poor performance

[44anthony44]

my AMC 304 idles fair,revs okay in first gear,when i get into 2nd,or 3rd,no real power,sometimes backfires,not sure if vacum tubing is correct,everthing is stock,did upgrade to v8 cap adaptor,gm hei module

 

[gert]

Welcome aboard from Texas unfortunately poor performance can be caused by several things and you hit on two of them, the carburetor might need to be adjusted/rebuilt. Bad fuel, ignition timing off, not enough juice from coil, and a worn out motor. Not knowing the condition of the motor or its history I would say to start with color of spark plugs to rich/lean/ covered in oil. check/set timing. fresh gas. spray your vacuum lines with carb cleaner to check for vacuum leaks, spray base of carb for leaks as well. How many miles on motor? is this a recent thing? happen when you did ignition upgrade? let us know so we can help

 

[Torxhead]

Vacuum tubing should be a snug slip on fit, and different sizes will be available at your local parts store. loosing vacuum thru a bad hose can rob power here. Running a 35" tire with a 3 speed stick and assuming you have the stock rear gear ratio is a bit demanding for the AMC 304 . Ignition timing should also be checked along with the other items required in a tune up like spark plugs and ignition wires.

 

[mtnwhlr]

no real power,sometimes backfires

This make me think it's timing.

 

[Lumpy Grits]

:ww:

with mtnwhlr. The backfiring is the biggest 'tell' here. When was the last time you ck'd the timing with a timing light? It's real easy to bump/move the dizzy when work'n in that area. BTDT.
LG

 

[44anthony44]

i set timing 5degrees,not sure on vacum tubing routing

 

[Lumpy Grits]

Ok-that should work. Can you hook up a vacuum gauge and tell us what your reading is?
Does this help?
79 AMC 304 Vacuum Diagram help - JeepForum.com
http://www.jeep-cj.com/forums/f2/another-vacuum-thread-304-engine-14569/

LG

 

[FLYNHYCJ7]

When you set the timing, did you discount and plug the vacuum advance on the distributor?

Sent from my SM-N920V using Tapatalk

 

[Hedgehog]

When does it back fire? During idle, during acceleration, during deceleration. Mine will pop during hard deceleration, but it runs very well other wise.

 

[44anthony44]

Ordered rebuilt motorcraft 2100. Could not get carb to work

 

[gert]

Ordered rebuilt motorcraft 2100. Could not get carb to work

Sometimes they refuse to co operate let us know how it goes

 

[JR74CJ5]

my 304 idles fair,revs okay in first gear,when i get into 2nd,or 3rd,no real power,sometimes backfires,not sure if vacum tubing is correct,everthing is stock,did upgrade to v8 cap adaptor,gm hei module

Couple things here:

1) I'm going to mention this to save you a head-ache if you didn't know about it. The HEI distributor gear will (most likely) eat your camshaft gear quickly. Did you remove the gear at the bottom of the old distributor and use it on the new distributor? If not, you will most likely have a issue soon, and you'll need to disassemble the front of the motor to the timing chain / cam gear location, and change both gears to a good matching set. If you can get the old gear off the old distributor and it fits on the new distributor, this is the easiest way to avoid this, assuming they're still in good shape. The root of the problem here is most of the GM HEI units have a hardened gear and the stock setups were usually a softer metal. Hard to hard is fine, soft to soft is fine, hard to soft is bad...

2) With changing the distributor to HEI style, your plugs / plug gaps, and timing will not be the same as stock most of the time. I believe mine (with DUI HEI distributor) wanted 12 degrees of timing if I remember correctly, and yes set it with the vac advance disconnected and plugged. Your HEI should have come with paperwork detailing timing settings, but if not, post what you got and we can help check it out maybe... Might be a trial and error thing, but don't just take my word on the timing number above, I haven't set timeing on mine in 3 or 4 years...

When you did the HEI upgrade, remember the power of the spark is higher (hence the larger gap on plugs usually, but sometimes need different plugs because over-gapping stock plugs will not fire right) so most people will ensure you use a new set of spark plug wires - 8.0mm or 8.5mm i believe... otherwise you could have spark jumping out of the wires now and not getting to the plugs to ignite your fuel / air mixture.

From there, I would start with the vac line routing to ensure it's all correctly ran again, no cracked tubes / connections, etc. Then look at rebuilding or swapping the carb - whichever you prefer.

Then it may be your gearing in your diffs, but like others said, backfiring usually not caused by too high of gearing with stock tranny and larger tires...

Try to approach it one thing at a time, or (if you're like me) you'll get lost in 5 projects at once...

:ww: