Motor Bogs

nawlins-tim

nawlins-tim

Member
I have a fairly new sbc 400. Just over 500 miles on it. 232/242@ .050 crower cam, msd 8360 distributor, holley 750(mechanical) with no choke on a RPM manifold. The thing friggin surprised me when i got some Nitto drag radials on it. Even won a street race against one the Famous 6.0 LS guys in my neighborhood. But all of a sudden my motor developed a sudden bog/miss. It just happened for the first time the other day so i just started diagnosis. Threw in some new plugs cuz I think the last set was a little cold for me. But so far the bog is only present when the motor reaches full running temps( 180*-200*) until then i could just about stomp it with almost NO hesitation. Seems to only be noticeable when I get into the secondaries though.
Its a simple setup but what gets me its the thing was running great a couple days ago. I need to extend the fuel gauge so I can see it while driving. It is mechanical and not leaking and has 6psi at idle. Please dont' say head gasket yet.
Grumpy what do you think about the carb suddenly needing adjustment. Odd huh?
The advance weights are not sticking and snap back as they should. Timing is set set at 12 degrees initial 33 total.
Please Help
 
Also I guess if I was tuning a new carb that Never did run right I would say maybe it need a different pump cam or squirter but this carb has been running A1 for six months of weekends. I dont kno........
 
As always drop back to basics and verify the engines functioning correctly,
Id sure start with a compression check, on all cylinders and like previously stated, checking the fuel pressure entering the carb , or feeding an engine is consistent,and the floats are correctly set. but theres a dozen other factors to verify, like checking the cams not wearing out a lobe, the ignition advance is consistent, theres no fouled spark plugs or burnt ignition wires, partly clogged fuel filters or a fuel pump that's not consistently supplying pressure,the exhaust or a catalytic converters not partly clogged, etc. its always just a process of inspect and verify, and never assuming a darn things working correctly until its been tested.
simple stuff, like a partly clogged fuel filter, debris in the carbs float bowl or needle valve, a cracked distributor cap , burnt spark plug wire, defective sensor, loose vacuum hose, or a loose electrical ground could easily be the source of your problems.
or it might be something a bit more serious like a detonation damaged piston, burnt valve , worn cam & lifter, the point is you can,t tell until you inspect each potential area,and verify.

When an engine is bogging it is frequently the result of a sudden change in the air/fuel ratio or ignition curve advance ,that causes a momentary interruption of the correct fuel/air ratio,or proper ignition timing, so generally youll find that a bog can be traced to the use of the wrong accelerator pump cam, wrong power valve or secondary throttle blade control vacuum control or springs, but low fuel pressure or incorrectly set floats, a slipped ignition timing, a weak valve spring or two, or a clogged fuel filter are likely as well.

http://garage.grumpysperformance.com/index.php?threads/holley-accelerator-pumps-cams.1790/

http://garage.grumpysperformance.com/index.php?threads/holley-annular-vs-down-leg-boosters.5229/

http://garage.grumpysperformance.com/index.php?threads/holley-carb-power-valves.1639/
 
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Well i found my problem. It turned out to be a bad spark plug wire. They were Taylor and had very little run time( about 500 miles). Instead of pulling them off one at a time i just swapped the whole set. Remember the misfire was only showing up when I stomp it fairly hard. The wires ohmed as they should and i couldn't see any damage to the wires. I hate to toss out that set, and buy another "quality " set. For testing purposes I threw in some mismatched oem type plug wires that look like crap.
Thanks for the help, glad it wasn't anything major.
 
nawlins-tim said:
Well i found my problem. It turned out to be a bad spark plug wire. They were Taylor and had very little run time( about 500 miles). Instead of pulling them off one at a time i just swapped the whole set. Remember the misfire was only showing up when I stomp it fairly hard. The wires ohmed as they should and i couldn't see any damage to the wires. I hate to toss out that set, and buy another "quality " set. For testing purposes I threw in some mismatched oem type plug wires that look like crap.
Thanks for the help, glad it wasn't anything major.
Click to expand...
I am glad you found the problem Tim.
Very strange you had a Bad set of New Taylor Ignition wires.
I used them in the past on my own cars with no issues.
At work we have witnessed At least 1-2 bad ignition wires for LS -X Corvettes.
MSD Brand new out of the box.
Issue is Natiowide.

I use MOROSO Blue Max Ignition wires.
My Favorite .
 
you might be amazed at the number of times,
INTERMITTENT OR MYSTERIOUS engine function issues,
are only found, and cured,
once the owner, or mechanic,
Stops assuming he KNOWS what the cause IS,
and in FRUSTRATION resorts to ACTUALLY,
dropping back and CHECKING THE BASICS, and
verifying through testing, the proper function of each component!

http://garage.grumpysperformance.co...p-after-running-out-of-fuel.11309/#post-51444

http://garage.grumpysperformance.co...e-won-t-start-after-running.10692/#post-46394

http://garage.grumpysperformance.co...-idles-and-sometimes-stalls.10688/#post-46303

http://garage.grumpysperformance.co...g-tpi-crossfire-or-lt1-vette.1401/#post-39419

http://garage.grumpysperformance.com/index.php?threads/c4-c5-corvette-trouble-codes.2697/
or as my DAD used to say
DON,T GUESS! DON,T ASSUME!
VERIFY ITS WORKING BEFORE ASSUMING IT FUNCTIONING CORRECTLY!
 
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