Stalling issue(under throttle)

[NA&CH]

I just did a search and found you explaining the 123ignition. Pretty neat system. Looking into that now. I'll look through that thread as well. 

Thank you sir. 

Chris 

[NA&CH]

Starting tinkering. 

Pulled the wires from the plugs and 2&3 have no change when pulled. All other drop idle significantly. Pulled all 1 at a time. Switch wire locations? I am matching up wires from cap. ?

I plan to replace the fireball system with something newer and current then maybe the 123 after I figure this out. 

Thanks again,

Chris

[siteunseen]

I'm most likely totally off base here but #1,2 and 3 runoff the front carb.  May be a fuel problem.  I would pull those plugs one at a time a check their spark.  Good luck. 

[NA&CH]

Spark plug Pictures from this past weekend. I have some tools arriving this week to do test on various items. Also something I should have done before jumping to the modification pages... the plugs are less then 2 months old. 

Any more insight is greatly appreciated. 

Chris 

[240260280]

Front carb is leaner than rear carb from the plugs. Rear carbs look better.

 

You can lower the front jet 1/4 turn  to balance the fuel better.

[NA&CH]

Using the Uni-syn and the front carb has little to no air pulling when at 2k. The rear is working. It is rich but working. What would cause the front carb to not be "working" or is this normal. Also where should the distributor be set at advance wise? 

Reading how to tune Su carbs now...

Chris

[Mark Maras]

 Sounds like the carbs are out of balance. Any early Z shop manual will tell you how to balance them. It's not difficult. I'd start with resetting the nozzles 2 1/2 turns down and then going thru the balance procedure. Dist. is usually set at around 10 degrees advance. There is a good thread about SU tuning. Google "Quick and dirty SU tuning.

Edited July 19, 2018 by Mark Maras

[Zed Head]

Read the chapter in the FSM about the carbs.  Or just Google SU's.  They're not "normal", they use intake vacuum to raise a piston which then allows air flow.  What you see on the gauge is the vacuum on one side of the carb.  A higher number actually means less flow.  You might have a stuck piston.  They also use oil to damp the movement of the piston.  They're odd mechanisms!

[240260280]

Step 1. Idle Adjustment:  https://www.classiczcars.com/forums/topic/50683-need-advice-on-properly-tuning-both-hitachi-su-carbs/?tab=comments#comment-461005

 

Step 2. Off-Idle Adjustment: https://www.classiczcars.com/forums/topic/50683-need-advice-on-properly-tuning-both-hitachi-su-carbs/?tab=comments#comment-461047

 

[heyitsrama]

I believe you will need to get a front mounted airflow measurement tool, measuring from where you are is after the balance tube.

But I could be wrong, I would want someone else to double triple confirm.

Was there a filter in the engine compartment? There are two additional filters at the float chamber of the SU carb, for me it was throwing off my float measurements, and causing my stalling issues, after cleaning them out, I was able to get a good tune.


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[siteunseen]

Agree with what's been said above. 

A simple test would be to raise both pistons and see if they fall at the same rate, pretty slow fall if the damper oil is right.  They should make their "clunk" sound at the same time when they hit the bottom.

You need one of these if you have dual carbs, makes things so much easier. 

https://www.amazon.com/Latest-Rage-Deluxe-Carburetor-Airflow/dp/B00CMC57R0/ref=sr_1_fkmr0_4?ie=UTF8&qid=1532074358&sr=8-4-fkmr0&keywords=unisyn+carb

[Zed Head]

Here's another good SU link.

http://sucarb.co.uk/technical-su-carburetters