I've just got done refreshing / mod'ing the BBC in my 72, and now when staring the engine for the first time after the work, I have observed the same symptom in 3 different, previously good Holley carbs. When I attempt to start the engine, a gyser of gas erupts from the carb vent!

I had installed an electric fuel pump, and  measured 6-6 1/2 psi pressure at the carbs.  It doesn't erupt when the ignition switch is in the on position, just the start, so I don't think it's blowing the carb inlet vlave off it's seat.

Mods done to engine:

New Crane Cam, lifters & timing gear set. ( Crank gear dot @straight up (12 O'clock), cam gear dot straight down (6 O'clock)).

New roller rockers, push rods.

A set of Edelbrock Performer aluminum heads.

Edelbrock performer intake manifold.

I had the engine out of the car to replace the heads, and ran through the firing order as I turned the crank to insure that the crank and cam were doing what they are supposed to do, when they're supposed to do it.  All looked good.

This is somewhat embarressing for me, as I've successfully rebuilt a couple of small blocks, 1 other big block, and a bunch of motorcycle engines over the last 35 years.  I fear I just forgotten some simple issue, here, but I'm sctraching whats left of my hair on this.  It seems like the intake track is getting pressurized instead of pulling a vaccum, which would point to the cam / crank alignment.

I plan to measure the pressure in the manifold when I turn over the engine tomorrow.

Anyone have any thoughts?

 

TIA

 

NJ BB Ken

 

windrider120038730.7943055556

  CHECKED THE FLOAT LEVEL?

                      REID '72 T-TOP

The float is stuck down.

I hadn't checked the float level, but I will.  I'm not sure I understand why the float would stick when cranking the engine, but not when just the electric pump is on, and on 3 good carbs in a row.  But I will tear into the current carb to see whats up.

This exactly why I posted my problem, for you guys to challenge my assumptions.  I keep going over my mental checklist, and may be glossing over or ignoring something that will jump out as obvious to the forum.

PS One other thing I omitted in my original posting it that the rockers weere adjusted to the point of no free play, then tightened 1/2 additional turn, per the factory manual.

Thanks again

NJ BB Ken

 

 

 

Thanks

I missed the fact that you had the 'lectrical pump . Does it "erupt" with the 'lectric pump off?
Have you checked the fuel pressure while your cranking it? The combination of the mechanical pump & 'lectric pump is probably where the trouble starts, as both of them pumping together might push the pressure up above 9/10 lbs, which is too much for the needle valves to handle. Jest a thought.

Adam;

I only have an electric pump, removed the old mech. pump and blocked it off.  I tried spinning the engine with the +12V removed from the electric pump, and it still spits up through the carb.

I heading back to the point where I now question if the cam / crank alignment was correct. 

Damm this old age junk, I can't remember anything anymore.

Will be pulling off the timing chain cvr this weekend to see what I can find.

Bizarre.

NJBB Ken

 

OK, NOW it sounds like the engine is "backfiring" thru the carb. And yes, if the cam timing is off, it can do this.
If there is NO fuel pressure (pump unhooked/unplugged), then there is no way it could be a fuel pressure/level problem. Check the cam timing, and the plug wire routing, to be sure they are both correct. If both are correct, then you may have a valve adjusted too tight, or stuck open. Ain't this fun!?

Update:

 

As I feared, when I indexed the cam timing set, I screwed it up.  I installed the crank gear dead-on ( vs either adv or retarded), but then I must have used either of the incorrect marks to match the mark on the cam gear. 

After rectifying the issue, surprise, surprise, the engine fires, and no gas gyser!

Lessons learned:  Old age memory issues, too many distractions, and way too much part time effort leads to bad assumption etc.

 

Thanks to all for your thoughts.

BB NJ Ken