I recently built a 350 for my 85 TA. I have just solved a little vapor lock problem and now when the distributor advances, it blows a flame out the carb. I have a vacuum advance HEI and I'm running autolite 26 sparkplugs. Does this mean its advancing too far?...If so should i take the distributor out and drop it again maybe a tooth back?

 

have you set your base timing? make sure your vacuum advance hose is unplugged when you do it too

 

Yes i did and it was 4 degrees retarded at base. I did unplug the vacuum line when i did this also. Could too much of a retard in timing also cause a backfire through the carb?

 

i doubt if your timing is off far enough to cause your problem. WAG i'd say put your timing around 6 to 10 BTDC. make sure your valves are all closeing, run the valve and make sure none are out.

 

I'm thinking this happens when combustion starts before the intake valve closes... Too much advance, if you ask me...
Are your valves closing properly? Did you degree the cam right? (not that I would know much about degreeing a cam..)

 

by 4 degrees retarded do you mean 4 degrees after TDC? if so, that's way too retarded. the most retarded i've seen is 0°. I run 16degrees before TDC base timing. any more retarded than about 12 btdc and i start to get dieseling when i shut the car off

 

Sorry for the confusion, what i meant by retarded was before tdc. On the timing tab, it has before and after and the notch on the balancer is at 4 degrees before when i put the distributor in.

 

ok. try advancing it more. stock timing is i believe 6btdc so i wouldnt go any more retarded than that. try 6-16btdc, i felt a noticeable increse in the butt-dyno when i went to 16btdc from about 8 i think

 

By advancing, you mean leave the distributor where it is and turn the cap, correct?

 

yeah, leave the teeth engaged but loosen the dist. hold down on the intake and turn thed dist. which will turn the cap in relation to the rotor

 

Ok i tried turning it in relation to the rotor and turning it towards the front of the car made it idle rough and stall and towards the back of the car didnt help either but i cant exactly describe what it did.

 

If you have a timing light, you could have someone turn the dist for you while you watch at exactly what timing it is @ base. Maybe your carb needs a little tuning. Of the top of my head, I'd put the dist @ 10 BTDC or wherever you feel like the engine is choking on gasoline and then lean-out the idle. Or maybe it wasn't choking on gasoline, maybe you need to enrichen the carb; I think you'll feel when it's too lean.. Or maybe I am talking , I'm still learning about OHV V8s...

Try have it to where it sputters and stutters and gently start opening the throttle plate. If the engine seems to rev more-less normally, the timing is somewhere close to correct and then just tune it a little and tune the carb.

At what RPM does it backfire like that (flame out the carb)?

BTW, triple check that all your sparks are OK, and that all your plug wires are connected correctly. If you mismatched some plug wires, the engine would still run, but horribly. I've seen very experienced people accidentaly plugging the wires in wrong (swapping 2&4, for example) and then wondering for an hour or so why the engine is missing...


UkraineTrain, what compression are you running?

 

Its at about 3000 when it pops the flame out the carb. Also today I went to fire it up and i has gas leak all over the place, even in the vacuum line going to the distributor. I had a vapor lock problem before and i could hear the fuel boiling in the carb. Do you think this would hurt the carb at all?

 

It's about 9.6 or 9.7:1. corvette L98 was 9.5:1 and the head gaskets are a little thinner than stock so my CR is a touch higher.