i have a 302 that was cfi at one time now its carb it has a 850 cfm witch i know is to big i am geting a smller one the thing is when i get up to like 65 it cuts out and studders and now when i try and give it gas it jsut stalls out and studers and backfires out of the carb do i need to get an el dis or somethig i have a brand new mallory unlite dule points but dont know the points gap and when i am in over drive it boggs like crazy can anyone help

 

It sounds to me like a timing problem, possibly floating points, or fuel starvation.

The first thing to check out is your ignition - get those point gap specs (online from Mallory is a good source). Set that up right, set your distributor timing, and then see what it does.

For the carb spec:

0.85 x 4,000 RPM x 302 = 1,026,800

Divided by 1,728 (for cubic feet per minute) = 594.212...

0.85 is the max volumetric efficiency possible, you multiply the max RPM divided by to into your engine size in cubic inches, then divide it by twelve cubed to get cubic feet per minute (CFM).

A 550 CFM would be your most efficient, a 650 is about the biggest you want for the engine. Most mild street engines run about 0.70 to 0.75 VE unless they have a totally radical set of heads on them. And the above assumes a max RPM of around 8,000 - above that you need to look into spending some top dollar on internals for the engine, unless you like watching things explode and scatter...

Depending on how many miles are on the engine, you may have a timing chain problem as well. Ask yourself how much you really know about this particular engine - when was it built? Has it been abused? How much running time is on it? What quality parts went into it?

All of these factors need to be taken into consideration when thinking about any modifications to it. I would never think of hot-rodding an engine unless I built it up from scratch myself.

~Wolf out...

PS: DUAL POINT 'stribs are are a bit tricky to set up, make sure you have a real good understanding of what it is designed to do, and how to set the leading and lagging points before setting it. They are intended to about double the spark at the plug by extending it, thus providing a more positive ignition. Again, the manufacturers instructions and product description are your best bet.

May I suggest http://www.msdignition.com (The Official MSD Performance website) They have a very good tech assist forum

 

we rebuilt the motor it has a 447 lift and i think a 270 dur with a timeing gears we are makein a drag motor and its not wokrin out the car and motor only had like 73250 on it so i mean everything soudl be right and everything we just can figger this out do i need a bigger carb i dont think that would be it but its werid it will smoke em at like a 20 punch adn sometimes it will stall out i need a stall converter too but i jsut dont understnad why its still doing this

 

try only running one set of points on the distributor,i know those dual points can ba a pita!see if that helps!if it does it's prob. just a matter of dialing in the points and the timing! good luck!!!

 

we burned the points up on the other dizzy we have the mallory in there and its runns lil better it was a 65k volt coil on a stock dizzy and just burned up we found the points gap and all that so we are trying to time it right now

 

if you keep burning up points you need to install a ballast resistor block to reduce the voltage to the dizzy,ran into the same problem in the past when going from a electronic ign. setup to points!

 

You could also be leaning out the motor if your fuel pump is going bad. Is it stock or old? I get this with mine when my fuel filter stops up all the time. Try replacing the fuel filter and put a gauge inline at the carb to check your pressure.

I hope the timing helps but if not you may try these things. Also what vehicle is this in.

 

I'm with wolf, sounds like a timing problem. Most backfires are, and with dual points the possibility of messing up the timing doubles (at least for me). that hot cam probably works better if you set it up different than stock, but the paperwork that it came with will let you know where to put it. personally I'm not the greatest at setting modified cam's timing.

 

Wolf is good on all his figures, and as he says, the Msd site is where you need to go for info on the points issue. Okay, Matt is right too, i always tell people you need a ballast resistor on the ignition side of your coil as well. Seems like tonight i'm just recalling what everyone else has said, but only confirming it. I would also consider a single point setup.

Now also Amish could be very right on the fuel filter thing, but first lert's make sure a common old time mistake isn't in the works here, Always place fuel filters BEHIND fuel pumps, and don't be afraid to use a BIG one. What occurs with that common mistake (when people put fuel filter between pump and carburetor+= wrong way, the force of the fuel pump against the filter element crushes it and prevents flow, then relaxes after it sats and reoccurs again, a very aggravating issue i learned years and years ago, good luck


Janet

 

its a racing carb that have the filters on the inlets to the bolows and there new i am goin to get a restior so i dont mess up this mallory and the times is right its got timeing gears and not a chain so there is no slack in the timeing the carb is to big i got a 650 and it dosnt back fire as much but i have 1.73 rockers on my heads i think its staving the motor for fule i dont know