"Sneezing" carbs

Hi guys,

Picked up my little Dino this weekend, after a 9-month time at the paint shop.

We drove it for 500 miles, and slowly she started to run better. Still not quite good though. One thing that struck me was how she sounded like she was sneezing through one of the carbs. I recall her doing something similar when I was tuning the carbs: a cough upstream, coming from the engine up throught the carbs.

According to the books, my valves aren't due for adjustment yet, but I am not sure if I quite trust the mechanic who has done them last time. Is it a silly idea that the sneezing could come from valves that need their clearing adjusted?

Thanks

Hans

 

I think I have a simular problem. Did my first drive last week and eventhough the valves are recently adjusted, I still hear the engine popping. Is it the cold weather or do I need to readjust the carbs? Also I still hear a tiny explosion when turning off the engine.

 

both are common when the carbs are adjusted too rich.

 

Kris,

I agree with Steven: rich mixture will flow down into your exhaust and pop on the overrun.

Steven: how about my sneezing? When I had the air filter housing off, I could actually see a fountain of fuel being sneezed up from one of the carbs. There is definitely an air flow from the engine toward my air filter housing at that time. Valves??

 

i had exactly the same after i rebuild my gtb. This sneezing from one carb and some afterburning after ignition shutoff.

The latter one is common for a too rich mixture so i altered the settings of all carbs by 1/2 turn. Than I noticed the sneezing of this one carb was noticeble less. I ended up adjusing this one a little bit more and it dissappeared completely.

just for info. The engine was rebuild and all valves were set spot on. So i'm not saying that a bad valve setting cannot case this sneezing but i do know for sure that this sneezing can happen with the proper valve clearance.

I think a bad ignition can cause a similar thing too (but as you are running electromotive the only thing that can go bad causing this are your leads.) And you know, leads are best checked in complete darkness

 

The sneezing occurs on my bad carb only (one carb was destroyed by an over-zealous mechanic who at one time screwed in the CO adjustment screw at an angle). The bad running that I am having now has got everything to do with my 7+1 setting (7 50's and 1 56 idle jet). This worked well with hot weather and seems completely off now.

Okay, EFI first, then set valves...

 

I have experience sneezing due to bad plug wires, bad extenders, bad ignition, bad dizzy caps...

From what I have learned, and I am certainly no expert, the carbs should be the last thing you adjust after making sure everything else is in order on the ignition/timing side of the house.

 

Ignition and timing IS perfect. Al-new, electronically controlled (BSM), and verified to work properly (and timed properly).

 

extenders and plug wires? I bought 8 new extenders, assumed they were all good, and one was bad. it zeroed out fine on the ohmeter, but when i wiggled it while testing resistance from cap terminal to extender it shorted out.

 

It isn't your valves, unless one vale isn't completely closing due to carbon build up on the stem, or bad valve seat, i.e, your valve shim/cam lobe clearance didn't get smaller while sitting there for 9 months.

Backfiring through teh carbs is caused by too lean of an intake mixture, your carbs are probably varnished up, your old gas went bad.

Buy a couple bottles of fuel injection cleaner and add them to your next tank of gas, repeat a time or two, it should clean the varnish out and save you a bunch of labor.

Doug

 

+1 lean mixture will "sneeze" through the intake. If the car really had this problem before it went in I would have the valve adjustment checked. The last thing you want is a valve hung open due to (no) clearance; it will burn and require the head to be removed over time.

The seat or stem may have rusted up from sitting for so long but you mentioned this was a pre-existing condition. I would check the valve adjustment if this doesn't cure itself before the next 100 miles.