Howdy all. Got an issue. '68 F100 stepside with a swapped 460, C6 auto. Edelbrock 1407 carb, MSD Streetfire HEI ignition/dizzy. No vacuum lines of any sort, manual steering/brakes, no air conditioning. Vacuum advance on dizzy is plugged. As I got into this, there are a few problems. First, I called MSD and they don't make a dizzy like that for a Ford, so someone made a Chevy dizzy work. Haven't tried to figure that out yet. I have a backfire thru the carb at load. Seemed like a standard blocked passage problem. The truck sat I think for a while on empty, so I took the tank off, cleaned it out, blew out the hard fuel lines, replaced the soft ones, installed a new fuel filter, removed, cleaned and inspected the pump, and rebuilt the Edlebrock 1407. I DID notice that one of the jets looked like it had been stripped, but when I blew air thru it, it was at least clear and jets don't come in the kit. Accelerator pump seems to be working correctly. I also noticed a substance that looked and behaved exactly like super glue inside the carb fitting supplying fuel. Cleaned everything out, took my time. Reinstalled carb, fired her up, same backfire. Timing not set correctly, but is at ~12 DBTC. The hand-made mark on the pulley is at 10 ATC. Still scratching my head on that one too. Hard to tell, as the block is '71, the intake is '74, the heads are '72 and the timing pulley is '79, all of which would be fine if I had done it, but trying to find a baseline is killing me. Motor is very strong otherwise. Trying to rule out an intake or exhaust leak. I know this can also be a valve train issue, but am working from most likely to least. Picking up new jets for the carb today, factory spec ones that were shipped with carb. Metering rods looked ok when I rebuilt the carb, but again, no idea what prior owner did. Also trying to rule out the very likely possibility that someone was just putting parts in her with the "bigger is better" mentality and didn't know what they were doing. Comp test show all cylinders are strong and equal. Just got a vacuum tester so I'll let ya know. Also waiting for the computer cable for my camera so I can upload pix. I've already figured out it's easier to take pix if I can't take the part in for comparisons at the parts counter.
Thanks, Joe

24APR Edit: Thanks for the responses, all. Two great things happened yesterday: got the cable for the camera, so pix are incoming, and I hooked a vacuum tester gauge up. Gauge readings say leaking intake manifold so I pulled that off, but then got busy stripping the ugly red paint off and repainting the intake manifold. Install is today. Pix later tonight as my wife has to help me upload the pix. I'm not so good with current tech.
Thanks, Joe

24APR evening edit: Installed the intake, hooked everything up. Fired on first roll-over, still had a pop thru the carb. Taking GWF1985s idea, took a break, returned and checked all ignition systems. Spark wires in correct order, everything looks ok. Hooked up the timing light, loosened the distributor and started making adjustments. Using my hand-made timing mark at ~12BTDC I steadily advanced the timing by about 3-5 degree increments. At ~20BTDC the backfire stopped except for an on-fuel demand rev. It's also not a constant pop. Really intermittent until ~2000 rpm. Haven't road tested yet, ran outta daylight. When I rebuilt the carb I checked the accel pump and installed a new o-ring, not the entire pump. Pretty sure the on-demand pop is a faulty accel pump, got a new one this evening. I checked the crankcase breather/oil cap and PCV valve, both full of gunk, so I'm replacing them as well. Still working on dialing in the timing. I have manuals that say it ranges from 6-22BTDC. Maybe I'll just have to play around to find the sweet spot. Wife's at the ball game, so hopefully pix tomorrow.
Thanks again, all, I really appreciate the support.
Joe

4/27 edit: All this work and I still have a pop thru the carb. Starting to get discouraged and I'm not a mechanical moron. I did plug in a vacuum line from the dizzy to the lower port on the carb. Have not road tested it yet, but I can bring up the RPMs slowly and not get a pop until about 2500. Kick it once and I get an instant pop. Replaced the accel pump today as well, but have not replaced the jets yet. Starts great, idles well. I have a new set of plug wires on order because the old ones are stretched a little too tight across the #1 and #5 cylinders and the runs are sloppy. I just can't seem to figure this out. The pop at 2500 is intermittent, which seems like a fuel issue to me. Kicking the gas gets a pop, which seems like fuel to me. Motor runs strong, no surging. Could it be that these guys put a too large carb on? It's got a 750 cfm, but the motor is a 460. Maybe I should step down to a 600 cfm? I'm not racing, just want a daily driver.

Thanks again,
Joe

 

Hi Joe, I had the same issue has you do, but mi 69 F-250 camper special with a 360 and auto C6 didn´t have any electronic ignition, so my backfire tru the carb problem was a bad timing and a bad points. Replaced points and have it right on timing and no more backfire issues.
I saw an electronic distributor for our vehicles for a very good price from CRTPerformance on ebay´s and i bet you it´s way better that the chevy hybrid that you may have.

 

First thing I would do is bring #1 cyl to TDC(compression stroke) and verify/mark correct timing marks. Backfire thru carb is "usually" a timing issue. As far as the "chevy hybrid", all HEI's are a chevy hybrid as Ford never offered it. Vacuum to distributor should be hooked to ported vacuum of carb after initial timing is set. Then at least you have a solid baseline to work from. Comment on distributor is confusing, you say MSD Streetfire and then MSD says they don't make one like that for a Ford. Got no clue whats going on there.

 

MNKEEKING, It sounds like you have a DUI distributor, the only thing that I can think of is how it is wired. Those distributors need more amperage to operate, and at least a 12 gauge wire with no resistor. You should run a soldered dedicated circuit from the ignition switch to by-pass the resistor circuit. You can contact the manufacturer @www.performancedistributors.com for how to wire it. Kenny Nunez

 

Thanks, Kenny. I looked at the pix on the DUI site, and although my distributor is red in color, it looks just like the one they sell for Fords, right down to the wiring. That really helps as I was trying to wrap my head around how/if the previous owner made a Chevy part work in a Ford. At least I won't have to figure that out too. Hope to have pix of my truck uploaded tonight for all to see. I know it's easier to help when everybody can see the problems/parts I'm talking about.

Thanks,
Joe

 

sounds like you have the procomp hei dizzy , they use all the chevy stuff but fit the FE i have one , got it on ebay
this weekend i was messing around took my cap off and put it back on just to see what was what . well i started it us and it ran bad sputtered and popped , i shut it off and looked at the dizzy (only thing i touched ) when i put the cap back on i pinched the wire under the cap (blue wire) i fixed the pinch and all is good so you might want to check for pinched wires .

 

Thanks, Mike. I'll check that in the morning if we don't get rain. I have taken the cap off to try and see who made it and could've easily pinched a wire putting it back on.

Thanks,
Joe