Hey all,

I am currently running twin Hitachi-SUs on my A14, a mechanic told me they are getting pretty tired and are sucking a fair bit of air (ouch!)

He suggested i go and look for 40mm Dellortoes(sp?) ...with a hefty price-tag..are there any alternatives... ?

Cheers

How good are you at fabricating? I think a set of motorcycle carbs from a 1200cc bike would be sweet. You'd get the advantages of both systems. Four throats like the dual Mikunis or Webers and the continuously variable venturis like the SUs.
I bought a set from a guy once who made an adaptor to mount the four bike carbs to an old dual side draft manifold. I never got around to using them though. Bet they would have screamed.
Just a thought.

The dellorto 40s would be good, it's partly a matter of being patient, they come up all the time, at around the NZ$5-700 with manifold for the A series. But they can come up for as little as $150, a good place to look maybe talk to some guys that race in the midgets class of speedway, in Dunedin anyway there is a class that runs only A12s, and I found a guy that was willing to help me put in a new diff etc, there, as they are wrecking B210s and 310s all the time.

hey
WEBERS :) ya can't go past 'em. a set of 40's or 45's would be good but u will have to get it jetted properly otherwise fuel consumption will go even further out the windowthey r pretty expensive but they r a brilliant carby
hope this helps DAVE
ps you could even use 38's but theyr are hard to find

Dimlight

In the weekend i have the same idea of puting a four carburetor motorcicle ramp on my car. I can get them for peanuts, since around here motorcicle wreckage is frequent. However it seems to me that a 1000-1200 motorcicle engine carburetors will have to be rejeted to work properly on a car (don't you think?) because the maximum power (on speed bikes) is delivered at something like 10000 RPM and at a A series engine it will be at 6000-7000 RPM. However if you think that it will work, let me know so I can include it on the next modifications.

Thanks

Ricardo

or 42's like me or 48's....blah, blah

actually it doesnt matter what size you get as the chokes (venturi type thing that goes in the throat of the carby) that suit a 1200 are around 30-32mm and with any size carb you will still be putting these chokes in effectively reducing the size of the carb to that size, so in other words 40's are as good as 48's

Quote:
I wouldn't think they would need much rejetting. It seems to me that 1200cc's is 1200cc's. The different location in the rev range hadn't really ocurred to me though. You may have something there. I'd run them the way they came off the bike then read the plugs and tune from there.
Of course, anyone who knows me, knows that isn't true. I'd get them running and never mess with them again. Have I ever mentioned how lazy I am?

Popular V8-talk says that if you as much as change the exhaust system to be freer flowing, like go from cast exhaust to tubular headers, a re-jet can be beneficial -- even though it's the same engine, let alone same size engine. If the camshaft is changed, a re-jet is just about demanded.

This suggests different engines need different jetting. I would think if the air flow is the same (at same temp/barometer) it shouldn't matter, the carb should give the same Air/Fuel mixture. I think the reason it does matter has to do with things like the overlap of the intake to exhaust cycles (less backpressure will change the flow), compression ratios, efficiency of combustion chamber (swirl, quench, etc.) Some engine combustion chamber designs can run leaner than others (like the Honda CVCC as an extreme example).

Then there is the matter of the application of the engine. A 1200cc pulling a 600lb motorbike doesn't need much to take off, while a 1200cc pulling 1600 lbs might need a richer accelerator pump and richer mixture during part-throttle acceleration.

On the other hand, I would just bolt 'em on and see how well it runs. Then fine-tune it. But remember those "hot-rodded" cars going down the road belching out black smoke after putting on a "new carburetor". The driver seems to think his car is running well! Custom jetting is worth it.

Everything ddgonzal said is true. But to play Devil's advocate, I'd have to throw in that the continuously variable nature of the carbs in question would sort of self regulate. They will only flow the air and fuel that the engine requires at a given load, speed and throtle position.
I guess what I'm saying is the CV type carb is more forgiving of sloppy tuning than a standard fixed venturi carb.
Then again, I could be wrong. They do require tuning and have different needles available for a reason.

I have just purchased a set of twin Hitachi SU's and an oval port (GX or A15???) head with the factory twin system exhaust (extractor). All seems good but Im just wondering how much of a noticeable difference I will get from this setup over the standard carb, this is on an A12 by the way.

I am yet to check the compression on the head but I have notcied that it has been shaved before. The bloke reckoned it never did head gaskets or anything. You can see it has been shaved by looking at the combustion (under) side of the head and where the manifolds bolt on the casting bit around there is also shaved down. Does this sound dodgy?