will this work if i have different pipes and air cleaner or is it too big a carb for a standard motor?

 

It'll work.....

But it is a bit much.....

Better off with a 42, IMO, as the 45 is normally used for larger displecements...

 

I agree. You'll lose low end power which is what you need most on this type of engine. Remember, a carb works on the venturi principle, and the bigger the venturi, the more displacement you need to get good velocity of air coming in. With bigger displacement, you pull more air and the velocity stays good. With your displacement, you'll have to keep the revs up to keep the speed of the incoming air up.

JB

 

FYI - When trying to compare carbs ... Mikuni vs CV ... the Mikuni will flow as much as a CV that is 4-5MM larger. Example - a 40MM Mikuni will flow about the same as the 44MM CV. The 48MM Mikuni flows more than the51MM CV. That 45 Mikunis is WAY too big for that stock motor.
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Something I ran across a while back .....

Flow data at 10" of water. For this test data, there was no carb backplate, velocity stack or intake manifold used:

Keihin 40mm CV: 159.2cfm
Keihin 51mm CV: 250.1
Mikuni HSR45: 214.7
Mikuni HSR48: 263.5
Super E w/Thunderjet: 197.2
Super G: 225.3
Modified Super G: 240.3
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I have put the carb on the bike and its starts right up no problem and idles.That is with the jets that came with the carb.I might need to put a smaller pilot jet?

 

Well, you can try driving it. There's a common misconception about carbs and that includes with hot rodders of cars. Bigger isn't better unless you have more cubes and/or want to operate at higher rpms.

A carb's operation is about velocity in the venturi. (the opening where air flows through.) Think of a soda bottle that's almost full. You blow hard across the open top and you'll draw liquid up and into your airstream. The faster (higher the velocity) of the blown air, the more liquid you pull.

A smaller venturi will give you a higher velocity (a given amount of air will have to travel faster to go through a smaller opening) and pull "harder" on the jets.

The jets get their "signal" (vacuum) to give fuel based on the velocity of the air flowing through the carb. (Through the venturi.)

You can google all of this, but the point is that the bigger your opening/venturi the more air you will have to pull to keep the velocity up. You can get there with more cubes and/or more rpms.

Too often in the search for more power a newcomer will buy a bigger carb. Unfortunately the low end punch is lost. The engine bogs upon sudden wide open throttle.

For normal street driving of the type that won't excite the cops into action, smaller may be better. You can use the smaller venturi for more velocity, and then increase jet size to add more fuel.

When a fluid, in this case air, increases in speed, it thins out. This is what creates the low pressure area to pull the liquid out of the neck of the pop bottle and it's what pulls fuel out of the jets. It creates what we call vacuum although it's not true vacuum but rather reduced pressure.

At a given modest rpm, your engine can displace just so much air and that will travel through the carb venturi into the engine. The smaller the venturi the faster the air will travel and therefore the lower the pressure. Lower pressure is like vacuum; you might think of it as "sucking" on the jets.

An oversimplified and incorrect but useful way of looking at it is this. If you take a deep breath the air will come in at a given speed. If you could take in that same amount of air in the same time span but through a drinking straw, the air would have to scream through that straw. The pressure in your mouth would drop, feeling like a vacuum because of the restriction of the straw. If you had "jets" in your mouth with a liquid behind them, that liquid would be pulled on hard. Not so without the straw. Making any sense here?

Anyway, give it a try. I think you're better off getting a smaller carb or even just tuning the stock one but you can see how you do.

JB

 

Hey,i got the bike on the road today equipped with its hsr 45 Mikuni and it pulls like a train like it never did before!!It had a Holley twin choke on before with Screamin Eagle pipes,now with the Mikuni and a pair of cheap big bore pipes with V&H baffles and torque cones im as happy as can be!No spluttering even when it`s cold! Deeeelighted!

 

Sounds bad,

I would definitely put the 40mm Keihn back in,

[sm=innoc.gif]


PS, pick up the April 2007 issue of "American Rider", magazine. Page 94 contains an article by Joe Minton, a highly respected Harley tuner. He writes about the Mikui 42, 45 carb install and states that the 45 is quite acceptable in a 88 C.I motor. A gain of 7 H.P. with a 45install.

I am going to put one on my88 C.I. motor. I have the S&S cam gear drive and the Andrews TW-37G cams installed, along with SuperTrapp SuperMegs 2:1 exhaust, and the SE Stage 1 Air Cleaner.

 

Sorry to drag this old thread out but I was curious to others opinions on this. I also read the article by John Minton where he said that the 45 Mikuni is fine on a stock 88 motor and that there is no differance between the 42 and the 45 except that the 45 offers more top end with the same low end as the 42. I was already planning on putting a Mikuni on before spring and I'm just trying to decide between the 42 aand 45.
Mintons article claimed the 42 added three horse while the 45 added seven horse with no sacrifice in torque. What do you guys think?

 

Er, no! You need a smaller carb, as already suggested. I speak from experience.

I had my evo tuned and stroked and the builder fitted a carb which proved to be too small. When opening the throttle quickly the engine could be made to stall, because it couldn't breath. By the time I identified this my tuner had retired, so I took advice from another tuner and changed carbs. What I then found was that the engine could baulk when opening the throttle quickly, because it was unable to consume what the carb was feeding it. A third tuner was unable to adjust the new carb to run properly.

That was an 89" with the equivilent of a 45mm carb. Too big! You have set yourself an impossible task.

Hopefully Minton is an expert and the whole engine package was adjusted to suit the bigger carb. The OP here is an amateur tinkering. My experience is that too large a carb introduces problems and can knock fuel consumption for six, along with pleasure when riding!