How do you know it's ignition? Have you checked the spark plugs to see if they are getting spark? How do you know that the carb is getting a continuous feed of fuel? From what you've posted as symptoms you're a little quick to decide that it's the ignition. You could have something as simple as a vacuum leak if it just dies. Could be a defective carburetor also. I wouldn't jump to such a hasty decision especially with the cost of DUI.
The DUI was a planned upgrade, it's just that all of this foolishness started up over the past couple of weeks and I'm hoping it changes something.
The old carb had a leak and was missing a couple of check balls, small parts, etc., so I just replaced it altogether to simplify troubleshooting.
I installed a brand new Holley 4160 carb and it didn't change anything.
The vacuum diagnosis sounds like it could be the thing, but here's my question.
Does the starter motor enable the vacuum to take effect? I am definitely getting fuel in for the inital blast, but then it craps out.
My mainfold bolts are tight, my carb studs are tight, but I may need to replace all the hoses from the distributor and the intake manifold. They look a little old. I can't spray WD-40 on where the intake manifold meets the engine block and where the carb meets the intake, because the thing won't crank long enough for me to find the leaks.
I had a CJ7 that did this with the stock carter carb. I would pour a little gas in the carb (yeah i know that's a no no) and it would crank up, and then die. There was a blockage where the line went into the carb; the float hung in one place and wansn't allowing fuel in there. It sounds like it has to be a fuel starvation problem, check you fuel pump and your fuel filters. Keep messing with it. One day you'll get to go "OH, so that's what was doing that!" What a great feeling that is....
85 CJ7 258, borla header, Team Rush, MC2100 ,optima batt, Warn 8274, agr super box 2 & pump, T5 w/ B&M shifter, centerforce 2, superior 1 piece axles, warn hubs 2.5 in lift, 31" BFG MT
does it seem to stall out as you allow the ignition to spring back from the start position to the run position?
Have you fooled with the solonoid at all since this problem started?
I had the same problem, i cant remember the exact details but i think the ignition wire going to the solonoid was on the wrong terminal and it only had power to the coil when the key was in the start position.
Try turning the key to the run position and with a test light see if the coil is getting power.
1982 cj7. Frame off. shell valley kevlar body, stainless hinges, Bestop seats and supertop, KC titanium lights, Homemade swing out tire carrier with spare front wheel bearings/hub, Built 304,DUI,Edelbrock shorty headers with dual stainless 21/2 tubes into incynerator cans 21/4 dumped out the back,Edelbrock 600cfm, performer intake and cam, Borgeson lower column, Centerforce clutch, NV-4500, Dana 300 w/custom built twin stick, Homade 1/4" steel skid plate, 2.5 soft ride w/ 1" shackle lift, 33x12.5 mtr's. Stainless fuel and brake lines, Braided hoses. more...
Figured it out. The Centech wiring instructions for the ignition failed to include what was formerly the resistance wire that went directly from the ignition switch to the positive terminal on the coil. I rigged up a second wire from the ignition switch and attached it directly to the ignition post on the solenoid (since I switched to a DUI distributor) and the rig fired right up.
Problem solved. This one of the areas where Centech was NOT helpful at all. They kept telling me I needed a new alternator and would not help me trouble shoot the thing. Keep that in mind if you buy a new harness from them.