razor1115

razor1115
Club Chopper Member


Registered: Mar 2004
Location: peoria, il
My Bike: 2001 Ultra GPST
Posts: 7
razor1115 is now Online:

Rivera DUAL runner with dual 42mm Mik's

or anyone having luck with the older siamesed style manifold (2 into 1)

Anyone run these? What size engine and what did you think of them? Help or hurt drivability, response, hp/torque? Did you have trouble setting it up/ idling?

I am going to possibly try the dual 42mm on the new Rivera dual runner manifold. Price? OUCH. Anyone know of any good deals out there?

One other guy, a dealer, in the area said he was told to run dual 45mm's on his 113" set-up. He was told he needs these on a 113". I think this is going to kill his throttle response, signal to the carbs at idle due to drop in port velocity, and pool the fuel in the manifold...I don't even think top end hp will be higher for 45mm over 42mm because 42 should flow more than enough all the way past 6500 rpm. I am NOT revving mine past that... any insight here?

I have a 113" I just put a new cam, port/polished heads, cleaned-up. I think 42's would more than support this based on there published airflow numbers...opinions?

Thanks
Zack



no one has ever tried duals or have ant info?

Ha,,erdown

I use the real deal...Dellorto DHLA 40 Work great for me.
Puzzled uses twin Mikuni's with a plenum manifold...he seems to like them.
But I would think twin 45's are a bit much for almost any V-Twin.


Hammerdown

I thought the same, talked yesterday with the guy taht designed the mikuni carb and the whole dual set-up.
He said the 42's run super rich. Reason why, the port velocity is incredibly high, therefore it's really hard to get them leaned out enough = engine always runs rich. The 45's a a better csrb overall and they slow down the velocity somewhat. This makes adjustment / fine tuning/ signal to meter fuel A LOT better. He said they have proved it on several bikes and the single cylinder engine they used to develop the system. He said and I questioned this, on same engine on dyno same day just a swap of dual 42's to 45's made 25 more hp. That seems ASTRONOMICAL. Would like to see a dyno print out and some air flow numbers....

Oh, by the way, he also told me they quit making the 42mm Mik. I understand for duals, but what about the guyd runnin' singles. He said the characteristics of the 45 are just that much better


Also called Rivera tech desk, don't even bother. Response I got was 45 is a better carb. I said how? Reply, it's a better carb. But WHY? Because it's better...

Geesh

Zack

HammerDown
Senior Club Chopper Member

"velocity is incredibly high, therefore it's really hard to get them leaned out enough "
Hmmm so the larger 45's slow down the port velocity, OK but that intake track really builds torque/power like a tunnel ran on a V8...slow down the intake speed> would that then make the fuel want to drop,puddle or not have enough vacume signal to properly atomize the fuel at lower RPM???
This is why I kinda like the Dellorto DHLA...you can tune that carb to work great on a toaster...almost a infinite amount of tuning capabilities.
I agree about Rivera...their CS isn't what it was 10 years ago.

Bottom line...the Mikuni/Edelbrock Twins are popular...they came about because everyone at one time wanted the Dellorto/Weber look hanging off their Engine...but were hard to find. This is also why "ForceWinder" came about. I'm sure they work or Mikuini wouldn't develope it...or would they do it to cash in on the original (dellorto/webber) side draft demand?
Sometimes it's all about the look...and the Manufactures and Marketing know it.




I also asked about puddling in the manifold/ falling out of atomization. He said NO WAY - very definitive. I also asked about carb signal, low RPM throttle response being sluggish and he replied it will be A LOT better everywhere...

I do like the duals, gotta say they look great, but I'm not one to spend a ton on looks without gettin' some performance. I have been told some guys have bought a "cheap" dual set-up only to put a block-off plate behind one carb. Dual look with out any hassle or change in performance. 1. I don't have that money and am an engineer so it needs to be used 2. If it's not too harsh to say, I'm not that vain...

I'm still trying to figure out the velocity thing... The engine will only pull as much air as it can physically pump. The high velocity part I believe because it's acting like a tunnel ram. But does the carb flow more fuel at a higher velocity even though the mass of the air passing through the carb is the same. ie, if it were a larger carb, the velocity would drop, but would the fuel? If the carb is large enough that it is not a restriction, then the engine would still pull the same air mass on every rotation just at a lower velocity. So does velocity help meter the fuel or does it act like a SUPER strong carb signal and cause a rich condition?

Zack


sorry so long winded

Reed Jensen

Air velocity effects fuel delivery more on a carb with a auxiliary venturi. If you have modern carbs like a Weber with an accelerator pump, auxiliary venturi, fuel well, emulsion tube, air correction circuit, they pretty well compensate for velocity stacks and can be more tuned. If you are talking about Dellortos that have a straight bore... or a single venturi, they can have some quirks when you put a velocity stack on them. The most obvious adjust to them is the shape and length of the needle on the slide and the main jet. Large cams with lots of overlap and a short intake length, (like a motorcycle) can actually suck in air, mix it with fuel, and then push it back out into the velocity stack to only suck it back in and put in more fuel,,, causing a rich condition at lower rpm ranges. Weber carbs or any carb with an auxiliary venturi draws fuel from the well when air passes through the ring. If you were to "unwrap" the venturi it would resemble the shape of an airplane wing. The faster the air moving through it the more vacuum signal on the well. Weber carbs have infinite adjust-ability because you can play mix and match with the air correction jet and the emulsion tube,besides changing the main jet . They can be adjusted for lean running at low rpm's... rich running at high rpm's.. Most people don't have a clue as to how to tune them though.

mcollinstn

Idle mix on large carbs is seldom an issue, as the throttle slide (or plates on a CV)is dang near all the way closed, and the large venturi is no longer large (cause you ain't pulling fuel from the circuit in the venturi, you're pulling it from the little tube thingys right in the airflow past the plates/slide..

Similarly, since we are dealing with slide valved carbs (whether they are direct or CV), the "venturi" of which you speak is a variable one. When the slode is closed, the venturi is small. When the slide is open, the venturi is large.

Over carbing with a flatslide or direct slide carb is not a huge problem.

Over carbing with a CV carb does cause some tuning frustration, but it can usually be tamed fairly well.

To give you some idea of carb sizing, I have a 1000cc 4 cylinder with four 41mm flatslide carbs on it. That's the same as a 500cc motor with two 41 mm carbs on it. No bog, no troubles. Granted, this motor is a 12,000 rpm motor, but it still mixes just fine at lower revs.

Should give you some indication of how reasonable a pair of 45's are on an 1800cc bike...

(and I also owned a Husaberg single cylinder 500cc dirtbike that came with a 39 DellOrto, but the hot upgrade was a 41 FCR Keihin that really woke it up. That was a single cylinder 8500rpm motor, a little closer to your sort of motor than the inline 4 mentioned earlier.)

Reed Jensen

What the hell is a Husaberg?

mcollinstn

Rogue mad scientist motorheads from the hardcore Husqvarna 4 stroke MX program. These guys wanted to make a real hairy nuts open class 4 stroke MX bike. To h3ll with oil pumps and lube reservoirs, and rubber cush drives, and anything else absolutely not required to make power. If it didn't contribute, they didn't want to use it.

They made "back room" racers, removing the gear driven counterbalancers from the Husky motor. They made sand cast engine cases and welded them to a 2 stroke gearbox. They removed the pressure lube system and utilized a tiny low mass water pump for cooling. They designed an oiling system that operated off crankcase pressure pulses and cam chain sling off.

Their monstrosities stomped all over the available 4 strokers of the time. Corporate thought they were nuts and told them to stop wasting time.

The mad scientists left and formed Husaberg.

Their bikes were the top notch balls out fastest 4 stroke no frills dirt bikes known to man. All castings sand cast, and unfinished looking like they came from behind the Iron curtain. Some of the fasteners looked like they ought to have square nuts off of a swingset (the fasteners were all cad plated, not nickel plated and very quickly tarnished in use). The bikes vibrated in an evil manner, and had a shockingly quick revving nature.

They made em like that for several years until the Husaberg emblem was absorbed into the KTM family. At that point, pressure lube systems were added (cause donks were griping that they had to change the oil after every ride or it would eat the cam lobes up) and high quality fasteners were used, and then the engine itself used the KTM base with Husaberg side covers... Blasphemy.

Husabergs were only useful to somebody who LIKED to work on a bike five solid hours to prepare for a day of riding (after which it required, you guessed it - five solid hours of disassembly and reassemly).

The good ole days. You pretty much can't give em away any more, unless it is to somebody who just needs one for spare parts.