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strange miss under throttle

842 views 10 replies 4 participants last post by  1982 SS 
#1 ·
On my chevy 383 stroker i have been noticing a strange miss. Almost it seems as the motor is starving for fuel for a second and then everything seems to be good and it goes like heck
I'm running two 4 390 holleys with 57 jets I think and about 14 degrees on my light but for about five seconds it seems to starve, not bog and then i squeal as the transmission shifts at 5500. I've got the vacum secondaries tied together and watching my vacum gauge tere appears to be no problem, i was wondering if maybe I had to change my vacum advance to a lower hg setting, maybe it is advancing to quickly, points are not there i'm running a crane breakerless. anyone have any ideas. anyone with any experience at setting the time up for the two four systemn?
 
#7 ·
I,m Not Sure Of The Pump Size And I'm Pretty Sure I Have The Pump Cam Set At It Highest, Wondering If The Air Idle Circut Could Have Anything To Do With It, Increased My Timing On The Light To 14 Degrees And It Seems To Be A Bit Better , Have To Check The Pump Size Tonight To Make Sure But I Think I've Got The Larger Pump In The Carbs Because They Are A Part Of The Tric Kit I Installed On Both Carbs.
 
#8 ·
Whao over-capitalization!

Anyway, how bout the squirters (shooters whatever...) Is there a chance they are too small and giving you a lean conditon? I would imagine that it would be something in the fuel delivery at that point, whether it be accelerator pump volume or timing.

I doubt that it is ignition related. 14 initial is acceptable (to me anyways) I like to run 12 -14 initial on my 383. Also, vacuum advance will have no bearing on how it performs at WOT. There is no vacuum under WOT. If you had too much advance too early it would ping or pop through the carb(s).

My guess is fuel delivery.
 
#10 ·
Sorry

Sorry about the capitals! It is not as much as 5 sec. bog but it seems like it if I apply the gas on a constant steady movement it goes like hell but when it hit it hard it seems like the rpm's build a lot slower, it's bit like flooding initially but it doesn't really flood, I think the squirters might be a idea but when i snap the throttle lightly its nice and crisp.
 
#11 ·
loaded vs. unloaded. That is why you can have a too much ignition timing and it revs great out of gear but detonates like crazy under a load. Same kind of things apply. This is one thing where you are going to have to experiment with. Your setup demands different things than other engines. every in is different. I would try the squirter first (easiest to get at) go up (or down) a little bit and try it. Keep going until it gets worse than the previous test and go the other way unitl you find the ideal set up. Also change one thing at a time otherwise you will not know which change made the difference. I would document what change you did and how it performed so you have a reference for future tuning efforts. This works real well if you can get track time, which is not always accessable to everybody. That gives you hard data to work from.

If you find that squirter size does not make a difference or it is as good as it gets, then move on to the next tunable item (either acelerator pump volume or timing via the pump cam).
 
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