Enderle barrel valve adjustment question

[tony1966]

First time working on mechanical FI and I am trying to get rid of an off idle stumble by richening up the idle mixture.  I had the leakdown set at 28% and figured out that one flat on the adjuster is worth about 2-3% at this point on the barrel valve.  What amounts to a sizeable change in leakdown?  I don't want to go too far, but don't want to make too small of a change.  It's not popping or breaking up at the hit of the throttle and with no load on the motor you really don't notice much of a stumble.

Thanks!

Tony

[dreracecar]

Leak is only a number and not written in stone and alc is very forgiving. Make a coarse adj to see if going in the right direction. To be honest I dont know what my leak is and have not adj it in over 15 years, played with it in the beginning to get the off idle leave and havent touched it since.

[wideopen231]

Not sure richening is correct way to go.Normally a slight lean would have lots of response. Will to rich might have stumble. 28% is very close in the ball park. Is sytem just rich?

Heck try 2 maybe 3 flats thats pretty big move IMO if does not work go back then 2 flats over direction.Remember theres plenty of fuel sitting there when you open barrle to full flow engine has to pull air in to mix with it .Its not like a crapurator where the incoming air pulls fuel.

 Without knowing full system its hard to say how to tune it with a edumacated guess.Pump size nozzle size  and main jet all play into it.

[tony1966]

Thanks guys, the guy i who ran the car last told me he set it at 30%, but he typically ran 4000 ft alt.  After checking it again I saw I  had it set to 28% so I figured i better richen it up.  It doesn't build any heat at idle so I figured it can't be extremely lean.  I'm going to move it two flats richer and go from there.  if no improvement, i'll go the other way.

thanks for the direction!

[ricardo1967]

... To be honest I dont know what my leak is and have not adj it in over 15 years, played with it in the beginning to get the off idle leave and havent touched it since.

On the same fuel pump?

[dreracecar]

Warming it up at idle with full pump is not the thing to do, once the motor is running, trim back the fuel shutoff till the RPM starts to increase and leave it there to build heat, then when temp gets to where you want it , give it full pump and make adj from that point.

[tony1966]

The fuel pump (and the rest of the system) is just as it was except a put a larger vent (was -4, now -8 with a roll over valve and filter).  It took the valve apart to fix a leak, and had to reset it.  I found that i set it at 28, not 30 as instructed, so i figured i better head in the richer direction.  But we'll see later on to night.  If it seems snappier with a richer mixture, i'll give it a go, if not, I'll try in the other direction.

I tried shutting off the fuel to warm it up, but could only shut it off 1/4 or so before the motor would start to die.  I did have the water pump going, i'm going to shut that off next time.  Racing on gas for so many years, that just seems weird, but I need to get used to the alky stuff!

Tony

[masracingtd1167]

Tony just a couple of thoughts . If the car was tuned to run at 4000ft what altitude are you ? How hot was it when you staged and how hot was it at the end of the track ? The motors ability to build heat or no heat can be a good indicator of how rich or lean you are . I like to stage my car at around 170 and it is usually about 180 at the end .It is much safer to go a little richer first .Keep us posted.Bill

[Spud Miller]

 Leakdown is just a way to  measure the size of the aperture in the barrel valve that the fuel flows through at idle. It is only a reference to get you close and then you adjust from there. After you hit the sweet spot and things are working good, check it again and see what your number is. Now if you have to fiddle with things, you can get back to goodness quickly.
 
 The biggest thing that skews leakdown percentages between people is their idle check valve setting. Two people may have the absolute identical setup in every way, but one guy runs 80% leakdown with an idle check valve set to 3 PSI. The other achieves the same result with only 60% leakdown and a 16 PSI idle check valve. The fuel pressure against the aperture in the BV is much higher with the higher idle check setting, so his aperture must be SMALLER to get the same fuel at idle. Both answers are right if they work!

 For naturally aspirated setups on methanol with the proper 1-3 PSI idle check, 7% of the engine size is always danged close place to start. So, a 350" motor would be:   350 * .07 = 25%

 For supercharged methanol Enderle setups, I usually start with a 7 PSI idle check and 70% leakdown under 15% overdrive. I use more leakdown percentage as overdrive percentage increases. Something in the 40% OD range would start at 80% and adjust from there.

 When you check leakdown, be sure to cap off the idle check valve, a secondary if you use one and also the pump saver check valve. Air should ONLY be allowed to escape through the OUTLET of the barrel valve. I also recommend disconnecting a couple of nozzle lines to allow air to escape if you run small nozzles. The leakdown is a measure of the barrel valve aperture, NOT the nozzle area. very small nozzles can cause the leakdown number to be wrong as air backs up against the nozzles.

 The goal of the initial leakdown percentage "guess" to get the motor started and running on its own without drowning it (rich) or back firing through the blower (lean). Once running, always lean the link (shorten the hex link) until the RPM climbs. At that point, you know it's lean. Richen it until the RPM falls back down and give it another flat or two rich. Whack the throttle and see what you get. If it won't make heat as quickly as you want, lean it a flat. If the oil is getting tons of fuel in it, it's generally because your idle is rich...NOT the main pill.

 Changes to the main pill will slightly affect the leakdown as pressure drops or increases slightly at idle with pill changes. Usually though it will take 3 or 4 .005" steps on the pill to make the idle change a bunch, so it isn't something you have to chase everytime you change the pill.

[tony1966]

forgot to mention DA around here is typically around 1000-2000 ft, the best I've ever seen is 500 feet.  I did check in the middle of winter and saw -1000 ft, but it was -10 deg!

But an update from last night.  Started the car in pits to warm it up, with the valve at 32%, and it was a big difference.  Motor ran fine, but the exhaust was noticeably richer, would tear your eyes, before you couldn't really notice the exhaust fumes.  Tried to warm the motor by closing the shut off valve 1/4 and leaving the water pump off with no success, couldn't get the needle off of 140, but you could feel the heads were warm to the touch.  Made a run in high gear to avoid any driver shifting errors    Got to half track and had to lift as i was close to the center line, at the shut off was around 150 (forgot to check temp when staging).

For the second run i leaned it up one flat (30%), still tough to build heat in the pits, got the needle to budge of the 140 mark, but not much more (still closing the shut off valve 1/4 and no water pump).  When i got to the line it was a maybe 145 deg.  Made a more complete pass, easing into the throttle and approx 1/4 throttle the full quarter.  had about 160 deg at the shut down area.

As far as the stumble goes, i am thinking its more my limp wristed driving style while i am trying to get comfortable with the car, combined with a cold engine.  I have been easing on the throttle off the line.  Doing a burn out, however, i stab it and it really didn't stumble at all yesterday.

So for my next steps, i am going to figure out what spring i have in the idle return, and work on building heat in the motor at idle (after I change the oil!)  I can do that in the driveway without upsetting the neighbors too much i hope!

I can't thank you all enough for your help/advice.  The amount of knowledge and experience here is amazing!

Tony

[dreracecar]

If the idle rpm does not rise when you close off the shut off you need to turn it some more. I have to go about 1/2 way to get rise in rpm.  Alc is a heat and compression sensitive fuel, when the engine is cold the fuel will ignite closer to TDC because the magneto has a long spark duration to cover that range and being closer to TDC gives you more compression. When heat is introduced that ignition point gets further away for TDC and starts to make power at the beginning of the magneto spark. Leaning on the shutoff trims away the excess fuel that is now being used to cool a cold engine. You have up to 240* of temp before you have problems.