The Stovebolt Site Forums The Shop Area The Electrical Bay mallory dual point versus electronic distributor

I'm running a 235 with dual single barrel rochester carbs(they've been rebuilt) on a fenton intake. The distributor is a Mallory dual point. I have a hesitation, dead spot on acceleration. My mechanic suggested I replace the dual point Mallory with a new style electronic distributor and that might cure the hesitation. Any suggestions would be appreciated. I've heard that heating the intake manifold might help, I've also heard that increasing the jet size might help. One suggestion was to drill out some things in the carburetor. Where should I start looking?

bobshollow,

I a similar setup many years ago. If it were me, the LAST place I would look would be the distributor...the FIRST place I would scrutinize would be the dual Rochester's.

If the points are set properly, and you have enough timing, the ignition should be OK. Synchronizing the Rochester's takes some fiddling...as I recall, the available throttle linkage is pretty funky. More folks will be along that have had similar problems, and have good answers.

If this dead spot is only noticeable when the engine is cold, lack of carburetor heat could be SOME of the problem.

My Mallory setup had the gigantic condenser mounted outside the distributor. I wonder if this is absolutely needed for the dual point setup...what does your distributor have?

Stuart

I had a similar dead spot with mine, however I have the electronic dizzy, so it makes no difference in that respect. In my case, it wanted more timing, 15 degrees advanced. I'm under the suspicion that your mechanic either doesn't know how to set up points, or just doesn't want to fool with them.
I would advise against fooling around with the Rochesters by drilling or enlargine anything, they have enough issues as they are. Adding heat to he intake would help more.

Longbox55, you said you've advanced to 15 degrees on your distributor. I was having trouble with the same thing several weeks back but with a 390 Holley and a Mallory distributor. I wanted to try but the advice was was not to advance much beyond stock timing (4 BTDC). My dizzy doesn't have vacuum advance just mechanical. It still has a hint a bog off idle...would it hurt to give it a try and how do I know when I go to far? Sorry for jumping this thread a bit.

I'm not running a vacuum advance either. I went through pretty much the same situation, tried carburation, which was another problem althoghether, checking the valves, coil issues, the whole enchilada. My dad just happened to get a call fom my uncle, who has been messing with these things since the mid-50s. He's the one who told me to try advancing the timing. I just advanced it a little at a time, about 5 degrees, until it sounded happy. I actually drove it at 10 for a while, then tried 15 on whim. Mine likes it better at 15. I did also find that the electronic dizzy works better if you eliminate the ballast and run a spark control box, like the Mallory 3RLi. The dizzy seems to work better getting 12 volts to the electronics.

bobshollow,

An unheated intake manifold will cause a hesitation on acceleration (as will the other things mentioned above).

Tim

Thanks Longbox55...I'll give it a try. Bobshollow, good luck with the Rochesters, I had a setup with two B's and they gave me fits even after the great help from CarbKing (guru of old carbs) and others.

Heat to the carbs will definitely help this situation. I might surprise you!

Joe

Bob, when having trouble like this, don't be afraid to try things like a lot of timing or jet changes. Keep away from the drills unless you have replacement parts, just incase! The 235 will take a whole lot of abuse, so extra timing won't hurt it abit. Check the voltage to the distributor like one of the above post mentioned, make sure its a full 12 volts till you get this straightened out. Thats one of the advantages of HEI, a stronger more steady spark at low rpms. I notice a better idle quality when I switched my 250 over.

You are southeast USA, whats the temps. like there? is it cool and damp?

Heated intakes help no matter where you are, just not as much if its hot and dry air.
Try making a crude air duct around the exhaust manifold and pipe the air up to the intake so as to heat it as much as you can.

Try bending the accelerator pump linkage, if its external, so they don't squirt as much fuel.

Try turning the idle jets way rich or lean.

Theres plenty to try, just keep after it.... Joe

I am under the impression the Mallory unit being referred to is a dual-point distributor...it has points! If this is a twelve volt system, wouldn't a person expect this to RUN on reduced voltage, just as any 12 volt point system would.

A solid state ignition would be a different animal, and probably require 12 volts.

Bobshollow hasn't indicated what voltage his rig is running....this could be a 6 volt system!

Stuart

This is Bob, I have converted to a 12 volt system. Truck starts good, idles good, but stalls out while accelerating.

I'll bet 100% of your problem is lack of manifold heat. Chevrolet engineers bolted the manifolds together for a reason and you've found it. I bet if you tried the stock exhaust manifold bolted to your intake it would disappear.

Curt B.