Tuning 40 DCOE Weber 151 on an L24

[Zedyone_kenobi]

OH blue, thanks for reminding me.

I meant to include that the 180 Air Corrector reintroduced the slight lag in between the progression circuit and the primary circuit. This happened with the 30mm chokes as well. When I went down to the 170 Air corrector with the 30mm chokes it was gone. I tried the 180 Air corrector on my L24 as well before the engine swap and I had a noticeable flat spot between the two circuits. The 170 air corrector fixed that there too.

I wanted to give them a try again with the bigger chokes, but the transition stumble was back. I have installed the 170 air corrector again, and I will see what the AFR is at 4 and 6. I have hard time getting 6k rpm 3rd gear runs,as that is really darn fast on public roads! But I will see what I can get you Blue.

Hopefully those 120 mains will be on your doorstep this week or early next week . I kind of wish I had 125 mains. I feel another order of jets coming on.

[240260280z]

... I will have 125's freed up once I get the 120's so hang tight.... it sounds like symbiosis.

I read that more air corr. does move the main's rpm start point out. Good to see it happen in your experiments. I think the only way to counter balance is with etube changes and fuel levels...but at 25mm down in the well, the fuel won't come on any earlier without overflowing the bowl...so e-tube is your only trick left.

I also read that a rule of thumb is 0.50mm between Fuel and air.... I also read 0.6mm too . So for 125fuel you will need 175 to 185 air. The 180 may be worth re-trying with the 125's.

Check your AFR holding at 4000 to see if you have too much or too little fuel jet.

Check your AFR holding at 6000 to see if you have too much or too little air corr. (get an assistant for this in third or do it in 2nd on a long gentle hill)

[Zedyone_kenobi]

I have not done the runs yet Blue, but I have been doing ALOT of driving. I have not totally eliminated my stumble at transition, but gosh it is close to being gone. I have ordred some larger pump jets though as a trial (expensive trial since they are 10 bucks each! OUCH). I want to get more fuel into the car faster. I noticed that the current jet and spring combination the fuel continues to come out from the accelerator pump for a time after the throttle plates go wide open.

When I had the carbs off to install the 32mm chokes, I had to empty the fuel bowls. Well just tilting the carbs do not work on webers like they do no holleys so I just activated the Accelrator pumps via the throttle shaft many times, and when I went WOT I noticed how long the fuel kept streaming out. I thought that getting it more fuel for a shorter time period may help out the hole when I just go WOT very quickly.

I cannot slam open the throttles on my car at low rpm without a brief pause and the taking off quickly. There is definitely a lean spot then it goes back to about 13:1ish.

This is what I am thinking is happening. I am going wide open on the throttle plates when the volume of air being taken in by the engine is relatively low, so the carb main circuit is not sensing enough flow through the venturi to draw fuel up the main jet and into the etubes and then into the main venturi.

I am currently running 40 pump jets. I bought 50 pump jets. This will dispense the same amount of fuel but in a shorter amount of time.

This could have two results...

I could dump too much and it will not atomize and may pool up in the manifold and make the instant WOT hole much worse. Or it will get the fuel it needs and will fill the void left by going to instant WOT at lower gears.

It is a calculated risk. I bought 2 sizes up on the pump jet (going with a 50 vs a 45) so I could get a more drastic delta. If it gets much worse I will know I went perhaps the wrong way.

the beauty of the webers design is to be able to do so much tuning so quickly without removing the carbs. They were made to work on, which gives me a smile each and every time I take them apart. I cannot fathom a more user friendly design.

[240260280z]

Friendly for sure!

Another way to get more fuel is to buy 0mm bleed-back (pump spill) (pump exhaust) valves for the bottom of the fuel bowl.

3 X $5

http://www.piercemanifolds.com/product_p/79701.000.htm

[Lazeum]

Something else you could try to help pouring more fuel would be to close the bypass valve (spill valve) at the bottom of your fuel bowls. You have 1 per carb.

On mines, previous owner has shut the holes with solder so 100% of the fuel from the accel pump system is going thru the throttle instead of having some getting back into fuel bowl.

I don't have any flat spot at tip in, except if I try at 2000rpm to hit WOT super fast (something we never do that fast anyhow)

Edited October 2, 2012 by Lazeum

[Zedyone_kenobi]

Well my my issue I am trying to solve is just what you describe Lazeum, WOT at 2000 rpm super fast. I am not sure I really need to, but something in me just loves to tinker with these darn things! Under normal driving, the car runs almost flawlessly.

[madkaw]

Good luck getting racing carbs to act like FI!

In no way am I being sarcastic , it's just the way I am looking at my triples. Not sure you can get racing carbs tuned well enough to stomp on them at. 2krpm and think they will react the same as stomping on them at 4krpm. At 2krpm there is probably too much fuel for your engine to swallow- thus hesitation. Then your AFRs look way off while the motor is trying to burn off all that fuel.

Thankfully you enjoy tinkering, because it will take a ton of it!!!

[Zedyone_kenobi]

Unfortunately, I know this is true, but I love it.

[milgeo]

[hello guys i need your advise i have a 2.8 l in my 240z with tripples idle55f8 main 130 air 170 ef16 the car idles perfect when about 1500 stumbles and misses spits up top is fine while cruizing it nmisses now if i pull the choke while it idles the miss goes away but it doesnt idle can somebody help with a diagnosis on what i need to do

[240260280z]

What size Choke (Main Venturi)?

What size carb (40,42,45)?

What model variation if it is a DCOE?

First step is to set the fuel level to 25mm down from the main jet well on all 3.) Read This: http://www.classiczcars.com/forums/thread47405.html

Second step is to balance all carbs at idle

Third step is to ensure all linkages are the same length

Fourth step is to balance air flow at 3000 rpm with linkage adjustments.

Edited October 7, 2012 by Blue

[Zedyone_kenobi]

Agreed, the more info you have the better. Also, do you have a wideband?

[pjoe]

How do you guys balance carbs at 3000 rpm? If I try with my sk meter, the meter is off the scale and unreadable. Also how do you keep it at steady 3000 without using throttle stop screws and messing up balance at idle or am I missing something? I just visually balanced throttle linkage operation and its pretty good but maybe it can be better. Its perfect at idle as far as balance goes. Milgeo....from a seat of pants tuner, I would try going up on idle jet and see if it makes a difference. Are your plugs on the white side after idling for a few minutes?

Brian