440 lumpy when coming down on revs.

[Animal]

Timing is set @ 36*,vac plugged.freshley built 440 stock, Holley 750 sec vac.If you rev the engine in neutral,when it goes back to idle (900)it tends to stumble,then picks itself up again to 900 revs.I have set the mixture up via a vac gauge & the plugs are a nice tan colour.The engine run between 180 & 200 temp.would it be wise to advance it more.Thanks Adam.

[firefighter3931]

Adam, what is the base timing...how much advance at idle. The 36* sounds fine for total advance but it might need more inital timing.

Ron

[Animal]

Hello Ron,I will check tomorrow.I always thought that if you had 36/38* with vac plugged,the rest would follow.If I set the timeing @ 12 initial (please let me know otherwise),then if I adjust it @ 2800 revs,it will then put the initial out.Nice to hear from you Ron. Adam.

[firefighter3931]

Adam, sometimes the ignition curve needs to be modified depending on the advance plate that originally came with the distributor. For example : if the original plate supplies 26* of mechanical advance....that would leave you with only 10* of base timing at idle (if you set it at 36* total). See how much advance you've got at idle and report back.


Ron

[Animal]

Ron,set the timing @ 8* @ 900rpm,when I take it up to 2800rpm,with vac plugged,all I can get is 30* on timing light.car seems to run better like this,but it tends to pop & bog when you hit the throttle hard from standstill.When it is set up as before @ 36*,it runs great,apart from the problem I stated in original post.Thanks in advance.Adam.

[firefighter3931]

Try bumping up the timing to 14* at idle and leave the vacuum advance plugged. Take it out for a spin and see how it responds.


Ron

[Animal]

Thanks Ron,I'll try that tomorow.Would that put me back to 36* again.as I am advanceing it 6*.BTW,going to santa pod for the weekend to try the 1/4 mile. .Adam.

[firefighter3931]

Would that put me back to 36* again.as I am advanceing it 6*.

Yep, but you'll be eliminating the vacuum advance that pulls in extra timing. It should run better, almost every BB mopar likes lots of initial timing. If it bogs or stumbles we'll have to look at the carburator and tune it.

Good luck at the track, you'll be hooked after the first pass 


Ron