has backfired thru carb upon giving slight gas off idle creating a lot of white smoke from carb. 365 hp. 65. .?

Otherwise seems to run rough cold and well after warmed.

 

Backfiring through the intake is usually a result of running too lean. Is your choke working properly ???

 

It is a new carb and I believe it was working last time I checked. The backfire happened when engine was warm. Started to drop idle, gave it gas, and backfire.

 

A couple of thoughts...

1. With a timing light attached, what happens when the RPM increases? Does the mechanical advance in the distributor work correctly?

2. What pressure do you get from the gas pump? Could you be running into a lean out situation?

3. Is your vacuum advance working correctly? When a vacuum source is applied, does the timing change from when there is no vacuum?

4. When the engine is off from idling about a minute, look into the carb (with the air cleaner off). Either by moving the linkage or with someone in the car, floor the gas pedal. When the pedal is going down, do you see two streams of gas going into the venturi? If not, then think about your accelerator pump in the carb could be misadjusted or something's plugged up.

5. When was the last time you changed the cap / rotor / points? A small crack in the cap could cause arcing.



-- Joe

 

Yes

No idea, new pump

Yes, but I don't think my light will measure the advance timing.

I believe in will see fuel,

All are new, also had the dist. Rebuilt by someone who put it on a sun? Machine.

Sorry for not listing your questions but I have not figured out how to work the quotes.

 

The Sun machine should be something like: http://paramountd.com/sale.html

Assuming that you trust the guy with the Sun machine, I would:

Spark:

Recheck your spark plug wiring order to make absolute 100% sure it's correct.

Recheck your timing to make sure it's correct. Is it at all possible that the timing tab is incorrect?

Check for a vacuum leak. An air leak can cause carburetor backfiring. Other symptoms of an air leak include a slow return to idle or an irregular idle.

I'm assuming that the guy with the Sun checked the vacuum and mechanical advance and the associated curves for the RPM.

Fuel:

Excessively lean carburetor settings can cause backfiring. If the mixture is too lean, it may burn very slowly and unevenly. This condition, in turn, may result in burning mixture remaining in the cylinder until the beginning of the next intake stroke when it can ignite the incomming air/fuel mixture.

A too-small or partially blocked pilot jet can bring about this condition. In the off chance, is the carb new / fresh rebuild by someone? Could they have jetted it incorrectly in error?

An accelerator pump adjustment that starts the pump too little or too late can cause this problem.

A partial vacuum in the fuel tank can reduce fuel flow and bring about a lean condition

Inadequate pressure from your fuel pump could cause a lean condition. I've seen new ones not produce the correct pressure.

Other items:

Only after exhausting the above, here are a few more ideas:

Have you looked at your valves / timing chain lately? Could the timing chain have slipped a tooth? You can check this by removing the spark plugs and valve covers. See: http://www.pirate4x4.com/tech/billav...%20a%20cam.pdf.

Could you have a burned valve? If you do a quick compression test, this will quickly identify if you have incorrect pressure in a cylinder that could indicate a burned valve / other condition.

Have you wiped a lobe on your cam? During your last oil change was there metal particles?



-- Joe

 

OK, after re-reading your post, you indicate there is a lot of white smoke. Are you using antifreeze? If your seeing lots of white smoke, then you have water getting into the combustion process.

Have you done a compression test? That will tell you if you have a blown head gasket / cracked block or head / etc. See: http://www.youtube.com/watch?v=ovvXn...eature=related. Otherwise, you can do something like: http://www.youtube.com/watch?v=QA7KV...eature=channel.



-- Joe

 

The carb is new out of the box.

Yes antifreeze but The white smoke only happens through the carb, there is nothing out the tail. Also after I shut it off, even if no backfire, I notice a slight lingering white smoke from carb how much is normal I don't recall. I'm curious if it may be leaking slightly into the intake?

Idles too well to have a miswired cylinder and i would think a valve problem and vacuum leak would be evident here also?

New vented gas cap and tank

I just rebuilt the top half and all Appeared fine.

I pulled one plug and though Blackish as expected with all the idling it wasn't wet or white.

Will look at your suggestion and try to tune this carb richer perhaps.

 

Check your fuel filter.
You say the car runs well when its warmed up.
With the car ice cold lift the air cleaner off and make sure the choke is closed after 'blipping' the throttle linkage rapidly one time.

 

After you get a handle on your problem, and if you have a Holley, you may wish to change out your power valve. For some reason, backfires blow the power valves out. Jerry