The topic says it all, but basicly I'd like to use a pair of Harley application carbs on a mild, streetable engine. The engine is a 1.8 liter four cylinder that revs to about 5000 RPM or so. The head's got four intake ports, so I'd be making two "Y" manifolds with a balance tube between them. Harley's are an unexplored territory for me. Do most of the carbs have an accelerator enrichment circuit and idle circuits like automotive carbs? I know a lot of the sporty Japanese bikes don't, but figgured the slow reving, large combustion chamber Harley might be more car like in it's carburation. No nay-sayers please. I've seen it done, but it was on a racing engine. Oh, and carb recomendations are welcome. Make, model and size...
so i'm not the only one who's thought about this,hmmmm.i wanted to do 3 bendix carbs sidedraft on a chevy stovebolt,for 2 reasons.1st because i can't afford an early vette manifold w/carters,2nd because i have a bendix on my sportster,so they're familiar.the bendix has an idle circuit,an accelerator pump (which most times has three different holes to adjust the pump shot) and there's a kit (pretty cheap too!) for an adjustable main jet.they come in 36mm and 38mm venturis,they might have a 40mm,or you could easily bore out the smaller ones on a lathe.the other big factor is that they are cheap,if not free,from guys who remove them to install S&S carbs.i'm sure the S&S is a perfectly fine unit,but i usually see them installed on bikes with too much cam and too big pipes,along with a too big carb.the bike ends up sounding like ****,and won't get out of it's own way until you crank it to about 4000 rpm.*****s hope this helps-george
Hmmm - It just so happens that I have a set of 4 Keihin CVKs from a Kawi Concourse on my shelf for just such a purpose. Can't gripe about $80 for carburation (if they work ) I don't know much from experience, but here's what I learned in my half-***ed research: Between Keihin and Mikuni, you can get about any throat size you want and (I think) should be able to get them tuned by changing jet size and needle position. FWIW - mine are 34mm, which I based on recommendations for sizing 2 Weber side-drafts for a 1.8L 4 cyl. Here's my basic understanding of how these things operate: The main throttle slide is controlled by vacuum rather than by your foot. More foot delivers a stronger vacuum signal which opens the slide, which decreases manifold vacuum, and balances the slide to hold position until you move your foot again. Kinda like the top ****erfly on the Q-jet secondaries. You only get the amount of air and fuel that the engine demands. MX bikes connect the throttle cable directly to the slide for better throttle response. I forget the downside to that approach - bogging? Maybe just a 2 stroke thing. Later carbs for Jap bikes tend to be more down draft than side draft - late 70s through 80s bikes tend to be side draft. From my little experience, Mikuni seems to be a little more focussed on aftermarket and Kiehin seems to be a little cheaper. I haven't set it up, yet and will be interested to hear what others have to say. Can I ask what engine you have in mind?
I do not know what motor you are using, but there is a guy on the Inliners site that built an intake and is running 4 Mikunis on a 200ci six in a Mustang. I have only seen pictures and heard a sound clip of it, but it sounds really good. I do not think he has it on the road yet, so no idea of how it runs.
40Tudor, sounds like they work just like SU carbs. The engine is (no backtalking) a Nissan KA24e out of an '89 240sx. It's a cross flow SOHC so it doesn't look like an Offy, more like an Iron Duke, or a little like an OHV converted Model A. I'll be doctoring it up to erase any hint of modernity. After the EFI is stripped off, there isn't any plastic left on the engine and very little grinding is needed to hide it's oriental origins. Regardless, I'll be cutting off the top half of the valve cover to make one that resembles an OHV converted banger. I'd like to use Harley carbs (Bendix, Mikuni, S&S or maybe even SU) because they offer a short intake track and somewhat resemble pre-war Winfield racing carbs. I'll use a mechanical distributor from an L16-L18 Datsun engine - something I'm very familar with. Before the poop starts flying, this engine choice was made because I've been burned out on this car and put it aside for a year or so. I'm ready to start working on it, but just can't get excited about pouring a ton-o-money into a Ford banger, or building another Flathead V8. So, a dressed up SOHC Four will have to do. I've got to save some of my cash for the racecar. BTW, racecar spelled backwards is racecar! Any specific carb recomendations? Or just try to get two of the smallest carbs possible?
Just go back about 20 years to when Nissan/Datsun ran Mikuni/SUs and start adapting. Might not even take much adapting,since it's in house. I know '70 240Z had twin Mikuni copys of SUs. There usta be a running joke on the RRT about how many motorcycle carbs it would take for a 500Caddy to breathe...
I think it's very workable. Sizing is in the ballpark, as a Sporty is 'round 1000cc, a big twin 1300cc, and your four is 1800cc, but revs higher than the average Harley, so roughly equivalent to two Sportsters. Me, I'd grab non-CV carbs, mostly because I understand them better . Get two sized for a 883/900 Sportster, mostly because it's easier tuning with a slightly small carb than a too large of one. Most Harley carbs have an accel pump, IIRC. A balance tube between manifolds would be a good idea. And do something more thoughtful than just a K&N pod filter off the bellmouth of the carbs; that's just a lack of imagination/effort. Cosmo Oh, yeah, I see no problem making this streetable, and very liveable at that.
1000cc sportster=36mm Bendix.1800 sohc=2 36mm bendix.you could always do a couple of SU carbs,but i hate tuning them and it just ends up looking british.mikuni=expensive usually.
I think it will work great.I'm planning on using a M-B 4 cylinder 2.3 Dohc in my '34 pickup. The factory intake has to go to get the look and I'm torn between a Gm 2.5 TBI under a period air cleaner or the motorcycle carbs. The carbs sure look bad to the bone and should give power and mileage. Keep us posted on your progress.
Modernbeat: What application ? I'm thinking you will need accelerator pumps on the street. The bikes are so light,they can get away without them. A much heavier car will accelerate slower,so you need that extra shot of fuel.
Now that I'm home and have access to the library, here's some info on venturi sizing. I know Webers operate differently from M/C carbs, but I think the same principles hold true when looking at the size of the main venturi - plus there's a LOT more info out there. As I understand it, driveability=low end torque which you get from high intake velocity (which comes from smaller main venturis). So, we're just dealing with air delivery here - fuel delivery is a whole different thing. This from "How to Build and Power Tune Weber and Dellorto Carbs" by Des Hammill: For 1750-2000cc engines operating between 2500 and 7500 rpm, he puts you between 34 and 36mm venturis. In this case, he's going for peak HP and Hi-R operation, so I'd take this as a max size. Another data point comes from "Mazda Miata Performance Handbook" by Norman Garrett. Ol' Norm set up Webers on 1.8L Miata engines and recommends a 32mm main venturi as a starting point. FWIW, the Miata is a crossflow DOHC and redlines at 7200 rpm (and now you know what I'm up to ). Since you're not revving that high, maybe even 30mm would work. Either way, you now have a range to start with. Unkl Ian, Isn't the accellerator pump there to compensate for the lack of air flow that you have relative to throttle position when you stomp on it? As soon as you get on it, manifold vacuum drops fast, but air flow doesn't pick up until you get the beast moving, so you don't have the vacuum signal to pull enough fuel out of the main well to get it going. I guess I'm thinking that the vacuum-controlled throttle (and direct relationship between air and fuel metering) that you have in CV carbs negates the need for an accelerator pump. Dunno - just theorizing at this point. Chris Now, for that 500ci Caddy - I say 8 carbs at 46mm or 16 at 38mm.
I was running an SU carb from a Triumph sports car-it operates as described .when the demand is applied the amount of vacuum produced dictates the opening of the venturi. It is on a larger displacement 4 cyl on an old TRACTOR that I have. the triumph was a much smaller displcement 4. it was equipped with two of these carbs. I only used one of them and it seems to be plent big enough for the larger four-[Ihave no displacement figures] on either. odd thing is it really woke up the old tractor when it was installed?????
I had the same thought a while back, Harley Bendix carbs on a 4 Cyl. Chevy 151 (2.5L?). Figured a 1200 HD at 74 Cu. In. X 2 is very close and wasn't looking for every ounce of HP and thought the simplicity and compact size of the Bendix would be good looking as well. I guess the Bendix carbs all have the accelerator pump like the one on my '73 Sporty? Is the firing order on most 4 Cyl. engines split evenly between the front and rear pair of cylinders so the intake pulses are staggered evenly on siamised (sp?) ports?
I think the firing order is 1-4-3-2,and I get where your coming from. Pairing the #1 and #3 cylinders,and #4 and #2,would create more even induction dynamics. But the plumbing involved would be more complex,so packaging could become a problem. First choice for peak performance is one venturi per cylinder,looks better too. So how about 4 CV carbs ? There should be a million stock Harley carbs out there gathering dust. --------- I ran this question past my local engine Guru a couple years ago. I don't remember all the logic behind it, but he seemed the think accelerator pumps would be a good idea.
I'm running a carl's speed shop harley carb large bore/with velocity stack on my a banger with a b head, runs like a ****d ape
Cosmo, the engine I'm looking at is 2400cc and will actually be revving to about 5500-6000 rpm. So roughly equivelant to two big bikes. I understand air velocity theory. Yorgatron, a Harley really uses a 36mm carb stock? That's on a 1000cc bike with a low redline - right? Seems really small to me. 40Tudor, those number you quoted: [ QUOTE ] For 1750-2000cc engines operating between 2500 and 7500 rpm, he puts you between 34 and 36mm venturis....Webers on 1.8L Miata engines and recommends a 32mm main venturi as a starting point. [/ QUOTE ] I'm guessing that those guys are talking about two-twin venturi carbs, meaning four 36mm holes to feed the engine. That is about the same flowrate as two 44mm carbs, which would be about the same as two big twins. I know all about the Miata. Had one for a while. Lots of fun, but way too much necessary plastic on the engine that you can't get rid of. BTW - if you want to go distributor rather than coil packs, you can use the cams, cam cover and distributor off a late '80s Mazda 323. It stick off the end of the cam pointing towards the flywheel end of the engine. TonyBones, don't worry about Linkerts. If I had any I'd sell them, buy something that works and plow the rest of the money into the racecar. I've been looking at the late '60s Tillotson carbs. They've got a traditional ****erfly (longevity), the throttle cable or linkage is on the side or below the carb (for looks and engineering) and from the tuning guide that I've got on it, it looks like it has a non-adjustable accelerator pump. They're incredibly short and have a flange on the back like a proper carb. Winfab, you mentioned the later '70s Bendix carbs. Can you verify that they have adjustable pumps? Any other advice?
You got it, my numbers are for Weber DCOEs. Thanks for the tip on the distributor. I was thinking the 323 dizzy would work with the Miata cams and cover. I'm waffling between that and a cog-belt driven distributor hanging on the side - thinking there might be clearance issues between the rear mount dizzy and the firewall in a 27T. Got a NOS '75 Civic distributor for $8 - Pertronix will supply the modern guts if it comes to that. On the engine plastic - I'm planning on an exposed timing belt to clean up the front. I know it's not a chain, but is there other plastic on that engine that I'm not thinking of? Am I off track on the need for an accelerator pump?
The only problem I see is harley carbs are gravity fed so you will have to run really low fuel pressure. and at high rpm you will probablly run out of gas !! sorry that is one reason I use S&S carbs instead of stock harley !!!
Dirty, I thought about the accelerator pump. I think it's mandatory. Fortunately, a lot of Harley carbs have one. That's why I was looking at Harley carbs rather than Suzuki Sportbike carbs. As for the high-flow at low pressure problem, that's easily taken care of with a flow-through fuel system. You use a return fuel line with a pressure restrictor after the carbs. For a pic, Google images shows: Another poke at ebay turned up this one: And yes, after a little more reading and asking around, it looks like a pair of S&S Super E carbs might be the hot ticket. Dang, this was supposed to be cheap!
modernbeat, I was gone a couple days but I'll look at my carb for accelerator pump adjustability. The blowup posted does look like the same carb though. As mentioned in another post, I had never thought about the fuel pressure issue but even at gravity feed pressure (maybe .25 to .50 PSI at best?) my Harley didn't have any issues.
I think we ran 1 1/2 -2 PSI on a Jap bike powered Formula car when I got out of College. Once we found a regulator that would go that low,no problems. Too bad I didn't take any pics.We hand made just about EVERYTHING. Space frame,hubs,uprights,brake calipers,8" dia. Leather wrapped steering wheel, Fiberglas gas tank,seat,and body work,Foam Filled wings, adjustable brake bias set up,expansion chambers,push rod suspension, right hand shift,etc. I'm still paying for that one.
The blowup is the same carb as my '73 Sportster. #2 in the blowup is the actuation lever/cam for the pump and has no adjustability for stroke of the accelerator pump that I can tell. The geometry of it would give a larger squirt in the early rotation of the throttle shaft than the latter, (i.e. more in the first 45 degrees than the last 45 degrees). I, for one, would appreciate a follow up post if you build it.
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