Tuning..backfire/misfire

[Drew67]

Ok...I'm trying my first tune up of my 67 Targa...it has been sitting for 10+ years. I have pulled and cleaned the carbs, and just put on new dist cap, rotor, cond, plugs, points and plug wires. I have checked the level in the float chambers, and the fuel pump appears to be pumping adequately. I can't get it to idle below about 1600 rmp, without backfiring through the carb about every 5 or 6 seconds..not always the same cylinder. It seems to respond to the throttle pretty well, and seems to lose a lot of the missing and backfiring when revved to about 3000. I have not checked timing yet, nor lifters. Any ideas as to the best direction to go next? Thanks.....Drew

[WFBowen]

Drew:
Just to be safe, I'd go ahead and adjust the valves & check the static timing. Also, make sure the advance is working properly and check for a vacuum leak, especially near the carb on the questionable side (it's a little dangerous, but spraying carb cleaner (using the red spray aimer stick) in small quantities around suspected areas will quickly find the leak. Are you sure all your jets/bowls are clean? Float valve not sticking? Accel.Injection spray correct volume/duration?
Good luck,
Bill.

[Jones Low]

After sitting that long, changing the engine oil & filter would be a good idea and the transmission oil after you got the engine running.

I would adjust the valves and set the timing.
Make sure all 8 carb to manifold riser bolts are tight.

You might want to try cleaning the the carbs with a spray carb cleaner to washout the gunk but a carb re-build and boil out would be better.

Backfiring/miss-firing thru the carbs can be due to carbs out of adjustments. Idle mixture, carbs out of balance (all 4 carbs drawing equally, front set vs back set, left side vs right side).

Balancing the carbs requires knowing the art of synchonizing multi-carbs. You'll need a Unisynch or Synchometer to balance the 4 carbs. As in most things this skill is learned by trial and error. At least for me it was.

Jones Low
69-912

[Drew67]

I didn't boil out the carbs, but I took them apart and soaked them in some over the counter carb cleaner (with the little dipping basket)...all the varnish and gunk seemed to be pretty much removed. I couldn't really synchronise them, because I couldn't get it to idle down to the 900 or so rpm level and remain running. I had someone email me and suggest the timing...which I was leaning towards, so I think I'll stop and get a new timing light (mine is an antique) tonight and check it...static first, then running, correct? This feedback really helps, guys..it's been a looooong time since I messed with points, plugs, timing...all that fun stuff...these new cars are just too dependable...Oh, yeah, I almost forgot, I had already drained and replaced the oil, but not the filter...I will do that pretty quickly as I plan on changing the oil again in the next few days....thanks again... Drew