I'm the lucky owner of a 2001 Roadking with: Vance & Hines Dresser Duals + Oval Slip-ons, SE (29745-00A) Aircleaner, SE 95 Big Bore + Flat Top Pistons, SE Performance Heads + 203 Cams, a powercommanderand a Stock EFI (Magneti Marelli). The bike is tuned and a dynorun shows 90HP and 108 lb-ft torque. Two questions:

1. The EFI isn't running smooth and never ran smooth, so I'm thinking of replacing it with a carb. Can/should I use a standard CV carb or do I need a bigger one? Which one do you
recommend?

2. I would like maximum torque. How do I get that? Should I change the cams and if so which ones to choose? Or should I change something very different?

Thanks!


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Check out www.head-quarters.com they sell a kit to go from EFI to carb. Call and talk to Doug about it and he will hook you up.

 

Talk to Zippers about a Magnetti Marelli EFI convertion, with a larger throttlebody and a ThunderMax auto tune unit.
They'll do your bike including labour for about $2,600.

 

A larger TB will increase MAX HP numbers, at the expense of low-end torque. I would not do that.

There are a few options available to you, but it;s really gonna depend on how mechanoally inclined you are and/or how much trust a local shop to do it for you.

1) You can get a Daytona TwinTec TCFI-IID and the adapter harness listed at the bottom of this page (it allows for use on EFI bike with the Magnetti Marelli (SP?) EFI / ECM). This system is REALLY sweet and allows for the greatest tuneability.

2) Convert to carb. There is a list of required parts on at www.head-quarters.com.

3) Resolve whatever issue is causing your problem now....

 

I just want to make sure I'm not somehow missing something. For those of you that don't know either fo us, PhilM is a mechanic, I'm an armchair mechanic.
So you're advice is to stay with a 38mm throttlebody for this aplication Phil?

 

Wally, I see that BC worked your TB over.

I had on injected 01 w/the stock MM TB and at one point I had the exact build that was mentioned above with a PC (II, if I recall correctly)asa tuning device. It ran decent, but I ended up going with as a set of TW26 cams in that one and it worked out great.

Keep in mind that there is benefit to dual independent runner TB's.. You can not compare a siamese runner, 44mm/ 46mm TB to a dual independent runner unit - even the stock MM -I thought it was 40mm, but you may be right (it has been a while). It's kinda apples & oranges.

My point it that it's really easy to go too big and one of the stated objectives inWizard's opening post was that he wanted increase torque. Generally speaking, larger intake, does not equal more toqrue. It does provide greater flow at higher RPM (greater peak HP), but it will usually reduce velocity at lower RPMs.

This is certainly not a global statement and some configs may actually be designed for more flow, but this example is not one of them.

Just my opinion... I'm sure others will chime in with theirs too.

 

Back to your carb question. The Stock CV would work fine and give you better low end and shouldn't hurt you on top end. I actually like the flat slide Mikuni HSR-42 because of the instant throttle response. Great for low end torque.

As PhilM stated, a smaller port increases velocity and therefore better low-end/mid-range torque and response. Larger ports benefit from higher flow rates and do better at the top end of the RPM Range were you actually could use the higher flow rates. Since they have bigger ports, they have slower velocity and create a bit or laziness or staggering and turbulence (intake stream) in the lower rpm ranges.

A decent analogy would be a water hose. Take a 3/4" water hose and watch the high flow come out the end. Now, take a finger and cover half the bib and watch the water squirt to the other side of the yard.
Intake systems don't exactly work like that but it's sort of close enough because the cam is actually acting like a valve stopping the flow quickly then turning it back on. Small ports will recover in velocity much quicker than the large ports. Make any sense?

Cams will really effect thisintake flow as well. Small ports, low Duration cams will provide lots of torque and lower RPM's and Large ports and higher duration cams are for higher RPM's and HP numbers.

 

Hi Guys,

Thanks for the replies.
I get the picture. My best options are:
1. Try to get the EFI configuration fixed.
2. Convert the EFI to Delphi $2600
3. Convert to carburator and use the stoch CV or the 42mm Mikuni

And last but not least change cams to increase torque. Any thoughts on make and type?

If I get the carburator I will need an ignition module. But would I be wise to consider a module while still using the EFI? Can the igintion make a big difference in torque and/or smoothness of the ride?

Thanks again!

Michael.