high rpm bogging

[hispeed]

Here is the scenerio-- 1976 350 Chevy engine. 4-bbl quadrajet carb. Everything is stock except for the cam. It is rated just a little over oem for a little better performance. When the rpm's get to about 2800 the engine begins to bog down. When you open up the 4-bbl it wants to spit the fuel back out of the secondaries.

Tried running with an open set of headers(reduce backpressure) didn't help.

Changed out the HEI internals with new vaccum advance canister,rotor, weights and replace the condenser(all stock GM replacement parts) just a slight bit of difference at the low end, nothing noticeable at the top end.

Readjusted the timing. Made it worse going either direction.

Carb. was rebuilt before it was placed on the engine by a rebuilder. I don't know anything about him or his reputation but I have never heard of him. (I generally rebuild my own)

At this point I am open to suggestions and questions. I have tried everything I can think of to do.
At the back of my mind I am wanting to tell this guy to get rid of his stock intake and carb. and move up to a better flowing intake and a 650 or better carb. Thought I would pick your brains first.
Thanks in advance.

[River Bum]

Fuel filter or fuel pump bad?

[hispeed]

fuel flow is real good and there aren't any restrictions in the filter. Doesn't seem to be a problem with the fuel getting there. How long would a power valve and oem spring last? Carb is probably 20+ years old.

[dancerman]

Do you know if the new cam was properly timed when installed?.... the problem you describe sounds like the intake valves are not seated and letting cylinder pressure back up through the carb. You might also check the valve springs for proper specs so they will close the valves quickly and hold them closed.

[mikey]

poping thru the carb. sounds like lean misfire If your secondary are opening and little or no fuel could cause your problem.

[wileys_farm]

Well have to say I had the same trouble with my 350ci small block. The problem was the cam was one tooth out of adjustment and the vacuum advance on the elderbrock carb was on the wrong side. Work with the vacuum advance first to see if it is working properly then try using a degree wheel on your cam. Did you read your cam profile sheet. If ya lost it or cant come up with a new one: line your dots up 0 to 0 straight up and down and then advance or retard with your distributer. Doesn't sound like a carb problem though if it was rebuilt by an honorable mech.
Hope I could help.
'

Wiley

[micropterus2]

Install in-line fuel pressure gauge (a good one - Mallory for example) in the fuel line near the carb. Check the PSI when you rev the engine. A four barrel quadrajet stock config should handle 7-9 PSI, anything more and the needle will pop out too far from the seat. Also, you may need to remove the carb, pull off the cover and measure the float drop setting. Could be causing flooding condition. Problem may have been introduced with carb rebuild job.

[jtpredator]

ok, grab your sldge hammer, line it up carefully as to not hit anything else when you swing, and SMACK THAT QUADRA JUNK !!! It does sound like your timing is either off, or you have the rocker arms too tight. try readjusting your rocker arms . first, start the car w/ the valve covers off( messy, but the ezest way) now go to EACH rocker arm & loosen them until the start to tick, tighten until the tick disappears, and then go 1/4 turn tighter.....Good luck !!
JT

[grundydj]

Here is the scenerio-- 1976 350 Chevy engine. 4-bbl quadrajet carb. Everything is stock except for the cam. It is rated just a little over oem for a little better performance. When the rpm's get to about 2800 the engine begins to bog down. When you open up the 4-bbl it wants to spit the fuel back out of the secondaries.

Tried running with an open set of headers(reduce backpressure) didn't help.

Changed out the HEI internals with new vaccum advance canister,rotor, weights and replace the condenser(all stock GM replacement parts) just a slight bit of difference at the low end, nothing noticeable at the top end.

Readjusted the timing. Made it worse going either direction.

Carb. was rebuilt before it was placed on the engine by a rebuilder. I don't know anything about him or his reputation but I have never heard of him. (I generally rebuild my own)

At this point I am open to suggestions and questions. I have tried everything I can think of to do.
At the back of my mind I am wanting to tell this guy to get rid of his stock intake and carb. and move up to a better flowing intake and a 650 or better carb. Thought I would pick your brains first.
Thanks in advance........Hi ..did you ever find the problem. I have the same symptoms with my 350 chev

[grundydj]

Did you ever solve your prob with the qjet/cam etc.?
I have a similar prob .

[KA9MOT]

Did you ever solve your prob with the qjet/cam etc.?
I have a similar prob .
It is a shame but this guy has posted 24 times since 2001. He probably wont be answering your question.