discussion: Oldskool carbs or Motorbikes Keihin?

[mark]

My housemate and I have a discussion about carbing a car.

He's going to put Keihin motorcycle carbs on his vw derby 1100cc.
He says that if I want a carbed 4ag in my celica, Keihin would be an option.
He prefered Keihin above weber/mikuni/solex, because they're not that old.

Does anyone have experienced/seen Keihin carbed 4ag, or know something about it??

Mark

[XJS]

http://www.stageoneimports.com/main.pl?s...AE86FCRKIT

[mark]

I've seen that, but I think that could be less expensive

[XJS]

I'm not a big fan of carbs over EFI. Played with webers and dellortos on cars, keihins on bikes. If somebody like oldschool, and has the ability to properly jet and synchonise carbs, go for it. If more a computer geek, the EFI would be easier to tune with some piggy back stuff.
In case of which carb q's, Keihin CV carbs would be superior over any non CV carbs for street, I'm sure.

[jamiemirror]

The Delorto, Weber and Solex/Mikuni share the same bolt pattern (as some ITB bodies also). This is advantage when you must buy the adapter flange. They are old - yes. But they can be rebuilt for cheap - rebuild kits are still available.

[NoHachi]

Keihins from modern dirt-racing bikes are cool..they can stand a lot of sideways G-s without ruining the fuel delivery. They're also nice and compact so you don't get into trouble with the spacing between the head and enginecompartment..I do believe they are pretty expensive..about twice the price of what it would cost me to do a better EFI system and about the same price as an uber-EFI system.

[firehawk]

Before I bought the AE86, I had a KP62 Starlet with a 4K engine and I put on it a set of four Mikuni BDS37 CV-carbs off a Yamaha FZR1000 Genesis. I had a simple steel intake manifold and the carbs attached to it using four small pieces of heavy duty rubber hose and clamps. Compared to getting a pair of Dellorto DRLA36 downdrafts and a manifold for them, the bike carbs were about half the price. Couldn't find any suitable velocity stacks for them, though - the outer diameter was just too weird. I ended up just putting the filters directly onto the carbs with re-useable zip-ties.

Getting the correct jets and needles can be quite expensive and a tedious job, so one needs to be prepared for trying out different settings and testing the car in different conditions. In my case, the jetting was already quite good for a 1300cc engine revving up to 7500rpm, so I only needed to change the needle clip positions a bit, tweak the air screws to get a good stable idle and sync the throttles. Once these were done, the car ran quite nicely and no longer pushed out huge clouds of black smoke out of the exhaust. They did spray back some fuel mist on overrun but I believe this is due to the cam overlap I had (304 deg rally camshaft). Had some 30cm long flames shooting out of the carbs when I was adjusting the ignition timing and retarded it a bit too far.

Here's a few photos of the carbs and manifold;
http://paranoia.tuug.fi/gallery2/v/jh/album51/album66/

...test fitting them on the car;
http://paranoia.tuug.fi/gallery2/v/jh/album51/album68/

And the final result;
http://paranoia.tuug.fi/gallery2/v/jh/al...6.jpg.html
http://paranoia.tuug.fi/gallery2/v/jh/al...G.jpg.html

[NoHachi]

Hmm..I have heard of motorbike carbs seizing up under lateral G's..Bikes lean into a corner and as a result most of g's are in the top-bottom direction..

though saying this, all the cars we've built and ran with carbs (almost all of them during the testphase never showed any difficulties..all but one were also capable of pulling well over 2 G's lateral..so i can't really see it being a problem in a hachi that strugles to reach 1G.

[Matt Skinner]

I'd go for keihin FCR's personally if I had to use carbs. Only problem is finding a place that knows what they are doing with them to do the tuning!

[NoHachi]

unlike car carbs there are MASSES of people setting these carbs up. FCR's are the carb of choice in the motorcross world..really competitive bunch with lots of experience in tuning these buggers..usually pretty friendly folk too.
Learn how to sync them yourself I'm sure you could come up with excellent settings...

Still, not as easy as EFI though...lataly i have been toying with the idea of how to write an algorithm that makes auto tuning of the WOT or full boost map possible in realtime and closed loop. At the moment cars still switch to a preset (rich) map at these conditions because Lambda sensors are simply to slow to keep up..Think I have found a way of using the information still contained in the measurements, even though they are delayed. Combine that with a Ion-Sensing ignition module from a Saab or BMW -M and true plug and play capability would be achieved..car tunes itself as U drive non-stop and adapts to your driving style within a couple exhaust pulses....now just to find a programmer capable of writing this to a megasquirt ecu..