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sackattack84

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Since: Sep 07, 2004
Posts: 14



(Msg. 1) Posted: Tue Nov 06, 2007 12:05 am
Post subject: big block hesitation
Archived from groups: alt>autos>dodge (more info?)
Hey, what's up, everyone? Been a while since I posted a topic here, but I
finally finished rebuilding my engine and, of course, now I am running
into problems tuning the thing. It is a 400 big block Chrysler .030" over
with Keith black 9:1 hypereutectic pistons, Summit hydraulic cam and
lifter kit with 282 degrees intake and 292 degrees exhaust advertised
duration with .465" intake and .488" exhaust lift and a 114 degree lobe
separation angle, stock crank and rods, rebuilt 452 heads w/ 88cc chambers
and a freshly rebuilt Holley 4160 style model 3310 dual feed 750 cfm
carburetor. The carb has a Quick Fuel Technologies externally adjustable
vaccuum diaphragm (really cool!!)and a new power valve. The cam is also
advanced 4 crankshaft degrees. Initial timing is 15 degrees before TDC. It
runs very well, but hesitates when the throttle is yanked open. The floats
are spot on, the idle mix seems to be about right. I don't recall exactly
what size jets were in the carb when I tore it apart, but I believe they
were like #76 or similar. It has a Mopar performance electronic ignition
distributor with the stock weights and springs (for now). My first thought
was carburetion, but I adjusted the secondaries throughout their entire
opening range and adjusted the accelerator pump cam and have seen no
difference as of yet. Anyone have any ideas?

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dodge-him

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Since: Nov 08, 2007
Posts: 1



(Msg. 2) Posted: Thu Nov 08, 2007 12:34 pm
Post subject: Re: big block hesitation [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
Where did you plug the vaccum line in??? it should be on the outlet on
the front pass side of the holley (ported Vacuum) not the one under
the front off the base plate. (manifold vacuum)
15 initial sounds like a lot?? Total with vacuum unhooked and plugged
is the way to tune it.
Set total to 36 or 38
You may also want a advance spring kit add one at a time.
Could be you need to tune the accelerator pump system on the front of
the carb??
dodgem
I like to plug vacuum advance till everything is sorted out then if
you must try to work the vacuum in???? Try It
If it causes pinging it must be tuned with a 3/32 allan wrench in
through the vacuum port.

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sackattack84

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Since: Sep 07, 2004
Posts: 14



(Msg. 3) Posted: Mon Nov 19, 2007 4:06 pm
Post subject: Re: big block hesitation [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
The vaccuum advance on the distributor is capped off for the moment, as are
the vaccuum line in on the baseplate (manifold vaccuum) and on the
passenger side (ported vaccuum) of the carb. I have an advance spring kit,
but have not installed it yet. I did atempt to adjust the accelerator pump
cam, but it did not seem to have any effect. Maybe I just need to play
with it a little more?

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dodge-him

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Since: Nov 20, 2007
Posts: 3



(Msg. 4) Posted: Tue Nov 20, 2007 7:47 am
Post subject: Re: big block hesitation [Login to view extended thread Info.]
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It may need bigger squiters in the front. what is the total advance??
may need lighter advance springs.
You say cam is advanced 4 deg you mean you degreed it and it cam out
at 110 ATDC intake max lift (intake centerline) ???? or you advanved
it another 4 from manufactures centerline 109 to 105????
You checked and rechecked timing marks?? (not nesesary if you actually
degreed the cam)
dodgem
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dodge-him

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Since: Nov 20, 2007
Posts: 3



(Msg. 5) Posted: Tue Nov 20, 2007 7:49 am
Post subject: Re: big block hesitation [Login to view extended thread Info.]
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It's a vacuum secondarie carb right??? and you have tried a multitude
of advance springs or has someone put a manul opening kit on it but
with no provisions for accelerator pumps on the back two barrels??
Dodgem
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dodge-him

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Since: Nov 20, 2007
Posts: 3



(Msg. 6) Posted: Tue Nov 20, 2007 7:56 am
Post subject: Re: big block hesitation [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
The power valve can be critical too it should be one to two numbers
above idle in gear vacuum but optimum advance must be dialed in first.
i would buy and install lighter advance springs.
then set total to 35 to 37 if ping occures back total down. or advance
it up till it pings and then retard it till ping gpes away if you have
no way of setting total timing.
Then get it idling in gear and check vacuum if its 7.5 to 8.5 go with
a 6.5 valve if it is 6.5 to 7.5 go with a 5.5
Dodgem
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sackattack84

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Since: Sep 07, 2004
Posts: 14



(Msg. 7) Posted: Tue Nov 20, 2007 8:52 pm
Post subject: Re: big block hesitation [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
Thank you for your advice. Yes, it is a vaccuum secondary carb. Instead of
the stock secondary diaphragm housing, however, I installed a billet
secondary housing from quick fuel technology which allows you to adjust
spring tension by turning a screw on the outside of the housing rather
than having to actually change the spring. I will definitely recheck total
timing and power valve size and let you know what I find. Thanks!

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