The Definitive HEI and MC2100 Thread

[Rescue Diver]

Ok, I got a new really nice timing light for my birthday and decided to re-tune my HEI and take a few pics while I was at it.

My new handy dandy Craftsman timing light also has a built in Tach, so I started with checking my idle and found that it was 820 RPMs.

I then checked the timing initial advance. With the vacuum advance hose unhooked and plugged, my initial advance read 12 degrees before top dead center. That's what I had found it to be previously with a borrowed timing light.

 

[Rescue Diver]

I next checked the mechanical advance at 2500 RPMs. It was reading 28 degrees, so that tells me that with the 12 degrees initial plus the mechanical, I have 16 degrees of mechanical advance at mid throttle. That should be pretty close to what my AMC 258 i6 / 4.2l likes.

 

[Rescue Diver]

I then checked the timing at 4000 RPMs. With the vacuum advance still unhooked and blocked off, It was reading 32 degrees total advance. That means that my total mechanical advance at 4000 RPMs, (which is around the red line of a AMC 258 i6 / 4.2l ) is right at 20 degrees. 20 degrees of mechanical advance might not seem like a lot, but it should be pretty good for a low RPM AMC 258 i6 / 4.2l Jeep motor.

 

[Rescue Diver]

Now for the more contentious issues. It has been falsely claimed on here that the ported vacuum on an MC2100 does not work correctly for operating a vacuum advance. I tested mine, and at idle, it read zero inches of vacuum. At mid throttle(2500 RPMs) it read 15 inches of vacuum. Exactly as it should.

That settles that.

 

[Rescue Diver]

Now for the second contentious issue. It was claimed on here by a member that an adjustable vacuum advance is not available for the HEI distributor.

I hooked my vacuum pump to my distributor's vacuum advance and pumped it to create 15 inches of vacuum while the engine was at idle. The timing read 32 degrees before top dead center. So my vacuum advance,being artificially operated with a vacuum pump at idle was providing 20 degrees of advance at 15 inches of vacuum.

I decided that 20 degrees of vacuum advance was a bit too much, so I took out my 2.5mm allen wrench, inserted it in the tit where the vacuum hose hooks to it, and I turned it a few turns counter clockwise to reduce the amount of vacuum advance. I then rechecked it to find that it is now only providing 15 degrees of vacuum advance at 15 inches of vacuum.

So much for the HEI not having an adjustable vacuum advance.

 

[Rescue Diver]

With the vacuum advance being reined in a little, I decided it was a good time to see if I could add a little initial advance for better throttle response, and with it, a couple more degrees of total advance.

I set the initial advance to 14 degrees before top dead center with the vacuum advance again unhooked. I then verified that the total advance at 4000 RPMs was reading 34 degrees before top dead center. I then hooked the vacuum advance back up and took it for a test drive.

It definitely has better throttle response with the 2 extra degrees of initial advance, and there is still no drag on the starter.


(Before backing off the vacuum advance, with the initial and mechanical totaling 34 degrees, it pinged slightly on steep hills with the vacuum advance hooked up. That's why I had backed the total timing, initial and mechanical to 32 degrees.)

Now that I reduced the vacuum advance to only providing 15 degrees, under load going up hills it no longer pings with 34 total degrees of advance, so everything seems to be working great!

 

[Rescue Diver]

Before I forget, for those of you using an MC2100 carb, here is the ported vacuum location on the passenger side of the carb that you should use for your vacuum advance, it's just below the choke. Pay no attention to anyone that says this port does not work correctly. Test yours, if it doesn't read zero at idle, and nearly full vacuum off idle, you'll want to find what's wrong with your carb and fix it. When working correctly, this port should read zero vacuum at idle, and good vacuum at mid range throttle.

I am using a screw in plastic nipple on mine to plug the hose in to.

 

[Rescue Diver]

In summary, I set my initial advance(at idle) to 14 degrees. I left my mechanical advance alone. It provides 16 degrees at 2500 RPM and 20 degrees at 4000 RPM. When added to the 14 degrees of initial advance, it makes a total of 30 degrees advance at mid throttle, and 34 degrees at full throttle.

My "very much adjustable HEI vacuum advance" is now set to allow as much as 15 degrees advance instead of the 20 degrees it was set for from the factory.

The cheapy aftermarket HEI I purchased from ebay for less than $60 delivered has been proven to have an adjustable vacuum advance, and my cheapy MC2100 carb that I bought from one of our awsome Jeep-CJ members has been proven to work great and it has a good ported vacuum source to run a vacuum advance on a distributor.

Any questions?

 

[Rescue Diver]

Oh, and thanks to Shirley for giving me such a cool birthday gift, whithout which I wouldn't have had the motivation to re-tune this stuff, and take pics.

 

[Petescj]

I knew Id find something wrong with this thread the minute I saw it. Pleases refrain from the vulgarities.

Now for the second contentious issue. It was claimed on here by a member that an adjustable vacuum advance is not available for the HEI distributor.

I hooked my vacuum pump to my distributor's vacuum advance and pumped it to create 15 inches of vacuum while the engine was at idle. The timing read 32 degrees before top dead center. So my vacuum advance,being artificially operated with a vacuum pump at idle was providing 20 degrees of advance at 15 inches of vacuum.

I decided that 20 degrees of vacuum advance was a bit too much, so I took out my 2.5mm allen wrench, inserted it in the tit where the vacuum hose hooks to it, and I turned it a few degrees counter clockwise to reduce the amount of vacuum advance. I then rechecked it to find that it is now only providing 15 degrees of vacuum advance at 15 inches of vacuum.

So much for the HEI not having an adjustable vacuum advance.

 

[sapulpa cj]

In summary, I set my initial advance(at idle) to 14 degrees. I left my mechanical advance alone. It provides 16 degrees at 2500 RPM and 20 degrees at 4000 RPM. When added to the 14 degrees of initial advance, it makes a total of 30 degrees advance at mid throttle, and 34 degrees at full throttle.

My "very much adjustable HEI vacuum advance" is now set to allow as much as 15 degrees advance instead of the 20 degrees it was set for from the factory.

The cheapy aftermarket HEI I purchased from ebay for less than $60 delivered has been proven to have an adjustable vacuum advance, and my cheapy MC2100 carb that I bought from one of our awsome Jeep-CJ members has been proven to work great and it has a good ported vacuum source to run a vacuum advance on a distributor.

Any questions?

your numbers are very close to were mine came out to, and yep the H.E.I. cheapie i bought also is totally adjustable for mechanical as well as vacuum advance.

the one i got also has a top quality cap with brass terminals as well as a rotor with brass tip.

the machining on the aluminum housing also seems to be top notch also.

the drive gear also looked identical to the gear on the stock distributor.

i am using this in a AMC 258 i6 / 4.2l and not a AMC 304 though,the AMC 304 results may vary as i have not tried one in a AMC 304 yet.

 

[WAXER]

Great set-up info.
HAPPY BIRTHDAY !

Waxer

 

[Cheepjeep85]

I knew Id find something wrong with this thread the minute I saw it. Pleases refrain from the vulgarities.

Damn pete did it make you blush
Tit tii tit tit tit tit rotflmao

Seriously, good job david


DROOOID2

 

[Rescue Diver]

I knew Id find something wrong with this thread the minute I saw it. Pleases refrain from the vulgarities.

I would have used the word boob, but he hasn't posted in a while!

 

[Rescue Diver]

your numbers are very close to were mine came out to, and yep the H.E.I. cheapie i bought also is totally adjustable for mechanical as well as vacuum advance.

the one i got also has a top quality cap with brass terminals as well as a rotor with brass tip.

the machining on the aluminum housing also seems to be top notch also.

the drive gear also looked identical to the gear on the stock distributor.

i am using this in a AMC 258 i6 / 4.2l and not a AMC 304 though,the AMC 304 results may vary as i have not tried one in a AMC 304 yet.

On the AMC 304 , I would seriously heed the warnings and verify the distributor gear is soft metal. From everything I've read, the soft cam gear that's an option in the AMC 304 , will be eaten by a hardened distributor gear. I understand that this is easily fixed by using a stock(soft) distributor gear from some other motor. I think someone might have mentioned a mopar 360 distributor gear fitting the HEI shaft and matching well with the AMC V8 cam gear, but my memory is a little fuzzy on it. I'd do some research to verify this if I were building an AMC V8.

 

[Rescue Diver]

Great set-up info.
HAPPY BIRTHDAY !

Waxer

Why thank you! Thank you very much!

Just took her for a long cruise through the countryside. It's running smooooooooooth!

 

[Cheepjeep85]

Ah yeah just seen that, happy birthday

DROOOID2

 

[Rescue Diver]

Ah yeah just seen that, happy birthday

DROOOID2

Thanks!

It was really nice of Shirley to give a gift that not only helped me out, but also put to rest the bogus info being thrown around, and can give a little peace of mind to all the many HEI and MC2100 owners on here.

 

[83cj7]

The other gear option for a AMC 304 is to switch the gears from old to new dizzy. My cheapo ebay HEI even has the indent on the cap for what looks like the Mallory sticker. That must be why mine was $20. more.

 

[Jessica]

Which HEI did you get? What one do you recommend and where can you buy it? All the ones I see seem to have the hardened gear which someone said wasn't good for the V8.