304 Fuel/spark Upgrades?

I'm working on a '78 CJ7 w/304, and the owner's summary statement was, basically, make it dependable. Somebody before them had messed with the coil and distributor (currently has an MSD Blaster coil and some red cap vacuum-delete billet whiz-bang distributor) and an Edelbrock intake w/Motorcraft 2 bbl. on top of an inch spacer. They aren't worried about every ounce of power, but they do want it to be dependable so I'm more concerned with putting it back to original components unless said original component is legitimately flawed and will cause trouble. I've never fooled with the Motorcraft 2 barrel carbs. - is it worth keeping? I'm partial to the Rochester 2G and 4G, and as I understand a 2G will bolt to the same studs as the original Motorcraft 2100. Also, I have no problem going back to a plain jane OEM distributor - is the late 70's electronic ignition design reasonably durable? If not, what's the best alternative? Another factor is that whatever I do wind up doing, if not OEM, that it be fairly easy to troubleshoot and find replacement parts for so as not to cause the owner too much fuss if it causes trouble in spite of my efforts.

 

i went through this with my 75/304.. The best carb i installed was a Motor Craft 2100.. I believe it was a 1.08 venturi.. Had a larger venturi for a while, 1.21 or so, but it ran better with the 1.08.. The carb that came on my heap was a Holley. Tossed that right away and started in using the 2100's. The biggest issue on mine was the junk Motorola ignition... I finally bit the bullet and installed a TBI system and totally new ignition that was tied into the TBI computer..

The 78 oem Duraspark ignition is easily upgraded.. Lots of info out there.. And upgrade articles.. First I'd see if you can determine if your ignition has already been upgraded.

 

The 2G is a different pattern from the 2100.

The 2100 is a fine carburetor if it's not worn out. It works very well on the street and the trail.

IMO there's nothing wrong with the original Motorcraft Duraspark distributor used by Jeep in 1978. The main complaint is that the plastic in the connector crumbles after a few decades. Supposedly the aftermarket Duraspark modules are not reliable (though my J20 has its Jeep OEM module, with 130K hard miles in the Arizona heat). The Duraspark is a conventional VR (variable reluctance) design and can trigger many different modules - GM HEI, MSD, etc. Google "Stealth HEI" for articles about using the GM module with the Duraspark distributor.

 

very funny this post popped up..
I have been chasing an intermittent issue in my CJ6 (360, TBI)
ill update my build thread with some detail, not to steal the original posters thunder..

the Motorcraft ignition is very reliable.. issue is like Tim says is junk aftermarket parts...
2 failure prone items being the pickup coil and the module itself.

 

I too am running the MC2100 and TFI. No complaints here.

 

Cool, thanks for the advice. I'm content to stick with stock equipment so they can walk into a parts store and ask for parts for that vehicle, and they actually get what they need. :-D

 

been running the 2100 for 5 year without an issus.


I've gone with tbi for the cold start (6-8 month winter over here)

 

I added a pressure regulator @4.5psi and bent the float down slightly to lower the bowl fuel level in my MC2100.. Now it works great on the trail. I haven't flooded out in the better part of a decade. I don't do a lot of extended full throttle pulls, so I wasn't worried about potentially running it lean.

I also added a chinese HEI, with my original drive grear swapped on to it. Made cold starts and throttle response much better. These two mods make my jeep run almost as good as fuel injection out on the trail.

I've got a thread on here about my HEI conversion from some years ago.

Hei install Writeup

 

I put a Davis Unified Ignition (HEI) in my 73. It's a nice piece, well manufactured, and looks great. I coupled it with the Davis wires too. A lot of folks go this route if they don't want to piece part an HEI system from scratch.

-Troy

 

Lots of options. The only real bad system was the one on the 76 and 77's. I think it was called the pertronix system. The motorcraft system is supposed to be a good system. There is a guy who has done a lot to promote jeeps and ignition upgrades. However, he can be a little...odd. Here is the link to his page: Genuine Junk Yard Genius.com Ignition Upgrade, Jeep 258 CID I-6 and the folks who do his ignition upgrades say they work well. What Tim said, the stealth HEI system is also a good system.

After a lot of research and seeing what other folks did, I decided on the MSD system. I don't know if it is the best but it is what I decided on.

 

Prestolite BID (breakerless inductive discharge). It was used 1975-77. Trouble from the start.

Pertronix is an aftermarket breakerless conversion that is rather well liked, from what I gather.

 

FWIW...on my 360 I have the Motorcraft dizzy "large cap" upgrade with an MSD TFI coil, hooked to an MSD 6 ignition module. I also tuned the dizzy for a decent advance curve while using manifold vacuum. All of this with an MC2100 1.08 venturi carb. Has been pretty reliable on and off road after all the minor tuning is out of the way.

Had some issues with vapor lock, but that has gone away except in really hot Georgia weather, probably due to a better tune along with an aluminum radiator. I recently did a very long day trip that was 12+ hours including offroad and highway use and only had vapor lock on the return trip at 70MPH in 95*F ambient temps.

 

A word about vapor lock.. I had issues on my 75, and did some research. Vapor lock occurs in the intake fuel line most of the time, the fuel turns to a vapor, and the pump can't get suction. Old timers would attach clothes pins to the fuel line and the problem would go away, as the clothes pins act like a heat sink.. I had issues because i installed TBI and was using an electric fuel pump, which doesn't really suck fuel well.. In fact it causes the pressure in the line to the pump to drop slightly. This pressure drop causes the boiling point of the fuel to drop.. Thus vapor lock especially in hot weather. Install an electric in the tank and end of problem. Mechanical fuel pumps do not seem as prone to vapor lock issues, but do happen..

One time I had a vapor lock, I ended up changing the mechanical fuel pump. Fixed the problem for about a half hour and then, it happened again. The whole time I thought the fuel pump was tits..

 

Sometimes folks replace their fuel filter with a 2 port clear filter rather than a 3 port metal with return line.... they like the cute sight glass. But, that can cause a vapor lock situation.

-Troy

 

Big issu i see from lot of people with and external fuel pump, they mount it over the lowest point of the gaz tank. Mine is mounted in the midlle of the frame rail, lower than the tank. This way the fuel don't need ot be suck up from the tank, it create some siphon and feed the pump withou any issu.

Other than that you have to make sure that you have the evap canister and the vapor/fuel separator.

 

Fuel Pump Retrofit

he's not lying...
wasn't my only problem... but FP position effects it tremendously...