Thread: Tunnel Ram Tunning???

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Well this is an old question but here it goes anyways.
I am also new to his forum and it seems like a great place to find the knowlege and experience I need.

I have a 1966 El Camino and here is my new combo:

-Earlier 4 bolt chevy 350 bored .020 with TRW cast aluminum pistons. (10.25-1 CR)
-Crane cams with a .488 lift I am not sure of the specs. I will get later
-Petejackson gear drive
-MSD probillet distributor and crane cams ignition box.
-Headers
-And of course the weind tunnel ram with two holley 450cfm mechanical choke carbs.

The car starts and idels great it also revs fine.

Here is the problem When accelerating hard at all it feels okay up to about 2200RPM then hesitates until I ease it up to about 2900RPM, then the engine starts to really pull well!

At Idle it is running really rich and I cant figure out how to adjust these damn holleys(I am an edelbrock guy)

I think I am undercammed and I need to play with the timing more.
sorry for the long post
Any input is greatly appreciated.

thanks, will

play around with the air bleeds? maybe get bigger ones if its running to rich you might have to tap the hole out. i bought a proform mainbody for my 750 dbl pumper now its a proform 750 lol, and i had to ritchen it up so i got smaller air bleeds. you might need bigger ones look into it...............scooter

I'm not a chebbie guy, but I have played with tunnel rams a bit. Air bleeds are a good place to start on the hesitation. Idle mixture screws on a holley are on the front jet plates, 1 small screw per side. Where is your timing coming on at, and what RPM is it fully in at?? Have you played with the secondary opening rate at all, are they just maybe coming on too soon???

I am not sure at all what the air bleeds are. Do you adjust them or get new ones.

If I was to re-jet the carbs what size would be optimal?

I need to put a timing tab on the engine I forgot to do that so I am trying to time it by ear. What should I time it to?

How can I adjust the mechanical secondaries to open up later.

Thanks for the quick replys, will

I'm running vacuum-secondary 390's on a mild-cammed SBF with a Weiand dual-quad tunnel ram.

There is a definite lull, almost a half-second stumble, between the time the secondaries open up (3000 rpm) and the time the car goes ape$#!+ (about 3500rpm) sort of like the car is taking a deep breath before sprinting. I have been told that this delay is typical of tunnel rams, and is a function of the amount of distance between the carbs and the cylinders.

Is this the kind of hesitation you're talking about, or is it missing completely?

You should be able to adjust the secondary opening point, not sure on your Holley, but it should either be by bending the linkage arm from the primaries to the secondaries or by an adjustment. Mechanical secondaries are usually a bit much on the street, I much prefer the vaccuum secondaries, then adjust the opening point and rate by changing the spring in the vaccuum chamber for the secondaries. Might want to invest $20.00 in one of the many good "How to tune your Holley" books that are available.

The hesitation/stumble wasII described was alot like I am feeling but mine lasts more than a half second maype 1and a half, but then it really does seem to wake up around 3000RPM and it does pull really well. It doesnt sound like its missing.

one time during that little hesitation period going over a hill during a test driv it stalled out but gave me no trouble starting back up. I think it is getting too much fuel to eraly in the RPM range?

I think I might start looking for a set of 390s.

thanks, will

Well I finally had the car running really good by advancing the timing a lot and by leaning outh the carbs, so I decided to take the car on the freeway for the first time and after flooring it for while (about 85mph) it kind of started to miss, then it back fired through the exhaust. After that I got off the freeway and it was runnning like crap, So I took it home and checked the plugs and the 3 back ones on each side were badly fouled.

What could cause this?
how do I fix this?

thanks, will

First thing I'd do is check the plugs....This will be a tell all....Sometimes when you nail the gas and it pulls well till 2500 or so then falls short you may be running out of fuel? Plugs will tell this...

Dark or black....no

tan or light....yes

Atleast thats what I get from it....

Plug reading can tell you alot about tunning a carb...I run on very light pedal for 30 miles...jump out check the plugs....then run it just hard enough to use the power valve...check plugs....

Make a hard full throttle pass...let up...turn it off and....check plugs.....Usually I do 2 in a row on the same side...so you get off both runners.....enjoy

I checked the plugs and the three back ones on each side are badly fouled.

will

If they are both vacuum secondaries, you probably have no pump shot to the two rear barrels on TWO carbs. This would create a much amplified dead spot that is typical of vacuum carbs when not tuned correctly. It would be magnified with the large plenum area of the tunnel ram. My susgestion would be play with the shooter size ( squirter size ) on the primary side of both carbs. make gradual changes.

When it's close you might try to fine tune it with the pump cams. Do the same for the back as the front. I have heard that some folks running vacuum secondaries on tunnel Rams stagger the vacuum springs by ONE color so that they come on somewhat progressively at slightly different vacuum levels in an attempt to not "shock" the engine with a large intake of air with no pump shot all at once.

Good luck.

JS

I have mechanincal secondaries right now.

thansk, will

Originally posted by willyc
I have mechanincal secondaries right now.

thansk, will

sorry don't know how i missed that.

BUT you COULd have too big of a HIT if this is true. With the plugs looking dark, could be.

Mine just started doing this.

It's a SBF with dual Holley vacuum-secondary 390's (sorry to invade Chevy-land ) and it lugs right at takeoff.

It was really bad yesterday; dying at lights and backfiring at freeway speed. I went over it this morning and couldn't find anything out of place or changed / disconnected; I narrowed it down to the fuel pump and/or filter -- the pump was the original mechanical one; the last unsullied OEM anything in the engine bay, I believe. I swapped it out with a high-peformance mechanical pump and a new filter. Ran like crap for about five minutes, then ran fine, then started hesitating again, just not as often.

The hesitation is between 1500-2000 rpm (idle in Drive is about 1000; it won't idle below 900); it nearly dies and then comes back on strong. Usually, though, it runs fine. Starts great, idles great, tons of power from 2000-up.

The kicker is, it ran KILLER until last night. Now it runs well enough but I have to baby it through the hiccup now and again.

I'm all confused. Ideas?

EDIT: Plugs are reddish, no fouling.

EDIT II: The gas tank was filled to the absolute top last weekend for the first time in the three years I've owned the car -- it sat all winter with very little gas in it so there may be water and/or some kind of schmutz in the gas. THis started when the gas got to about a half-tank. I dumped some HEET into it.

Thanks, Denny.

If bad fuel is the culprit, how do I make it go away? (The search function only allows four letters or more; can't search for "bad gas," or even "gas.")