Cold Start Problems and Backfire from Weber Carb

[DavidRGallagher]

85 CJ7
Nutter Bypass http://www.off-road.com/jeep/jnutter1.htm
TFI Upgrade http://www.jeepz.com/modules.php?op...file=engine_tfi
Weber Carb
New 258

Problems:

Hard to start in morning. Turns over and dies right away. If I hit gas after it turns over it dies

Backfire / breakup from carb under heavy acceleration

Losing manifold vacuum under heavy acceleration


Checked the following

Cold start issues:

Choke is set right

Backfire issues:

Thought it was a timing issue - Timing OK - set to 10 BTC
All hoses look OK
Vacuum advance is holding vacuum

Checked ignition module - OK

Did not check compression yet.

Vacuum is 20 inch Gs @ idle

Installed vac pump onto vac advanced – pumped to 15 of vac – backfire problem went away and it was fairly smooth up to 3500Rs

At idle manifold vac @ 20 in - @ throttle response, vac drops to 0 and ported vac went to 5 inches of vac

Before vac applied, motor has major hesitation with, vac applied hesitation goes away – still breaks up slightly @ top end.


Other info:
Ran fine with all mods (NBP, TFI, Weber) and old motor.
Swapped motors and have not been able to figure out the problem.

What could be causing the problem??

Thanks,
-David

 

[jeep90]

sorry i cant give you a direct answer but i can give you some info on the experiences that i had. everything that you are explaining here are the exact problems that i had with my weber carb. i tried everything that i could think of over a span of 6 months. never got the issue resolved. finally sold my weber on ebay and got back what i paid and got a motorcraft 2100 carb. after i installed the motorcraft and tuned it all of those problems went away. that makes me think that the weber was junk. i hate weber carbs because of this but i have heard of people having great success with them. good luck and try a fuel pressure regulator.