258 runs like crap

[st0rck]

Heres the scoop:

84 Jeep Grand Wagoneer w/ an AMC 258... Accel ignition coil, new plugs, wires, filters, oil change x3, fuel tank completed drained and cleaned.

I ditched the stock intake/exhaust and carb in favor of the old school setup off of a 71 AMC Javelin ( Carter YF 1BBL).

She runs like absolute crap. She warms up fine, but once the choke plate is fully open the idle surges like crazy.

I have pulled the carb back apart (it was completely rebuilt prior to putting it on) and cleaned out all of the jets with Berryman's but to no luck. It doesn't matter how you adjust the idle screw or the fuel/air mixture screw it still does the same thing. There are only 2 vacuum lines currently on (PCV and brake booster). The Xfr case vacuum and cruise control vacuum are currently disconnected. I rechecked all the torque on the manifold gaskets and they are all tight as well as the throttle nuts.

HELP!!!!

[Ryan]

if it surges, could there be a vacuum leak somewhere?

[st0rck]

I dont know where... The brake booster line and PCV line are brand new and ive checked them several times. Ive tightened the manifold and carb bolts and nothing changed. I sprayed everywhere I could think of! This problem did not start to happen until I filled the tank up w/ gas halfway but the tank was thoroughly cleaned out prior... Im currently dumbfounded.... Im fairly certain I have the valve cover setup correctly... front has breather filter rear has PCV running to intake manifold...?

[davpratt]

After it warms up remove the vacuum advance hose and plug it.
If it smooth out some check timing and ensure the plug wires are in the right place.
Are you using a vacuum advance engine temp sensor?
This enables the vacuum advance till the motor warms up.
If the float is at the wrong level the fuel may be to high causing a rich idle.
If to low will cause a lean idle.
If the fuel level is shifting up and down under a lean idle it could cause the engine to serge.
Manual open the choke to see if the same problem exist with a cold engine.
plug all the vacuum lines to the carb to start with. Add one accessory at a time to find the problem accessory.

It's possible to have a bad cylinder. Have you done a conpression test?
If it is a cylinder remove one plug wire at a time; the bad cylinder will not change the problem.

[st0rck]

Sorry for the long delay in my response, weather has been crappy and I've been running around like crazy planning my daughters birthday party. I will take a look at all of the things you mentioned above Mr. Davpratt and post my findings this week.

Thank you all for all the helpful advice!

My friend has a 74 Ford Maverick, currently garaged as he's on deployment, with the same carb setup as my Gdub. I know it performs flawlessly so if I narrow it down to something with the carb im going to swap them out to verify and go from there after I check all of the things you mentioned above. Hopefully the weather clears up this afternoon and I get a few minutes to mess around with her.

[st0rck]

Now that I think about it, the Engine Temp Sensor that is connected is the one (no idea when or if it was ever replaced) that was originally on the head (drivers side firewall)... intake/exhaust swap from the 71 Javelin deleted the intake sensor... It worked great for... oh... about 2 days of actual driving then pegged to hot (even when the car has been shut down for several days, isnt running, ACC on it pegs to hot before ever starting her up. I did not have this issue prior to that happening. That is the only sensor im currently running on her. I will replace it today if I get the chance since its only $5 and see if it changes any of the symptoms.

[st0rck]

Got a chance to play around with her for a little while today and here is what I found:

Brand new coolant temp sensor, gauge still pegged on Hot even before car is started (has been sitting for quite some time as well). Checked cable for frays into the cab and found nothing.

Plugging the Vacuum advance coming off the carb does nothing to help the surging.

Not sure what a vacuum advance coolant temp sensor looks like, but fairly certain that mine isnt one? The only one that is on the car is the little tiny one located on the drivers side near the firewall. Original one worked fine for a few drives, and presumably still works but gauge is pegged on hot?!

With the new carb setup, (if you want to call it new), there is only 1 vacuum line coming off and that is the vacuum advance running to the distributor. I have checked all of the other vacuum lines (there are only 3 in total to include brakes and PCV I dont have the vacuum canister hooked up for the 4x4 since the vacuum motor on the xfr case is bad currently.

I will pull the carb back apart tomorrow to check the float level... I imagine the specs for that can be found somewhere in the tech manual for how far down it is supposed to be?

I have replaced the plugs, wires, coil, fuel sending unit, fuel lines, fuel filter, and last chance filter, temp gauge, temp sensor, changed and flushed oil 3 times, and flushed coolant twice to clean her out since she sat for 7 years prior to me getting her.

[Ryan]

gauge pegging means grounding issue. on the vacuum not going to the 4wd canister, note that any plugs / opened vacuum areas are considered a leak if not capped and / or rerouted properly, which can cause some surging issues.

[st0rck]

Thanks everyone for the responses. I finally figured out what was causing the surging... a few of the intake bolts had backed slightly out and was causing a MAJOR vacuum leak... DOH! Now im chasing another gremlin... one step forward... two steps back... sigh....