Bogg down...why?

[speednmark]

So ive replaced my HEI cap and rotor assmbly, about to replace the spark plugs...Problem is, when i floor it, my truck tends to bogg down-(stop accellerating) at around 2 to 4 grand rpm....Ive got a 350, 750 cfm carb. I dont know if this is a timing issue, or a carb issue..if its either, does anyone know who can help me time my truck/ and or tune my carb....I live in Austin Texas...can you help? or know someone that i can take it to? Thanx alot.
-Mark Taylor-

[OLDROCK&ROLLER]

#1 is your timing set per spec? #2 is your vacuum advance working? Sounds like you have a timing - firing issue.

[truckdude239]

i dont know if you carb has it but sounds like an accletor pump on the carb gone bad happened on my buddys honda

[Palf70Step]

I'm suspecting carb issues myself. Like truck dude said maybe an accelerator pump or I am also thing a 750 cfm carb is a lot of carb for a stock 350 (I assume, since you didn't mention other mods). You may need to rebuild and rejet that carb so it doesn't wash out the engine.

[ChevLoRay]

Definitely check/replace the accelerator pump, but check the vacuum advance, too. It may be just fine, but it's difficult to look at it and see what it's doing.

Back in the day, we'd hook 'em up to a Sun diagnostic machine and check all kinds of stuff like cylinder balance, timing, etc.

But, I suspect the accelerator pump is the prime suspect although it should also be apparent on initial take off. If the pump is bad, it's bad all of the time, not just at higher RPM's. Do you ever just pat the gas pedal to get it to take off from a stop? If so, then it becomes more of a suspect. Also, check the choke pull-off, just to be sure it is working. Does the bog happen more after it has warmed up? If so, the pull-off could be bad. Make sure the choke is properly adjusted.

One more possibility: I once had a coil-to-distributor wire that would break down on hard acceleration.....had the same effect as turning off the key. A new set of wires solved that one.

[byrd]

I Agree with chevloray on the last issue, I had a bad wire from the HEI pickup coil and would cut off like turningon/off will under hard acceleration. Wire was shorting out when the dizzy was advancing...

[QKENUF4U]

i think carb myself but we dont have enough info on the motor itself , built ??? stock ???

[Superron21]

uh,
is your carb a quadrabog?

[speednmark]

This bogging down ONLY happens when the engine is under full throttle accelleration....its been rebuilt, bigger heads but no competition cam or intake...4 bl edelbrock 750 cfm carb.....keep it coming thanx

[speednmark]

Does anyone have a 650cfm carb for sale??

[toolpimp]

It could also very well be that the fuel cap is not vented. It does happen creating low pressure.

[GMCMAX]

It'll run fine slow, but dies out under full load acceleration?
Sounds to me like it's starving for fuel, either from a half plugged filter or a piece of trash in the secondary jet; the front 2 barrels carry it fine, the secondarys open up letting all that extra air in with no fuel to go with it.

[speednmark]

Holy ****, my gas cap SEALS doesnt vent for ****. so when u take it off allll this pressure bursts out. That makes soo much sense....ill try a new cap and get back to yall. thanx lots...