Tuning 40 DCOE Weber 151 on an L24

[Reverend]

My head hurts to read this, too much technical data All i wanna know is how big performance boost do you get with triples?

[240260280z]

My head hurts to read this, too much technical data All i wanna know is how big performance boost do you get with triples?

I noticed crazy low rpm torque boost. It is nice to see a 2nd opinion with the same finding here...and data: http://datsunzgarage.com/weber/

[conedodger]

I followed a link posted here and ended up on Sidedraft.org or some such site. I joined and posted and Keith Franck himself has offered to meet me at Thunderhill and tune my carbs! He says if the tune is right, density altitude will not make much difference...

[LeonV]

I noticed crazy low rpm torque boost. It is nice to see a 2nd opinion with the same finding here...and data: http://datsunzgarage.com/weber/

I noticed the same thing. I can take off from a standstill in 2nd gear, as if it's first.

I followed a link posted here and ended up on Sidedraft.org or some such site. I joined and posted and Keith Franck himself has offered to meet me at Thunderhill and tune my carbs! He says if the tune is right, density altitude will not make much difference...

Nice! I should hopefully be meeting with Keith next week.

[madkaw]

OOPS double post

I know I'm not a Weber guy, but I will agree with the great gain in lower end. Of course this is probably subject to the cam each of us are running. With my Mikuni's I kept pushing the envelope of the pilot side by seeing how rich I could get it. When I thought I was putting too much emphasis on the pilots and tried making corrections elsewhere, I would still be fighting the 'dead spot'. I started with 200 main airs and ended up with 180's. Started with 57.5 pilots and ended up with 67.5's. Had 40's acc.pumps and went back to 47's.

In MY CASE, my motor wanted it down low. My engine pulls hard right from 1500rpm straight thru to 6000rpm. Only on a dyno will I know for sure what the number look like.

I am idling anywhere from 12 to 13, and cruise is around 14 AFR. As I have read before, they like to run rich. Thus the advantage of EFI, nice lean idle and cruise, then dial in the power zone. Makes me want ITB's even more.

Edited August 31, 2012 by madkaw

[madkaw]

I know I'm not a Weber guy, but I will agree with the great gain in lower end. Of course this is probably subject to the cam each of us are running. With my Mikuni's I kept pushing the envelope of the pilot side by seeing how rich I could get it. When I thought I was putting too much emphasis on the pilots and tried making corrections elsewhere, I would still be fighting the 'dead spot'. I started with 200 main airs and ended up with 180's. Started with 57.5 pilots and ended up with 67.5's. Had 40's acc.pumps and went back to 47's.

In MY CASE, my motor wanted it down low. My engine pulls hard right from 1500rpm straight thru to 6000rpm. Only on a dyno will I know for sure what the number look like.

I am idling anywhere from 12 to 13, and cruise is around 14 AFR. As I have read before, they like to run rich. Thus the advantage of EFI, nice lean idle and cruise, then dial in the power zone. Makes me want ITB's even more.

[240260280z]

But it is a great double post!

[Reverend]

How have you guys accomplished the positive crankcase ventilating? I read from the link Blue gave that there is no pvc inlet in triples. Someone might have wrote about it in this thread, but my eyes go crossed when trying to find it in the middle of technical jungle.

Edited September 5, 2012 by Reverend

[cygnusx1]

I am not sure if this counts but I once tapped into the filter boxes to vent my Alfa crankcase back into the carbs.

[240260280z]

How have you guys accomplished the positive crankcase ventilating? I read from the link Blue gave that there is no pvc inlet in triples. Someone might have wrote about it in this thread, but my eyes go crossed when trying to find it in the middle of technical jungle.

Check this one: http://what-when-how.com/automobile/crankcase-emission-control-automobile/

[LeonV]

How have you guys accomplished the positive crankcase ventilating? I read from the link Blue gave that there is no pvc inlet in triples. Someone might have wrote about it in this thread, but my eyes go crossed when trying to find it in the middle of technical jungle.

http://www.zcar.com/70-83_tech_discussion_forum/pcv_system_triple_carbs...pics_686437.0.html

[Zedyone_kenobi]

We last left our hero with a very functional setup of the following:

120 Main Jets

170 Air Corrector

F11 Emulsion Tube

60F9 Idle jets

This yielded a decently smooth idle and a steady state cruise AFR of around 12.9:1.

Going to lunch the other day though, my friend who was following me told me that I was reeking of gas behind the car. This concerned me. Needlessly running rich does not yield any advantages at all.

so lets try to figure out what was happening. First at around 2600 rpm in 4th, the throttle plates are barely cracked. I think it is very safe to say I am NOT pulling form the main circuit at this time. So it has to be in the idle jet. The more I thought about this, the more clear it seemed. Simple tests for idle jet 'correctness' at least from an AFR point of view.

When I was idling at 12.5:1 the mixture screws were barely 1.5 turns out. As Blue noted and I confirmed through more reading, the 151's really need more than this. More like 2 full turns. But I will get back to that.

Keeping in mind the mixture screw does not adjust Air/Fuel mixture. It is merely an opening that allows premixed air and fuel to enter the throat of the carb. The more you open it, the more premixed air and fuel enters. This means that you can get the car to idle with darn near any idle jet by making adjustments to the idle screws to get enough fuel in there. I would wager that there are limits to this, but for the most part if you are close you can get her to idle. So how do you know if you are crazy rich on the idle jet?

My moment of clarity came as I was taking a long tuning drive down the freeway. Any tip in I did in 4th gear at around 60 mph I immediately dropped to 10:1 AFR. If I kept my foot more in it (meaning I introduced the main circuit into the equation), my AFR got closer to 13:1.

So my webers were talking to me and I was not listening!! What do I mean? Well since I had to go so far down on my mixture screws to get my idle AFR in a happy place (deemed as 12.5:1 by popular opinion) and my AFR while solely in the progression circuit (which is also fed by the idle jet) was dipping in to the 10's it tells me that the premixed air/fuel from the 60F9's was too rich! Now post #34 seems to contradict this, but looking back at my hand written notes, I made that assumption too quickly. I did not take her on the freeway long enough or do a long enough drive. I think I was getting into the main circuit when I stated that my part throttle AFR were spot on. When I carefully drove on the free way at very slight openings of the throttle, the AFR is indeed in the 10's.

My biggest problem is that I never have enough time to do more than one test per week. I need more time to test and document these things. GRRRR.

my quickie fix was to remove the 60F9 and install the 50F9's. I was able to adjust the mixture screws 2.25 turns from fully seated, when I attained the 12.5:1 AFR at 1000 rpm. Also of note, my idle did get smoother and the AFR reading was not as bouncy.

I may still need to install the 55F9s. We will see. But all of this will be thrown out the window as I have ordered my 32mm chokes from www.carbsunlimited.com. So we will have to tweak these all over again at a later date.

If you wonder if I am having fun messing around with these. Well the answer is a resounding yes!!! I love carburetors. I love the fact that it requires a certain skill set to make them work correctly. I love the trial and error portion of the work.