Vacuum Advance ?

[74 chev]

The motor in my truck is a pretty much stock 350 bored .030 over with an RV cam aftermarket intake and headers.

Ever since i rebuilt the thing it seems to run great until it hits about 2250 RPM where it pretty much does not build anymore power and the Tach will start to flutter a little up to 3000 RPM at which point it seems to max out in RPM's.

I have the most problems with it at highway speeds as when i am in fourth gear doing 65 mph i am right in that 2300 RPM range. The engine because it seems to have issues building power at these RPM's will be very weak and start to back fire on the slightest grade or even when i put my foot into it to try and accelerate.

Could this be a vacuum advance issue?

I honestly don't know how the whole system works or how to test it.

I tried disconnecting the vacuum line to the advance module on the distributer and nothing changed whatsoever, which is what is kind of leading me that way.

 

[4X4HIGH]

Could be weak valve springs that is limiting your RPM range. The vacuum advance system is really nothing more than for fuel mileage. If your vacuum advance diamphram is ruptured then you have a vacuum leak and that can change the way the engine runs but it's doubtful that is casuing your issue.

 

[74 chev]

Something else i noticed today while working on it was that at TDC my harmonic balancer timing mark it at 12:00 but my timing mark tab on my timing chain cover is at 2:00.

While searching the forum on this i saw a couple people mention that there were two different harmonic balancers offered on a 350 each had different locations for the timing mark at TDC. Is this true? could i have a timing chain tab that is mismatched with my harmonic balencer?

I have never put a light on it before so i never noticed this till now. I also pulled the cap off and the rotor is pointed at #1 so thats good.

I think im going to buy a light tomorrow and try and time the thing.

 

[4X4HIGH]

I've never seen a 350 with the timing mark at the 12 O-clock location (those were all 305's AFAIK) but there are 2 different sized harmonic balancers and each uses their own timing tab. When the proper tab is used the tab should be real close the the balancer (like only 1/8" away).

 

[74 chev]

I may have the wrong balancer then because mine is def at the 12:00 position at TDC.

My tab is real close as you say it should be.

 

[K85 Octane]

so what happened here?
would a wrong balancer cause this?
Or is the problem still there and someone just found out they have a 305?
bump for curiosity