Lemans 1000 dyno connundrum and question

[lazlokovacs]

took my lemans down to the dyno today....

jetting is as per ed's famous 'recipe'

128      68      50/3      265      K4 bottom clip         no accel pump


engine is stock but for mild clean up of the heads

running Mistral pipes and pod filters

Valves are set, throttles synched, compression tested, engine rebuilt 3000 miles ago etc etc


Tester found that the idle jet was a little large (confirming my suspicions)

tester also said that anything above 40-50 throttle was way way way lean. Tester recommended going up to 150s mains or re-fitting pumps. I said I'd think about it....

As many people have had excellent results with ed's jetting, I wonder why my findings might be so different?

could the presence or not of accel pumps make a difference?

Thanks as ever

[pressureangle]

Lots of possibilities.

Ed's jetting was far too lean on mine as well, but there are a couple things to mind; first, the condition of your valve job. If it leaks any, it will produce less manifold vacuum and require larger jets. Secondly, Italian quality control... well, reading that may be the first time I've ever seen those words used together. So if your camshaft is 2* advanced where Ed's was 2* retarded, that can make a substantial difference in jetting as well. As I said in PM, IIRC mine wanted 168 mains when it was stock with open cans, K&N filters, and 60k miles on factory valves/guides. It ran great and got about 40mpg over the road. Bottom line is jetting is only as stable as your production tolerances, altitude, and efficiency make it.

[spmoto]

I also found the same when I fitted Ed's recommended jetting. I do however still have the accelerator pumps.
The 68 pilots are way too rich. I'm running 62's right now but have 60's and 58's on order.
I've moved the needle clip up one notch and midrange is very strong. I personally think this needle / atomizer combo is very good.
I'm currently running a 145 main. I have a pair of 135's I may try when I swap out the pilots.
All in all I think I'm very close and way better than stock.

What was you reason for removing eliminating the pumpers? I don't recall this being recommended anywhere.

FYI I'm running Mistrall exhaust w/ DB killer in place. K&N filters and Delrin manifolds, Dyna ignition and coils with a fresh tune including complete carb cleaning and rebuild.

Be patient, you'll get it sorted and once you do it will all be worth it.

Steve M

[lazlokovacs]

I also found the same when I fitted Ed's recommended jetting. I do however still have the accelerator pumps.
The 68 pilots are way too rich. I'm running 62's right now but have 60's and 58's on order.
I've moved the needle clip up one notch and midrange is very strong. I personally think this needle / atomizer combo is very good.
I'm currently running a 145 main. I have a pair of 135's I may try when I swap out the pilots.
All in all I think I'm very close and way better than stock.

What was you reason for removing eliminating the pumpers? I don't recall this being recommended anywhere.

FYI I'm running Mistrall exhaust w/ DB killer in place. K&N filters and Delrin manifolds, Dyna ignition and coils with a fresh tune including complete carb cleaning and rebuild.

Be patient, you'll get it sorted and once you do it will all be worth it.

Steve M

good info

I have mistrals with no db killer, massive Pod filters (K&N I think), also delrin manifolds with sachse ignition curve 4

[Antietam Classic Cycle]

Different gasoline could be another factor: "race gas" vs. pump gas, "pure" gas vs. E10, etc.

[SED]

Yes.

Been thinking about this same thing for my LMIII because of problems with idle to open transition, poor mid-throttle response and poor gas mileage.  It's finally mostly sorted but still going to take it to the dyno - tomorrow if they've got an opening. 

It's been thirsty and flat - not bright like the Monza and the Ariel unless you rev it over 6,000.  Plugs have been dark.  Thought removing the accel pumps would help.  No - it wouldn't accelerate without falling flat.  (I'll bet you'll really notice yours if you lean out the idle jet.)

Tried richer and leaner main jets (104, 115, 120, 125, 130, 135) richer idle jets (55, 60 and 65) and richer slides (50/3) and needle positions from 2nd to 4th notches.

Reinstalled the accel pumps and balanced them so they would sguirt for >1 sec after snapping the throttle open. Ran OK, but flat. Two days ago I opened the accel pump adjusters another 1/2 turn and it woke up on the bottom. 

Everything is stock now (including airfilter) except that it's running 120 mains and 55 idle jets without emulsion tubes.  Haven't burned enough gas to measure mpg yet. Still going to take it to the dyno man.

This is for an 850 so the only real message is that the accel pump seems important.  But I notice that the your atomizer is leaner than the 850 and your slide richer and idle jet much richer.

My understanding is that idle jet dominates at closed throttle with a little extra richness covering the transition to opening.
Slide cutaway dominates 0 to 1/4 throttle.
Needle and atomizer 1/4 to 3/4 throttle.
and main above 3/4 throttle.




Current Carb specs:
Mains 120 (115 stock)
Atomizers (needle jets) AB268 (stock or AB265 depending on the reference)
Slides 60/3 (stock)
Needles K-18 3rd notch (stock)
Idle jet 55 no emulsion tubes (50 stock with emulsion tubes)
Choke jet 70 (stock)
pump jet 33 (stock)

[Chuck in Indiana]

I've posted this many times, but it's a good visualization..
carb_jet_circuits by Charles Stottlemyer, on Flickr

[Groover]

Not sure where you live, but my guess is elevation is playing a big part into this (on top of other variables). Is Ed in San Francisco? If so, that is only 52' above sea level.

Here is a calculator I just came across that might help.

http://www.jetsrus.com/FAQs/FAQ_rejet_elevation_and_temperature.htm