Surging at 5,000 rpm

I have recently noticed some surging starting between 4,750 and 5,700 rpm's any ideas what is going on?

I'm running a well built 350, Pertronics ign., John Osborne carb, GS118 cam. It almost feels like it is running out of fuel, changed the filter today .. no luck though. Any help will be much appreciated.

David

 

Are you driving at 5000 rpm's when this is going on? Or is your Gauge needle bouncing around?
Ivan

 

Driving

I am on it wide open and as it approaches 5k it happens.

David

 

does it only do it in 3rd gear at the top end or all gears until it shifts... I had a prob. exactly like that with my carb (holley) putting too much gas into it at high RPM... Jetted it down and the prob went awayo No:

What felt like no gas was infact too much gasou:

If your running a Qjet... then I dunno.

Good luck

 

Jeff,

Happens in 1, 2, and 3rd gear.

David

 

Have you done anything to the fuel system or ingition and then noticed the surge... or did it just come on with no changes to those systems??

If there hasn't been any changes I'd look at your Ignition as a culprit. But I couldn't help you there. If you have a spare dist. I'd try swapping that in to see if there is a differenceo No:

I seem to recall some people having probs. with the pertronix distributers... Can't recall the symptoms tho. Sorry.

Good luck

 

Sounds to me like its an igition issue, not a fuel issue. I have heard of a lot of issues with the pertronix (mostly on this board)... I think IgnitionMan (Dave) would have the answer :TU:

 

Timing Advanced

Could my timing be to far advanced? I have no pinging, but I am running 50% 110 octane.

David

 

David, it could also be running out of fuel, as you mentioned. The q-jet has a relatively small capacity fuel bowl, and at WOT and high rpms, the bowl could be running dry. I know it happened to me before, the cure was a higher output fuel pump. My old V-8 Vega would fall flat on it's face at about 4500-500 rpms, then all of a sudden pick up, then flat, etc. It was not a minor surging, it was like all or none. Like I said, the cure was a higher capacity pump.

I do not know if there is a high flow needle and seat available for the q-jet, but I am sure there are some differences in designs. Be careful running too much fuel pressure to overcome the problem, it is a fuel capacity, not pressure problem.

If you are running a stock mech pump, you could supplement it by adding an electric pump in back near the tank. Elec pump work best as pusher-type application.

 

thanks

Thanks for the reply Terry!!

David

 

You can get high flow needles or the Q-jet. I'd assume John Osbourne used one when he did the carb.
Also don't forget the obvious stuff, ignition wires, cap/rotor... I've heard of caps that look fine but give symptoms like that at higher rpms...

 

More Info.

Ok guys some more info, I checked all my plugs tonight and found number's 5,7,8 were all black and damp with gas. Also I noticed that after I turn the car off for a few minutes I smell gas. Lastly it takes a lot of cranking at start up and a lot of pedal pushing before she starts. Is something not closing in the carb?

The other 5 plugs were a nice beige/gray.

David