vacuum advance. NEEDED????

F

flathead30

Junior Member
I'm running a '53 flatty bored .60 over, Isky 400Jr. offy dual intake with 2 97's, dual point dist. using Mobil hi test. My question is, should I be using a vacuum advance? When running it I get pinging going up a long grade, back fireing when just touching the throttle. Any suggestions??
 
Number one your timing is probably off if it's pinging. Back off the timing a few degrees. What kind of dual point dizzy are you using and is it a full centrifugal advance type? If not I would get it changed over. Are the heads stock?
 
Vacuum advance is of most benefit at part throttle cruise conditions and it's generally accepted that it can improve fuel economy in any engine, but I would check your total advance. Consensus here seems to be 24 deg and all in by 2000 rpm. You could be a little lean also; others will better guide you to best jet sizes. Did ypou read the plugs?
 
flathead4rd'
I'm running Mallory dual points, offy heads, merc 4" crank, timing has been checked and tried different settings. I tried different springs in the dist.
 
joel,
I'm running #44 jets. I've replaced the plastic floats to new brass folats (compliments of Stromburg),(Freebe). Plugs were running great, all even, just to eliminate a possible tire plug, I just replaced all plugs, made no difference. Also replaced ign. coil.
 
After you get the timing straightened out, you might consider putting 2" rizers under the carbs. I say this because the 400jr is a short track cam and the overlap causes low rpm stumble in a street engine, It also improves throttle response.

Bubba makes a SBC conversion that works pretty good.
 
I guess i8 need to know what version Mallory you have . The early YCs had a vacuum retard just like the ford crab used. If thats the unit you have then yes you really need vacuum for spark retard etc. The later ones didnt use the vacuum unit etc.
A mallory is very easy to adjust on a machine with a total max adjustment and springs that allow adjustmnet by bending the tabs.

If you look into the unit the springs are visable .....the lighter of the two springs ( light for low speed and heavy for high speed) you can adjust tension by bending the tab the spring hooks on to.
Spark knock at low speed ? Increase the tension on the low speed spring etc..........
 
I agree with Ol'Ron. My harley suffers a little with the same symptoms; It is fuel inj. but a combination of cam timing and exhaust tuning produces poor flow and mixture problems between 2400 and 2700 rpm, which is compensated for by overly riching the fuel map.You may have a similar situation for different reasons completely. I'd definitely look into the risers. JMO
 
http://www.malloryperformance.com/pdf/Single_Dual_point.pdf

Here is a link for adjusting the advance on Mallory Dual point distributors. I'm not sure if it applies to the vintage ones?

You should not need to run a a vacuum advance to solve your problem. Ford used factory dual points with mechanical advance on all their hipo engine in the sixties and they worked just fine. I have one on my '66 Shelby GT-350 with 10:1 compression and it does not ping a bit. You either have the initial timing off, too much advance, a lean fuel condition or too much compression. What are you using for a timing mark and what is the initial timing set at?

Did you check the total advance with an adjustable timing light? If not go buy an adjustable timing light. The intial timing only tells half the story. Never buy a timing light that is not adjustable for checking total advance. They cost a little more but you need one if your going to play with hot rods.
 
Thanks guys, appricieate all the input. Will try all suggestions, and keep you posted on the results. When help is needed, this is the place to come to. Thanks again.
 
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