Can't mash the throttle

[QWKDTSN]

My motor is really touchy. I'm not sure if it has anything to do with the ignition, but it seems like the main culprit is the carb. It is a Holley 650 double pumper (mechanical 2ndaries) with no changes, other than basic setup (idle mixture, idle RPM, float level). At the moment I'm running with stock main jets (67s) and dropped the secondary jets a size (to 72) because it seemed like it was just dumping too much gas in at once. Here are the symptoms.

 

I have to really ease it off the line, like really baby it, slipping the clutch and slowly modulating the gas. it's not as bad as it sounds because I'm used to it; But if I let the clutch out too fast, it dies very quickly. First gear seems to go smoothly, but if I stick it in second and just jam the gas, the car does something that is hard to describe - it's like it just hits a brick wall. I can hear the motor gulping in tons of air through its four throats, but none of that mixture seems to get the car going forward. Tons of loud poppings, jerkings, backfirings - like the motor is doing all this work but the explosions just aren't working out right, and the car isn't being propelled forward. This is what makes me curious about the timing, because it seems like it should just haul ass instead of bogging. I'm using an HEI with a 50k volt coil but no ignition boxes or anything. I set it to 10 initial but not entirely sure what the total timing is. It's stock, anyway - haven't changed it. I know it should be 36 degrees total advance, but I haven't checked.

 

So what can I do? I'm really not good enough with engines to just say "oh, that's rich" or "lean" or whatever. I want to be able to just give it some gas and dump the clutch and let my V8 torque toss me off the line; I can't even give it full throttle because it just doesn't run smooth. If I ease into full throttle instead of jamming it to the floor, it will rev through the range instead of bogging, but I can feel all kinds of un-smooth poppings, like it's still not running right, or getting too much gas.

 

I know it's hard to help over the net, but what do you guys think?

[fl327]

i would like to assume the carb is ok for now, maybe take a vacum guage and see where youre at.

pop off the dist. cap and check out the igniton module, and the advance weights, also check out the vacum advance.

is this a new hei unit or a used one, i had one that ran fine the first couple hundred miles, then i started having all kinds of popping under load, and had to drive it just like you say. its worth checking out, and i would change that module with a autozone module, they are pretty cheap. also would look into an advance kit and an adjustable vacum advance, pretty cool stuff for those old v8 out there.

[QWKDTSN]

What kind of vacuum should I be looking for?

 

I will check the under cap stuff in the HEI as you recommend in the morning. It's a new unit. I got it from some no name company on eBay but it's definitely new.

[Guest greimann]

Nion, what you describe really sounds like ignition problems. Popping and bogging a typical symptoms of bad timing, malfunctions or all around bad karma.

 

When looking for a solution to a bewildering situation like this, make absolutely sure that your basics are covered first:

 

Plugs are new and gapped properly. I would suggest .040 gap.

 

Cap and rotor are new

 

Plugs are installed with conductive antiseze. If the plug does not have a good ground to the head, the spark voltage intended for that plug will scatter to another path to ground like another plug wire.

 

Plug wires are in top notch condition, or new.

 

10 degrees is a good start at initial timing, but if your mechanical advance springs are loose and sloppy, the timing will jump all over the place, especially at idle. The vacuum advance is mainly for fuel economy. Disconnect it for trouble shooting purposes and then reconnect it when things are sorted out.

 

As a last resort, replace the module or the whole unit with a name brand. Maybe there is some hidden reason that the e-bay guy is selling the distributior?

[QWKDTSN]

Greimann, thanks for the tips, when I get a chance I will check them all out.

 

Just so you know, the car idles smoothly and runs beautifully most of the time. It will rev through the range at low throttle application, but when you get into the gas is when it starts having problems.

[Graeme]

Also check the resistance on your leads including the coil lead. If there is a large variance replace them all. Use your multimeter on Ohms resistance.

[jap tin]

Check your acc pumps and squirters. Sounds like your lean.

[Guest Anonymous]

DELETE

[Guest Darthmentos]

If this is a new set up, does it have vacuum advance distributor?

If so please check and make sure that your vac. hose is plugged into a ported vac. source. I E, a vac. port on the carb that has little or no vacuum at idle , but progressively rises with RPM. If it is plugged into a vacuum port on the carb that has high vacuum at idle, it will make your advance curve BACKWARDS, which is prolly not helping much at all.

[fastzcars]

Hi Neon. I have to agree with Greimann on this, You Can't assume anything, Barrow a timing light, Vacuum gauge, and a fuel pressure Gauge. It could be from a clogged fuel filter to a bad accelerater pump on your carb. But you have to take it one step at a time. Good luck, I'm sure you'll find the problem. 8)