and Solex carbs are substantially lighter than the Weber, and their venturi sizes (29 and 30mm) are more suited to the 650 engine. All the side-draught carbs require supports, again easily available. Lastly, and not to be ignored, is the standard carb that Fiat fitted, the Weber 28IMB. Yes, it is a simple carb but for a standard engine it will do its job perfectly adequately. All carbs are, to a greater or lesser degree, a compromise between performance and economy---"yer pays yer money and picks yer tune"
 
That carb was fitted to some of the 704cc Fiat 126 Bis models so could well be OK as it is. That type of manifold is a more recent design so it will not be an old conversion. The vacuum part will not be required. Whoever worked on the engine I can see fitted an alloy rocker cover and dome nuts on the head so they may also have made internal modifications complimented by the carb. The other carb that would fit that manifold would be the 30DGF or the older and simpler 30DIC.
 
Thanks for those words! Gives me something to look into. As per TOSHI975 post, I understand this carb comes from a 126 BIS model, and it does not seem a too common a fit for the 650. It seems to run ok - thought I have no reference of alternatives! It is a very tight fit to the underside of the rear shelf and doesn't give many options for a filter. I will get round to having a look inside the engine to see what is there but my knowledge levels are starting from zero so it may not help! I did think going with a simple 28IMB as a starting point may be a good idea, but a twin choke side-draught def floats my boat to a greater extent!
Thanks again - and there may well be more questions once I've done some digging into the options you describe. Don't want to over complicate things so I'm likely to opt for something fairly accessible.
Cheers
 
You can buy 'spacer plates' which go into the rear engine mount and will lower the engine at the back. However, the thickest spacer is only about 12mm, so whilst it will give you clearance at the top of the carb, it may not be enough for a filter.
Be careful regarding 'side-draught carbs' they aren't cheap and require some careful setting up (don't forget the carb support). Ask away with your questions, that is what the Forum is for.
 
I have to agree with the Hobbler that if your knowledge of mechanics or about what lies inside your engine is limited then the side draught twin choke carb is definitely the one to avoid. The Bis carbs do not have a very good reputation partly because they have a tendency to fall apart plus although they are a progressive twin choke carb the venturies are restricted which may be ok for a standard 650 engine but lack potential on a tuned engine. The Weber 30DGF carb from a Panda 30 (not Bis) is a better carb and will fit that manifold but hard to get. Only other option with that manifold is the Weber 30DIC, also rare. Easy to fit a standard carb there though if you have problems with the carb you have.
 
Back
Top