Hey yall.

So my monza is ready to hit the roadsand tear emup...only I got a problem.

Im running a tunnel ram (weiand street ram) with dual 600 single pump vac sec. holleys.
Both carbs are identical with the same jets, cams, squirters, and pumps.

Intake is heavily modified...so I know everything is working together.

But...I seem to be getting some problematic backfiring through the carb wheneverI stick my foot in it hard...this equates to a giant fireball through the carb followed by a mushroom cloud of black smoke at about 3000rpms...So i am assuming I need to replace the power valves.

but I dont think I have any vaccum leaks  and I would think that 1200 cfm of carb wouldnt run lean anywhere.

Does anyone have any experience tuning tunnel rams?
Please help if you can.

PS: before you tell me that running one carb would be easier...this I know...but the harder it is to do...the cooler the results...soImsticking with the ram...plus I have about 20 hours of labor in the intake alone.

God bless
-Shred

Shred, you've been working on this Frankenstein a long time now.

You're problem is that the mixture is dropping lean when you pop the throttles open. Certainly vacuum secondaries would soften the problem perhaps even eliminate it. But the fix is more fuel from the accelerating pumps. If they're maxed, then you'll really have to get clever on timing the seconday dump to slow things down a bit to give the accelerating mixture time to get into the combustion chambers. And yes part of this is stalling the port speed with all that throttle area which smaller venturies or fewer of them would improve. You're now into one reason why Holley went to 4 corner idle circuits and dual accelerator pumps.

Yeah, you probbaly have blasted the power valves.

Bogie

Welcome to tunnel rams on the street, it's really hard to get them to behave, but they are well cool and very menacing

Thank you kindly Bogie.

I really appreciate you knowledgable expertise and input.
I have to take the bowls off anyway to replace a leaking transfer tube seal so I'll replace the PV's.

I might also up the pump shots with new cams.

I'll keep you posted.
Thank you again for responding to my barrage of Tunnel ram questions.

God bless
-Shred

Hey...my mistake

I have 67 jets all the way around...not 47's
All with 30cc accelerator pump diaphrams
9.5hg rated power valves

Thing is...I thought i was getting a lean pop and fire ball out of the carbs but I checked the plugs and they where horribly fuel fouled so I stepped up to a hotter plug....I was running R42ts' and switched to R44ts'
and gapped them a touch wider at . 040 over the 35 that I had the 42's set at.

Also someone brought up a good point that i might be running out of fuel because I only have one electric pump and 3/8 steel line to fill two carbs.
I know Ive got enough pressure but i think volume might be the problem.

Im going to try stepping the jets down to somthing like a 60 and throw another feed line onto my fuel cell with a second pump (one pump for each carb) and regulate them at the intake.

Im also considering using the electric pump as a supplementary pump and adding a high flow mechanical pump on the block...I just dont have alot of room down there to work with cause Im using the Hooker/TD style front plate mounts and I need a fuel pump that can be re-clocked to face the back of the motor.

I know its running rich because the plugs where fuel fouled pretty bad and when I removed the carbs I had a nicely atomized fuel/air fog in the intake just from trying to start the motor.

Please let me know what you guys think about the changes I have in mind...this is my first TR setup.
I know I should probably have 450's but those were not in the budget...cause the 600's where paid for...haha.

God bless
-Shred

Shred, we need to peel this problem apart. It's entirely possible for a carb to run rich in one circuit and lean on another.

The soaked spark plugs on one hand indicates rich, the explosion out the intake indcates lean on the other hand.

Once plugs become fuel or oil fouled they can also mimic a lean condition because they can miss or delay fire which might catch an open intake and explode the manifold mixture.

What may cause the engine to be running rich at this point is an open question. It could be the mains are rich, or the air bleeds are too big which would cause raw fuel to dribble out the boosters, if the globs get big enough combined with no manifold heat to force vaporization, the engine could find itself swimming in pools of fuel.

The explosion out the intakes can also strongly suggest that the mixture falls lean upon throttle opening. What happens with 1200 cfm capability and mechanically opened 8 barrels is that when they're popped open the mixture velocity drops off or stalls inside the manifolding and ports. The accelerating pumps deliver a shot of fuel to make up for the lag in main metering which will fall further lean when the velocity through the venturies falls off.

This is why tunnel rams are not popular on the street as they are very difficult to tune and cylinder to cylinder distribution gets to be a large problem when you try to limit how many barrels are used at low to medium speeds.

Your fighting a bunch of different problems all at the same time. Between the carbs throttle plates and any intake valve you have inertia of the mixture where flow at the valve lags behind a suddenly opened throttle and a lot of distance compared to a motorcycle engine where a carb per cylinder works well. To add to the inertia problems, fuel flow lags even further behind air flow when a throttle is suddenly opened and overshoots when it's closed.

These open plenum set ups also tend to reverse flow thru the carb with a fuel cloud forming above the intake, this of course is fuel lost to the engine.

I'd come at this problem by trying to remove some of the options, first would be to lock out the secondaries and get the primary system functioning. If that means blocking out one entire carburator and resticing the seconday on the remaining one, do so. Get the problem down to as simple as possible and go forward in baby steps so you can single out trouble spots one at a time.

Bogie