Hesitation at higher RPMs

[XJ1517]

4.3L V6, rebuilt engine, 4 barrel Q Jet, cobra drive.

Planes out pretty well but once I get to about 3200 RPM and try to increase RPM, it loses power. Sort of a bog/hesitation.

New plugs and wires, timing confirmed at 1 deg BTDC at proper idle RPM (570ish). Carb is cleaned, new fuel filter, water separator filter, good gas, proper engine temps and good oil pressure. Checked the vacuum line for the secondary pulloff and there's no cracks or leaks. Carb base gasket is new and torqued properly. Idles great, shifts great and planes out nice. Just cant get on it at higher RPMs.

Any idea where to look?

 

[HT32BSX115]

Howdy,

Welcome aboard!

I'll first offer the "standard answer" for this......

Please post your model number.

There are MANY variations of the 4.3L engine used with the Cobra over many years, it helps if people reading this can look at exactly what you have. (pictures help too!!)

There's a thread on low WOT RPM with a lot of stuff to consider:
https://forums.iboats.com/forum/eng...69-must-have-technical-information-for-diyers

Have a look at all of it when you can, #15 speaks directly to things that can cause low WOT RPM.

Regards,

Rick

 

[ci2hi]

I had the same issue with my Johnson Surfer with the Quadrajet Carb. The problem with mine was that the secondaries wanted to open too soon and it couldn't handle the fuel. There is an adjustment on the secondary butterfly shaft. You use a small allen wrench to loosen the set screw and tighten about 1/4 turn against the butterfly spring. A crude test of whether the spring is too loose would be to simply push down on the secondary butterfly and if it doesn't readily pop back up, it needs adjusting. There should be some resistance. I hope this helps, if this is your problem.