backfiring

[cudaaah]

My car's been running great   426 stroked 2 4's everything's pretty much new.  I was out driving yesterday and twice when I was taking off (quickly). the car backfired 3 times quickly.  pop pop pop .   Any ideas??  the car was just tuned by my engine builder a month ago and I've had no problems. 

[cudabob496]

timing may be too advanced.
what is timing curve?

[jhaag]

through carb or exhaust? carb backfire (too lean and or timing)

[Chryco Psycho]

probably going lean what carbs ?

[cudaaah]

Thought I posted??  let's try this again.   My Cuda has twin 650 Edlebrock carbs.  I think my timing is correct  14/34.   Spoke w/ my engine builder and he agreed w/ you all that the car be too lean or rich and suggested I adjust the linkage that controls the plunger on top of the carb.  Thanks all

[Chryco Psycho]

It could have to do with the squirter size also , this is where I like Holley type better , 7 cams with 2 positions & 14 sizes of squirter , Eddy / Carter has small medium & large & you have to buy all 3 for each carb as they are not sold individually , anyway if the squirter size is too small the fuel will not enter the air stream fast enough when the throttle is snapped open

[cudaaah]

I've never worked on carbs...I was wondering why this would happen all of a sudden??  I've run these carbs since I finished the car 3 years ago.  Last year I had to rebuild so I stroked, roller cam, few other goodies.  I just took it in last month for a tune and we adjusted the carb linkage to have 2nd carb kick in sooner.    As mentioned my car runs like a bat out of hell, but just started backfiring.  do you think his suggestion to adjust the linkage is a place to start?

[Chryco Psycho]

With the engine rebuild the engine will work differently with the existing carbs , so as the engine breaks in etc it may need to be retuned + different air temps etc , you can try adjusting the linkage , easy to do & see if it responds differently , float level could be low also delaying the time to draw fuel into the venture of the carb .  what do the plugs look like the whole tune could be lean ?

[cudaaah]

I'll have to get back..spark plugs were changed last month.  I may not get to this until the weekend.  Thanks again, cudaaah

[hemiken]

Was it actually a backfire through the carby's or felt like that and you heard popping Not knowing how old your engine build is or how often you have used it or what parts were used, but i know that sometimes valve springs go off and do this same thing you described, i have been behind the wheel in cars that have had valve springs go soft and they will sit and idle nicely and eben free rev fairly well, as soon as you put some load on the engine and try taking off hard the engine starts popping. If you can not find a problem with your carby's, it could be a good idea to pull the valve covers and check spring pressure, this can be done on the engine and in the engine bay too

[Chryco Psycho]

Tuning first , if it will not tune out then you need to look further for problems

[73EStroker]

Last time I had a car do similar it was weak ignition!!!

[cudabob496]

see if problem goes away without vacuum advance hooked up.

[MEK-Dangerfield]

see if problem goes away without vacuum advance hooked up.

I don't see how vacuum advance fits here.

The problem was on takeoff. Vacuum advance doesn't get involved until you are at cruising speed.

[cudabob496]

I don't see how vacuum advance fits here.

The problem was on takeoff. Vacuum advance doesn't get involved until you are at cruising speed.

Incorrect timing can cause backfire. You are assuming the vacuum advance is working properly.