engine and drivetrain DCOE Stumble on throttle transition

[2joejoe2]

Hi, 

 

I am having some issues tuning my car. My car stumbles when transitioning from the idle circuits to the main circuits.The car Idles fine and pulls very hard once I get past the stumble. I am also running a wide band O2 with an afr gauge. The car Idles a little rich 11-12afr and it sits between 12 and 13 during hard acceleration. When the car stumbles I can see on the afr gauge that it is leaning  way out. also If I just get on my car really hard accelerating it does not stumble    Below is what I am running:

 

Engine and exhaust 

-9.5:1 IE pistons 

- E12 head with mild port and 296 cam

- IE long tube headers with 2.25 exhaust 

- Mechanical advance dizzy with pertronix

 

Intake

dual mikuni PHH 40s

- 35 mm large venturi

- 170 mains 

- 200 Air

- 62.5 pilot 

- 40 pump nozzle 

 

[zinz]

You're up, Daron... 

[KFunk]

Mikunis aren't DCOEs.... DCOEs are Webers.

[2joejoe2]

Mikunis aren't DCOEs.... DCOEs are Webers.

ha ha Bla Bla bla  ...............Fine PHH tuning issues

[zinz]

Daron is busy, so I'll ask...

 

Where are you setting your ignition timing?

 

Ed

[Guest_anonymous]

Before this comes up, Todd Walrich of Wolf Creek racing recently passed away.

[2joejoe2]

I knew this was going to be brought up. I honestly do not know where my ignition timing is set. I set it by ear. I advance it while idling until it runs rough then turn it back a hair............ Kind of ghetto I know 

[2joejoe2]

Before this comes up, Todd Walrich of Wolf Creek racing recently passed away.

very sad. do you know what happened? He didn't sound very old when I talked to him a year or so ago

[KFunk]

ha ha Bla Bla bla  ...............Fine PHH tuning issues

 

 

Well, I could've maybe helped you with Weber DCOEs myself, which is why I clicked here.  If you want help with Mikuni PHHs, then you're going to need to find a whole different other set of people.

[2joejoe2]

Well, I could've maybe helped you with Weber DCOEs myself, which is why I clicked here.  If you want help with Mikuni PHHs, then you're going to need to find a whole different other set of people.

 

I figured the principles would be the same.......

[zinz]

Sorry to hear about Todd Walrich... The Datsun and Mikuni crowd will feel that one...

 

Spot-on ignition timing with sidedrafts is crucial for best running.  Without knowing exactly where you are setting the timing, it's pointless to speculate any further.  I would only suggest advancing it a few more degrees and see how it runs. Be careful of pinging...

 

Which filters and velocity stacks are you running?

 

FWIW...I finally ditched my Tii mechanical advance-only dizzy in favor of the 123Ignition, programmable distributor.  All my poor-running symptoms went away, mostly because I was able to add vacuum advance into the mix.  My issues had more to do with cruise and off-idle running, not transition during acceleration, though.  Initially, I was timing to the ball@1400rpm and getting terrible running.  I eventually timed more like 32degrees@2000rpm and the engine came alive.  Your 9.5/1 comp ratio will limit how much advance you can throw at it.

 

Ed Z

[2joejoe2]

Thanks Ed for the pointers. I am runing some basic ~ 2-3" stacks with Pod filters from IE....I forget the brand of the filters.  

I have been hearing a lot of really great things about the 123 ignition....I will probably go that route once I get some spending money.........I just got married and bought a house so  at the moment I am broke 

[2joejoe2]

Ed, You were correct on your diagnosis. advanced the timing just a little bit more and it the stumble has totally gone away. 

 

Thanks!!!

[zinz]

Hey...that's great!  Glad it was such a simple fix.  Falls in line with the old saying about "99% of your carb problems are ignition.."

 

Thank Daron, he was offline, but runs Mikunis, too.  I texted him and he said... "it's ignition timing..."

 

As for filters and stacks, that's a good setup, IMO.  I run a bigger version of those UNI filters and been very pleased.

 

Have a great weekend... go run the snot outta that car

 

Ed

[TobyB]

 

ha ha Bla Bla bla

 

It does matter- Mikuni and Weber are similar beasts of a different species,

 

So if you tried to splice their DNA, well...

 

it's like that Loverboy song, pig and elephant dna just don't splice....

 

t