43 Baffled confused retarded

"Long story here. I'll gi

"Long story here. I'll give basics first.
4.3 Vortec 2v merc t-bolt V elec fuel pump no knock senser, 1996.

Replaced long block due to cracks. Ground crank. new bearings. New cam (roller). New t/c. New cam and bal shaft brgs. Heads pressure tested, milled, valve job. New oil pump and pickup tube (always). Assembled, preoiled adjusted valves. New cap, rotor, plugs (mr43t), wires. Used marine vortec intake (excellent!!! condition). New fuel stainer and assembly.

Problem:
Test run before installing in boat to adjust carb, timing etc.
Backfires upon rapid acceleration (flames out carb), other than that it runs like a swiss watch.

Idle rock steady at 700 RPM on my fuel tank.

Checked or replaced for testing:
Carb 2 reman 1 used, no change
T-bolt V module, no change.
Coil, no change.
Hall effect switch, no change.
compression 180 in all six.
timing 8BTC idle 24BTC at 3000RPM
advance timing, no change
Retard timing, no change
Remove carb spacer, no change
Adjust valves 2x, no change
Vacuum 16in and steady
All cyliners firing
checked cam timing, no change
Drained and refilled shop fuel tank, no change

Baffled, confuesd, retarded, or do I need a voodoo doctor?????????????????????/"

What are you using to control

What are you using to control the back pressure while doing the test run?

Logic would say that one of th

Logic would say that one of the new lifters on the intake side is a dud.

"Did you use a hot cam with to

"Did you use a hot cam with too much duration? Set the idle up and try it. Also, pull each wire off individually and try it. At least you might narrow down the cylinder. Good luck."

"1. I run engines on the the

"1. I run engines on the the ground every day with no back pressure other than the Y pipe and have not encountered this.

2. I might agree with the lifter theory except for the fact of the cylinder pressures being right on the money.

3. It's a stock 170 hp marine from mercruiser. Been the idle route no joy. I have a balancer degreed 360 to check the firing and timing of each cylinder, all fire with no mishaps

???????????????????????????????????"

"If you can pull a plug wire,

"If you can pull a plug wire, stomp on the throttle and the backfiring stops, at least you'll know what cylinder. Maybe a lazy valve spring?"

"Maybe a carbon tracked distri

"Maybe a carbon tracked distributor cap, rotor button not fully seated, Defective plug/wire, firing order off (hey I've done it after 15 years), pushrod length ok? some chivys use a different intake length and different exhaust length..., cam is degreed incorrectly???

Just some ideas..."

"Sounds electrical to me, afte

"Sounds electrical to me, after all the mechanical thiings you have done. I'd follow Peter D's lead. If it doesn't isolate to one cylinder, I'd bet on the distributor (cap/rotor?/) and try to replace the whole thing (seems to be the route you have been taking). It is a common distributor, maybe you can "borrow" one.
Tough ones are not fun until you got 'er solved.
good luck
Harry"