Off Roading Forums banner
1 - 2 of 2 Posts
G

·
Discussion Starter · #1 ·
MAYDAY,MAYDAY!!!! I have 84CJ7,I-6 258. just had engine rebuilt and a new carter-bbd put in. The proablem I' having is that when I'm prepared to start moving and give it gas I have to do it with ease because it has a tendency to become sluggish if I give it to much gas. Even harder if I'm at a red light at the bottom of a hill and start there....the momentum is what keeps me going up?..the funny thing is that she runs really great on the highways. But gas mileage has really suffered and it has never done that....Now the things that I have tried so far to see what the trouble could be is, running it without the aircleaner cover, running it without the smog stuff, fiddled with carb jets (no expert),checked the timing................I do have a thought though does the diameter of the vacume hose from the vacume advance to the carb matter? Because it's smaller than usual....... .ANY IDEAS ANYONE PLEASE HELP!!!!!!!!!

 

·
Registered
Joined
·
6,784 Posts
Try this bit of good basic diagnostic proceedure, and stop fiddling with the carb jetting until you know what you are doing!
What you are describing is called 'Off the line stumble', and is usually the too lean of idle mixture, or not enough accelrator pump shot getting into the carbuerator venturies, or both. It can also be caused by some other things, but that is rare.

1. Check the vacuum advance on your distributor.
Flip the distributor cap so you can see the vacuum advance arm move the trigger plate.
Put a clean hose on the vacuum advance and pull some vacuum.
If the trigger plate moves, and the canister holds vacuum for one minute, and the trigger plate returns when the vacuum is let off, the vacuum advance is working properly.
Connect it to venturi ported vacuum, not manifold vacuum.
2.Check your cap and rotor. I don't know why, but winter time is the worst for showing bad caps & rotors. Probably the drier air causes more ozone, and that shows up as cross fire and ground fires (dead miss).
3. Advance weights stuck.
While your vacuum advance line is disconnected and plugged, use a timing light to see if the timing goes up and back down when the RPM is increased and allowed to go back to
idle.
4. Has cold affected your ignition module?
It is unlikely, but if it is the module, it will be very hard to diagnose, because intermittent modules are notorious for working correctly when they get warm, and doing strange stuff when the temperature changes.
5. Check your idle mixture.
LIGHTLY turn both idle mixture screws in until they bottom out, then back both off the same amount, about 1-1/2 turns.
Attach a vacuum gauge to intake vacuum. (Carbuerator base plate is fine)
Start engine and let it warm up.
If it is an automatic transmission, put it in reverse with the emergency brake on and the wheels chocked.
Turn the screws in THE SAME AMOUNT, 1/4 turn at a time until the the highest vacuum is found.
You are done with the idle mixture.
6. Check your accelerator pump. (With the engine off)
Take your air cleaner off, and look straight down the carb throat with a light.
Now, pull your throttle linkage all the way open with one smart stroke.
Did you see a good, 'thick' stream of fuel get shot into the Venturi bores?
No bubbles, sputtering, or weak 'gurgling' pump shot?
If it was anything but a good, long, strong pump shot, have someone good with carbs look at it.
NOTE: Cold air is more dense, and needs more fuel for proper fuel ratios. A lean idle mixture or weakaccelerator pump shot, or vacuum leak or combination of any will really show up on cold days.
7. Fuel pressure and float level. Self explanatory.
8. Make sure your choke is pulling all the way off.
9. Check each end of every vacuum line for leaks. A little leak can cause a lean problem.

Hope this helps, Aaron.

So many cats.... So few recipes...
 
1 - 2 of 2 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top