Backfire, timing?? vacuum advance??

[jetsg4]

I have been running my truck the same way it was when i got it, without the vacuum advance hooked up. When i hooked it up before, it would backfire when i let off the throttle.

Well, i finally got around to putting the timing light to it. The timing was set around 22, i adjusted it to 12 and hooked the vacuum advance back up. Now it backfires more. Read some posts to adjust down to the 6-8 range and try it again, as I did. Still backfires.

So, where to now? New vacuum advance? New distributor? Turn it back up and leave the advance off??

Thanks

 

[jetsg4]

forgot to mention, while adjusting the timing, i get a nice jolt every time i touch the #5 wire boot.

 

[blubuckaroo]

Chevy mechanics beware!

 

[Madgyver]

What carb?

 

[Viperwolf1]

Does the vac advance diaphram have a hole in it causing a vac leak?

 

[broncnaz]

How does your balancer look specifically the rubber ring between the outer ring and the hub? If its cracked and missing chunks it could have slipped and is causing bad readings might want to check to see if TDC lines up correctly.

Does your timing still read 12 at idle after the vacuum advance is hooked up?

Where is it backing firing? exhaust or intake?

Might want to try and get those wires fixed maybe some di-electric grease on the terminals might help if the wires are still good. What wires do you have? if stock type they could be part of the problem as they break down over time especailly when they've gone through several plug changes.

 

[blubuckaroo]

#1 cylinder is the passenger side front on a Ford. Driver side front on a Chevy.

 

[jetsg4]

Carb is a new edelbrock performer 600CFM, the PO had the vacuum advance unhooked and the timing advanced this far running the stock carb and intake. i don't believe it is a carb issue seeing as the PO obviously had the same issue with the stock setup.

checked for vacuum leaks on the intake, and carb, no problems, as well as all the fittings on the intake. i don't know what the comments on the chevy has to do with anything, so i don't know how to respond to those. it is backfiring through the exhaust. the timing doesnt change after hooking up the vacuum advance. the balancer is in good shape, but doesnt appear to be stock, it is red.

the vacuum advance is hooked up properly on the carb, on the higher port, and has been confirmed to be pulling vacuum only when revving engine, not at idle. i'm replacing the distributor today hopefully, but i'm not very confident in this being the problem.

i'm changing the wires also. i don't think i was clear on the shocks i was getting. i can take my finger and touch it to the top of the #5 boot on the distributor and get a good jolt. the boot isn't broken that i can see, but it's definitely something out of wack with it.

any bases i've missed?

 

[70_Steve]

Stock 302?

The backfiring in the exhaust is the burning of fuel that didn't get burned in the cylinder. Lots of reasons for unburned fuel in the exhaust. Start with a compression test. Make sure you don't have a slightly burned exhaust valve.

Also, the Edelbrock carb generally come set up so they will run rich at sea level. You didn't include your Location in your profile, so I don't know at what altitude your engine is running. Get a jetting kit, and download the Owners Manual from the Edelbrock web site, if you haven't already done that.

 

[jetsg4]

i'm in Baton Rouge, LA. i don't think it's the carb. the PO had the same issue with the stock carb and intake. the only way they could get it to stop doing it was to disconnect the vacuum advance and turn the timing up.

 

[broncnaz]

Backfiring in the exhaust is probably due to the timing being to far advanced. The only other time you see it happening is when the jetting is to rich or there is a big exhaust leak.
I understood you about the shock it doesnt matter any shock is bad its probably dirt or mositure related and has caused carbon tracks to the path of least resistance could be making sparks to the hood or other metal under the hood. The di electric grease helps prevent this from happening. Since your going with new wires I'd also consider a new cap to.

 

[blubuckaroo]

jetsg4,
The reason for the sarcastic Chevy comments was that people will often use the right front cylinder to time the engine since that would be #1 for a Chevy. The fact that it runs better so far advanced sounded like you may have done that.

 

[Viperwolf1]

The front right on my 302 is #1, veiwed from the driver's seat.

 

[jetsg4]

put in a new distributor last night and it's running like a top now. i believe the vacuum advance wasn't operating properly. probably could have gotten by with just changing the advance but now i know everything is new, and should be in good order for a while.

thanks for the help.

 

[Mao]

If it starts popin' when reving a little and while parked and with the vacuum line attached, try turning the screw inside the vacuum can counterclockwise a couple turns a time with a 1/8" allen wrench. The screw is inside the vacuum hole where the tube attaches.