283 bakcfires through carb

I've got a fresh 283 in my truck. About 500 miles on it. 11 to 1 pistons, vette intake, new 600 d pump holley. Dual point mallory, comp cam 270 straight up no degree. Edlebrock heads (Not old school I know). It starts fast, idles sweet but when you give it quick throttle it backfires through the carb. The carb horn is black with soot. Checked coil voltage 12v. It's timed @ 3000 rpm. Got a fuel guage it stays around 5-6 lbs. Help is there anything obvious that I'm missing?

 

are the points set correctly ?

 

Backfireing through the carb is a symptom of a lean condition. Maybe a vacuum leak; too small of a carb or carb jets; timing or vacuum advance off a little bit. My suggestion for you is to refer to a Motors Manual to help get some more clues.

 

The points were set bright out of box. Disconnected them one at a time and set dwell. I checked my power valves today and checked jet sizes. 66 front and rear. How do I know if thats enough? Also I've got a vacuum canister to run my wiper. Engine runs 10" vac until you give it throttle then it drops out.

 

May not be getting a big enough squirt from the accelerator pump. Holley makes a bigger pump. I think its called a 50cc pump. It may be a good idea to go to a vacuum secondary carb. The double pumper may be too much for the 283 when you open all 4 bbls at once.

 

Try disconnecting the secondaries. A 600 double pumper with mechanical linkage is probably too much at low RPM for your 283. Lobucrod's suggestion of a vacuum secondary carb will likely fix it. Or just teach your right foot to move slower!

 

Same thing happened to me , It turned out to be a flat cam. Hope you have something easier.

 

I got the same issue with my 283, we cannot get the thing timed!!! last time I ran it, it back fired through the carb and I had a small engine fire!

I am going to follow this thread, I am curious too!

 

Unfortunately thats what I'm thinking. Will rounded lobes show up on a compression test? I've got a 500 edlebrock on another motor that I'm going to try this week. Then I can eliminate the carb. I had a pontiac motor with strong valve springs and rhodes lifters(remember those) that wore out lobes on a new cam and backfired through carb.

 

And the crowd hushed in antisipation.

 

what do the plugs look like ( white, brown, black, wet,dry,)

 

It idles fine, and after it pops it revs smooth. I don't floor it. It's got a banjo and a 3 speed. But I do wind it. It could be the acc pumps. Is there a rule for setting the springs on the pumps? Also disconnecting rear pump is a good idea for testing.

 

I have this same carb on mine,brand new! sorry to say but I do not think either of us have carb problems! ..... I think 2dueces64 might be on to something.

 

OK engine guys, does this sound like the dreaded lack of zinc problem??

 

Glad you get a good yuck outta my misfortune. Anyway plugs look good. Pulled the r43s and put in r45s.

 

I think it needs more cow bell.


But seriously, I do think it's a lean condition.

 

Sounds like acelerator pump .

 

it's out of time

 

Are cow bells traditional enough? It doesn't smoke like its rich. A 283 with close to 300hp ought to handle 600 cfm. Maybe the acc pumps are squirting too much too soon. I've got 3 dueces ready to go on it, but I want to figure this out before I complicate it by 3.

 

mine was a bad cam too!!!

 

This is going to sound stupid but have you checked the firing order? I have seen sbc's with 5 and 7 crossed that sound ok until there revved a bit. Just a thought.

 

what is the Curve in the Dist if its 12 degress that the Timming should be bet 36-38 totall at 3000 rpm

 

Pull the valve covers off and ck how far valves open, if ok try to re adjust the valves.Is the dist advance working,why is it timed at 3000 rpms?

 

a 600 double pumper is Too Much for a 300 hp engine on my Stock 327/300 hp I have a AFB and works Great

 

You mean cam gear outta time or distributer outta time?
I did the finger in the plug hole tdc. Then set timing at 3000rpm. After the mechanical advance kicked in. I think its at 28 deg. Other than the popping, it runs and idles good. Thats why I'm not thinking vacuum leak. Could I be a tooth off on the cam?

 

on the Damper it should be 12 degrees at Idle or a Total of 36-38 at 3000 rpm

 

The Dist is out of time

 

You guys are a lot of help. I'll set timing at 12 deg. Put the smaller edlebrock carb on. I think I'm going to loosen all the rockers and set valves again cold. I might bhave valves too tight. Then I'll watch to see if they all open all the way.

 

Your Mallory Dist comes with a Curve chart to tell you what to set the Timming at

 

if you losen the Rockers first set the Timming Last! since the Valves alter the Timming