hesitation with my 340

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moparpat88

moparpat88

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freshly rebuilt 340, holley street avenger, orange box,and 2 wire ditributor. stock 6 cyl coil and voltage regulator. problem occurs when i am at crusing speed and "floor it" the motor spits and studders then takes off like a bat out of hell. i am almostpositve it isn't detonation,i pulled myplugs they were normal. i realized that my vacum advance was disconected i hooked it back up and the problem was still there it just didn't seem as bad. however my last run with the car ihad the head lights on and when it spits and studders it seemed like the lights went dim. any advice?
 
the carb does have vacumsecondaries and it came with 3 springs black, stock, yellow. i think i used the yellow which i thought was the lightest spring, i'll have to check
 
i had the same exact problem with my 360 and i have the same carb as you so maybe i could help because i have resolved my problem. I changed two things. first thing i changed was the vacuum secondary diaphragm. i took apart the carb and checked to see everything was ok and found my seal for the diaphragm had a tear in it causing me to lose vacuum and in return would cause my vacuum secondaries to not open up when i wanted them to. The second thing i did was saw that my power valve was a 7.5 WAY to big for the cam i am running (comp 284XE) so i bought a 6.5 and a 5.5 and stuck the 5.5 and the car runs a lot better. When i was crusing on the freeway and would stomp it the car would hesitate and THEN pull, same thing with cruising on the street but now that i have changed thest two things the car runs perfect. So give it a shot if you want it just may be the same thing i went through. How old is the carb?
 
You might try advancing the timing a few degrees and see if it helps. Like the guys said ,check your vacuum advance to make sure it works and works properly.
 
and if you are going to be doing the spring change alot you may consider a quick change spring housing so you dont tear up the diaphragm.
 
When you open up the vacuum diaphragm, before you put it back together, lube the 4 holddown screws with vaseline so they don't catch the edge of the rubber diaphragm and pull it and rip it.
 
My 670 Avenger carb came with the quick change housing and the 3 springs he described in the original post. I to had a hesitation, tried changing springs, shooters, power valves and jets (just proved how impatient I am). Put everything back to original and was going to seek out a Holley God here in Idaho. Just tinkering, I bumped the initial timing from 16 to somewhere like 22 degrees, cured everything. Then I backed the timing 1 degree and kept doing it until the hesitation reoccurred. I ended up with 19 degrees. Lesson learned, well almost, I'm still impatient!
 
well thanks for all the help, my vacum advance hosekept coming loose so i repaired that. I messed withthe most of the afternoon then finally i gave the distributor a slight turn. with a little more tweaking i think i got this problem solved what had happened was that when we were swapping out transmissions the dist. got bumped retarding my timing. i have not checked it with a light yet but the motor is screaming pretty good with no detonation or hesitation........my nieghbors hate me
 
Rotate the distributor clock-wise to advance? It's been a while and the memory ain't what it used to be.
 
you just go opposite the rotaion of the distibuter to advance it,this holds true to any motor. a small block mopar has a clockwise rotation so you go counter clockwise to advance the timing however a big block is just the opposite
 
The easy way to remember is the vaccum advance points the way you want to turn it to advance the spark. Small block is counter clockwise, big block clockwise..
 
moper said:
The easy way to remember is the vaccum advance points the way you want to turn it to advance the spark. Small block is counter clockwise, big block clockwise..
Click to expand...

Thanks... I needed to know that. I could never find a way to remember.... now I have.
 
Thanx guys! I wasn't looking forward to getting my hand wedged under the tunnel rams while trying to guess my way through this with the engine running.

20081012_03.jpg
 
yea just don'tdo like my brother did, he left the hold down a little loose so that when we were shakin it down he could just jump out of the car and adjust it as needed but he left it too loose and it kept on moving on us, it was really agravating but he is the best for sticking his hands into a hot motor tomess with it.
 
Been there, done that. Very frustrating. I kept adjusting my old carb thinking it was taking a dump when I realized the distributor was just a spinnin' at will.
 
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