CARB FOR A FIAT TWINCAM

[samuria]

which is the best carb for the 2liter engine, for descent power without the price tag

[bmcecosse]

2 X SUs ??

[Innovator]

Another vote for the twin SU`s.

They were such an improvement over the standard carb.

[ratrodmog]

I third that. And I know that someone on here made the manifold to connect it all up

[samuria]

thanks, which carb will bolt striaght on???? its for a mate and he doesnt want to go changing the manifold,

[bmcecosse]

You asked for best carb, descent(sic) power and without price tag. Only SUs will satisfy all that. Otherwise - I guess you are looking at a Weber of some kind! A picture of the inlet manifold would help us!

[MartinB]

You are only really going to get decent power gains by going multiple carbs, better still one choke per cylinder (twin DCOEs) but I guess you already know that.

If you want to simply bolt on to the standard manifold then I don't think there is one which will be much improvement over the standard carb (with K&N filter etc).

If you can do your own fabricating, I would be tempted to try some bike carbs. I was surprised how driveable bike engines are from 3000 rpm to 11000 rpm (ZZR1100) in my Radical (race car), there was no peakiness of power delivery at all, just smooth power all the way. A lot of that is down to the carbs.

The carbs tend to be needle jets (much like the SUs) rather than the fixed jet (DCOEs). The carb spacing may need to be altered slightly but I don't think it would be too far off if the carbs came from a big bike. The 1100 bikes also normally come with around 40 or 41mm carbs so should easily be ok for a 2 litre fiat in fairly stock spec.

[samuria]

thanks guys, my mate only wants to bolt on a carb so he can use the car as it doesnt have a carb, when he bought it it had some expensive carbs on which the guy kept. he was told a weber was quite good but he has forgot which one to look for? thanks

[bmcecosse]

Well - likely a DCOE 40!

[samuria]

he rang the guy who sold him the car, he said it was a weber 32/36 df. that was on it when he first had it? mean anything to you guys

[PSL184]

I'm sure I have a 32/36 in the stash somewhere. I'd have to check but I'd be looking for £150 and that would guarantee a good 'un....

[bmcecosse]

That's a twinchoke downdraft carb - nothing special! Only the DCOE and IDA style Webers are considered 'good' . A picture of the inlet manifold is required!!

[Jon H]

PM sent...

[dp]

Do you still have a manifold or do you need a manifold and the carb?

If you have a manifold that looks like this:



Then a standard carb is the Weber DGV as used on a Ford Pinto engine (Cortinas, Capris). RRP new is about £220 from Webcon.co.uk - sorry, I sold off mine last year. Keep an eye out on Ebay - you'll probably need to jet it to suit the Fiat but it'll probably run on fitting

If you have a manifold that looks something like the one on this link (best I could dig up):

http://www.watsonsrally.co.uk/products/products6.html

You need Weber twin 40s or twin 45s which are more performance orientated.

If you have to buy a manifold, have a look at bike carbs. I mean compare the cost of carbs and manifold to that for a Weber and manifold.

From my own personal experience, when I fitted bike carbs with a ballpark jet & a slightly hotter cam (which works against smoothness) the engine idled and picked up smoother than it ever did on the DGV.

Pros:
bike carburettor development only stopped a few years ago while Webers are '60s technology.
second-hand bike carbs will be cheaper and probably less worn than second-hand Webers of any sort. Ie you'll easily pick up a set just a few years' old. Second-hand Webers will probably need a rebuild.
Simpler design, easier to tune as only one jet to change.

Cons
You'll have to get a manifold made (bogg brothers will make you one)
less people know how to tune bike carbs, lack of data available.
negativity from traditionalists and people who haven't tried them.

Mine

[MartinB]

Looks good dp, did you have to alter the carb spacing to suit the Fiat head?

[dp]

Looks good dp, did you have to alter the carb spacing to suit the Fiat head?

No, you can do that but it's a lot of intricate stuff to make up if you do; not just butterfly spindles & chokes but fuel tubes between carbs.

My eventual solution was to have a manifold made up (Bogg Brothers) but the interim was to use a Lancia injection manifold and cut it at the point where the holes where closest in size to the spacing of the carb throats. Actually drew up both in CAD and overlaid one over the other to get the best match. The carb throats weren't equispaced. As the bike carbs throats are closely spaced for a 1 litre engine, you can (just) keep the distributor. Throat 4 is parallel with cyl 4 and the other angle back to make the space. Can't find the CAD file unfortunately but here are a few pics -



I hope it wasn't an ultra rare manifold, I picked it up years ago cheap

As bike carbs attach with rubber hoses, I used rubber to take up the difference. Ground off the strengthening fins and smoothed it off a bit


Some bike carb info on the web reckons that bike carbs are insensitive to mounting angle. This isn't true as I found out when fitting like this:


The float's didn't close off the fuel supply so it leaked out - these carbs (Yamaha R1s) need to be in a downdraft position - others are pure sidedraft - whatever angle to the ground they were on the bike should be the same on the car.

Next phase was to incorporate some 60deg exhaust bends



Ideal would be to weld on some tubes to the stub manifold at the appropriate angle but I don't have the facilities or skills. If you can make up a manifold it's a cheap option.

Actually, you've just given me an idea, I started a welding course and they said we could bring in some small projects - might make my own manifold up after all.

[samuria]

the manifold he has is the same as photo.

[dp]

the manifold he has is the same as photo.

Just replied to your PM

[badobsession]

sorry to jack this thread but i am also having a problem with my engine not running quite right

so i got a other carb off a mate to try and eliminate what is the problem
looked like the same carb until i removed them and checked the no.s stamped on them

the one i took off the 2lt (no guarantee it is the original carb )it was fitted when i got the engine
it is stamped 32 ADF2 250.
the other one it take it came off a 2lt and was on a fiat manifold is stamped
34ADF15 250.

any info on which one is supposed to be on a 2lt would be good thanks
mark..

[plastic_orange]

I think the SU conversion would be the best way to go. In my experience with carbed Fiats, the twin choke never seems to be particularly smooth when going from cruise to power - they always seem to bog momentarily. This could probably be tweaked to work properly, but there are very few places (particularly where I stay) to get this done. However, my mate had a twin cam minor with the 1600 engine with twin downdrafts which was as smooth as a smooth thing - find a set of them perhaps.
Has anyone considered fuel injection?

Pete