Hello Gents,

As the title states I am experiencing some issues during deceleration when coming to a stop using the gears. I can put the car in neutral and it stays running. But when I use the gears to help with the stop especially when coming in hot and fast the engine just wants to die. It always dips to 500 RPM and most of the time just stops running. It idles good, it runs good going thru the gears, sounds freaking awesome! but the damn stop.....

Been tuning the carbs for a few weeks and I think it is real close. Idles at 1000. Fuel PSI is 3.5. Fuel return line is capped. I barely have the 2-3K rpm stumble. I can tell it pulls very nice all the way to 5500 but that is as far as my butt is calibrated....anyway I think the cam tops out of 6400???

Timing set to 12 degrees at 1000 rpm and 34 degrees advance at 3000 rpm ( no creep when rpm increased to 4000)

I have read many Weber tuning manuals and haven't come across the "dies upon decel" troubleshooting steps. The carbs were good when they came out of a L24 and have been sitting for a few years. I cleaned them up like a rookie would and did a minor overhaul using the Peirce Manifold kit. Change the chokes and the idle and main jets per Peirce Manifold tech reps guidance.

I don't have a clue what my next step should be other than checking for some restrictions in the carbs.

Here is the specs of the engine:

CARB SPECS

CHOKE 34

AIR CORRECTION 180

MAIN JET 140

IDLE JET 50F9

EMULSION F11

AUX VENT 4.5

PUMP JET 1.75

NEEDLE SEAT 1.75

INLET VALVE .55

ENGINE SPECS

N42 block overbore 3mm

KA24E PISTONS ITM RY6660 CUT .5mm

N42 head port polished gasket matched

ISKY L480 Cam

Cosmetic head gasket 1.2mm

71 240z connecting rods

MSA 6-2-1 header

2 ½ “ Magnaflow glass pack and Magna flow exhaust

Canon Intake

Vacuum plugged

Weber DCOE 40-18

1975 280z distributor

3 ohm Petronix flamethrower

Taylor 8mm spark plug wires

Edited January 24, 201411 yr by dawg7
wrong engine pic

Do you have an air flow meter to set up carbs? Do you have an O2 sensor?

These make tuning so much easier.

I have the SK airflow meter and I have the carbs sync'd within 0.5. And I am planning on installing the O2 sensor and AFR reader next month. I will be researching those products in the next few weeks. This week and weekend will be spent on fixing the binding.

Fix your linkage and make sure the throttle plates are in sync. It sounds like your idle is too lean. If you're idle mixture screw is out more then 1 turn you need to richen the idle jet. The idle circuit in a Weber DCOE is not just for idle. I is critical to engine running up to about 2,000 rpm. If you have a stumble around 2,100 to 2,500, which is about where the carbs transition to the mains, you're idle circuit is also too lean or you have the wrong emulsion tubes in the carb.

+1 on ensuring all throttle plates are set the same, sounds like you already had that figured out with the progression hole alignment you mentioned earlier. It looks like you have 3 linkage-rod mounts (I've read sometimes the 3 mounts arent always aligned and causes slight binding)...does your linkage rod rotate freely when the engine is off?

More importantly, it doesn't look like you have an external throttle return spring? I would DEFINITELY implement that as soon as possible (for safety). I use the set-up sold by piercemanifolds and would recommend it.

p.s. an O2 meter is a great tool, take the guesswork out!

Edited February 3, 201411 yr by TBone028

A huge percentage of Weber problems are linkage related...problem is when the linkage doesn't work precisely, tuning them is a moot point.

First of all I appreciate the feed back and tips. From what I am reading to what I am seeing on my setup it leads me to believe that I have a binding issue. So I am going to replace the linkage. I don't like that look of it anyway... I rushed this project trying to beat some established timelines. Big mistake on my part. So first thing I am going to do is look through this site and check out some setups. I have seen some nice billet sets, (cygnusx1 yours looks amazing) I just can't find them online. I already am using a Lokar throttle cable.

BTW the PSI is a constant 3.5. I have a 4 psi fuel boost and the mechanical pump installed.

I have been working the issue for the past days and have made progress. BLUF. The linkage was binding and timing was off (for triple webers). I bought the universal set from Pierce Manifolds and it works great; looks good too! I also replaced the dizzy with one from a 79 280zx. Reading the Weber power tuning manual I increased the timing at idle until the RPM stopped increasing. The idle timing now is 17 and the mechanical advance is 17 for that dizzy. The idle is really smooth; what a difference that dizzy makes and the engine doesn't die at all. Next is the AFR for final tuning. Again thanks for the replies.

Edited February 18, 201411 yr by dawg7

On the timing, you are where I tuned a 240z with triples. Good to have convergence.

btw Lazeum is spot on when it comes to webers and timing. Read his achived of posts.

Ah, the linkage on 240z triples, I have fought this good fight many times, and I am finally going to kill it. The throttle has never felt as good as it did with the OEM push pull rod set up. I have a lokar kit and I have never liked it. I added stronger return springs in my carbs and still it does not return all the time without a blip or two. And now I am stuck with the damn hard as hell to push gas pedal.  I am dumping the cannon manifold for the Harada one Mike W put me onto.  Larger beefier throttle control rod and it can hook up to the OEM push pull rod set up, which to me is far superior.  My SU's were pure butter compared to my damn throttle cable. It is the one thing that can make a Z less than a joy to drive. My Roadster has a sublime throttle feel.   The best my Z ever felt was when I had my new Ztherapy SU's with fresh OEM linkage. I want that back.

 

Take your time bud. You will get it right.

Ah, the linkage on 240z triples, I have fought this good fight many times, and I am finally going to kill it. The throttle has never felt as good as it did with the OEM push pull rod set up. I have a lokar kit and I have never liked it. I added stronger return springs in my carbs and still it does not return all the time without a blip or two. And now I am stuck with the damn hard as hell to push gas pedal.  I am dumping the cannon manifold for the Harada one Mike W put me onto.  Larger beefier throttle control rod and it can hook up to the OEM push pull rod set up, which to me is far superior.  My SU's were pure butter compared to my damn throttle cable. It is the one thing that can make a Z less than a joy to drive. My Roadster has a sublime throttle feel.   The best my Z ever felt was when I had my new Ztherapy SU's with fresh OEM linkage. I want that back.

 

Take your time bud. You will get it right.

I felt you weren't too happy with your Z when you mentioned selling it.  

 

Reading your thread about the motor swap and all is when I first started reading this forum daily and is what put two 240s in my garage.  The wooden crate you gave us dimensions to build one was when I knew I had found the right group of people on a forum, sharers not just takers.  I never really saw any special differences between the 240s and the 280s until I kept up with your build.  You changed my mind, thank you for that. 

That is very kind bud. I have been driving her a lot more lately. And my love affair is back with a vengeance. My Z is about to get a lot more love (read as money) dolled out on it.

 

To know I helped out my fellow man, well you just made my day buddy.

 

My Z is not going anywhere anytime soon. 

 

Well unless some crazy person offers me obscene money for it...

 

Nah, even then I am keeping it.

Edited October 29, 20159 yr by Zedyone_kenobi

I can attest to linkage bind on my Mikuni's as well. Worked all Summer adjusting linkage,

changing a 280Z firewall link rod, different lengths of individual carb link rods.

All trying to free up bind and using better linkage mechanical advantage.

I finally got it to work and return to idle position good enough to remove the added

return spring that just created more pedal effort.