backfire at throttle

[TK73]

OK, I get backfire at mid-throttle when tranny shifts into 2nd, this is "intermittent" - not every time I'm at mid throttle and tranny shifts.  very light throttle, or hammering it, I don't get this going 1st-2nd.

Timing maybe?

[Chryco Psycho]

Maybe under hard load

[deputycrawford]

What type of ignition do you have? Do you have a vacum advance still in place? What is your engine build? What is your idle timing? Maximum mechanical timing? Details Details..

[TK73]

What type of ignition do you have? Do you have a vacum advance still in place? What is your engine build? What is your idle timing? Maximum mechanical timing? Details Details..

orange box electronic, vacuum advance in place, uknown cam specs, stock 318 heads and manifolds, 650 (? from what I remember) cfm 4bbl on 360 intake, haven't checked timing... can do tomorrow...

Please don't make fun of the current owner, the prior redneck owner "hopped up" the engine... 

[deputycrawford]

Ok, check timing at idle and unplug that vacum advance. Check vacum at idle also. I hope no one here will ever make fun of any one who is learning about what they have to work with. I certainly won't. You  will ask questions now and give advice and experiences later. That's what its all about. Oh, and tell us the readings on the timing and vacum stuff. We can make edumacated quesses after that. 

[TK73]

Manifold vacuum @ about 700 rpm = 7"

this is "unsteady", bounces around 7" with an "occasional" drop to 6"
cam specs unknown, cam is very "bumpy"

=======================

no advance timing @ 750 rpm = 5 btdc

vac adv timing @ 750 rpm = 12 btdc

[myk]

Where are you hooking up the vacuum guage at?  The location of the guage can affect the type of reading that you get.  7" though, that's like, really low.  Must be one helluva' cam in there...

[TK73]

Where are you hooking up the vacuum guage at?  The location of the guage can affect the type of reading that you get.  7" though, that's like, really low.  Must be one helluva' cam in there...

did base of carb and then manifold vacuum, 7" at both...

helluva cam for sure; the redneck "hop up" = overcam, overcarb...

Runs REALLY GOOD at high rpm   

[Chryco Psycho]

you need to advance the timing to 16* or so at idle , this should increase vacuum , lose the vacuum advance or it will over advance at higher rrpm
BTW if you have more timing at idle with the vacuum advance hooked up it is hooked up worng , so you would have vacuum retard as rpm increased which will make the car stumble even more

[TK73]

16 degrees without vacuum, gotcha...

The timing tab goes to 10, is is there some way to make it longer to time 16?  aftermarket tab or something?

[myk]

The best piece of equipment that I own and that every car person should also have is an Equus digital timing light (#3568) with LED readout, that features electronic advance/retard capabilities.  In your situation I would just set the timing light to 16*, and then adjust the distributor until the timing mark landed exactly on the TDC mark on the timing chain cover.  That puppy cost over a hundred bucks, but it allows me to dial in ANY increment of timing up to 99*, if I wanted to. 
You can buy cheaper timing lights without the LED readout-these timing lights usually have a dial or something that you can set the timing to, and then you would just aim the light and adjust the distributor until the timing mark on the balancer hit TDC on the timing chain cover.  The Equus 3555 for example costs about $70, but don't let the cost of these things throw you off, as messing with timing tapes that are a pain to install and fall off after the first week or so are lame anyway.
Trust me, you'll love these lights and it makes ignition timing an easy thing to do...

[Chryco Psycho]

make a mark on the damper 2 3/8" ahead of the TDC mark & time the egine to this mark [36*] at 3000 rpm , without vacuum you will be in the 16-18* range at idle , the total timing at 3000 is more important as 90% of the time the engine is in mid 2000 rpm operating range when in use

[dodge freak]

  Why or how this check the timing at idle speed got started I have no idea-it is the total timing that really counts. Yes if the is too much timing at idle the motor will be hard for the starter motor to crank and not enough timing at idle the motor might not idle as good. But if the dist. springs are good and the weights move freely then if the timing is just set at around 36-38 degrees max it should be ok at idle.

Wish I knew this before I turned 30 years old.

[myk]

The timing at idle is a shop-manual, stock motor kinda' thing.  Meanwhile, thanks to you guys I can now drop the hammer and burn out instead of popping and stalling out...