It is very possible to have a carburetor set up rich and still have a lean backfire. Idle to WOT is the most difficult maneuver for any carburetor to accomplish. When you slam that throttle open the air moves a lot faster than the fuel. The result, lean out. Putting larger jets in it will do you no good.

There are seven major systems inside modern carburetors that were designed to make the engine run the best it can. One of those systems is the accelerator pump system. Accelerator pumps were invented to solve this problem. Maybe you should start your search there.

BigBlockk

Later.....

 

So, I should get a larger one?

 

Maybe you should make sure that the one you have is working.

 

the pump set up i would suggest is a pink cam with a 0.031" squirter. the duration spring tension is weaker on the new replacement holleys than it was in the "old days" , i use a custom wound duration spring (the spring on the pump arm) but you can get about the same tension by putting 2 or 3 3/32" flat washers between the spring and th pump arm. if the duration spring is too weak the pump squirt will not squirt a quick / strong enough pump squirt for the engines needs.

henry @ oles carb

 

I squrits fuel for sure.
So I know what the cam is but what is the squirter? Are those just he holes in the cam?

 

the squirter is between the primary venturis under the choke valve

henry @ oles carb

 

does it back fire once or multiple backfires?have you check the push rods?a bent pushrod on the exhaust side or even an a bad exhaust lobe on the cam will cause rapid backfire under acceleration.after every thing else you have tried i would check these.BTEAGUE

 

It is not multiple backfires. Just one. Then it would like to die on me but I can normally keep it running.

 

check fireing order 18436572(we all make mistakes).if order is ok try advancing timeing a few degrees at a time.maybe the timeing pointer and balancer are mismatched.BTEAGUE

 

The initial problem is backfire through the carb right? That means compressed air/fuel has been ignited in one of the cylinders and then not released through the exhaust.

Possible causes:

1. Valve timing...intake valve is open when the cylinder is full of compressed/burnt air/fuel mixture.

2. Intake valve is still open...rocker adjuster nut is too tight, intake valve is damaged or shaft is bent so that it won't close all the way.

3. Exhaust valve is not opening enough...rocker adjuster nut is too loose, exhaust valve is damaged or shaft is bent so that it won't open enough, or foreign obsticle is wedged between the valve and valve seat.

4. Timing becomes so far advanced that spark occurs while the intake valve is still open.

5. Very heavy carbon deposits which become hot enough to ignite the air/fuel mixture when the intake valve opens.

Things to check:

A. Valve Timing...make sure the intake valve is closing before piston starts up on it's compression stroke...it doesn't have to be completely closed at the bottom of the stroke, but it needs to be almost closed.

B. Ignition Timing...make sure you don't have spark when an intake valve is open...this happens if your plug wires are crossed or non-supressor wires are running parallel and there is some cross-inductance. This can be avoided by making sure the wires are not touching...there's rubber spacers which help prevent this situation.

C. Inspect rockers, adjusting nuts, and pushrods for correct adjustment. Check for binding and double check gap for solid lifters and # of turns for hydraulic.

D. Perform a compression test on each cylinder to ensure that all valves are closing properly.

 

Compresion tests are all good. They are withing 2-3 psi of eachother. around 160 after 2 strokes.
I'm running supressor core wires with wirelooms al over the place.
I'm worried about playing with my valves again since I am no good at adjusting them with the car off and it makes a huge mess with the car on.

 

Which color cam for my accelerator pump will give me the most squirt?

 

plugs look not too rich nor lean, they look allright to my eyes
plugs fm a rich carb look like leaking fuel and oil, those lean look white like a business shirt on a monday morning

 

I put the biggest accelerator pump cam I had in the kit on it. It is better. I noticed a "stumble" on the passanger side at low rpms. Also if you listen to the driver side exhaust then the passanger side they sound diffrent. I can't explain what I hear from the passanger side but it is not right. I checked the timing the initial is 12 advanced.

 

I'm puzzled...it sounds like something really strange...like a plugged exhaust pipe...or perhaps a catalytic converter melted partially shut. If you can hear a difference then perhaps there is one...a pressure test at each exhaust opening might reveal the problem.

 

This could be an indication of a vacuum leak between the intake manifold and cylinder head on that side.

BigBlockk

Later.....

 

The things you have listed here would make the car run terrible all the time. From reading some of his other posts, the car seams to run fairly well at cruise. It is when he applies heavy throttle that the backfiring accrues. This is because air will react quicker than liquid fuel. When this happens a lean hole bevelopes in the mixture going to the cylinders. Nine times out of tin, backfiring through the carburetor can be traced to a faulty or mis adjusted accelerator pump.

BigBlockk

Later.....

 

Could the advance unit in the distributor be bad? My .02 Al

 

On the primary or secondary?

 

Big Blok is right here. This is a problem with going lean on tip-in.

The accelerator pump arm must not be loose at idle. While it can not be loose, you do not want to bottom it out either. The .015 additional travel adjustment is measured at wide open throttle (engine off!). This is to prevent damage to the pump arm and diaphragm. You may need to adjust the external spring one way or the other to get it tight at idle, yet still have the .015 clearance at WOT

The different sounds from the exhaust could be fouled plugs on some cylinders.

-Mark.