I have run 2 tunnel rams in the past. 1st one was a SBC Weiand with 2 450 Holley's and ran well with 40° timing. The 2nd one was a BBC tunnel ram with 2 600 Eddy's, because the 450's had such a sheety idle circuit and the Eddy's were the best at the time, I used to run that BB with a locked out 40° but at times it was a little cranky starting. Yup you can't run the large cap HEI but there are other small cap distributors that work just as good.

 

Thanks for the input. Of course right after I post asking for help I found a thread with exactly what I was experiencing and questioning (https://www.chevelles.com/threads/distributor-tunnel-ram-problem.98396/?post_id=675943#post-675943). In later threads s/he switched from Holleys to Edelbrocks.

Anyone friends with HopkinsChevelle? I found a thread from '05 but our site says there hasn't been any activity on the account since 2020. I would really love to make contact and see what the final verdict was.

I think I'm headed in the right direction with the timing, the plugs will tell me what it wants. Any input on increasing gap? Necessary?

I still have a question about it rapidly accelerating at about 2500 rpm. Is that also timing related or can that be tuned out with futher carb calibration?

Thanks!

 

I have ran many dual carb tunnel-ram combos on the SBC and they are not finicky on the jetting.
None of my single carb to dual carb swaps needed a timing adjustment.
I ran 2 600 edelbrocks 1405 with stock jetting stock rods and springs and the part throttle cruise was 14.7-14.5 on a wheel dyno and full throttle power was 12.5 AFR.

This was a 350" with 280H comp magnum flat tappet and ported Iron 601 heads.
It made 53 HP more everywhere vs the single 750 on a performer RPM intake.

If your timing curve is not advancing until 2500 that could be the runaway issue you are feeling.
I had my timing at 22 initial and 38 total.
But that is dependent on the heads chamber and how quick the flame travel is.

I used light springs in the distributor so all timing was in by 2200 rpm.

I also had my carbs linkage set up so both carbs opened equally (not progressive)

MPG was actually the same as a single carb.
My tunnelrams were tall .
I also ran a velocity stack type air filter as there is power there.
The filters I ran are wix 42040 and they are thick and flow plenty of air and keep everything very clean.
I ran these on a 7000 rpm bbc 396 also with 2 edelbrock 600's.

Here is a good tunnel-ram read for you.

https://www.chevelles.com/threads/the-tunnel-ram-bug.641977/#replies

 

Thanks for the input guys. I made a couple calls last week and ended up with a replacement distributor and the 2500 rpm surge is now gone. Today I took it out for the first rip and I have to say this thing is VIOLENT now. The tip-in is a little stiff but once it gets going it's a monster. I don't know if the tunnel ram/dual quads are making any more power than before but you sure as heck can feel the torque!

The issue I have now is keeping it idling. I fired it up, set/checked timing which is 28 initial / 40 total, let it idle until up to temp. Put maybe a mile on it and it feels like its lightly surging at part throttle but as soon as you roll into it there's no hesitation to go. I was thinking fuel pressure, so I pulled over to adjust the regulator and it sputtered out on me. It fires right back up with help from the throttle, get back out on the road and no change in the surging. First intersection I come to it shuts off again as soon as I stuff in the clutch. Pulled back into my drive and I can't get it to idle on its own.

Does it need more timing or is this a fuel delivery issue?

 

I would invest in a uni-sink to balance the carbs,I got mine from Dan Dvorak Racing. I did my inline dual-quads and a friend t/ram set-up. Get them flowing the same air first then start tuning. Given that,it sounds like a fuel issue;I think those carbs don't like a lot of fuel pressure? You might want to try bringing your timing up to 34*@idle for a test to eliminate timing.