FLH coming together S&S jetting question

[waltcentral]

  Thanks to many here I finally got the 1983 FLH highway worthy.  Does real well at 60-62 mph and smooth.
I started with the stock cam and installed Velva Touch evo lifter blocks with an Andrews EV-13.  Hated it, sounded like I had a wrist pin knock.  Ungodly noisey.
Ordered a Mackie DME 500 evo cam (in the shovel with standard shovel rockers around .440 lift). Dead quiet. Running 20W50 and fully warm on a hot day just the slightest tapping lifter sound.
I was able to get the bike jetted to where the mid range power and pull on hwy was pretty good.
  I do notice one thing though.  At hwy speed if I open the throttle full open the speed actually will increase if throttle is closed 20-25% (a guess).  Is this indicator of slight lean getting?
 

[Ohio HD]

Do you have enough compression to run that cam? 1983 motors didn't have much static compression.

[waltcentral]

  This is not a radical cam but I do expect it to give a little more when I have the heads done with a bump in compression and evo rockers. The bike runs great.
  Are you saying the tuning question I have is related to the cam? The bike does not feel over cammed.

[Ohio HD]

I don't know if it's the issue, that's why I asked what the compression is. Radial isn't the question, intake closing degrees and static compression is the question. You have a larger carburetor, and a cam designed for an Evo motor that would have faster responding heads as far as flow velocity. So if the compression isn't on par with the cam, then it can feel just as you explained. No pull at wide open throttle. 

What jets do you have, and what is the cranking compression?

[JW113]

Hey Walt, I went throgh all kinds of tuning hell with mine, with a combination of Crane 288-2b and a CV carb. That cam is not 'radical' but at the end of the day, in a stock shovelhead, it did not work well. I think Mark made a sticky of my ordeal. I'm not familiar with the cam you are using, but if it has much duration at all, and you're using stock heads, probably not a good combination.

The problem that I was having was similar to yours. Yes, typically backing off the throttle from WOT and feeling the power surge up means lean main jet. However, no matter what I changed mine to, it would not help. No matter what I did, past 1/2 to 3/4 throttle, the power would just go flat. But below that, it ran fine.

Here is what I think is the problem, with no hard facts to back it up. Shovelheads have enormous ports, especially on the intake. And big valves as well. I am guessing the thinking in the Shovelhead days was "bigger is better". Well, as they know now, it ain't. The intake tract on a Shovelhead acts basically like a big plenum. This is low restriction, but terrible for velocity. And cams that have much intake valve timing past BTC are relying on velocity to keep the air coming into the cylinder while the pistion is coming back up and trying to push it back out.

Hence, my unproven theory is that with a stock heads on a Shovelhead and cam with some intake duration, what happens is just that. At full throttle, the pistion is pushing air back out past the intake valve into the "plenum". At part throttle, at least you have the throttle plate, which is not fully open, helping to hold the air in somewhat. But at full throttle, air just goes back out the carb the same way it came in.

The basis for my theory is that on my bike, all I did was pull the Crane cam out and put a stock Shovelhead H cam in. And that was it. Guess what? It now takes full throttle with no problem, and overall has more torque and "snap" at any RPM. The stock cam is no high RPM cam by any means, but I never spin the motor over 4000 maybe 4500, so for my use case, who cares? It makes all it's power from idle to 4K, which is perfect for the kind of riding I do with it.

Maybe not the same situation that you're having, but I thought I'd throw this out there for sake of conversation.

-JW

[david lee]

gotta pic ?

[waltcentral]

David,
Still have not figured out how to post pics with this Chromebook. Not your standard laptop.

JW113,
Thanks for your reply.  The only anomaly I have with the MAckie cam is that flat spot at full throtle. Runs great everywhere else.

I need to recheck compression with this cam.

[Burnout]

Your top end flat spot may be a carb that is too big or heads that don't flow enough or both.