HEI, 1971 CJ5 Carb. Adjustment

Ok, so I've done my due diligence and looked at all the posts. I just installed a new HEI distributer. I have a 1971 cj5, Daughntless V6 with (I think) a Rochester 2G Carb. What I'm trying to do: Set all the initial variable so it runs smooth. It backfires now through the pipes when I accelerate it ...

What I've done:
1. Bypassed the ballast resister

Is this the sequence.
1. Set idle speed
2. Set Mixture = 20" Hg on manifold vacuum
3. Set timing (10-12 BTDC) without vacuum advance
4. Hook vacuum advance back up
Anything else?

I've heard that some people don't even run with the vacuum advance on ... although don't you need that when you're accelerating? I've also heard others who think the vacuum advance is too sensitive on the HEI and you need to buy a "adjustable vacuum advance diaphram"? Any thoughts? Anything else I'm not thinking of? Should I be concerned with the fuel filter/fuel pressure? Thanks guys.

 

Do you do timing/electrical first and then carb adjustment?
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I've had good luck getting a baseline on the carb with the vac disconnected first, but remember to plug the advance port on the carb when doing this.

Once you get a baseline, then hook up the advance.

Remember on the odd fire you really need to work carefully to make sure your HEI reluctor is in correct phase with your plug wires.

I've had good luck with the NAPA (Federal Mogul) vac advance unit for '75 Buick Apollo with 231.

My vac advance HEI seemed to work well at 6* initial. Also very important to check total advance, somewhere in the 30* ballpark, wouldn't recommend more than 32*.

 

I thought it wouldn't matter if the advance port is plugged on the carb.? ... because it's ported vacuum...

Also, how do I check total advance? Where/how do I measure it? The timing marks on the engine only go up to 15 degrees or so (checking with the timing gun) ...how do I check for 30 degrees? thanks guys

 

thanks guys

 

Opening port vac will still effect the signal past the venturis. Plug the vac advance port on the carb while you are getting a baseline. Set mechanical advance springs and weights at this point, too. At the very least, you should be able to get your engine to accelerate and run well without backfiring, then hook up the vac advance and dial in for driveability.

 

On mine I did the same paint marks on balancer to find out total advance and changed the springs in the distributor to stop over advancing. Also mine backfires on decelerating when my old headers develope new cracks (weld them up no more backfiring) may check exhaust

 

Also, don't get hung up on the internet's "absolute best way" to do something. Play with both manifold and port vacuum to determine which one works better for you. You'll find very polarized opinions on both.

 

Fresh O2 entering exhaust through cracks gives unspent fuel an opportunity to reignite, not super-related to timing, but definitely annoying. Exhaust pressure in pipe from acceleration usually prevents O2 from entering, thus you hear it on decel. My headers do this after evey off road trip, too. Accumulating a big pile of booger welds on my #6 exhaust tube.

 

How do you set the mechanical springs and weights? I can actually open up the distributer and change springs? For the mechanical advance and the vacuum advance? So if I'm hearing everyone right.

1. Plug my ported port
2. Set timing at 5 BTDC
3. Hook up advance and check to make sure it's advancing for a total of around 30 degrees (with the marks that I painted on the balancer)
4. If it is ... great ... move on to the setting the carb stuff.
5. If it isn't, then I have to mess with the advance springs (mechanical and/or vacuum)

 

jayhawkclint ... the previous owner put on an aftermarker header ... may be it doesn't fit exactly right ... and o2 is getting into the exhaust igniting the unburned fuel ... but the popping should decrease if I get the timing and the mixture set right ... before welding/messing with the exhaust manifold???

 

It will decrease as you lean out the fuel more than timing. Might fix up the exhaust first before you go on a wild goose chase. I highly recommend manifolds and a good quality muffler over headers.

 

Pretty much, other than springs are mechanical, nothing vac about them. Make sure everything is plugged up. Vac advance should be near 0 deg at WOT anyway, which is why you're checking for total mechanical at this point. Some folks refer to advance curves, but it's more accurate to think of total advance in old distributors as a table since they rely on RPM (mechanical) and kPa (vac). You are trying to eliminate variables one at a time to make incremental changes. Changing two variables at a time will cause headache and frustration as you don't know which of your variables made things for the better or for the worse. By starting with mechanically sound engine (fix the exhaust, make sure your gaskets are fresh), then moving on one at a time to initial advance, baseline carb adjustment, mechanical (total) advance, then vac advance, you'll save yourself some grief. Then when all is running well, hook up a vac gauge and drive around to make fine tuning adjustments.

 

Aside from making the additional timing marks, another way is to use a timing gun with the setback dial on the back. I got mine at Sears.